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Abstract Background Plant-parasitic root-knot nematode (Meloidogyne incognita) causes global yield loss in agri- and horticultural crops. Nematode management options rely on chemical method. However, only a handful of nematicides are commercially available. Resistance breeding efforts are not sustainable because R gene sources are limited and nematodes have developed resistance-breaking populations against the commercially available Mi-1.2 gene-expressing tomatoes. RNAi crops that manage nematode infection are yet to be commercialized because of the regulatory hurdles associated with transgenic crops. The deployment of the CRISPR/Cas9 system to improve nematode tolerance (by knocking out the susceptibility factors) in plants has emerged as a feasible alternative lately. Results In the present study, a M. incognita-responsive susceptibility (S) gene, amino acid permease (AAP6), was characterized from the model plant Arabidodpsis thaliana by generating the AtAAP6 overexpression line, followed by performing the GUS reporter assay by fusing the promoter of AtAAP6 with the β-glucuronidase (GUS) gene. Upon challenge inoculation with M. incognita, overexpression lines supported greater nematode multiplication, and AtAAP6 expression was inducible to the early stage of nematode infection. Next, using CRISPR/Cas9, AtAAP6 was selectively knocked out without incurring any growth penalty in the host plant. The ‘Cas9-free’ homozygous T3 line was challenge inoculated with M. incognita, and CRISPR-edited A. thaliana plants exhibited considerably reduced susceptibility to nematode infection compared to the non-edited plants. Additionally, host defense response genes were unaltered between edited and non-edited plants, implicating the direct role of AtAAP6 towards nematode susceptibility. Conclusion The present findings enrich the existing literature on CRISPR/Cas9 research in plant-nematode interactions, which is quite limited currently while compared with the other plant-pathogen interaction systems.

Background: Plant-parasitic root-knot nematode (Meloidogyne incognita) causes global yield loss in agri- and horticultural crops. Nematode management options rely on chemical method. However, only a handful of nematicides are commercially available. Resistance breeding efforts are not sustainable because R gene sources are limited and nematodes have developed resistance-breaking populations against the commercially available Mi-1.2 gene-expressing tomatoes. RNAi crops that manage nematode infection are yet to be commercialized because of the regulatory hurdles associated with transgenic crops. The deployment of the CRISPR/Cas9 system to improve nematode tolerance (by knocking out the susceptibility factors) in plants has emerged as a feasible alternative lately. Results: In the present study, a M. incognita-responsive susceptibility (S) gene, amino acid permease (AAP6), was characterized from the model plant Arabidodpsis thaliana by generating the AtAAP6 overexpression line, followed by performing the GUS reporter assay by fusing the promoter of AtAAP6 with the β-glucuronidase (GUS) gene. Upon challenge inoculation with M. incognita, overexpression lines supported greater nematode multiplication, and AtAAP6 expression was inducible to the early stage of nematode infection. Next, using CRISPR/Cas9, AtAAP6 was selectively knocked out without incurring any growth penalty in the host plant. The 'Cas9-free' homozygous T3 line was challenge inoculated with M. incognita, and CRISPR-edited A. thaliana plants exhibited considerably reduced susceptibility to nematode infection compared to the non-edited plants. Additionally, host defense response genes were unaltered between edited and non-edited plants, implicating the direct role of AtAAP6 towards nematode susceptibility. Conclusion: The present findings enrich the existing literature on CRISPR/Cas9 research in plant-nematode interactions, which is quite limited currently while compared with the other plant-pathogen interaction systems. [ABSTRACT FROM AUTHOR]

Fusarium wilt in Cymbidium ensifolium, caused by Fusarium oxysporum, is highly contagious and poses a severe hazard. It significantly reduces the ornamental value of C. ensifolium and causes substantial economic losses in agricultural production. Nucleotide-binding site–leucine-rich repeat (NBS-LRR) genes are key regulatory factors in plant disease resistance responses, playing vital roles in defending against pathogen invasions. In our study, we conducted a comprehensive analysis of the NBS-LRR gene family in the genome of Cymbidium ensifolium. Phylogenetic analysis identified a total of 31 NBS-LRR genes encoding NB-ARC proteins, which were categorized into five classes (CNL, CN, NL, N, RNL) based on their protein structural domains. These genes were found to be unevenly distributed across eight chromosomes. Physicochemical analysis revealed significant variances in molecular weight and sequence length among the family members. Subcellular localization results indicated that most genes primarily reside in the cytoplasm and cell membrane, suggesting that the primary sites of disease resistance responses may be the cell membrane and cyto-plasm. Furthermore, noticeable disparities were observed in gene structures and conserved motifs among different categories of family genes. Promoter analysis indicated that cis-regulatory elements are mainly associated with plant stress, jasmonic acid, gibberellin, and other development-related factors, suggesting that CeNBS-LRR genes mainly resist external stress through hormones such as abscisic acid and jasmonic acid. We characterized twenty-seven CeNBS-LRR gene expression patterns of healthy C. ensifolium at different periods after Fusarium wilt infection, and found that those genes exhibit a temporospatial expression pattern, and that their expression is also responsive to Fusarium wilt infection. By analyzing the expression pattern via transcriptome and qRT-PCR, we speculated that JL006442 and JL014305 may play key roles in resisting Fusarium wilt. This study lays the groundwork and holds considerable significance as a reference for identifying disease-resistant genes and facilitating genetic breeding in C. ensifolium. [ABSTRACT FROM AUTHOR]

Vegetables constitute 12% of world agricultural produce. Solanaceous and cucurbitaceous crops constitute the major share of vegetable production, but their productivity is greatly impaired by plant-parasitic nematodes, among which root-knot nematodes pose the greatest threat. Due to climate change, water scarcity, shrinking of arable land, and ill effect of pesticides, a major shift in world agriculture is taking place toward sustainability, including organic and protected farming of high-value vegetable crops year-round. Grafting offers a sustainable alternative to conventional and transgenic breeding for nematode resistance. The technique can potentially reduce the phytonematode damage relying on several factors. These include R gene-mediated plant responses, efficient cross talk of defensive genes, alteration of plant metabolism and nutrient mobility, changes in plant vigor and physiological attributes, and modification of rhizosphere microbial community. Additionally, epigenetic factors also determine the success of graft union between the scion and rootstock. Grafting should also be included as a tool in integrated nematode management practices. Studies on identifying potential rootstocks and using grafted vegetable crops to manage nematode incidence are exhaustive but scattered. Here, we review the current status of vegetable grafting for nematode management using resistant rootstocks in both open-field condition and greenhouses. This is the first review, which compiles and summarizes the information on managing nematodes using grafted vegetables. We conclude the review with futuristic research perspectives of grafting that may aid in improving vegetable productivity in a sustainable manner. [ABSTRACT FROM AUTHOR]

Powdery mildew caused by Podosphaera xanthii is a serious fungal disease which causes severe damage to melon production. Unlike with chemical fungicides, managing this disease with resistance varieties is cost effective and ecofriendly. But, the occurrence of new races and a breakdown of the existing resistance genes poses a great threat. Therefore, this study aimed to identify the resistance locus responsible for conferring resistance against P. xanthii race KN2 in melon line IML107. A bi-parental F2 population was used in this study to uncover the resistance against race KN2. Genetic analysis revealed the resistance to be monogenic and controlled by a single dominant gene in IML107. Initial marker analysis revealed the position of the gene to be located on chromosome 2 where many of the resistance gene against P. xanthii have been previously reported. Availability of the whole genome of melon and its R gene analysis facilitated the identification of a F-box type Leucine Rich Repeats (LRR) to be accountable for the resistance against race KN2 in IML107. The molecular marker developed in this study can be used for marker assisted breeding programs. [ABSTRACT FROM AUTHOR]

Main conclusion: As an important biotic stressor, plant–parasitic nematodes afflict global crop productivity. Deployment of CRISPR/Cas9 system that selectively knock out host susceptibility genes conferred improved nematode tolerance in crop plants. As an important biotic stressor, plant–parasitic nematodes cause a considerable yield decline in crop plants that eventually contributes to a negative impact on global food security. Being obligate plant parasites, the root-knot and cyst nematodes maintain an intricate and sophisticated relationship with their host plants by hijacking the host's physiological and metabolic pathways for their own benefit. Significant progress has been made toward developing RNAi-based transgenic crops that confer nematode resistance. However, the strategy of host-induced gene silencing that targets nematode effectors is likely to fail because the induced silencing of effectors (which interact with plant R genes) may lead to the development of nematode phenotypes that break resistance. Lately, the CRISPR/Cas9-based genome editing system has been deployed to achieve host resistance against bacteria, fungi, and viruses. In these studies, host susceptibility (S) genes were knocked out to achieve resistance via loss of susceptibility. As the S genes are recessively inherited in plants, induced mutations of the S genes are likely to be long-lasting and confer broad-spectrum resistance. A number of S genes contributing to plant susceptibility to nematodes have been identified in Arabidopsis thaliana, rice, tomato, cucumber, and soybean. A few of these S genes were targeted for CRISPR/Cas9-based knockout experiments to improve nematode tolerance in crop plants. Nevertheless, the CRISPR/Cas9 system was mostly utilized to interrogate the molecular basis of plant–nematode interactions rather than direct research toward achieving tolerance in crop plants. The current standalone article summarizes the progress made so far on CRISPR/Cas9 research in plant–nematode interactions. [ABSTRACT FROM AUTHOR]

Fusarium wilt in Cymbidium ensifolium, caused by Fusarium oxysporum, is highly contagious and poses a severe hazard. It significantly reduces the ornamental value of C. ensifolium and causes substantial economic losses in agricultural production. Nucleotide-binding site–leucine-rich repeat (NBS-LRR) genes are key regulatory factors in plant disease resistance responses, playing vital roles in defending against pathogen invasions. In our study, we conducted a comprehensive analysis of the NBS-LRR gene family in the genome of Cymbidium ensifolium. Phylogenetic analysis identified a total of 31 NBS-LRR genes encoding NB-ARC proteins, which were categorized into five classes (CNL, CN, NL, N, RNL) based on their protein structural domains. These genes were found to be unevenly distributed across eight chromosomes. Physicochemical analysis revealed significant variances in molecular weight and sequence length among the family members. Subcellular localization results indicated that most genes primarily reside in the cytoplasm and cell membrane, suggesting that the primary sites of disease resistance responses may be the cell membrane and cyto-plasm. Furthermore, noticeable disparities were observed in gene structures and conserved motifs among different categories of family genes. Promoter analysis indicated that cis-regulatory elements are mainly associated with plant stress, jasmonic acid, gibberellin, and other development-related factors, suggesting that CeNBS-LRR genes mainly resist external stress through hormones such as abscisic acid and jasmonic acid. We characterized twenty-seven CeNBS-LRR gene expression patterns of healthy C. ensifolium at different periods after Fusarium wilt infection, and found that those genes exhibit a temporospatial expression pattern, and that their expression is also responsive to Fusarium wilt infection. By analyzing the expression pattern via transcriptome and qRT-PCR, we speculated that JL006442 and JL014305 may play key roles in resisting Fusarium wilt. This study lays the groundwork and holds considerable significance as a reference for identifying disease-resistant genes and facilitating genetic breeding in C. ensifolium.

Key message: A recently reported Pijx gene interacts and promotes the ATPb degradation through 26 proteasomal pathways activate OsRbohC mediated ROS burst, leading to broad-spectrum rice blast resistance in seedling and panicle. [ABSTRACT FROM AUTHOR]

Plant proteins with domains rich in leucine repeats play important roles in detecting pathogens and triggering defense reactions, both at the cellular surface for pattern-triggered immunity and in the cell to ensure effector-triggered immunity. As intracellular parasites, viruses are mostly detected intracellularly by proteins with a nucleotide binding site and leucine-rich repeats but receptor-like kinases with leucine-rich repeats, known to localize at the cell surface, have also been involved in response to viruses. In the present review we report on the progress that has been achieved in the last decade on the role of these leucine-rich proteins in antiviral immunity, with a special focus on our current understanding of the hypersensitive response. [ABSTRACT FROM AUTHOR]

Deployment of single or multiple blast resistance (R) genes in rice plant is considered to be the most promising approach to enhance resistance against blast disease caused by fungus Magnaporthe oryzae. At the proteome level, relatively little information about R gene mediated defence mechanisms for single and stacking resistance characteristics is available. The overall objective of this study is to look at the proteomics of rice plants that have R genes; Pi54, Pi54rh and stacked Pi54 + Pi54rh in response to rice blast infection. In this study 'isobaric tag for relative and absolute quantification' (iTRAQ)-based proteomics analysis was performed in rice plants at 72-h post inoculation with Magnaporthe oryzae and various differentially expressed proteins were identified in these three transgenic lines in comparison to wild type during resistance response to blast pathogen. Through STRING analysis, the observed proteins were further examined to anticipate their linked partners, and it was shown that several defense-related proteins were co-expressed. These proteins can be employed as targets in future rice resistance breeding against Magnaporthe oryzae. The current study is the first to report a proteomics investigation of rice lines that express single blast R gene Pi54, Pi54rh and stacked (Pi54 + Pi54rh) during incompatible interaction with Magnaporthe oryzae. The differentially expressed proteins indicated that secondary metabolites, reactive oxygen species-related proteins, phenylpropanoid, phytohormones and pathogenesis-related proteins have a substantial relationship with the defense response against Magnaporthe oryzae. [ABSTRACT FROM AUTHOR]

Plants have evolved two layers of protection against biotic stress: PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI). The primary mechanism of ETI involves nucleotide-binding leucine-rich repeat immune receptors (NLRs). Although NLR genes have been studied in several plant species, a comprehensive database of NLRs across a diverse array of species is still lacking. Here, we present a thorough analysis of NLR genes across 100 high-quality plant genomes (PlantNLRatlas). The PlantNLRatlas includes a total of 68,452 NLRs, of which 3,689 are full-length and 64,763 are partial-length NLRs. The majority of NLR groups were phyletically clustered. In addition, the domain sequences were found to be highly conserved within each NLR group. Our PlantNLRatlas dataset is complementary to RefPlantNLR, a collection of NLR genes which have been experimentally confirmed. The PlantNLRatlas should prove helpful for comparative investigations of NLRs across a range of plant groups, including understudied taxa. Finally, the PlantNLRatlas resource is intended to help the field move past a monolithic understanding of NLR structure and function. [ABSTRACT FROM AUTHOR]

Phytophthora infestans, the etiologic agent of late blight, is a threat to potato production in areas with high humidity during the growing season. The oomycete pathogen is hemi-biotrophic, it establishes infection on living plant cells and then spreads, kills, and feeds off the necrotized plant tissue material. The interaction between host and pathogen is complex with dynamic pathogen RXLR effectors and potato NB-LRR resistance proteins actively competing for dominance and survival. Late blight protection was brought to several cultivars of potato through insertion of the wild potato (Solanum venturii) NB-LRR resistance gene Rpi-vnt1.1. We have established that the late blight protection trait, mediated by Rpi-vnt1.1, is effective despite low expression of RNA. The RNA expression dynamics of Rpi-vnt1.1 and the cognate pathogen RXLR effector, Avr-vnt1, were evaluated following spray inoculation with up to five different contemporary late blight isolates from North America and South America. Following inoculations, RXLR effector transcript profiles provided insight into interaction compatibility in relation to markers of the late blight hemi-biotrophic lifecycle. [ABSTRACT FROM AUTHOR]

Magnaporthe oryzae is known for its genetic diversity and pathogenic variability, leading to rapid breakdown of resistance in rice. Incorporating multiple broad-spectrum blast resistance genes into rice cultivars would extend disease resistance longevity. Effective resistance breeding in rice therefore requires continual enrichment of the reservoir of resistance genes and alleles. We conducted a large-scale screen of rice blast resistance in about 2 000 rice accessions. Among them, 247 accessions showed at least medium resistance to the natural infection of rice blast and 7 novel Pik alleles were identified from them. Variations in gene sequences were then correlated with the phenotypic trait to enable the identification of favorable alleles. Among the seven novel Pik alleles, the resistant rate of Pik-R0/ME/7017 donors was greater than 80%, and the disease score was less than 3. Through molecular marker-assisted backcross breeding, we successfully transferred the three Pik alleles, Pik-R0/ME/7017, into an elite cultivated line Kongyu 131 to obtain BC3F2 lines, which showed enhanced resistance to rice blast compared with the recurrent parent. Assessment of these near-isogenic lines in the greenhouse using 31 isolates of M. oryzae from Heilongjiang Province of China revealed that the resistant levels of the BC3F2 lines with Pik-R0/ME/7017 were significantly higher than those of the established cloned resistance genes Pik-m and Pi1. Exploring such alleles will enrich our gene library for resistance to rice blast.

Abstract Plant pathogenic oomycete species pose a worldwide threat to crop production and ecosystems. During infection, oomycete pathogens secrete a series of effectors to manipulate plant immunity. Many of these effectors, which are indicated as avirluence gene candidates, will use components of immunity pathway to induce cell death in plants. This response given by plants is known as effector-triggered immunity (ETI). The identification of avirulence genes from pathogenic oomycete species opens a way to investigating their virulence function and uncovering related R gene repertoires in resistant plants. In this study, we screened eight cell death-inducing effectors from oomycete species in N. benthamiana and tested the requirements of ETI signaling components to induce cell death. SGT1 was required for PsAvh163- and PcRXLR25-mediated cell death, while silencing NbHSP90 abolished PcRXLR25-, PsAvh163-, PsAvh241- and PsCRN63-triggered cell death. The cell death induced by the tested effectors does not depend on EDS1, NDR1, NRG1 and ADR1. PcRXLR25- and PsAvh163-induced cell death was found to require NRC2/3/4, indicating that these two effectors are avirulence protein candidates. Finally, we found that auto-activated NRC2/3/4 also required SGT1 and HSP90 to induce hypersensitive response.

Clubroot disease is a soil-borne disease caused by Plasmodiophora brassicae. It occurs in cruciferous crops exclusively, and causes serious damage to the economic value of cruciferous crops worldwide. Although different measures have been taken to prevent the spread of clubroot disease, the most fundamental and effective way is to explore and use disease-resistance genes to breed resistant varieties. However, the resistance level of plant hosts is influenced both by environment and pathogen race. In this work, we described clubroot disease in terms of discovery and current distribution, life cycle, and race identification systems; in particular, we summarized recent progress on clubroot control methods and breeding practices for resistant cultivars. With the knowledge of these identified resistance loci and R genes, we discussed feasible strategies for disease-resistance breeding in the future. [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]

Blackcurrant reversion virus (BRV) is the most destructive mite-transmitted pathogen in blackcurrants. The understanding of the resistance to BRV is limited, hindering and delaying the selection process. To identify the resistance (R) gene for BRV resistance, a gene expression analysis based on de novo blackcurrant cv. Aldoniai comparative transcriptome analysis (mock- and BRV-inoculated samples at 2 and 4 days post-inoculation (dpi)) was performed. In this study, 111 annotated clusters associated with pathogenesis according to conservative R gene domains were identified. In virus-infected samples, only Cluster-12591.33361 showed significant expression at 4 dpi. The expression profiles of this cluster were significantly associated with the presence of BRV particles in plant tissues, making it a putative R gene in the dominant resistance strategy in the BRV–Ribes nigrum interaction. The newly identified gene R.nigrum_R belongs to the CC-NBS-LRR class and has 63.9% identity with RPM1 in Populus spp. This study provides new insights on dominant putative R genes related to resistance to BRV in R. nigrum, which could aid targeted research and genetic improvement in breeding programs of blackcurrants. [ABSTRACT FROM AUTHOR]

Garden cress (Lepidium sativum L.) is a Brassicaceae crop recognized as a healthy vegetable and a medicinal plant. Lepidium is one of the largest genera in Brassicaceae, yet, the genus has not been a focus of extensive genomic research. In the present work, garden cress genome was sequenced using the long read high-fidelity sequencing technology. A de novo, draft genome assembly that spans 336.5 Mb was produced, corresponding to 88.6% of the estimated genome size and representing 90% of the evolutionarily expected orthologous gene content. Protein coding gene content was structurally predicted and functionally annotated, resulting in the identification of 25,668 putative genes. A total of 599 candidate disease resistance genes were identified by predicting resistance gene domains in gene structures, and 37 genes were detected as orthologs of heavy metal associated protein coding genes. In addition, 4289 genes were assigned as "transcription factor coding." Six different machine learning algorithms were trained and tested for their performance in classifying miRNA coding genomic sequences. Logistic regression proved the best performing trained algorithm, thus utilized for pre-miRNA coding loci identification in the assembly. Repetitive DNA analysis involved the characterization of transposable element and microsatellite contents. L. sativum chloroplast genome was also assembled and functionally annotated. Data produced in the present work is expected to constitute a foundation for genomic research in garden cress and contribute to genomics-assisted crop improvement and genome evolution studies in the Brassicaceae family. [ABSTRACT FROM AUTHOR]

Main conclusion: By constructing an F2 population, a new potential dominant resistance gene to TuMV in Brassica rapa was mapped and identified. Brassica rapa is the most widely grown vegetable crop in China, and turnip mosaic virus (TuMV) is a great threat to its production. Hence, it is a very important work to excavate more and novel resistance genes in B. rapa. In this study, the resistant line B80124 and the susceptible line B80450 were used to construct the F2 populations, and through genetic analysis, the resistance to TuMV was found to be controlled by a dominant gene. Bulked segregant analysis sequence (BSA-seq) was used for the primary mapping, and an intersection (22.25–25.03 Mb) was obtained. After fine mapping using single nucleotide polymorphisms (SNP) markers, the candidate region was narrowed to 330 kb between the SNP markers A06S11 and A06S14, including eight genes relating to disease resistance. Using the transcriptome analysis and sequence identification, BraA06g035130.3C was screened as the final candidate gene, and it contained two deletion mutations, leading to frameshift in the susceptible line B80450. In addition, the phylogenetic analysis, hydrophilia and hydrophobicity analysis, subcellular location prediction analysis, amino acid bias analysis, and 3D modeling structures of BraA06g035130.3C were conducted to predict its functions. This study was conducive to the identification of a new TuMV resistance gene in B. rapa, which is of important scientific significance and application value for the improvement of TuMV resistance traits and molecular design breeding for Brassica crops. [ABSTRACT FROM AUTHOR]

Alfalfa is one of the most important legume forages in the world and contributes greatly to the improvement of ecosystems, nutrition, and food security. Diseases caused by pathogens and pests severely restrict the production of alfalfa. Breeding resistant varieties is the most economical and effective strategy for the control of alfalfa diseases and pests, and the key to breeding resistant varieties is to identify important resistance genes. Plant innate immunity is the theoretical basis for identifying resistant genes and breeding resistant varieties. In recent years, the framework of plant immunity theory has been gradually formed and improved, and considerable progress has been made in the identification of alfalfa resistance genes and the revelation of the related mechanisms. In this review, we summarize the basic theory of plant immunity and identify alfalfa resistance genes to different pathogens and insects and resistance mechanisms. The current situation, problems, and future prospects of alfalfa resistance research are also discussed. Breeding resistant cultivars with effective resistance genes, together with other novel plant protection technologies, will greatly improve alfalfa production. [ABSTRACT FROM AUTHOR]

Verticillium wilt caused by Verticillium dahliae results in severe losses in cotton, and is economically the most destructive disease of this crop. Improving genetic resistance is the cleanest and least expensive option to manage Verticillium wilt. Previously, we identified the island cotton NBS-LRR-encoding gene GbaNA1 that confers resistance to the highly virulent V. dahliae isolate Vd991. In this study, we expressed cotton GbaNA1 in the heterologous system of Arabidopsis thaliana and investigated the defense response mediated by GbaNA1 following inoculations with V. dahliae. Heterologous expression of GbaNA1 conferred Verticillium wilt resistance in A. thaliana. Moreover, overexpression of GbaNA1 enabled recovery of the resistance phenotype of A. thaliana mutants that had lost the function of GbaNA1 ortholog gene. Investigations of the defense response in A. thaliana showed that the reactive oxygen species (ROS) production and the expression of genes associated with the ethylene signaling pathway were enhanced significantly following overexpression of GbaNA1. Intriguingly, overexpression of the GbaNA1 ortholog from Gossypium hirsutum (GhNA1) in A. thaliana did not induce the defense response of ROS production due to the premature termination of GhNA1, which lacks the encoded NB-ARC and LRR motifs. GbaNA1 therefore confers Verticillium wilt resistance in A. thaliana by the activation of ROS production and ethylene signaling. These results demonstrate the functional conservation of the NBS-LRR-encoding GbaNA1 in a heterologous system, and the mechanism of this resistance, both of which may prove valuable in incorporating GbaNA1-mediated resistance into other plant species.

Plants and viruses coexist in the natural ecosystem for extended periods of time, interacting with each other and even coevolving, maintaining a dynamic balance between plant disease resistance and virus pathogenicity. During virus–host interactions, plants often exhibit abnormal growth and development. However, plants do not passively withstand virus attacks but have evolved sophisticated and effective defense mechanisms to resist, limit, or undermine virus infections. It is widely believed that the initial stage of infection features the most intense interactions between the virus and the host and the greatest variety of activated signal transduction pathways. This review describes the most recent findings in rice antiviral research and discusses a variety of rice antiviral molecular mechanisms, including those based on R genes and recessive resistance, RNA silencing, phytohormone signaling, autophagy and WUS-mediated antiviral immunity. Finally, we discuss the challenges and future prospects of breeding rice for enhanced virus resistance.

Abstract Background Phytophthora capsici root rot (PRR) is a disastrous disease in peppers (Capsicum spp.) caused by soilborne oomycete with typical symptoms of necrosis and constriction at the basal stem and consequent plant wilting. Most studies on the QTL mapping of P. capsici resistance suggested a consensus broad-spectrum QTL on chromosome 5 named Pc.5.1 regardless of P. capsici isolates and resistant resources. In addition, all these reports proposed NBS-ARC domain genes as candidate genes controlling resistance. Results We screened out 10 PRR-resistant resources from 160 Capsicum germplasm and inspected the response of locus Pc.5.1 and NBS-ARC genes during P. capsici infection by comparing the root transcriptomes of resistant pepper 305R and susceptible pepper 372S. To dissect the structure of Pc.5.1, we anchored genetic markers onto pepper genomic sequence and made an extended Pc5.1 (Ext-Pc5.1) located at 8.35 Mb–38.13 Mb on chromosome 5 which covered all Pc5.1 reported in publications. A total of 571 NBS-ARC genes were mined from the genome of pepper CM334 and 34 genes were significantly affected by P. capsici infection in either 305R or 372S. Only 5 inducible NBS-ARC genes had LRR domains and none of them was positioned at Ext-Pc5.1. Ext-Pc5.1 did show strong response to P. capsici infection and there were a total of 44 differentially expressed genes (DEGs), but no candidate genes proposed by previous publications was included. Snakin-1 (SN1), a well-known antimicrobial peptide gene located at Pc5.1, was significantly decreased in 372S but not in 305R. Moreover, there was an impressive upregulation of sugar pathway genes in 305R, which was confirmed by metabolite analysis of roots. The biological processes of histone methylation, histone phosphorylation, DNA methylation, and nucleosome assembly were strongly activated in 305R but not in 372S, indicating an epigenetic-related defense mechanism. Conclusions Those NBS-ARC genes that were suggested to contribute to Pc5.1 in previous publications did not show any significant response in P. capsici infection and there were no significant differences of these genes in transcription levels between 305R and 372S. Other pathogen defense-related genes like SN1 might account for Pc5.1. Our study also proposed the important role of sugar and epigenetic regulation in the defense against P. capsici.

Cyst nematodes are considered a dominant threat to yield for a wide range of major food crops. Current control strategies are mainly dependent on crop rotation and the use of resistant cultivars. Various crops exhibit single dominant resistance (R) genes that are able to activate effective host-specific resistance to certain cyst nematode species and/or populations. An example is the potato R gene Gpa2 , which confers resistance against the potato cyst nematode (PCN), Globodera pallida population D383. Activation of Gpa2 results in a delayed resistance response, which is characterized by a layer of necrotic cells formed around the developing nematode feeding structure. However, knowledge about the Gpa2-induced defense pathways is still lacking. Here, we uncover the transcriptional changes and gene expression network induced upon Gpa2 activation in potato roots infected with G. pallida. To this end, in vitro -grown Gpa2-resistant potato roots were infected with the avirulent population D383 and virulent population Rookmaker. Infected root segments were harvested at 3 and 6 dpi and sent for RNA sequencing. Comparative transcriptomics revealed a total of 1,743 differentially expressed genes (DEGs) upon nematode infection, of which 559 DEGs were specifically regulated in response to D383 infection. D383-specific DEGs associated with Gpa2-mediated defense mainly relates to calcium-binding activity, salicylic acid (SA) biosynthesis, and systemic acquired resistance (SAR). These data reveal that cyst nematode resistance in potato roots depends on conserved downstream signaling pathways involved in plant immunity, which are also known to contribute to R genes-mediated resistance against other pathogens with different lifestyles. [ABSTRACT FROM AUTHOR]

Cyst nematodes are considered a dominant threat to yield for a wide range of major food crops. Current control strategies are mainly dependent on crop rotation and the use of resistant cultivars. Various crops exhibit single dominant resistance (R) genes that are able to activate effective host-specific resistance to certain cyst nematode species and/or populations. An example is the potato R gene Gpa2, which confers resistance against the potato cyst nematode (PCN), Globodera pallida population D383. Activation of Gpa2 results in a delayed resistance response, which is characterized by a layer of necrotic cells formed around the developing nematode feeding structure. However, knowledge about the Gpa2-induced defense pathways is still lacking. Here, we uncover the transcriptional changes and gene expression network induced upon Gpa2 activation in potato roots infected with G. pallida. To this end, in vitro-grown Gpa2-resistant potato roots were infected with the avirulent population D383 and virulent population Rookmaker. Infected root segments were harvested at 3 and 6 dpi and sent for RNA sequencing. Comparative transcriptomics revealed a total of 1,743 differentially expressed genes (DEGs) upon nematode infection, of which 559 DEGs were specifically regulated in response to D383 infection. D383-specific DEGs associated with Gpa2-mediated defense mainly relates to calcium-binding activity, salicylic acid (SA) biosynthesis, and systemic acquired resistance (SAR). These data reveal that cyst nematode resistance in potato roots depends on conserved downstream signaling pathways involved in plant immunity, which are also known to contribute to R genes-mediated resistance against other pathogens with different lifestyles.

Magnaporthe oryzae is known for its genetic diversity and pathogenic variability, leading to rapid breakdown of resistance in rice. Incorporating multiple broad-spectrum blast resistance genes into rice cultivars would extend disease resistance longevity. Effective resistance breeding in rice therefore requires continual enrichment of the reservoir of resistance genes and alleles. We conducted a large-scale screen of rice blast resistance in about 2 000 rice accessions. Among them, 247 accessions showed at least medium resistance to the natural infection of rice blast and 7 novel Pik alleles were identified from them. Variations in gene sequences were then correlated with the phenotypic trait to enable the identification of favorable alleles. Among the seven novel Pik alleles, the resistant rate of Pik-R0/ME/7017 donors was greater than 80%, and the disease score was less than 3. Through molecular marker-assisted backcross breeding, we successfully transferred the three Pik alleles, Pik-R0/ME/7017 , into an elite cultivated line Kongyu 131 to obtain BC 3 F 2 lines, which showed enhanced resistance to rice blast compared with the recurrent parent. Assessment of these near-isogenic lines in the greenhouse using 31 isolates of M. oryzae from Heilongjiang Province of China revealed that the resistant levels of the BC 3 F 2 lines with Pik-R0/ME/7017 were significantly higher than those of the established cloned resistance genes Pik-m and Pi1. Exploring such alleles will enrich our gene library for resistance to rice blast. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) such as hydrogen peroxide and superoxide are produced in plants in response to many biotic and abiotic stressors, and they can enhance stress adaptation in certain circumstances or mediate symptom development in others. The roles of ROS in plant-pathogen interactions have been extensively studied, but far less is known about their involvement in plant-insect interactions. A growing body of evidence, however, indicates that ROS accumulate in response to aphids, an economically damaging group of phloem-feeding insects. This review will cover the current state of knowledge about when, where, and how ROS accumulate in response to aphids, which salivary effectors modify ROS levels in plants, and how microbial associates influence ROS induction by aphids. We will also explore the potential adaptive significance of intra- and extracellular oxidative responses to aphid infestation in compatible and incompatible interactions and highlight knowledge gaps that deserve further exploration. [ABSTRACT FROM AUTHOR]

Blackcurrant reversion virus (BRV) is the most destructive mite-transmitted pathogen in blackcurrants. The understanding of the resistance to BRV is limited, hindering and delaying the selection process. To identify the resistance (R) gene for BRV resistance, a gene expression analysis based on de novo blackcurrant cv. Aldoniai comparative transcriptome analysis (mock- and BRV-inoculated samples at 2 and 4 days post-inoculation (dpi)) was performed. In this study, 111 annotated clusters associated with pathogenesis according to conservative R gene domains were identified. In virus-infected samples, only Cluster-12591.33361 showed significant expression at 4 dpi. The expression profiles of this cluster were significantly associated with the presence of BRV particles in plant tissues, making it a putative R gene in the dominant resistance strategy in the BRV–Ribes nigrum interaction. The newly identified gene R.nigrum_R belongs to the CC-NBS-LRR class and has 63.9% identity with RPM1 in Populus spp. This study provides new insights on dominant putative R genes related to resistance to BRV in R. nigrum, which could aid targeted research and genetic improvement in breeding programs of blackcurrants.

Powdery mildew is among the most common diseases of both hemp- and marijuana-type cultivated Cannabis sativa. Despite its prevalence, no documented studies have characterized sources of natural genetic resistance in this pathosystem. Here we provide evidence for the first resistance (R) gene in C. sativa, represented by a single dominant locus that confers complete resistance to an isolate of the powdery mildew pathogen Golovinomyces ambrosiae, found in the Pacific Northwest of the United States. Linkage mapping with nearly 10,000 single nucleotide polymorphism (SNP) markers revealed that this R gene (designated PM1) is located on the distal end of the long arm of one of the largest chromosomes in the C. sativa genome. According to reference whole genome sequences and Sanger sequencing, the marker was tentatively placed in a cluster of R genes of the nucleotide-binding site (NBS) and leucine-rich repeat (LRR) protein type. PM1's dominant behavior, qualitative penetrance, and a co-segregating qPCR marker to track its inheritance were confirmed in two separate genetic backgrounds totaling 185 recombinant F1 plants. The goal of this study is to provide a foundation for the discovery and characterization of additional sources of genetic resistance to pathogens that infect C. sativa.

Abstract Background Effective management of rice blast, caused by the fungus Magnaporthe oryzae, requires an understanding of the genetic architecture of the resistance to the disease in rice. Rice resistance varies with M. oryzae strains, and many quantitative trait loci (QTLs) affecting rice blast resistance have been mapped using different strains of M. oryzae from different areas. However, little is known about the genetic architecture of rice resistance against the M. oryzae population in Hunan Province, which is a main rice production area in South China. Results In this study, we used three isolates from Hunan Province and the rice diversity panel 1 to perform a genome-wide association study (GWAS) of blast resistance in rice. A total of 56 QTLs were identified. One of the QTLs is localized with the resistance gene Pik locus which confers resistance to all three isolates. Genomic sequence analysis of the resistant cultivars led to the identification of a new Pik allele, which we named Pikx. Yeast two-hybrid and co-immunoprecipitation assays between AvrPiks and Pikx confirmed that Pikx is a new allele at the Pik locus. Conclusions Our GWAS has identified many new blast resistance QTLs. The identified new Pik allele Pikx will be useful for breeding cultivars with high resistance to blast in Hunan and other South China provinces. Further research on the relationship between AvrPiks and Pikx will provide new insights into the molecular mechanism of rice resistance to M. oryzae.

Alfalfa is one of the most important legume forages in the world and contributes greatly to the improvement of ecosystems, nutrition, and food security. Diseases caused by pathogens and pests severely restrict the production of alfalfa. Breeding resistant varieties is the most economical and effective strategy for the control of alfalfa diseases and pests, and the key to breeding resistant varieties is to identify important resistance genes. Plant innate immunity is the theoretical basis for identifying resistant genes and breeding resistant varieties. In recent years, the framework of plant immunity theory has been gradually formed and improved, and considerable progress has been made in the identification of alfalfa resistance genes and the revelation of the related mechanisms. In this review, we summarize the basic theory of plant immunity and identify alfalfa resistance genes to different pathogens and insects and resistance mechanisms. The current situation, problems, and future prospects of alfalfa resistance research are also discussed. Breeding resistant cultivars with effective resistance genes, together with other novel plant protection technologies, will greatly improve alfalfa production.

Sugar beet cultivation is dependent on an effective control of beet necrotic yellow vein virus (BNYVV, family Benyviridae), which causes tremendous economic losses in sugar production. As the virus is transmitted by a soilborne protist, the use of resistant cultivars is currently the only way to control the disease. The Rz2 gene product belongs to a family of proteins conferring resistance towards diverse pathogens in plants. These proteins contain coiled‐coil and leucine‐rich repeat domains. After artificial inoculation of homozygous Rz2 resistant sugar beet lines, BNYVV and beet soilborne mosaic virus (BSBMV, family Benyviridae) were not detected. Analysis of the expression of Rz2 in naturally infected plants indicated constitutive expression in the root system. In a transient assay, coexpression of Rz2 and the individual BNYVV‐encoded proteins revealed that only the combination of Rz2 and triple gene block protein 1 (TGB1) resulted in a hypersensitive reaction (HR)‐like response. Furthermore, HR was also triggered by the TGB1 homologues from BSBMV as well as from the more distantly related beet soilborne virus (family Virgaviridae). This is the first report of an R gene providing resistance across different plant virus families. [ABSTRACT FROM AUTHOR]

Background: Phytophthora capsici root rot (PRR) is a disastrous disease in peppers (Capsicum spp.) caused by soilborne oomycete with typical symptoms of necrosis and constriction at the basal stem and consequent plant wilting. Most studies on the QTL mapping of P. capsici resistance suggested a consensus broad-spectrum QTL on chromosome 5 named Pc.5.1 regardless of P. capsici isolates and resistant resources. In addition, all these reports proposed NBS-ARC domain genes as candidate genes controlling resistance. Results: We screened out 10 PRR-resistant resources from 160 Capsicum germplasm and inspected the response of locus Pc.5.1 and NBS-ARC genes during P. capsici infection by comparing the root transcriptomes of resistant pepper 305R and susceptible pepper 372S. To dissect the structure of Pc.5.1, we anchored genetic markers onto pepper genomic sequence and made an extended Pc5.1 (Ext-Pc5.1) located at 8.35 Mb–38.13 Mb on chromosome 5 which covered all Pc5.1 reported in publications. A total of 571 NBS-ARC genes were mined from the genome of pepper CM334 and 34 genes were significantly affected by P. capsici infection in either 305R or 372S. Only 5 inducible NBS-ARC genes had LRR domains and none of them was positioned at Ext-Pc5.1. Ext-Pc5.1 did show strong response to P. capsici infection and there were a total of 44 differentially expressed genes (DEGs), but no candidate genes proposed by previous publications was included. Snakin-1 (SN1), a well-known antimicrobial peptide gene located at Pc5.1, was significantly decreased in 372S but not in 305R. Moreover, there was an impressive upregulation of sugar pathway genes in 305R, which was confirmed by metabolite analysis of roots. The biological processes of histone methylation, histone phosphorylation, DNA methylation, and nucleosome assembly were strongly activated in 305R but not in 372S, indicating an epigenetic-related defense mechanism. Conclusions: Those NBS-ARC genes that were suggested to contribute to Pc5.1 in previous publications did not show any significant response in P. capsici infection and there were no significant differences of these genes in transcription levels between 305R and 372S. Other pathogen defense-related genes like SN1 might account for Pc5.1. Our study also proposed the important role of sugar and epigenetic regulation in the defense against P. capsici. [ABSTRACT FROM AUTHOR]

Dioscorea rotundata is an important food crop that is mainly cultivated in subtropical regions of the world. D. rotundata is frequently infected by various pathogens during its lifespan, which results in a substantial economic loss in terms of yield and quality. The disease resistance gene (R gene) profile of D. rotundata is largely unknown, which has greatly hampered molecular study of disease resistance in this species. Nucleotide-binding site–leucine-rich repeat (NBS-LRR) genes are the largest group of plant R genes, and they play important roles in plant defense responses to various pathogens. In this study, 167 NBS-LRR genes were identified from the D. rotundata genome. Subsequently, one gene was assigned to the resistance to powdery mildew8 (RPW8)-NBS-LRR (RNL) subclass and the other 166 genes to the coiled coil (CC)-NBS-LRR (CNL) subclass. None of the Toll/interleukin-1 receptor (TIR)-NBS-LRR (TNL) genes were detected in the genome. Among them, 124 genes are located in 25 multigene clusters and 43 genes are singletons. Tandem duplication serves as the major force for the cluster arrangement of NBS-LRR genes. Segmental duplication was detected for 18 NBS-LRR genes, although no whole-genome duplication has been documented for the species. Phylogenetic analysis revealed that D. rotundata NBS-LRR genes share 15 ancestral lineages with Arabidopsis thaliana genes. The NBS-LRR gene number increased by more than a factor of 10 during D. rotundata evolution. A conservatively evolved ancestral lineage was identified from D. rotundata, which is orthologs to the Arabidopsis RPM1 gene. Transcriptome analysis for four different tissues of D. rotundata revealed a low expression of most NBS-LRR genes, with the tuber and leaf displaying a relatively high NBS-LRR gene expression than the stem and flower. Overall, this study provides a complete set of NBS-LRR genes for D. rotundata, which may serve as a fundamental resource for mining functional NBS-LRR genes against various pathogens.

Blackleg is a devastating disease of cabbage (C genome), but so far, only a few resistant cabbage lines have been identified, and the resistance-related genes are yet to be identified. In contrast, numerous R loci have been mapped to the A or B genome. High ancestral synteny among Brassicaceae genomes suggest that homologous regions of R loci in the A or B genome may contain functional R gene(s) in the C genome. Here, we investigated the collinear region of a major Brassica napus R locus, LepR1′, in Brassica oleracea to identify genes of putative disease resistance class via comprehensive in silico analysis. The LepR1′ locus is collinear to a 17.29-Mbp region in chromosome C02 of Brassica oleracea and hosted a total of 1,392 genes, and 36 of these genes contained NBS, LRR, TIR, F-box and RLK domains. The expression of these 36 genes was profiled using qRT-PCR in the cotyledons of resistant (SCNU-03) and susceptible (SCNU-59) lines at 0, 6, 24, and 48 h after inoculation with Leptosphaeria maculans isolates 00–100s and 03–02s having the corresponding avirulent gene, AvrLep1. Among these genes, a cluster of 10 genes were differentially expressed. NBS-LRR gene Bo2g131620 had a 45-bp insertion/deletion (indel) mutation in the 3rd intron between resistant and susceptible lines. The higher expression in resistant lines against both isolates and the indel mutation in Bo2g131620 suggest that these genes may have roles in blackleg resistance in cabbage. Mapping and functional analysis will be necessary to validate such a role. Saturating the region with enough markers is recommended during mapping. [ABSTRACT FROM AUTHOR]

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Dioscorea rotundata is an important food crop that is mainly cultivated in subtropical regions of the world. D. rotundata is frequently infected by various pathogens during its lifespan, which results in a substantial economic loss in terms of yield and quality. The disease resistance gene (R gene) profile of D. rotundata is largely unknown, which has greatly hampered molecular study of disease resistance in this species. Nucleotide-binding site–leucine-rich repeat (NBS-LRR) genes are the largest group of plant R genes, and they play important roles in plant defense responses to various pathogens. In this study, 167 NBS-LRR genes were identified from the D. rotundata genome. Subsequently, one gene was assigned to the resistance to powdery mildew8 (RPW8) -NBS-LRR (RNL) subclass and the other 166 genes to the coiled coil (CC) -NBS-LRR (CNL) subclass. None of the Toll/interleukin-1 receptor (TIR) -NBS-LRR (TNL) genes were detected in the genome. Among them, 124 genes are located in 25 multigene clusters and 43 genes are singletons. Tandem duplication serves as the major force for the cluster arrangement of NBS-LRR genes. Segmental duplication was detected for 18 NBS-LRR genes, although no whole-genome duplication has been documented for the species. Phylogenetic analysis revealed that D. rotundata NBS-LRR genes share 15 ancestral lineages with Arabidopsis thaliana genes. The NBS-LRR gene number increased by more than a factor of 10 during D. rotundata evolution. A conservatively evolved ancestral lineage was identified from D. rotundata , which is orthologs to the Arabidopsis RPM1 gene. Transcriptome analysis for four different tissues of D. rotundata revealed a low expression of most NBS-LRR genes, with the tuber and leaf displaying a relatively high NBS-LRR gene expression than the stem and flower. Overall, this study provides a complete set of NBS-LRR genes for D. rotundata , which may serve as a fundamental resource for mining functional NBS-LRR genes against various pathogens. [ABSTRACT FROM AUTHOR]

In vegetables of Brassica rapa L., Fusarium oxysporum f. sp. rapae (For) or F. oxysporum f. sp. conglutinans (Foc) cause Fusarium yellows. A resistance gene against Foc (FocBr1) has been identified, and deletion of this gene results in susceptibility (focbr1-1). In contrast, a resistance gene against For has not been identified. Inoculation tests showed that lines resistant to Foc were also resistant to For, and lines susceptible to Foc were susceptible to For. However, prediction of disease resistance by a dominant DNA marker on FocBr1 (Bra012688m) was not associated with disease resistance of For in some komatsuna lines using an inoculation test. QTL-seq using four F2 populations derived from For susceptible and resistant lines showed one causative locus on chromosome A03, which covers FocBr1. Comparison of the amino acid sequence of FocBr1 between susceptible and resistant alleles (FocBr1 and FocBo1) showed that six amino acid differences were specific to susceptible lines. The presence and absence of FocBr1 is consistent with For resistance in F2 populations. These results indicate that FocBr1 is essential for For resistance, and changed amino acid sequences result in susceptibility to For. This susceptible allele is termed focbr1-2, and a new DNA marker (focbr1-2m) for detection of the focbr1-2 allele was developed.

Plant innate immunity mostly relies on nucleotide-binding (NB) and leucine-rich repeat (LRR) intracellular receptors to detect pathogen-derived molecules and to induce defense responses. A multitaxa reconstruction of NB-domain associations allowed us to identify the first NB–LRR arrangement in the Chlorophyta division of the Viridiplantae. Our analysis points out that the basic NOD-like receptor (NLR) unit emerged in Chlorophytes by horizontal transfer and its diversification started from Toll/interleukin receptor–NB–LRR members. The operon-based genomic structure of Chromochloris zofingiensis NLR copies suggests a functional origin of NLR clusters. Moreover, the transmembrane signatures of NLR proteins in the unicellular alga C. zofingiensis support the hypothesis that the NLR-based immunity system of plants derives from a cell-surface surveillance system. Taken together, our findings suggest that NLRs originated in unicellular algae and may have a common origin with cell-surface LRR receptors. [ABSTRACT FROM AUTHOR]

Multiple pathogens cause rice various diseases affecting its yield and quality. Pyramiding resistance genes or quantitative traits loci into rice cultivars to enhance their resistance is an operable and optimal strategy for rice genetic improvement. New technologies and methods accelerate the identification and cloning of the resistance genes from landraces, domesticated and wild rice germplasm accessions. Some of these superior resistance genes have been successfully pyramided into diverse rice cultivars worldwide based on molecular marker-assisted selection. The underlying molecular mechanisms of some resistance genes have been uncovered which support their stacking into rice cultivars in a proper manner. The genetically improved rice lines show broad spectrum and durable resistance to different pathogens, which can greatly contribute to high yield and outstanding quality of rice cultivars. This paper summarizes the cloned major resistance genes, elucidates the underlying molecular mechanisms, and proposes the operable strategies to use these genes for rice genetic improvement. [ABSTRACT FROM AUTHOR]

The objective of the present study was to investigate to what extent the macroscopic phenotype of incompatible host–pathogen interactions reflects differences in fungal development and host responses at the histological level. This was done by conventional and advanced microscopic analysis of six wheat near‐isogenic lines differing by individual R genes and inoculated with an avirulent isolate of Puccinia striiformis. Wheat line AvocetYr15 had the lowest macroscopic infection type (IT) 0–1, in which fungal growth was stopped at early stages due to extensive expression of a hypersensitive response (HR) at all time points (4, 8 and 16 days post‐inoculation, dpi) without any sign of haustorial bodies. AvocetYr5 and AvocetYr1 had IT 1, in which most fungal colonies developed secondary hyphae. Many colonies were encased by HR at 16 dpi, more extensively in AvocetYr1 than AvocetYr5. In AvocetYr6 (IT 2), HR was expressed after the formation of secondary hyphae at 4 dpi, after which fungal growth and HR increased simultaneously until most colonies became encased by HR. AvocetYr27 (IT 2–3) and AvocetYr17 (IT 4–5) showed similar fungal growth and HR at 4 dpi, where HR was only weakly expressed in a few host cells. Encasement of secondary and runner hyphae increased significantly in AvocetYr27, but at 16 dpi, HR was often circumvented by large, intermingled fungal colonies in both lines. No resistance responses were observed in Avocet S (susceptible control). The very different histological patterns conferred by the six R genes suggests differences in the timing of the host–pathogen recognition and onset of host defence pathways. [ABSTRACT FROM AUTHOR]

Tospoviruses are among the most important plant pathogens and cause serious crop losses worldwide. Tospoviruses have evolved to smartly utilize the host cellular machinery to accomplish their life cycle. Plants mount two layers of defense to combat their invasion. The first one involves the activation of an antiviral RNA interference (RNAi) defense response. However, tospoviruses encode an RNA silencing suppressor that enables them to counteract antiviral RNAi. To further combat viral invasion, plants also employ intracellular innate immune receptors (e.g., Sw-5b and Tsw) to recognize different viral effectors (e.g., NSm and NSs). This leads to the triggering of a much more robust defense against tospoviruses called effector-triggered immunity (ETI). Tospoviruses have further evolved their effectors and can break Sw-5b-/Tsw-mediated resistance. The arms race between tospoviruses and both layers of innate immunity drives the coevolution of host defense and viral genes involved in counter defense. In this review, a state-of-the-art overview is presented on the tospoviral life cycle and the multilined interplays between tospoviruses and the distinct layers of defense. [ABSTRACT FROM AUTHOR]