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Summary: Eukaryotic translation initiation factors (eIFs) are the primary targets for overcoming RNA virus resistance in plants. In a previous study, we mapped a BjeIF2Bβ from Brassica juncea representing a new class of plant virus resistance genes associated with resistance to Turnip mosaic virus (TuMV). However, the mechanism underlying eIF2Bβ‐mediated virus resistance remains unclear. In this study, we discovered that the natural variation of BjeIF2Bβ in the allopolyploid B. juncea was inherited from one of its ancestors, B. rapa. By editing of eIF2Bβ, we were able to confer resistance to TuMV in B. juncea and in its sister species of B. napus. Additionally, we identified an N6‐methyladenosine (m6A) demethylation factor, BjALKBH9B, for interaction with BjeIF2Bβ, where BjALKBH9B co‐localized with both BjeIF2Bβ and TuMV. Furthermore, BjeIF2Bβ recruits BjALKBH9B to modify the m6A status of TuMV viral coat protein RNA, which lacks the ALKB homologue in its genomic RNA, thereby affecting viral infection. Our findings have applications for improving virus resistance in the Brassicaceae family through natural variation or genome editing of the eIF2Bβ. Moreover, we uncovered a non‐canonical translational control of viral mRNA in the host plant. [ABSTRACT FROM AUTHOR]

Wheat dwarf virus (WDV) causes high yield losses in wheat and other cereals and is therefore an important pathogen transmitted by the leafhopper Psammotettix alienus. Climate change will increase infections by insect-transmitted viruses due to the increasing spread of vectors. In the context of integrated pest management, the cultivation of WDV-resistant/tolerant varieties is an effective way of controlling WDV. Evaluation of tolerant/resistant genotypes is based on inoculation with viruliferous leafhoppers and subsequent phenotyping in gauze houses under semi-field conditions. For successful screening, it is important to ensure the uniform and reproducible inoculation of plants. Abiotic conditions, particularly temperature, have a critical influence on inoculation success, and thus, variations in infection rates were observed within and between previous replicates in the field. Furthermore, the leafhopper population reared in the greenhouse has to be reestablished after each infection, which delays the screening process. We addressed these issues by developing an improved inoculation assay in which plants are inoculated in small infection hoods in the greenhouse before being planted out in gauze houses. This procedure allows optimal environmental conditions for WDV infection of test plants and allows the plants with WDV infection to develop under natural environmental conditions for symptom scoring. In addition, the viruliferous leafhoppers were recollected from the test plants after infection, allowing a sustainable use of the insects. The method thus enables more reliable phenotyping by increasing infection success and testing a greater number of genotypes in a shorter time. [ABSTRACT FROM AUTHOR]

Symmetry in mathematical models often refers to invariance under certain transformations. In stochastic models, symmetry considerations must also account for the probabilistic nature of inter- actions and events. In this paper, a stochastic vector-borne model with plant virus disease resistance and nonlinear incidence is investigated. By constructing suitable stochastic Lyapunov functions, we show that if the related threshold R 0 s < 1 , then the disease will be extinct. By using the reproduction number R 0 , we establish sufficient conditions for the existence of ergodic stationary distribution to the stochastic model. Furthermore, we explore the results graphically in numerical section and find that random fluctuations introduced in the stochastic model can suppress the spread of the disease, except for increasing plant virus disease resistance and decreasing the contact rate between infected plants and susceptible vectors. The results reveal the correlation between symmetry and stochastic vector-borne models and can provide deeper insights into the dynamics of disease spread and control, potentially leading to more effective and efficient management strategies. [ABSTRACT FROM AUTHOR]

Viral diseases of potatoes are among the main problems causing deterioration in the quality of tubers and loss of yield. The growth and development of potato plants largely depend on soil moisture. Prevention strategies require comprehensive protection against pathogens and abiotic stresses, including modeling the beneficial microbiome of agroecosystems combining microorganisms and immunostimulants. Chitosan and its derivatives have great potential for use in agricultural engineering due to their ability to induce plant immune responses. The effect of chitosan conjugate with caffeic acid (ChCA) in combination with Bacillus subtilis 47 on the transcriptional activity of PR protein genes and changes in the proteome of potato plants during potato virus Y (PVY) infection and drought was studied. The mechanisms of increasing the resistance of potato plants to PVY and lack of moisture are associated with the activation of transcription of genes encoding PR proteins: the main protective protein (PR-1), chitinase (PR-3), thaumatin-like protein (PR-5), protease inhibitor (PR-6), peroxidase (PR-9), and ribonuclease (PR-10), as well as qualitative and quantitative changes in the plant proteome. The revealed activation of the expression of marker genes of systemic acquired resistance and induced systemic resistance under the influence of combined treatment with B. subtilis and chitosan conjugate indicate that, in potato plants, the formation of resistance to viral infection in drought conditions proceeds synergistically. By two-dimensional electrophoresis of S. tuberosum leaf proteins followed by MALDI-TOF analysis, 10 proteins were identified, the content and composition of which differed depending on the experiment variant. In infected plants treated with ChCA, the synthesis of proteinaceous RNase P 1 and oxygen-evolving enhancer protein 2 was enhanced in conditions of normal humidity, and 20 kDa chaperonin and TMV resistance protein N-like was enhanced in conditions of lack of moisture. The virus coat proteins were detected, which intensively accumulated in the leaves of plants infected with potato Y-virus. ChCA treatment reduced the content of these proteins in the leaves, and in plants treated with ChCA in combination with Bacillus subtilis, viral proteins were not detected at all, both in conditions of normal humidity and lack of moisture, which suggests the promising use of chitosan derivatives in combination with B. subtilis bacteria in the regulation of plant resistance. [ABSTRACT FROM AUTHOR]

Soybean mosaic virus (SMV), an RNA virus, is the most common and destructive pathogenic virus in soybean fields. The newly developed CRISPR/Cas immune system has provided a novel strategy for improving plant resistance to viruses; hence, this study aimed to engineer SMV resistance in soybean using this system. Specifically, multiple sgRNAs were designed to target positive- and/or negative-sense strands of the SMV HC-Pro gene. Subsequently, the corresponding CRISPR/CasRx vectors were constructed and transformed into soybeans. After inoculation with SMV, 39.02%, 35.77%, and 18.70% of T1 plants were confirmed to be highly resistant (HR), resistant (R), and mildly resistant (MR) to SMV, respectively, whereas only 6.50% were identified as susceptible (S). Additionally, qRT-PCR and DAS-ELISA showed that, both at 15 and 30 d post-inoculation (dpi), SMV accumulation significantly decreased or was even undetectable in HR and R plants, followed by MR and S plants. Additionally, the expression level of the CasRx gene varied in almost all T1 plants with different resistance level, both at 15 and 30 dpi. Furthermore, when SMV resistance was evaluated in the T2 generation, the results were similar to those recorded for the T1 generation. These findings provide new insights into the application of the CRISPR/CasRx system for soybean improvement and offer a promising alternative strategy for breeding for resistance to biotic stress that will contribute to the development of SMV-immune soybean germplasm to accelerate progress towards greater soybean crop productivity. [ABSTRACT FROM AUTHOR]

Tobacco mosaic virus (TMV) was the first virus to be studied in detail and, for many years, TMV and other tobamoviruses, particularly tomato mosaic virus (ToMV) and tobamoviruses infecting pepper (Capsicum spp.), were serious crop pathogens. By the end of the twentieth and for the first decade of the twenty-first century, tobamoviruses were under some degree of control due to introgression of resistance genes into commercial tomato and pepper lines. However, tobamoviruses remained important models for molecular biology, biotechnology and bio-nanotechnology. Recently, tobamoviruses have again become serious crop pathogens due to the advent of tomato brown rugose fruit virus, which overcomes tomato resistance against TMV and ToMV, and the slow but apparently inexorable worldwide spread of cucumber green mottle mosaic virus, which threatens all cucurbit crops. This review discusses a range of mainly molecular biology-based approaches for protecting crops against tobamoviruses. These include cross-protection (using mild tobamovirus strains to 'immunize' plants against severe strains), expressing viral gene products in transgenic plants to inhibit the viral infection cycle, inducing RNA silencing against tobamoviruses by expressing virus-derived RNA sequences in planta or by direct application of double-stranded RNA molecules to non-engineered plants, gene editing of host susceptibility factors, and the transfer and optimization of natural resistance genes. [ABSTRACT FROM AUTHOR]

The shoot apical meristem culture has been used widely to produce virus-free plantlets which have the advantages of strong disease resistance, high yield, and prosperous growth potential. However, this virus-free plant will be naturally reinfected in the field. The physiological and metabolic responses in the reinfected plant are still unknown. The flower of chrysanthemum 'Hangju' is a traditional medicine which is unique to China. In this study, we found that the virus-free 'Hangju' (VFH) was reinfected with chrysanthemum virus B/R in the field. However, the reinfected VFH (RVFH) exhibited an increased yield and medicinal components compared with virus-infected 'Hangju' (VIH). Comparative analysis of transcriptomes was performed to explore the molecular response mechanisms of the RVFH to CVB infection. A total of 6223 differentially expressed genes (DEGs) were identified in the RVFH vs. the VIH. KEGG enrichment and physiological analyses indicated that treatment with the virus-free technology significantly mitigated the plants' lipid and galactose metabolic stress responses in the RVFH. Furthermore, GO enrichment showed that plant viral diseases affected salicylic acid (SA)-related processes in the RVFH. Specifically, we found that phenylalanine ammonia-lyase (PAL) genes played a major role in defense-related SA biosynthesis in 'Hangju'. These findings provided new insights into the molecular mechanisms underlying plant virus–host interactions and have implications for developing strategies to improve plant resistance against viruses. [ABSTRACT FROM AUTHOR]

Background: Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are components of the wheat streak mosaic virus disease complex in the Great Plains region of the U.S.A. and elsewhere. Co-infection of wheat with WSMV and TriMV causes synergistic interaction with more severe disease symptoms compared to single infections. Plants are equipped with multiple antiviral mechanisms, of which regulation of microRNAs (miRNAs) is a potentially effective constituent. In this investigation, we have analyzed the total and relative expression of miRNA transcriptome in two wheat cultivars, Arapahoe (susceptible) and Mace (temperature-sensitive-resistant), that were mock-inoculated or inoculated with WSMV, TriMV, or both at 18 °C and 27 °C. Results: Our results showed that the most abundant miRNA family among all the treatments was miRNA166, followed by 159a and 168a, although the order of the latter two changed depending on the infections. When comparing infected and control groups, twenty miRNAs showed significant upregulation, while eight miRNAs were significantly downregulated. Among them, miRNAs 9670-3p, 397-5p, and 5384-3p exhibited the most significant upregulation, whereas miRNAs 319, 9773, and 9774 were the most downregulated. The comparison of infection versus the control group for the cultivar Mace showed temperature-dependent regulation of these miRNAs. The principal component analysis confirmed that less abundant miRNAs among differentially expressed miRNAs were strongly correlated with the inoculated symptomatic wheat cultivars. Notably, miRNAs 397-5p, 398, and 9670-3p were upregulated in response to WSMV and TriMV infections, an observation not yet reported in this context. The significant upregulation of these three miRNAs was further confirmed with RT-qPCR analysis; in general, the RT-qPCR results were in agreement with our computational analysis. Target prediction analysis showed that the miRNAs standing out in our analysis targeted genes involved in defense response and regulation of transcription. Conclusion: Investigation into the roles of these miRNAs and their corresponding targets holds promise for advancing our understanding of the mechanisms of virus infection and possible manipulation of these factors for developing durable virus resistance in crop plants. [ABSTRACT FROM AUTHOR]

Phospholipids are important components of biological membranes, participating in various biological processes, including plant development and responses to biotic and abiotic stresses. A previous study showed that mutation of the rice OsCDS5 (CDP‐DAG Synthase) gene alters lipid metabolism, causing enhanced abiotic stress responses, yellowing of leaves at the seedling stage and delayed plant development. Here, we observed that the Oscds5 mutant shows enhanced resistance to rice blast, bacterial blight and bacterial leaf streak. Mutation of OsCDS5 promotes production of reactive oxygen species and increases the expression level of multiple defence‐related genes. Transcriptomic analyses indicate that genes involved in responses to stress, biotic/abiotic stimuli and metabolic processes are highly upregulated and enriched in mutant Oscds5. Metabolomic analyses showed that differential metabolites were enriched in the lipid metabolic and tryptophan metabolic pathways. The decreased level of phosphatidylinositol and increased level of serotonin probably contribute to enhanced disease resistance of the Oscds5 mutant. Taken together, mutation of OsCDS5 enhances abiotic and biotic stress responses, and OsCDS5 may be a promising target for genetic engineering to enhance the resilience of rice to abiotic and biotic stresses simultaneously. [ABSTRACT FROM AUTHOR]

Tomato (Solanum lycopersicum L.) is the second most important vegetable crop after potatoes, and global demands have been steadily increasing in recent years. Conventional and modern breeding techniques have been applied to breed and domesticate tomato varieties to meet the need for higher yield or superior agronomical traits that allow them to sustain under different climatic conditions. In the current study, we applied bulk population breeding by crossing eight tomato accessions procured from the Asian Vegetable Research and Development Center with three heat-resistant tomato inbred lines from Vietnam and generated ten elite tomato (ET) lines in the F8 generation. The individual F8 lines exhibited robust vigor and adaptability to climatic conditions of North Vietnam. Among the ten lines, ET1 and ET3 displayed indeterminate growth. ET2 showed semi-determinate, while all the other lines had determinate growth. The different ET lines showed distinctive superior agronomical traits, including early maturing (ET4, ET7, and ET10), highly efficient fruit set (ET1), higher yield (ET1, ET8, ET10), jointless pedicels (ET2), and partial parthenocarpy (ET9). Molecular analysis revealed that the ET3 line consisted of Ty-1 and Ty-3 loci that positively contribute to Tomato yellow leaf curl virus resistance in tomato plants. The elite tomato lines developed in this study would contribute significantly to the Vietnamese and Asian gene pool for improved tomato production and would be a valuable resource for various breeding goals. [ABSTRACT FROM AUTHOR]

Viruses are silent enemies that intrude and take control of the plant cell's machinery for their own multiplication. Infection by viruses and the resulting damage is still a major challenge in the agriculture sector. Plants have the capability to fight back, but the ability of viruses to mutate at a fast rate helps them to evade the host's response. Therefore, classical approaches for introgressing resistance genes by breeding have obtained limited success in counteracting the virus menace. Genetic modification (GM)-based strategies have been successful in engineering artificial resistance in plants. Several different approaches based on pathogen-derived resistance, antisense constructs, hairpin RNAs, double-stranded RNA, etc., have been used to enhance plants' resistance to viruses. Recently, genome editing (GE) strategies mainly involving the CRISPR/Cas-mediated modifications are being used for virus control. In this review, we discuss the developments and advancements in GM- and GE-based methods for tackling viral infection in plants. [ABSTRACT FROM AUTHOR]

Dof (DNA binding with one finger) proteins are plant-specific transcription factors involved in gene regulation during abiotic and biotic stresses. Our previous studies suggested that tobacco Dof proteins, including BBF3, can upregulate the expression of the virus resistance N gene as well as resistance-related genes. In this study, we generated and characterized transgenic tobacco lines carrying the N gene that overexpressed BBF3 cDNA constitutively. In the absence of virus challenge, the BBF3 overexpression caused no developmental defects and no changes in the N transcript level, although the transcript levels of some defense-related genes were affected compared with levels in non-transgenic plants. TMV infection induced a hypersensitive reaction (HR) with larger necrotic lesions in transgenic lines than in non-transgenic plants, but there was no change in total virus accumulation per lesion in a standardized area. Activation of the N gene expression in non-transgenic plants during synchronously-induced HR was followed by downregulation of BBF3 gene expression. Constitutive overexpression of the BBF3 transgene resulted in higher accumulation of the N gene as well as HR marker genes (Hin1 and Hsr203j) and lower accumulation of salicylic acid- and jasmonic acid-signaling marker genes (PR1-a and PR-1b). In particular, the expression of PR-1b was remarkably suppressed in the BBF3-overexpressing transgenic lines. Dof-binding motifs were confirmed in the upstream regions of all target genes examined. Our results suggest that BBF3 has a role in modulating the expression of genes associated with virus elicitor recognition and defense responses resulting in larger areas of HR-associated cell death. [ABSTRACT FROM AUTHOR]

Orchid mycorrhizal fungi (OMF) are vital biocontrol agents, especially for Odontoglossum ringspot virus (ORSV). The promising study helped identify the mycorrhiza isolate from native tropical orchids and determine its potential as a biocontrol. Sample collection of healthy roots of Phalaenopsis amabilis emanated in Yogyakarta, Indonesia, carrying out molecular identification with rDNA-ITS amplification using a set of universal primers ITS1 and ITS4. In vivo, antagonist tests began by inoculating viruses and mycorrhiza to determine the effect of growth and induction of secondary metabolites. The result showed one isolate of Trichoderma sp. associated with the molecular analysis has amplified the ITS1-5.8S-ITS4 section by 600-750 bp DNA. The sequenced products revealed insertion and substitution occurrences, which may have caused the variance by strain diversity and potential severity. Indonesian isolates have undergone speciation and separation from other isolates by a substantial distance. The considerable effects were the increase in leaf length, leaf width, root length, leaf count, the number of roots, fresh weight, and a lowering of the virus content. The analysis of the plant growth parameters and virus concentrations provided significant differences among the treatments inoculated with orchid mycorrhiza (Mycorrhiza [M], Mycorrhiza + Virus [MV], and Virus + Mycorrhiza [VM]) and those without orchid mycorrhiza inoculation (Control [C] and Virus [V]). The orchid resistance suggested that the virus infecting plant leaves contain more phenolic chemicals. This study is the first-ever report of the Trichoderma sp. isolated from native tropical orchids in Indonesia. [ABSTRACT FROM AUTHOR]

The antiviral response against influenza A virus (IAV) infection includes the induction of the interferon (IFN) signaling pathway, including activation of the STATs protein family. Subsequently, antiviral myxovirus resistance (MxA) protein and other interferon-stimulated genes control virus replication; however, the molecular interaction of viral-mediated IFN signaling needs more investigation. Host microRNAs (miRNAs) are small non-coding molecules that posttranscriptionally regulate gene expression. Here, we sought to investigate the possible involvement of miR-141 in IAV-mediated IFN signaling. Accordingly, the microarray analysis of A549 cells transfected with precursor miR-141 (pre-miR-141) was used to capture the potentially regulated genes in response to miR-141 overexpression independent of IAV infection. The downregulation of targeted genes by miR-141, in addition to viral gene expression, was investigated by quantitative real-time PCR, western blot analysis, and flow cytometric assay. Our findings showed a significant upregulation of miR-141 in infected A549 cells with different strains of IAV. Notably, IAV replication was firmly interrupted in cells transfected with the miR-141 inhibitor. While its replication significantly increased in cells transfected with pre-miR-141 confirming the crucial role of miRNA-141 in supporting virus replication. Interestingly, the microarray data of miR-141 transduced A549 cells showed many downregulated genes, including MxA, STAT3, IFI27, and LAMP3. The expression profile of MxA and STAT3 was significantly depleted in infected cells transfected with the pre-miR-141, while their expression was restored in infected cells transfected with the miR-141 inhibitor. Unlike interleukin 6 (IL-6), the production of IFN-β markedly decreased in infected cells that transfected with pre-miR-141, while it significantly elevated in infected cells transfected with miR-141 inhibitor. These data provide evidence for the crucial role of miR-141 in regulating the antiviral gene expression induced by IFN and IL-6 signaling during IAV infection to ensure virus replication. [ABSTRACT FROM AUTHOR]

Cassava (Manihot esculenta Crantz) is a food and industrial storage root crop with substantial potential to contribute to managing risk associated with climate change due to its inherent resilience and in providing a biodegradable option in manufacturing. In Africa, cassava production is challenged by two viral diseases, cassava brown streak disease (CBSD) and cassava mosaic disease. Here we detect quantitative trait loci (QTL) associated with CBSD in a biparental mapping population of a Tanzanian landrace, Nachinyaya and AR37-80, phenotyped in two locations over three years. The purpose was to use the information to ultimately facilitate either marker-assisted selection or adjust weightings in genomic selection to increase the efficiency of breeding. Results from this study were considered in relation to those from four other biparental populations, of similar genetic backgrounds, that were phenotyped and genotyped simultaneously. Further, we investigated the co-localization of QTL for CBSD resistance across populations and the genetic relationships of parents based on whole genome sequence information. Two QTL on chromosome 4 for resistance to CBSD foliar symptoms and one on each of chromosomes 11 and 18 for root necrosis were of interest. Of significance within the candidate genes underlying the QTL on chromosome 4 are Phenylalanine ammonia-lyase (PAL) and Cinnamoyl-CoA reductase (CCR) genes and three PEPR1-related kinases associated with the lignin pathway. In addition, a CCR gene was also underlying the root necrosis-resistant QTL on chromosome 11. Upregulation of key genes in the cassava lignification pathway from an earlier transcriptome study, including PAL and CCR, in a CBSD-resistant landrace compared to a susceptible landrace suggests a higher level of basal lignin deposition in the CBSD-resistant landrace. Earlier RNAscope® in situ hybridisation imaging experiments demonstrate that cassava brown streak virus (CBSV) is restricted to phloem vessels in CBSV-resistant varieties, and phloem unloading for replication in mesophyll cells is prevented. The results provide evidence for the involvement of the lignin pathway. In addition, five eukaryotic initiation factor (eIF) genes associated with plant virus resistance were found within the priority QTL regions. [ABSTRACT FROM AUTHOR]

Our previous study identified an evolutionarily conserved C4HC3‐type E3 ligase, named microtubule‐associated E3 ligase (MEL), that regulates broad‐spectrum plant resistance against viral, fungal and bacterial pathogens in multiple plant species by mediating serine hydroxymethyltransferase (SHMT1) degradation via the 26S proteasome pathway. In the present study, we found that NS3 protein encoded by rice stripe virus could competitively bind to the MEL substrate recognition site, thereby inhibiting MEL interacting with and ubiquitinating SHMT1. This, in turn, leads to the accumulation of SHMT1 and the repression of downstream plant defence responses, including reactive oxygen species accumulation, mitogen‐activated protein kinase pathway activation, and the up‐regulation of disease‐related gene expression. Our findings shed light on the ongoing arms race between pathogens and demonstrate how a plant virus can counteract the plant defence response. [ABSTRACT FROM AUTHOR]

Control of plant virus diseases largely depends on the induced plant defence achieved by the external application of synthetic chemical inducers with the ability to modify defence‐signalling pathways. However, most of the molecular mechanisms underlying these chemical inducers remain unknown. Here, we developed a chitosan‐coated lentinan‐loaded hydrogel and discovered how it protects plants from different virus infections. The hydrogel was synthesized by coating chitosan on the surface of the calcium alginate‐lentinan (LNT) hydrogel (SL‐gel) to form a CSL‐gel. CSL‐gels exhibit the capacity to prolong the stable release of lentinan and promote Ca2+ release. Application of CSL‐gels on the root of plants induces broad‐spectrum resistance against plant viruses (TMV, TRV, PVX and TuMV). RNA‐seq analysis identified that Nicotiana benthamiana calmodulin‐like protein gene 3 (NbCML3) is upregulated by the sustained release of Ca2+ from the CSL‐gel, and silencing and overexpression of NbCML alter the susceptibility and resistance of tobacco to TMV. Our findings provide evidence that this novel and synthetic CSL‐gel strongly inhibits the infection of plant viruses by the sustainable release of LNT and Ca2+. This study uncovers a novel mode of action by which CSL‐gels trigger NbCML3 expression through the stable and sustained release of Ca2+. Summary statement: Synthesis of chemical inducers with the ability to induce plant defence or modify defence‐signalling pathways is a practical way to control plant virus diseases. However, the molecular mechanisms underlying the action of chemical inducers remain largely unknown. This study demonstrates that a chitosan‐coated lentinan‐loaded calcium alginate hydrogel with prolonged and sustained release of lentinan and Ca2+ in plant roots promotes plant growth and enhances broad‐spectrum virus resistance by inducing NbCML3 expression in N. benthamiana. [ABSTRACT FROM AUTHOR]

Plant viruses infect a wide variety of economically important crop plants and cause significant loss in agricultural production around the world. Conventional control strategies are insufficient to combat rapidly evolving plant viruses. In recent years, genome editing technologies have paved new ways for manipulating viral genomes (DNA or RNA). Among them, the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) system has been seen to be able to engineer plant virus resistance by directly targeting the viral genome as well as by inactivating host susceptibility genes. In this review, we survey genome editing tools targeting viral genomes, with an emphasis on CRISPR/Cas9. The advantages of the CRISPR/Cas9 system for combating plant viruses as well as its limitations are discussed in detail. [ABSTRACT FROM AUTHOR]

Emerging evidence indicates that in addition to its well-recognized functions in antiviral RNA silencing, dsRNA elicits pattern-triggered immunity (PTI), likely contributing to plant resistance against virus infections. However, compared to bacterial and fungal elicitor-mediated PTI, the mode-of-action and signaling pathway of dsRNA-induced defense remain poorly characterized. Here, using multicolor in vivo imaging, analysis of GFP mobility, callose staining, and plasmodesmal marker lines in Arabidopsis thaliana and Nicotiana benthamiana, we show that dsRNA-induced PTI restricts the progression of virus infection by triggering callose deposition at plasmodesmata, thereby likely limiting the macromolecular transport through these cell-to-cell communication channels. The plasma membrane-resident SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1, the BOTRYTIS INDUCED KINASE1/AVRPPHB SUSCEPTIBLE1-LIKE KINASE1 kinase module, PLASMODESMATA-LOCATED PROTEINs 1/2/3, as well as CALMODULIN-LIKE 41 and Ca2+ signals are involved in the dsRNA-induced signaling leading to callose deposition at plasmodesmata and antiviral defense. Unlike the classical bacterial elicitor flagellin, dsRNA does not trigger a detectable reactive oxygen species (ROS) burst, substantiating the idea that different microbial patterns trigger partially shared immune signaling frameworks with distinct features. Likely as a counter strategy, viral movement proteins from different viruses suppress the dsRNA-induced host response leading to callose deposition to achieve infection. Thus, our data support a model in which plant immune signaling constrains virus movement by inducing callose deposition at plasmodesmata and reveals how viruses counteract this layer of immunity. dsRNA-induced antiviral pattern-triggered immunity targets plasmodesmata for callose deposition and is suppressed by virus-encoded movement proteins. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms underlying plant resistance to virus infections is crucial for viral disease management in agriculture. However, the defense mechanism of watermelon (Citrullus lanatus) against cucumber green mottle mosaic virus (CGMMV) infection remains largely unknown. In this study, we performed transcriptomic, metabolomic, and phytohormone analyses of a CGMMV susceptible watermelon cultivar 'Zhengkang No.2' ('ZK') and a CGMMV resistant wild watermelon accession PI 220778 (PI) to identify the key regulatory genes, metabolites, and phytohormones responsible for CGMMV resistance. We then tested several phytohormones and metabolites for their roles in watermelon CGMMV resistance via foliar application, followed by CGMMV inoculation. Several phenylpropanoid metabolism-associated genes and metabolites, especially those involved in the flavonoid biosynthesis pathway, were found to be significantly enriched in the CGMMV-infected PI plants compared with the CGMMV-infected 'ZK' plants. We also identified a gene encoding UDP-glycosyltransferase (UGT) that is involved in kaempferol-3- O -sophoroside biosynthesis and controls disease resistance, as well as plant height. Additionally, salicylic acid (SA) biogenesis increased in the CGMMV-infected 'ZK' plants, resulting in the activation of a downstream signaling cascade. SA levels in the tested watermelon plants correlated with that of total flavonoids, and SA pre-treatment up-regulated the expression of flavonoid biosynthesis genes, thus increasing the total flavonoid content. Furthermore, application of exogenous SA or flavonoids extracted from watermelon leaves suppressed CGMMV infection. In summary, our study demonstrates the role of SA-induced flavonoid biosynthesis in plant development and CGMMV resistance, which could be used to breed for CGMMV resistance in watermelon. [ABSTRACT FROM AUTHOR]

Induction of R-gene-mediated antiviral resistance results in phenotypically different responses depending on host R gene—virus combinations. The responses include a hypersensitive response (HR), in which virus infection is stopped within the initially infected tissues to form necrotic local lesions (NLLs) by induction of programmed-cell death (PCD), as well as an extreme resistance (ER), in which virus replication is suppressed at the cellular level without PCD induction. A response that causes only tiny NLLs is called a micro-HR, and a response that causes systemic death of the plant by systemic PCD induction is called a systemic HR (SHR). In this study, we used our RCY1—cucumber mosaic virus (CMV) coat protein (CP) system as a model system for R gene—virus recognition and resistance induction, and showed that artificial deletion/alanine substitutions in an arginine-rich motif in CMV CP changed the induced response from an HR to an ER and to intermediate responses between an ER and a micro-HR, where different numbers of tiny NLLs were formed. Using a micro-HR inducing variant, we showed that viral MOI (multiplicity of infection) reduced by 51.5% upon a micro-HR induction, which was much greater than the reduction observed upon an HR induction, providing the first quantitative evidence that a micro-HR is a result of enhanced resistance. Based on the obtained results, we discuss a possible molecular mechanism for the induction of enhanced resistance and the mechanisms for the induction of phenotypically different responses. [ABSTRACT FROM AUTHOR]

Virus-specific proteins, including coat proteins, movement proteins, replication proteins, and suppressors of RNA interference are capable of triggering the hypersensitive response (HR), which is a type of cell death in plants. The main cell death signaling pathway involves direct interaction of HR-inducing proteins with nucleotide-binding leucine-rich repeats (NLR) proteins encoded by plant resistance genes. Singleton NLR proteins act as both sensor and helper. In other cases, NLR proteins form an activation network leading to their oligomerization and formation of membrane-associated resistosomes, similar to metazoan inflammasomes and apoptosomes. In resistosomes, coiled-coil domains of NLR proteins form Ca2+ channels, while toll-like/interleukin-1 receptor-type (TIR) domains form oligomers that display NAD+ glycohydrolase (NADase) activity. This review is intended to highlight the current knowledge on plant innate antiviral defense signaling pathways in an attempt to define common features of antiviral resistance across the kingdoms of life. [ABSTRACT FROM AUTHOR]

Potato virus Y (PVY) infection causes necrosis and curling of leaves, which seriously affect the yield and quality of Solanaceous crops. The roles of nutrient elements in the regulation of plant resistance to virus infection has been widely reported, while the mechanisms are poorly studied. Previous studies in our laboratory have demonstrated that foliar spraying of MgSO4 could induce Nicotiana tabacum resistance to PVY by increasing the activity of defense-related enzymes. Consistent with the results, we found that exogenous magnesium (Mg) had a certain effect on N. tabacum anti-PVY infection. Meanwhile, Illumina RNA sequencing revealed that Mg induced resistance to PVY infection was mainly by regulating carbohydrate metabolism and transportation, nitrogen metabolism, Ca2+ signal transduction and oxidative phosphorylation. Moreover, we used virus-induced gene silencing assays to verify the function of homologs of five N. tabacum genes involved in above pathways in N. benthamiana. The results showed that NbTPS and NbGBE were conducive to PVY infection, while NbPPases and NbNR were related to resistance to PVY infection. These results suggested a novel strategy for resistance to PVY infection and provided a theoretical basis for virus-resistance breeding. [ABSTRACT FROM AUTHOR]

This review analyzes methods for controlling plant viral infection. The high harmfulness of viral diseases and the peculiarities of viral pathogenesis impose special requirements regarding developing methods to prevent phytoviruses. The control of viral infection is complicated by the rapid evolution, variability of viruses, and the peculiarities of their pathogenesis. Viral infection in plants is a complex interdependent process. The creation of transgenic varieties has caused much hope in the fight against viral pathogens. The disadvantages of genetically engineered approaches include the fact that the resistance gained is often highly specific and short-lived, and there are bans in many countries on the use of transgenic varieties. Modern prevention methods, diagnosis, and recovery of planting material are at the forefront of the fight against viral infection. The main techniques used for the healing of virus-infected plants include the apical meristem method, which is combined with thermotherapy and chemotherapy. These methods represent a single biotechnological complex method of plant recovery from viruses in vitro culture. It widely uses this method for obtaining non-virus planting material for various crops. The disadvantages of the tissue culture-based method of health improvement include the possibility of selfclonal variations resulting from the long-term cultivation of plants under in vitro conditions. The possibilities of increasing plant resistance by stimulating their immune system have expanded, which results from the in-depth study of the molecular and genetic bases of plant resistance toward viruses and the investigation of the mechanisms of induction of protective reactions in the plant organism. The existing methods of phytovirus control are ambiguous and require additional research. Further study of the genetic, biochemical, and physiological features of viral pathogenesis and the development of a strategy to increase plant resistance to viruses will allow a new level of phytovirus infection control to be reached. [ABSTRACT FROM AUTHOR]

Invasion of C. fulvum causes the most serious diseases affecting the reproduction of tomatoes. Cf-10-gene-carrying line showed remarkable resistance to Cladosporium fulvum. To exploit its defense response mechanism, we performed a multiple-omics profiling of Cf-10-gene-carrying line and a susceptible line without carrying any resistance genes at non-inoculation and 3 days post-inoculation (dpi) of C. fulvum. We detected 54 differentially expressed miRNAs (DE-miRNAs) between the non-inoculation and 3 dpi in the Cf-10-genecarrying line, which potentially regulated plant-pathogen interaction pathways and hormone signaling pathways. We also revealed 3,016 differentially expressed genes (DEGs) between the non-inoculated and 3 dpi in the Cf-10-gene-carrying line whose functions enriched in pathways that were potentially regulated by the DE-miRNAs. Integrating DE-miRNAs, gene expression and plant-hormone metabolites indicated a regulation network where the downregulation of miRNAs at 3 dpi activated crucial resistance genes to trigger host hypersensitive cell death, improved hormone levels and upregulated the receptors/critical responsive transcription factors (TFs) of plant hormones, to shape immunity to the pathogen. Notably, our transcriptome, miRNA and hormone metabolites profiling and qPCR analysis suggested that that the downregulation of miR9472 potentially upregulated the expression of SAR Deficient 1 (SARD1), a key regulator for ICS1 (Isochorismate Synthase 1) induction and salicylic acid (SA) synthesis, to improve the level of SA in the Cf-10-gene-carrying line. Our results exploited potential regulatory network and new pathways underlying the resistance to C. fulvum in Cf-10-gene-carrying line, providing a more comprehensive genetic circuit and valuable gene targets for modulating resistance to the virus. [ABSTRACT FROM AUTHOR]

Tomato chlorosis virus (ToCV) is a member of the genus Crinivirus in the family Closteroviridae. It has a wide host range and wide distribution, causing serious harm to the vegetable industry. The autophagy pathway plays an important role in plant resistance to virus infection. Viruses and plant hosts coevolve in defence and antidefence processes around autophagy. In this study, the interaction between ToCV p22 and Nicotiana benthamiana B‐cell lymphoma2‐associated athanogenes5 Nicotiana benthamiana (NbBAG5) was examined. Through overexpression and down‐regulation of NbBAG5, results showed that NbBAG5 could negatively regulate ToCV infection. NbBAG5 was found to be localized in mitochondria and can change the original localization of ToCV p22, which is colocalized in mitochondria. NbBAG5 inhibited the expression of mitophagy‐related genes and the number of autophagosomes, thereby regulating viral infection by affecting mitophagy. In summary, this study demonstrated that ToCV p22 affects autophagy by interacting with NbBAG5, established the association between viral infection, BAG proteins family, and the autophagy pathway, and explained the molecular mechanism by which ToCV p22 interacts with NbBAG5 to inhibit autophagy to regulate viral infection. [ABSTRACT FROM AUTHOR]

Environmental changes and global warming may promote the emergence of unknown viruses, whose spread is favored by the trade in plant products. Viruses represent a major threat to viticulture and the wine industry. Their management is challenging and mostly relies on prophylactic measures that are intended to prevent the introduction of viruses into vineyards. Besides the use of virus-free planting material, the employment of agrochemicals is a major strategy to prevent the spread of insect vectors in vineyards. According to the goal of the European Green Deal, a 50% decrease in the use of agrochemicals is expected before 2030. Thus, the development of alternative strategies that allow the sustainable control of viral diseases in vineyards is strongly needed. Here, we present a set of innovative biotechnological tools that have been developed to induce virus resistance in plants. From transgenesis to the still-debated genome editing technologies and RNAi-based strategies, this review discusses numerous illustrative studies that highlight the effectiveness of these promising tools for the management of viral infections in grapevine. Finally, the development of viral vectors from grapevine viruses is described, revealing their positive and unconventional roles, from targets to tools, in emerging biotechnologies. [ABSTRACT FROM AUTHOR]

Plant viruses cause crop losses in agronomically and economically important crops, making global food security a challenge. Although traditional plant breeding has been effective in controlling plant viral diseases, it is unlikely to solve the problems associated with the frequent emergence of new and more virulent virus species or strains. As a result, there is an urgent need to develop alternative virus control strategies that can be used to more easily contain viral diseases. A better understanding of plant defence mechanisms will open up new avenues for research into plantpathogen interactions and the development of broad-spectrum virus resistance. The scientific literature was evaluated and structured in this review, and the results of the reliability of the methods of analysis used were filtered. As a result, we described the molecular mechanisms by which viruses interact with host plant cells. To develop an effective strategy for the control of plant pathogens with a significant intensity on the agricultural market, clear and standardised recommendations are required. The current review will provide key insights into the molecular underpinnings underlying the coordination of plant disease resistance, such as main classes of resistance genes, RNA interference, and the RNA-mediated adaptive immune system of bacteria and archaea -- clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated Cas proteins -- CRISPR/Cas. Future issues related to resistance to plant viral diseases will largely depend on integrated research to transfer fundamental knowledge to applied problems, bridging the gap between laboratory and field work. [ABSTRACT FROM AUTHOR]

Plant immunity relies on nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) that detect microbial patterns released by pathogens, and activate localized cell death to prevent the spread of pathogens. Tsw is the only identified resistance (R) gene encoding an NLR, conferring resistance to tomato spotted wilt orthotospovirus (TSWV) in pepper species (Capsicum , Solanaceae). However, molecular and cellular mechanisms of Tsw -mediated resistance are still elusive. Here, we analysed the structural and cellular functional features of Tsw protein, and defined a hydrophobic module to improve NLR-mediated virus resistance. The plasma membrane associated N-terminal 137 amino acid in the coiled-coil (CC) domain of Tsw is the minimum fragment sufficient to trigger cell death in Nicotiana benthamiana plants. Transient and transgenic expression assays in plants indicated that the amino acids of the hydrophobic groove (134th–137th amino acid) in the CC domain is critical for its full function and can be modified for enhanced disease resistance. Based on the structural features of Tsw, a super-hydrophobic funnel-like mutant, TswY137W, was identified to confer higher resistance to TSWV in a SGT1 (Suppressor of G-two allele of Skp1)-dependent manner. The same point mutation in a tomato Tsw-like NLR protein also improved resistance to pathogens, suggesting a feasible way of structure-assisted improvement of NLRs. [ABSTRACT FROM AUTHOR]

Tomato leaf curl New Delhi virus (ToLCNDV, family Geminiviridae, genus Begomovirus) is a whitefly-transmitted virus that causes widespread damage in Cucurbitaceae and Solaneceae crops worldwide. The Spanish strain, ToLCNDV-ES, affects mainly cucurbit crops and has spread through the Mediterranean basin since its first detection in 2013 in the south of Spain. The control of the virus has been based on the adoption of measures to control the vector, which have not been sufficient to reduce production losses. Therefore, the identification of key genes for ToLCNDV resistance is essential for the development of resistant plants. Regarding genetic control of resistance in cucurbit crops, one major locus on chromosome 11 and two additional regions in chromosomes 12 and 2 of C. melo linked to ToLCNDV resistance have been described recently. Concerning C. moschata, a major QTL was also identified on chromosome 8 that resulted in synteny with a QTL on chromosome 11 of C. melo. In this work, we investigated the molecular basis of ToLCNDV resistance in contrasting accessions of C. melo and C. moschata by transcriptional characterization of 10 different candidate genes controlling host factors related to proviral or antiviral mechanisms. Two proviral factor genes, ARP4 in C. melo and SYTA in C. moschata, showed clear differences in expression levels when the susceptible and resistant accessions were compared. The knowledge of proviral factors associated with resistance could be used to screen an active mutagenesis TILLING platform. This is the case of C. pepo, in which no ToLCNDV resistance has been described to date. The relationship between the regulation of the genes ARP4 and SYTA, as well as the genome position of the described loci related to ToLCNDV resistance, is also discussed. [ABSTRACT FROM AUTHOR]

Simple Summary: As the dividing line between human and wild mammal habitats becomes smaller, virus invasion due to frequent environmental changes poses a significant risk to many mammals. It is becoming increasingly important to research the antiviral ability of wild mammals. As an antiviral gene family, the OAS gene family plays an important role in resistance to viruses. As an important group of mammals, Laurasiatherian mammals occupy a variety of ecological niches in nature and play a crucial role in maintaining the stability of the ecosystem. Our findings offer insights into the molecular and functional evolution of the antiviral ability of Laurasian mammals by exploring the adaptive evolution of the OAS gene family of Laurasiatherian mammals. Many mammals risk damage from virus invasion due to frequent environmental changes. The oligoadenylate synthesis (OAS) gene family, which is an important component of the immune system, provides an essential response to the antiviral activities of interferons by regulating immune signal pathways. However, little is known about the evolutionary characteristics of OASs in Laurasiatherian mammals. Here, we examined the evolution of the OAS genes in 64 mammals to explore the accompanying molecular mechanisms of the antiviral ability of Laurasiatherian mammals living in different environments. We found that OAS2 and OAS3 were found to be pseudogenes in Odontoceti species. This may be related to the fact that they live in water. Some Antilopinae, Caprinae, and Cervidae species lacked the OASL gene, which may be related to their habitats being at higher altitudes. The OASs had a high number of positive selection sites in Cetartiodactyla, which drove the expression of strong antiviral ability. The OAS gene family evolved in Laurasiatherian mammals at different rates and was highly correlated with the species' antiviral ability. The gene evolution rate in Cetartiodactyla was significantly higher than that in the other orders. Compared to other species of the Carnivora family, the higher selection pressure on the OAS gene and the absence of positive selection sites in Canidae may be responsible for its weak resistance to rabies virus. The OAS gene family was relatively conserved during evolution. Conserved genes are able to provide better maintenance of gene function. The rate of gene evolution and the number of positively selected sites combine to influence the resistance of a species to viruses. The positive selection sites demonstrate the adaptive evolution of the OAS gene family to the environment. Adaptive evolution combined with conserved gene function improves resistance to viruses. Our findings offer insights into the molecular and functional evolution of the antiviral ability of Laurasian mammals. [ABSTRACT FROM AUTHOR]

ADP-ribosylation (ADPRylation) is a versatile posttranslational modification in eukaryotic cells which is involved in the regulation of a wide range of key biological processes, including DNA repair, cell signalling, programmed cell death, growth and development and responses to biotic and abiotic stresses. Members of the poly(ADP-ribosyl) polymerase (PARP) family play a central role in the process of ADPRylation. Protein targets can be modified by adding either a single ADP-ribose moiety (mono(ADP-ribosyl)ation; MARylation), which is catalysed by mono(ADP-ribosyl) transferases (MARTs or PARP "monoenzymes"), or targets may be decorated with chains of multiple ADP-ribose moieties (PARylation), via the activities of PARP "polyenzymes". Studies have revealed crosstalk between PARylation (and to a lesser extent, MARylation) processes in plants and plant–virus interactions, suggesting that these tight links may represent a novel factor regulating plant antiviral immunity. From this perspective, we go through the literature linking PARylation-associated processes with other plant regulation pathways controlling virus resistance. Once unraveled, these links may serve as the basis of innovative strategies to improve crop resistance to viruses under challenging environmental conditions which could mitigate yield losses. [ABSTRACT FROM AUTHOR]

Involving the natural host-resistance mechanisms to pathogens are essential and one of the most promising approaches in development of first-line defenses against viral plant diseases. Polysaccharides isolated from natural sources are considered the most active resistance inducers. The biological activity of polysaccharides depends on the nature and chemical structure of the constituent components of complex preparations. In this view, the objective of our study was to evaluate the biological activity of complex preparations composed of glycans, rhamnolipids, and thiosulfonates as inducers of natural plant resistance and inhibitors of tobacco mosaic virus (TMV). Complex preparations were obtained using the following components: biogenic glycolipids - rhamnolipids of the Pseudomonas sp. strain PS-17, glycans - Ganoderma adspersum glucan and Candida maltosa mannan, as well as synthetic biocides - thiosulfonates (methylthiosulfanilate). The biological activity of the preparations was investigated in the host-virus model system Nicotiana tabacum L. and TMV. It was shown that preparations at concentrations of 10 and 100 µg mL-1 were active plant resistance inducers in N. tabacum cv. Immune 580, hypersensitive to TMV. At the same concentrations, complex preparations also reduced infectivity of TMV on Datura metel L. acting as viral infection inhibitors. The inducing activity of the complex preparations is sensitive to well-known transcription inhibitor actinomycin D (10 µg mL-1). This fact may indicate the important role of RNA synthesis in the activation of plant virus resistance by the studied preparations. [ABSTRACT FROM AUTHOR]

Introduction: All decapod crustaceans are considered potentially susceptible to White Spot Syndrome Virus (WSSV) infection, but the degree of White Spot Disease (WSD) susceptibility varies widely between species. The European shore crab Carcinus maenas can be infected with the virus for long periods of time without signs of disease. Given the high mortality rate of susceptible species, the differential susceptibility of these resistant hosts offers an opportunity to investigate mechanisms of disease resistance. Methods: Here, the temporal transcriptional responses (mRNA and miRNA) of C. maenas following WSSV injection were analysed and compared to a previously published dataset for the highly WSSV susceptible Penaeus vannamei to identify key genes, processes and pathways contributing to increased WSD resistance. Results: We show that, in contrast to P. vannamei, the transcriptional response during the first 2 days following WSSV injection in C. maenas is limited. During the later time points (7 days onwards), two groups of crabs were identified, a recalcitrant group where no replication of the virus occurred, and a group where significant viral replication occurred, with the transcriptional profiles of the latter group resembling those of WSSV-susceptible species. We identify key differences in the molecular responses of these groups to WSSV injection. Discussion: We propose that increased WSD resistance in C. maenas may result from impaired WSSV endocytosis due to the inhibition of internal vesicle budding by dynamin-1, and a delay in movement to the nucleus caused by the downregulation of cytoskeletal transcripts required for WSSV cytoskeleton docking, during early stages of the infection. This response allows resistant hosts greater time to fine-tune immune responses associated with miRNA expression, apoptosis and the melanisation cascade to defend against, and clear, invading WSSV. These findings suggest that the initial stages of infection are key to resistance to WSSV in the crab and highlight possible pathways that could be targeted in farmed crustacean to enhance resistance to WSD. [ABSTRACT FROM AUTHOR]

Tomato yellow leaf curl virus (TYLCV) causes tremendous losses of tomato worldwide. An elicitor Hrip1, which produced by Alternaria tenuissima, can serve as a pathogen-associated molecular patterns (PAMPs) to trigger the immune defense response in Nicotiana benthamiana. Here, we show that Hrip1 can be targeted to the extracellular space and significantly delayed the development of symptoms caused by TYLCV in tomato. In basis of RNA-seq profiling, we find that 1621 differential expression genes (DEGs) with the opposite expression patterns are enriched in plant response to biotic stress between Hrip1 treatment and TYLCV infection of tomato. Thirty-two known differential expression miRNAs with the opposite expression patterns are identified by small RNA sequencing and the target genes of these miRNAs are significantly enriched in phenylpropanoid biosynthesis, plant hormone signal transduction and peroxisome. Based on the Pearson correlation analysis, 13 negative and 21 positive correlations are observed between differential expression miRNAs and DEGs. These miRNAs, which act as a key mediator of tomato resistance to TYLCV induced by Hrip1, regulate the expression of phenylpropanoid biosynthesis and plant hormone signal transduction-related genes. Taken together, our results provide an insight into tomato resistance to TYLCV induced by PAMP at transcriptional and posttranscriptional levels. [ABSTRACT FROM AUTHOR]

Effector-triggered immunity (ETI) is one of the most studied mechanisms of plant resistance to viruses. During ETI, viral proteins are recognized by specific plant R proteins, which most often trigger a hypersensitive response (HR) involving programmed cell death (PCD) and a restriction of infection in the initially infected sites. However, in some plant–virus interactions, ETI leads to a response in which PCD and virus multiplication are not restricted to the entry sites and spread throughout the plant, leading to systemic necrosis. The host and virus genetic determinants, and the consequences of this response in plant–virus coevolution, are still poorly understood. Here, we identified an allelic version of RCY1—an R protein—as the host genetic determinant of broad-spectrum systemic necrosis induced by cucumber mosaic virus (CMV) infection in the Arabidopsis thaliana Co-1 ecotype. Systemic necrosis reduced virus fitness by shortening the infectious period and limiting virus multiplication; thus, this phenotype could be adaptive for the plant population as a defense against CMV. However, the low frequency (less than 1%) of this phenotype in A. thaliana wild populations argues against this hypothesis. These results expand current knowledge on the resistance mechanisms to virus infections associated with ETI in plants. [ABSTRACT FROM AUTHOR]

Viruses are acellular pathogens that cause severe infections in plants, resulting in worldwide crop losses every year. The lack of chemical agents to control viral diseases exacerbates the situation. Thus, to devise proper management strategies, it is important that the defense mechanisms of plants against viruses are understood. Resistance (R) genes regulate plant defense against invading pathogens by eliciting a hypersensitive response (HR). Compatible interaction between plant R gene and viral avirulence (Avr) protein activates the necrotic cell death response at the site of infection, resulting in the cessation of disease. Here, we review different aspects of R gene-mediated dominant resistance against plant viruses in dicotyledonous plants and possible ways for developing crops with better disease resistance. R gene-mediated hypersensitive response is one of the major sources of resistance against plant viruses. CC-NBS-LRR and TIR-NBS-LRR are two important intracellular resistance protein classes that recognize viral effector molecules to activate defense responses. Various miRNAs suppress the expression of R genes in the absence of virus to maintain the trade-off between growth and resistance. Modern technologies will help in the constant search for a new source of resistance in emerging resistance-breaking isolates of plant viruses. [ABSTRACT FROM AUTHOR]

RNA silencing, a conserved gene regulatory mechanism, is critical for host resistance to viruses. Liquid-liquid phase separation (LLPS) is an important mechanism in regulating various biological processes. Emerging studies suggest RNA helicases play important roles in microRNA (miRNA) production through LLPS. In this study, we investigated the functional role of RNA helicase 20 (RH20), a DDX5 homolog in Arabidopsis thaliana , in RNA silencing and plant resistance to viruses. Our findings reveal that RH20 localizes in both the cytoplasm and nucleus, with puncta formation in the cytoplasm exhibiting liquid–liquid phase separation behavior. We demonstrate that RH20 plays positive roles in plant immunity against viruses. Further study showed that RH20 interacts with Argonaute 2 (AGO2), a key component of the RNA silencing pathway. Moreover, RH20 promotes the accumulation of both endogenous and exogenous small RNAs (sRNAs). Overall, our study identifies RH20 as a novel phase separation protein that interacting with AGO2, influencing sRNAs accumulation, and enhancing plant resistance to viruses. • RH20 undergoes liquid-liquid phase separation in the cytoplasm, and interacts with AGO2. • RH20 regulates the accumulation of both endogenous and exogenous small RNAs. • RH20 plays a general role in the plant antiviral immunity. • RH20 and its homolog, RH30 play additive roles in plant resistance to virus. [ABSTRACT FROM AUTHOR]

Plant viruses are known to infect most economically important crops and pose a major threat to global food security. Currently, few resistant host phenotypes have been delineated, and while chemicals are used for crop protection against insect pests and bacterial or fungal diseases, these are inefficient against viral diseases. Genetic engineering emerged as a way of modifying the plant genome by introducing functional genes in plants to improve crop productivity under adverse environmental conditions. Recently, new breeding technologies, and in particular the exciting CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR‐associated proteins) technology, was shown to be a powerful alternative to engineer resistance against plant viruses, thus has great potential for reducing crop losses and improving plant productivity to directly contribute to food security. Indeed, it could circumvent the "Genetic modification" issues because it allows for genome editing without the integration of foreign DNA or RNA into the genome of the host plant, and it is simpler and more versatile than other new breeding technologies. In this review, we describe the predominant features of the major CRISPR/Cas systems and outline strategies for the delivery of CRISPR/Cas reagents to plant cells. We also provide an overview of recent advances that have engineered CRISPR/Cas‐based resistance against DNA and RNA viruses in plants through the targeted manipulation of either the viral genome or susceptibility factors of the host plant genome. Finally, we provide insight into the limitations and challenges that CRISPR/Cas technology currently faces and discuss a few alternative applications of the technology in virus research. [ABSTRACT FROM AUTHOR]

Summary: The cap‐binding protein eIF4E, through its interaction with eIF4G, constitutes the core of the eIF4F complex, which plays a key role in the circularization of mRNAs and their subsequent cap‐dependent translation. In addition to its fundamental role in mRNA translation initiation, other functions have been described or suggested for eIF4E, including acting as a proviral factor and participating in sexual development. We used CRISPR/Cas9 genome editing to generate melon eif4e knockout mutant lines. Editing worked efficiently in melon, as we obtained transformed plants with a single‐nucleotide deletion in homozygosis in the first eIF4E exon already in a T0 generation. Edited and non‐transgenic plants of a segregating F2 generation were inoculated with Moroccan watermelon mosaic virus (MWMV); homozygous mutant plants showed virus resistance, while heterozygous and non‐mutant plants were infected, in agreement with our previous results with plants silenced in eIF4E. Interestingly, all homozygous edited plants of the T0 and F2 generations showed a male sterility phenotype, while crossing with wild‐type plants restored fertility, displaying a perfect correlation between the segregation of the male sterility phenotype and the segregation of the eif4e mutation. Morphological comparative analysis of melon male flowers along consecutive developmental stages showed postmeiotic abnormal development for both microsporocytes and tapetum, with clear differences in the timing of tapetum degradation in the mutant versus wild‐type. An RNA‐Seq analysis identified critical genes in pollen development that were down‐regulated in flowers of eif4e/eif4e plants, and suggested that eIF4E‐specific mRNA translation initiation is a limiting factor for male gametes formation in melon. [ABSTRACT FROM AUTHOR]

Key message: A reliable locus confers broad-spectrum resistance to multiple plant viruses in soybean under field conditions. Soybean mosaic disease (SMD) can be caused by a variety of viruses, most of which have been largely overlooked in breeding programs. Effective mitigation of the adverse of SMD might result from breeding cultivars with broad-spectrum resistance. However, reports on broad-spectrum resistance to multiple virus have been limited. To catalog viral community members behind SMD, virus samples were collected from symptomatic field plots, and pathogenicity of component strains was assessed. Preliminary ELISA and PCR detection revealed that 39.58% and 66.67% of samples contained two or more virus strains, respectively. Only three soybean accessions were completely asymptomatic, while 42% exhibited moderate or severe susceptibility, indicating that co-infection of multiple virus remains a significant threat in current soybean production systems. Further, a RIL population consisting of 150 F7:9 strains derived from two soybean genotypes with contrasting reactions to virus infection was constructed and explored for significant markers and resistance genes. QTL analysis returned a reliable locus, named GmRmv, on chromosome 13. Significance of GmRmv in imparting resistance to SMD was further confirmed in NIL lines and delimited into a 157-kb interval that contains 17 annotated genes. Among these genes, three, Glyma.13G190000, Glyma.13G190300 and Glyma.13G190400, each contained LRR domains, as well as significant variation in coding sequences between resistant and susceptible parents. Hence, these three genes are considered strong candidate genes for explaining GmRmv significance. In summary, this research opens a new avenue for formulating strategies to breed soybean varieties with broad-spectrum resistance to multiple virus associated with SMD. [ABSTRACT FROM AUTHOR]

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated (Cas) system is widely used as a genome-editing tool in various organisms, including plants, to elucidate the fundamental understanding of gene function, disease diagnostics, and crop improvement. Among the CRISPR/Cas systems, Cas9 is one of the widely used nucleases for DNA modifications, but manipulation of RNA at the post-transcriptional level is limited. The recently identified type VI CRISPR/Cas systems provide a platform for precise RNA manipulation without permanent changes to the genome. Several studies reported efficient application of Cas13 in RNA studies, such as viral interference, RNA knockdown, and RNA detection in various organisms. Cas13 was also used to produce virus resistance in plants, as most plant viruses are RNA viruses. However, the application of CRISPR/Cas13 to studies of plant RNA biology is still in its infancy. This review discusses the current and prospective applications of CRISPR/Cas13-based RNA editing technologies in plants. [ABSTRACT FROM AUTHOR]

Plant viruses impose serious threats on crop production. Artificial miRNAs can mediate specific and effective gene silencing in plants and are widely used in plant gene function studies and to engineer plant viral resistance. To facilitate the design of artificial miRNA genes, we developed a webserver, AMIRdesigner, which can be used to design oligos for artificial miRNA synthesis using wild-type and permutated MIR171 and MIR164 backbones. The artificial miRNA genes designed by AMIRdesigner can be easily assembled into miRNA clusters for multiple target sites. To validate the server functionality, we designed four artificial miRNA genes targeting four conserved regions in the potato leafroll virus genome using AMIRdesigner. These genes were synthesized with the server-designed oligos and further assembled into a quadruple miRNA cluster, which was cloned into an overexpression vector and transformed into potato plants. Small RNA Northern blot and virus inoculation analyses showed that a high level of artificial miRNA expression and good viral resistance were achieved in some of the transgenic lines. These results demonstrate the utility of our webserver AMIRdesigner for engineering crop viral resistance. [ABSTRACT FROM AUTHOR]

Applied to plant viruses, most of these works agree in that maximum seed transmission rates require optimal plant reproduction and, therefore, lower virulence (i.e., effect of infection on seed number) [[13]]. Seed infection provides the virus with means to persist for long periods of time when hosts and/or vectors are not available, as many seed-transmitted viruses can survive within the seed as long as it remains viable [[6]]. However, in plants with sexual dimorphism, pollen infection allows seed transmission in uninfected females, although less efficiently than seed infection from the parental plant [[6]]. Similarly, for PSbMV and BSMV, the HC-Pro and the b proteins that are suppressors of the RNA silencing plant defense response, as well as mutations in other regions that are important for virus multiplication and movement, affect virus seed transmission rate [[28]-[30]]. [Extracted from the article]

The application of microbe-derived products as natural biocontrol agents to boost systemic disease resistance to virus infections in plants is a prospective strategy to make agriculture more sustainable and environmentally friendly. In the current study, the rhizobacterium Bacillus amyloliquefaciens strain TBorg1 was identified based on 16S rRNA, rpoB, and gyrA gene sequences, and evaluated for its efficiency in conferring protection of tomato from infection by Tobacco mosaic virus (TMV). Under greenhouse circumstances, foliar sprays of TBorg1 culture filtrate (TBorg1-CF) promoted tomato growth, lowered disease severity, and significantly decreased TMV accumulation in systemically infected leaves of treated plants relative to untreated controls. TMV accumulation was reduced by 90% following the dual treatment, applied 24 h before and after TMV infection. Significant increases in levels of total soluble carbohydrates, proteins, and ascorbic acid were also found. In addition, a significant rise in activities of enzymes capable of scavenging reactive oxygen species (PPO and POX), as well as decreased levels of non-enzymatic oxidative stress markers (H2O2 and MDA) were observed, compared to untreated plants. Enhanced systemic resistance to TMV was indicated by significantly increased transcript accumulation of polyphenolic pathway (C4H, HCT, and CHI) and pathogenesis-related (PR-1 and PR-5) genes. Out of the 15 compounds identified in the GC-MS analysis, 1,2-benzenedicarboxylic acid mono(2-ethylhexyl) ester and phenol, 2,4-bis(1,1-dimethylethyl), as well as L-proline, N-valeryl-, and heptadecyl ester were present in the highest concentrations in the ethyl acetate extract of TBorg1-CF. In addition, significant amounts of n-hexadecanoic acid, pyrrolo [1,2-a] pyrazine-1,4-dione hexahydro-3-(2-methylpropyl)-, nonane, 5-butyl-, and eicosane were also detected. These compounds may act as inducers of systemic resistance to viral infection. Our findings indicate that the newly isolated B. amyloliquefaciens strain TBorg1 could be a potentially useful rhizobacterium for promoting plant growth and a possible source of biocontrol agents for combating plant virus infections. [ABSTRACT FROM AUTHOR]

In this work we developed and exploited a spray-induced gene silencing (SIGS)-based approach to deliver double-stranded RNA (dsRNA), which was found to protect potato against potato virus Y (PVY) infection. Given that dsRNA can act as a defence-inducing signal that can trigger sequence-specific RNA interference (RNAi) and non-specific pattern-triggered immunity (PTI), we suspected that these two pathways may be invoked via exogeneous application of dsRNA, which may account for the alterations in PVY susceptibility in dsRNA-treated potato plants. Therefore, we tested the impact of exogenously applied PVY-derived dsRNA on both these layers of defence (RNAi and PTI) and explored its effect on accumulation of a homologous virus (PVY) and an unrelated virus (potato virus X, PVX). Here, we show that application of PVY dsRNA in potato plants induced accumulation of both small interfering RNAs (siRNAs), a hallmark of RNAi, and some PTI-related gene transcripts such as WRKY29 (WRKY transcription factor 29; molecular marker of PTI), RbohD (respiratory burst oxidase homolog D), EDS5 (enhanced disease susceptibility 5), SERK3 (somatic embryogenesis receptor kinase 3) encoding brassinosteroid-insensitive 1-associated receptor kinase 1 (BAK1), and PR-1b (pathogenesis-related gene 1b). With respect to virus infections, PVY dsRNA suppressed only PVY replication but did not exhibit any effect on PVX infection in spite of the induction of PTI-like effects in the presence of PVX. Given that RNAi-mediated antiviral immunity acts as the major virus resistance mechanism in plants, it can be suggested that dsRNA-based PTI alone may not be strong enough to suppress virus infection. In addition to RNAi- and PTI-inducing activities, we also showed that PVY-specific dsRNA is able to upregulate production of a key enzyme involved in poly(ADP-ribose) metabolism, namely poly(ADP-ribose) glycohydrolase (PARG), which is regarded as a positive regulator of biotic stress responses. These findings offer insights for future development of innovative approaches which could integrate dsRNA-induced RNAi, PTI and modulation of poly(ADP-ribose) metabolism in a co-ordinated manner, to ensure a high level of crop protection. [ABSTRACT FROM AUTHOR]

Management of viral diseases requires an integration of several methods aimed at preventing or delaying infection of crops, as the viruses overcome the resistance due to their genome plasticity. Plants have evolved a variety of active and passive mechanisms to defend themselves against viral pathogens. One such mechanism is systemic acquired resistance; a safekeeping system a plant has preserved to combat various pathogen attacks. The possibility of inducing resistance in plants against viruses with chemicals or beneficial microorganisms deserves more interest. This study was conducted to evaluate the efficacy of salicylic acid (SA) foliar spray against Chilli Veinal Mottle Virus (ChiVMV) infecting Capsicum annuum L. which induces systemic acquired resistance. Salicylic acid was used as a foliar spray in different concentrations against ChiVMV with reference to disease incidence, percentage inhibition of virus, virus quantification, plant growth and yield parameters, and internal SA accumulation, under pot conditions. Minimum disease incidence and maximum percentage inhibition were recorded when plants were sprayed with 100 ppm salicylic acid 24 h before challenge inoculation. SA 100 ppm foliar spray not only delayed the virus symptoms but also reduced the virus concentration with enhanced growth and yield. Exogenous SA increased the internal SA accumulation, a key factor for SAR. [ABSTRACT FROM AUTHOR]

The CDC48 protein, highly conserved in the living kingdom, is a player of the ubiquitin proteasome system and contributes to various cellular processes. In plants, CDC48 is involved in cell division, plant growth and, as recently highlighted in several reports, in plant immunity. In the present study, to further extend our knowledge about CDC48 functions in plants, we analysed the incidence of its overexpression on tobacco development and immune responses. CDC48 overexpression disrupted plant development and morphology, induced changes in plastoglobule appearance and exacerbated ROS production. In addition, levels of salicylic acid (SA) and glycosylated SA were higher in transgenic plants, both in the basal state and in response to cryptogein, a protein produced by the oomycete Phytophthora cryptogea triggering defence responses. The expression of defence genes, notably those coding for some pathogenesis-related (PR) proteins, was also exacerbated in the basal state in transgenic plant lines. Finally, tobacco plants overexpressing CDC48 did not develop necrosis in response to tobacco mosaic virus (TMV) infection, suggesting a role for CDC48 in virus resistance. • CDC48 overexpression disrupts plant growth, leaf shape and fertility. • Plastoglobules are larger and ROS level is higher when CDC48 is overexpressed. • Overexpression of CDC48 alters the rate of the storage form of salicylic acid. • Salicylic acid signalling is affected by the amount of CDC48 protein. • CDC48 overexpression limits tobacco mosaic virus infection. [ABSTRACT FROM AUTHOR]

Virus-host coevolution often drives virus immune escape. However, it remains unknown whether natural variations of plant virus resistance are enriched in genes of RNA interference (RNAi) pathway known to confer essential antiviral defense in plants. Here, we report two genome-wide association study screens to interrogate natural variation among wild-collected Arabidopsis thaliana accessions in quantitative resistance to the endemic cucumber mosaic virus (CMV). We demonstrate that the highest-ranked gene significantly associated with resistance from both screens acts to regulate antiviral RNAi in ecotype Columbia-0. One gene, corresponding to Reduced Dormancy 5 (RDO5), enhances resistance by promoting amplification of the virus-derived small interfering RNAs (vsiRNAs). Interestingly, the second gene, designated Antiviral RNAi Regulator 1 (VIR1), dampens antiviral RNAi so its genetic inactivation by CRISPR/Cas9 editing enhances both vsiRNA production and CMV resistance. Our findings identify positive and negative regulators of the antiviral RNAi defense that may play important roles in virus-host coevolution. Whether natural variations of plant virus resistance are enriched in genes of RNA interference pathway is unknown. Here, via genome-wide association studies, the authors identify regulators of the RDR6 and DCL2 antiviral pathways are involved in quantitative resistance to cucumber mosaic virus in Arabidopsis. [ABSTRACT FROM AUTHOR]

Different genome editing approaches have been used to engineer resistance against plant viruses. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas; CRISPR/Cas) systems to create pinpoint genetic mutations have emerged as a powerful tool for molecular engineering of plant immunity and increasing resistance against plant viruses. This review presents (i) recent advances in engineering resistance against plant viruses by CRISPR/Cas and (ii) an overview of the potential host factors as targets for the CRISPR/Cas system-mediated broad-range resistance and immunity. Applications, challenges, and perspectives in enabling the CRISPR/Cas system for crop protection are also outlined. [ABSTRACT FROM AUTHOR]