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Harpins play a key role in inducing disease resistance in crops, and identifying their core functional regions and establishing a system for their efficient expression would be very valuable. In this study, large amounts of soluble fusion proteins of harpin HrpZ and its subpeptides were obtained via the optimized induction conditions (28 ℃C with 0.5 mmol.L-1 IPTG for 6 h) in Escherichia coli BL21 (DE3). Hypersensitive response (HR) assays demonstrated that the C-terminal 66 aa of HrpZ (HrpZ_C_2_2) elicited a strong HR in tobacco (Nicotiana benthamiana) and grape (Flame Seedless) leaves. Additionally, treatment with HrpZ, and particularly HrpZ_C_2_2, significantly reduced the disease incidence and severity index of field vine leaves and those inoculated with downy mildew. The determination of the physiological parameters indicated that HrpZ, and especially HrpZ_C_2_2, improved the photosynthesis- and chlorophyll fluorescence-related parameters, enhanced the activity of defense-related enzymes, including SOD, POD, CAT and PAL, and increased the H2O2 level. Collectively, we efficiently expressed a core peptide of HrpZ and elucidated its strong ability to elicit a HR and resistance to downy mildew. This research provides insight into understanding the structure and function of HrpZ and will advance the application of HrpZ_C_2_2 to increase the resistance of grapevine to downy mildew. [ABSTRACT FROM AUTHOR]

SUMMARY Photorespiratory serine hydroxymethyltransferases (SHMTs) are important enzymes of cellular one‐carbon metabolism. In this study, we investigated the potential role of SHMT6 in Arabidopsis thaliana. We found that SHMT6 is localized in the nucleus and expressed in different tissues during development. Interestingly SHMT6 is inducible in response to avirulent, virulent Pseudomonas syringae and to Fusarium oxysporum infection. Overexpression of SHMT6 leads to larger flowers, siliques, seeds, roots, and consequently an enhanced overall biomass. This enhanced growth was accompanied by increased stomatal conductance and photosynthetic capacity as well as ATP, protein, and chlorophyll levels. By contrast, a shmt6 knockout mutant displayed reduced growth. When challenged with Pseudomonas syringae pv tomato (Pst) DC3000 expressing AvrRpm1, SHMT6 overexpression lines displayed a clear hypersensitive response which was characterized by enhanced electrolyte leakage and reduced bacterial growth. In response to virulent Pst DC3000, the shmt6 mutant developed severe disease symptoms and becomes very susceptible, whereas SHMT6 overexpression lines showed enhanced resistance with increased expression of defense pathway associated genes. In response to Fusarium oxysporum, overexpression lines showed a reduction in symptoms. Moreover, SHMT6 overexpression lead to enhanced production of ethylene and lignin, which are important components of the defense response. Collectively, our data revealed that SHMT6 plays an important role in development and defense against pathogens. [ABSTRACT FROM AUTHOR]

Accurate quantification of hypersensitive response (HR) programmed cell death is imperative for understanding plant defense mechanisms and developing disease‐resistant crop varieties. Here, a phenotyping platform for rapid, continuous‐time, and quantitative assessment of HR is demonstrated: Parallel Automated Spectroscopy Tool for Electrolyte Leakage (PASTEL). Compared to traditional HR assays, PASTEL significantly improves temporal resolution and has high sensitivity, facilitating detection of microscopic levels of cell death. Validation is performed by transiently expressing the effector protein AVRblb2 in transgenic Nicotiana benthamiana (expressing the corresponding resistance protein Rpi‐blb2) to reliably induce HR. Detection of cell death is achieved at microscopic intensities, where leaf tissue appears healthy to the naked eye one week after infiltration. PASTEL produces large amounts of frequency domain impedance data captured continuously. This data is used to develop supervised machine‐learning (ML) models for classification of HR. Input data (inclusive of the entire tested concentration range) is classified as HR‐positive or negative with 84.1% mean accuracy (F1 score = 0.75) at 1 h and with 87.8% mean accuracy (F1 score = 0.81) at 22 h. With PASTEL and the ML models produced in this work, it is possible to phenotype disease resistance in plants in hours instead of days to weeks. [ABSTRACT FROM AUTHOR]

This article explores the role of the WAK3 gene in Arabidopsis plants' immune responses to harpins, proteins produced by certain bacteria that activate plant defenses. The researchers used T-DNA insertion mutants to study WAK3 and found that it is essential for the necrosis and acquired resistance responses triggered by harpins. They also discovered that genetic variation in harpin perception may impact plant fitness. The study benefited from the use of the 1001 Genomes data, which eliminated the need for lengthy genetic mapping. This research provides valuable insights into the genetic basis of plant immune responses and its potential implications for crop protection. [Extracted from the article]

Imbibing watermelon seeds in 1 mM sodium tetraborate (Na2B4O7) for 24 h systemically protected plants against foliar infection by Stagonosporopsis cucurbitacearum in detached leaves and under greenhouse conditions. The treatment resulted in both a reduction in the overall percentage of leaf infection as well as in the size of lesions. Studies of the mechanisms by which Na2B4O7 protected watermelon showed that there was no direct effect on the S. cucurbitacearum mycelium growth in vitro. On the other hand, plants raised from seeds primed with Na2B4O7 showed a higher frequency of fluorescent epidermal cells compared to the plants treated with water. This indicates that a higher number of cells expressed the hypersensitive response after Na2B4O7 priming. In addition, there was an increase in peroxidase activity and an enhanced accumulation of a 45 kDa acidic peroxidase isoform during the early stages of infection in plants treated with Na2B4O7 compared to plants treated with water and this was positively correlated to the reduction of leaf infection caused by the pathogen. These results indicate that Na2B4O7 is able to induce systemic resistance in watermelon against S. cucurbitacearum by activating the hypersensitive reaction at penetration sites, increasing peroxidase activity and altering the peroxidase isozyme profile. Although each individual response may only have had a minor effect, their combined effects had a reducing effect on the disease. [ABSTRACT FROM AUTHOR]

Our previous research showed that a powdery mildew resistant barley line (MvHV07-17) maintains its resistance to Blumeria hordei (Bh) even if plants are exposed to a long-term high temperature of 35°C for 120 h before Bh inoculation, whereas such high temperature pretreatment further increases susceptibility to infection in the susceptible barley line MvHV118-17. In the present study, we extended this approach using short-term high-temperature water treatment (49°C for 30 s) to determine how it affects powdery mildew resistance in these barley lines. We found that this short-term heat shock (HS) impaired plant defense responses, as reflected by development of Bh colonies and visible necrotic spots on leaves of MvHV07-17, which does not develop visible symptoms upon Bh inoculation under optimal growth conditions. In contrast, both HS and long-term heat stress enhanced susceptibility to Bh in MvHV118-17 plants. These results were supported by the measurement of Bh biomass using a qPCR method. Furthermore, microscopic examinations showed that HS elevated the rate of successful Bh penetration events and the spread of cell death in the surrounding mesophyll area and allowed for colony formation and sporulation in resistant barley, whereas early and effective plant defense responses, such as papilla formation and single-cell epidermal hypersensitive response, were significantly reduced. Furthermore, we found that the accumulation of hydrogen peroxide in both resistant and susceptible barley was correlated with susceptibility induced by HS and long-term heat-stress. This study may contribute to a better understanding of plant defense responses to Bh in barley exposed to heat. [ABSTRACT FROM AUTHOR]

Sorghum relies on its immune system to defend against various pathogens, including Pseudomonas syringae syringae van Hall (Pss van Hall). However, the sorghum immune system is largely unknown. Reports on pathogenic effectors have provided valuable insights into the plant immune system; thus, we aimed to identify Pss van Hall effectors that can regulate the sorghum defense response in this study. Here, we first established the sorghum-Pss van Hall pathosystem and found that type III effectors played critical roles in the virulence of Pss van Hall to sorghum. To predict its effectors, the whole genome of Pss van Hall was sequenced, and 18 effector-coding genes were identified. Among them, five effectors belong to the core effectors of Pseudomonas syringae pathovars, and two may be monocot pathogen-specific effectors. Pss van Hall triggered the hypersensitive response (HR) in Nicotiana benthamiana. We found that the effectors of Pss van Hall can be divided into cell death inducers and immune repressors by examining their functions in HR induction and repression of PTI marker gene, ROS production, and pathogen growth. Finally, the roles of core effectors HopAJ2 and HopAN1, and specific effector HopAX1 were further confirmed in the sorghum-Pss van Hall pathosystem. Importantly, the functions of HopAN1 and HopAX1 in regulating plant immunity were reported for the first time. We believe that the identification of these effectors will facilitate the continued exploration of the sorghum immune system. [ABSTRACT FROM AUTHOR]

Background: Purple curl leaf disease brings a significant threat to the development of agave industry, the underlying mechanism of disease-resistant Agave sisalana. hybrid 11648 (A. H11648R) is still unknown. Results: To excavate the crucial disease-resistant genes against purple curl leaf disease, we performed an RNA-seq analysis for A.H11648R and A.H11648 during different stages of purple curl leaf disease. The DEGs (differentially expressed genes) were mainly enriched in linolenic acid metabolism, starch and sucrose mechanism, phenylpropanoid biosynthesis, hypersensitive response (HR) and systemic acquired resistance. Further analysis suggested that eight candidate genes (4'OMT2, ACLY, NCS1, GTE10, SMO2, FLS2, SQE1 and RCOM) identified by WGCNA (weighted gene co-expression network analysis) may mediate the resistance to agave purple curl disease by participating the biosynthesis of benzylisoquinoline alkaloids, steroid, sterols and flavonoids, and the regulation of plant innate immunity and systemic acquired resistance. After qPCR verification, we found that AsRCOM, coding a glycosyltransferase and relevant to the regulation of plant innate immunity and systemic acquired resistance, may be the most critical disease-resistant gene. Finally, the overexpression of AsRCOM gene in agave could significantly enhance the resistance to purple curl disease with abundant reactive oxygen species (ROS) accumulations. Conclusions: Integrative RNA-seq analysis found that HR may be an important pathway affecting the resistance to purple curl leaf disease in agave, and identified glycosyltransferase AsRCOM as the crucial gene that could significantly enhance the resistance to purple curl leaf disease in agave, with obvious ROS accumulations. [ABSTRACT FROM AUTHOR]

The I Striga i life cycle depends on host-derived signals: strigolactones trigger I Striga i seed germination ([5]; [10]; [26]; [6], [7], Preprint), while haustorium-inducing factors enable formation of the penetrative structure from the I Striga i radicle ([3]). Keywords: Cell type-specific defence; cell wall-based resistance; hypersensitive response; inducible defence; lignin; parasitic plants; post-attachment resistance; Striga EN Cell type-specific defence cell wall-based resistance hypersensitive response inducible defence lignin parasitic plants post-attachment resistance Striga 4903 4909 7 09/15/23 20230913 NES 230913 Parasitic plants of the I Striga i species significantly damage cereals in sub-Saharan Africa. Role of the defence mechanisms in post-attachment resistance against parasitic plants Natural variation in sorghum cultivar resistance to I Striga i can be used to elucidate target pathways to enhance resistance. Intercropping maize cultivars that are I Striga i resistant and herbicide resistant with legume crops has suppressed I Striga i seed germination and reduced the I Striga i seed bank in the soil ([20]). [Extracted from the article]

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]

Phospholipid signaling plays important roles in plant immune responses. Here, we focused on two phospholipase C3 (PLC3) orthologs in the Nicotiana benthamiana genome, NbPLC3-1 and NbPLC3-2. We generated NbPLC3-1 and NbPLC3-2 -double-silenced plants (NbPLC3s -silenced plants). In NbPLC3s -silenced plants challenged with Ralstonia solanacearum 8107, induction of hypersensitive response (HR)-related cell death and bacterial population reduction was accelerated, and the expression level of Nbhin1 , a HR marker gene, was enhanced. Furthermore, the expression levels of genes involved in salicylic acid and jasmonic acid signaling drastically increased, reactive oxygen species production was accelerated, and NbMEK2 -induced HR-related cell death was also enhanced. Accelerated HR-related cell death was also observed by bacterial pathogens Pseudomonas cichorii , P. syringae , bacterial AvrA, oomycete INF1, and TMGMV-CP with L1 in NbPLC3s -silenced plants. Although HR-related cell death was accelerated, the bacterial population was not reduced in double NbPLC3s and NbCoi1 -suppressed plants nor in NbPLC3s -silenced NahG plants. HR-related cell death acceleration and bacterial population reduction resulting from NbPLC3s- silencing were compromised by the concomitant suppression of either NbPLC3 s and NbrbohB (respiratory oxidase homolog B) or NbPLC3 s and NbMEK2 (mitogen activated protein kinase kinase 2). Thus, NbPLC3s may negatively regulate both HR-related cell death and disease resistance through MAP kinase- and reactive oxygen species-dependent signaling. Disease resistance was also regulated by NbPLC3s through jasmonic acid- and salicylic acid-dependent pathways. [ABSTRACT FROM AUTHOR]

The highly conserved angiosperm immune receptor HOPZ‐ACTIVATED RESISTANCE1 (ZAR1) recognises the activity of diverse pathogen effector proteins by monitoring the ZED1‐related kinase (ZRK) family. Understanding how ZAR1 achieves interaction specificity for ZRKs may allow for the expansion of the ZAR1‐kinase recognition repertoire to achieve novel pathogen recognition outside of model species. We took advantage of the natural diversity of Arabidopsis thaliana kinases to probe the ZAR1‐kinase interaction interface and found that A. thaliana ZAR1 (AtZAR1) can interact with most ZRKs, except ZRK7. We found evidence of alternative splicing of ZRK7, resulting in a protein that can interact with AtZAR1. Despite high sequence conservation of ZAR1, interspecific ZAR1‐ZRK pairings resulted in the autoactivation of cell death. We showed that ZAR1 interacts with a greater diversity of kinases than previously thought, while still possessing the capacity for specificity in kinase interactions. Finally, using AtZAR1‐ZRK interaction data, we rationally increased ZRK10 interaction strength with AtZAR1, demonstrating the feasibility of the rational design of a ZAR1‐interacting kinase. Overall, our findings advance our understanding of the rules governing ZAR1 interaction specificity, with promising future directions for expanding ZAR1 immunodiversity. SUMMARY STATEMENT: The angiosperm immune receptor ZAR1 displays specific interactions with diverse kinases, and rationally designed single amino acid substitutions in a kinase can affect interaction sensitivity. [ABSTRACT FROM AUTHOR]

Our previous study identified that the RepA protein encoded by the oat dwarf virus (ODV) was responsible for inducing a strong hypersensitive response (HR) during the virus infection in non-host tobacco plants. However, little was known about the molecular mechanism of the RepA-elicited HR. Here, a RING-finger protein, which is described as NbRFP1 and is mainly located in the cytoplasm and nucleus in Nicotiana benthamiana cells, was confirmed to interact with RepA. In addition, the accumulation level of NbRFP1 in N. benthamiana leaves was enhanced by either ODV infection or by only RepA expression. The knockdown of NbRFP1 by a TRV-mediated virus-induced gene silencing markedly delayed the ODV or RepA-elicited HR. By contrast, the overexpression of NbRFP1 in N. benthamiana conferred enhanced resistance to ODV infection and promoted RepA-induced HR. Further mutation analysis showed that a RING-finger domain located in NbRFP1 plays important roles in modulating RepA-induced HR, as well as in mediating the interaction between NbRFP1 and RepA. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS)- and hypersensitive response (HR)- mediated cell death have long been known to play critical roles in plant immunity to pathogens. Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) isa destructive wheatpathogen. Here, we report a quantitative analysis of the proportion of infected cells with local apoplastic ROS (apoROS) versus intracellular ROS (intraROS) accumulation in various wheat accessions that carry different disease resistance genes R genes) at a series of time points postinfection. The proportion of apoROS accumulation was 70 to 80% of the infected wheat cells detected in both compatible and incompatible host-pathogen interactions. However, intensive intraROS accumulation followed by localized cell death responses was detectedin 1 I to 15% of the infected wheat cells, mainly in wheat lines that carried nucleotide- binding leucine-rich repeat R genes (e. g., Pn13 F, Pm41, Tdfm60, MIIW72. and Pm69). The lines that carry unconventional R genes, Pm24 (Wheat Tandem Kinase 3) and pin42 (a recessive R gene), showed fewer intraROS responses. whereas 11 % of Pn124 line- infected epidermis cells still showed HR cell death. suggesting that different resistance pathways are activated there. Here. we also demonstrated that ROS could not act as a strong systemic signal for inducing high resistance to Bgt in wheat. although it induced the expression of pathogenesis-related genes. These results provide new insights into the contribution of intraROS and localized cell death to immune responses against wheat powdery mildew. [ABSTRACT FROM AUTHOR]

Bacterial blight resistancegene Bi has received little attention since it was first described in 1950. A near-isogenic line (NIL) of Gossypium hirstitum cotton, AcBj, was generated in an otherwise bacterial-blight-susceptible Acala 44' background. The introgressed locus Bi in AcB.i conferred strong and broad-spectrum resistance to bacterial blight. Segregation patterns of test crosses under Oklahoma field conditions indicated that AcBs is likely homozygous for resistance at two loci with partial dominance gene action. controlled-environment conditions, two of the four copies of Bj were required for effective resistance. Contrary to expectations of gene-forgene theory, AcBj conferred high resistance toward isogenic strains of Xanthomonas citri subsp. malvaceamm carrying cloned avirulence genes ar,·134. avi·b7. avi -Bin, avi·BIOL and arrB] 02, respectively, and weaker resistance toward the strain carrying cloned avrb6. The hypothesis that each gene. in the absence of a polygenic complex, triggers sesquiterpenoid phytoalexin production was tested by measurement of cadalene and lacinilene phytoalexins during resistant responses in five NILs carrying different B genes, four other lines carrying multiple resistance genes. as well as susceptible Ac44E. Phytoalexin production was an obvious. but variable, response in all nine resistant lines. AcBj accumulated an order of magnitude more of all four phytoalexins than any of the other resistant NILs. Its total leve[s were comparable to those detected in OKI.2, a highly resistant line that possesses several B genes in a polygenic background. [ABSTRACT FROM AUTHOR]

Increasing evidence is proving the biological significance of the phytoplasma-secreted proteins. However, besides a few Sec-dependent secretory proteins, no other phytoplasma-secreted proteins have been reported yet. Candidatus Phytoplasma ziziphi is a phytoplasma that causes witches'-broom, a devastating jujube disease prevalent in east Asia. In this study, using the SecretomeP server coupled with an Escherichia coli-based alkaline phosphatase assay, we identified 25 non-classically secreted proteins (ncSecPs) from Ca. P. ziziphi, a novel type of secreted protein associated with phytoplasmas. Among them, six were characterized as hypersensitive cell death response (HR) suppressors that significantly attenuated both Bax- and INF1-triggered HR and H2O2 accumulation in Nicotiana benthamiana, indicating a so-far unknown role of the phytoplasma-secreted proteins. Further, we demonstrated that despite the diverse subcellular localizations in the N. benthamiana cells, the six HR-suppressing ncSecPs enhanced the gene expression of several known cell death inhibitors, including pathogenesis-related proteins (NbPR-1, NbPR-2, and NbPR-5) and Bax inhibitor-1 (NbBI-1 and NbBI-2). Together, our data indicated that Ca. P. ziziphi has evolved an arsenal of ncSecPs that jointly circumvent HR by activating the plant cell death inhibitors, thus providing new insight into understanding the pathogenesis of phytoplasmas. [ABSTRACT FROM AUTHOR]

Downy mildew, caused by Peronospora variabilis, is the most important quinoa disease worldwide. However, little is known about the resistance mechanisms acting against this disease. The study goals were to identify quinoa accessions showing resistance to P. variabilis under Spanish field conditions and to characterize the resistance mechanism involved. Towards these objectives, a total amount of 229 accessions of Chenopodium quinoa and one accession of each of the species Chenopodiun berlandieri subs. nutillae, Chenopodium ugandae, and Chenopodium opulifolium were screened for resistance to P. variabilis under field conditions in Córdoba, Spain, during two seasons. The response to P. variabilis in the accessions showed a continuous distribution ranging from complete resistance to high susceptibility. Fifteen resistant and one susceptible accessions were selected for further histological studies. Histological results showed that resistance to downy mildew in quinoa acts mainly at the stage of colony establishment. In resistant accessions, no colonies were formed or success in colony establishment was significantly reduced compared with the susceptible control. Hypersensitive response was associated with colony abortion in a number of the resistant accessions. This work is the first proof of hypersensitive reaction occurrence in quinoa as a response to P. variabilis. [ABSTRACT FROM AUTHOR]

Summary: The oomycete Albugo candida causes white blister rust, an important disease of Brassica crops. Distinct races of A. candida are defined by their capacity to infect different host plant species. Each A. candida race encodes secreted proteins with a CX2CX5G ('CCG') motif that are polymorphic and show presence/absence variation, and are therefore candidate effectors.The White Rust Resistance 4 (WRR4) locus in Arabidopsis thaliana accession Col‐0 contains three genes that encode intracellular nucleotide‐binding domain leucine‐rich repeat immune receptors. The Col‐0 alleles of WRR4A and WRR4B confer resistance to multiple A. candida races, although both WRR4A and WRR4B can be overcome by the Col‐0‐virulent race 4 isolate AcEx1.Comparison of CCG candidate effectors in avirulent and virulent races, and transient co‐expression of CCG effectors from four A. candida races in Nicotiana sp. or A. thaliana, revealed CCG effectors that trigger WRR4A‐ or WRR4B‐dependent hypersensitive responses.We found eight WRR4A‐recognised CCGs and four WRR4B‐recognised CCGs, the first recognised proteins from A. candida for which the cognate immune receptors in A. thaliana are known. This multiple recognition capacity potentially explains the broad‐spectrum resistance to several A. candida races conferred by WRR4 paralogues. We further show that of five tested CCGs, three confer enhanced disease susceptibility when expressed in planta, consistent with A. candida CCG proteins being effectors. [ABSTRACT FROM AUTHOR]

Keywords: Effector; encasement; GEF; hypersensitive response; MVB; powdery mildew EN Effector encasement GEF hypersensitive response MVB powdery mildew 12 15 4 12/27/22 20230101 NES 230101 Membrane trafficking is key for different aspects of plant immunity such as the formation of papillae and haustorial encasements. The transport, tethering, and docking of target membranes is regulated by Rab GTPase proteins, which interact with membrane protein complexes to specify the tethering of membrane compartments ([6]). It is somewhat unsurprising that a I Bh i effector, such as CSEP0162, targets MON1 in an attempt to block immune responses, since membrane trafficking has a critical role in plant immunity during both pre- and post-invasion defences. As CSEP0162 may target MON1 to prevent MVB vesicle fusion to the plasma membrane, thereby preventing the HR, it will be interesting to test if the HR mediated by other CNLs (other than I Mla3 i ) is dependent on MON1. [Extracted from the article]

In this study, we identified a new citrus vein enation virus (CVEV) isolate (named CVEV-DT1) through sRNA high-throughput sequencing and traditional sequencing. Phylogenetic analysis based on whole genome sequences of all known CVEV isolates revealed that CVEV-DT1 was in an evolutionary branch with other isolates from China. Molecular variation analysis showed that the single nucleotide variability along CVEV full-length sequences was less than 8%, with more transitions (60.55%) than transversions (39.43%), indicating a genetically homogeneous CVEV population. In addition, non-synonymous nucleotide mutations mainly occurred in ORF1 and ORF2. Based on disorder analysis of all encoded ORF by CVEV-DT1, we identified that the CVEV-DT1 coat protein (CP) formed spherical granules, mainly in the cell nucleus and partly throughout the cytoplasm, with liquid properties through subcellular localization and photobleaching assay. Furthermore, we also confirmed that the CVEV P0 protein has weak post-transcriptional RNA-silencing suppressor activity and could elicit a strong hypersensitive response (HR) in tobacco plants. Collectively, to the best of our knowledge, our study was the first to profile the genomic variation in all the reported CVEV isolates and reveal the functions of CVEV-DT1-encoded proteins. [ABSTRACT FROM AUTHOR]

The protein P0 serves as the viral suppressor of RNA silencing (VSR) for poleroviruses, but elicits the hypersensitive response (HR) in specific Nicotiana species. We subjected P0 proteins from turnip yellows virus (P0Tu) and potato leafroll virus (P0PL) to serial deletion and performed extensive site-directed mutagenesis of P0Tu. Most deletions of the N-terminus and many substitution mutations disrupted both HR elicitation and VSR activity. Two conserved blocks of amino acid residues were found to be associated with HR. A double lysine to arginine substitution in HR-specific block 1 caused P0Tu to elicit a more robust HR. Conversely, deletion or mutation of block 2 in the C-terminus preserved VSR activity, but impaired HR elicitation, allowing virus escape from Nicotiana glutinosa resistance when expressed in the heterologous potato virus X vector. Our observations suggest that P0 residues responsible for suppressing RNA silencing and eliciting HR have overlapping, but distinct functions. • P0 proteins from Turnip yellows virus and Potato leafroll virus were studied by systematic mutagenesis. • P0 carboxy-termini were essential for hypersensitive response induction, but dispensible for RNA silencing suppression. • Two blocks of conserved amino acid sequence were associated with P0-induced hypersensitive response. • Amino acids responsible for distinct P0 protein functions are both separate and overlapping. [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]

Gibberellins are considered to play an important role in modulating plant–pathogen interactions. In order to find this, we studied the effect of GA4 on the interactions of Bipolaris sorokiniana (Scc.) (BIPOL) with Triticum aestivum. After inoculating the roots of hydroponically grown T. avestivum with BIPOL, the GA4 level shot up by 26%. The increased level of GA4 elicited a hypersensitive response (HR) in the T. aestivum seedlings. The elicitation in HR was confirmed through measurement of HR-inducing signaling compounds (i.e. c-di-GMP, cAMP, phosphatidic acid, pure and esterified oxo-phytodeinoic acid, and jasmonic acid). The concentration of HR-inducing signaling compounds in the treated T. aestivum seedlings was 31% higher compared to the control seedlings. Moreover, the induced HR response lowered the indole-3-acetic acid (IAA) level by 15% and the transzeatin (TZn) level by 22%. However, the application of 10 mM uniconazole through aerial spray inhibited GA4 biosynthesis in T. aestivum seedlings. Also, BIPOL colonized the roots of T. aestivum seedlings after uniconazole treatment and promoted seedling growth through increased relative growth rate (14%) and net assimilation rate (27%). [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]

A biotrophic fungus, Puccinia striiformis f.sp. tritici (Pst), which causes stripe rust disease in wheat is the most yield-limiting factor in wheat production. Plants have complex defense mechanisms against invading pathogens. Hypersensitive response (HR), a kind of programmed cell death (PCD) at the infection site, is among these defense mechanisms. Transcription factors (TFs) play a crucial role in plant defense response against invading pathogens. Myeloblastosis (MYB) TFs are among the largest TFs families that are involved in response to both biotic and abiotic stresses. However, little is known about the mechanisms of MYB TFs during the interaction between wheat and the stripe rust fungus. Here, we identified an R2R3 MYB TF from wheat, designated as TaMYB391, and characterized its functional role during wheat–Pst interaction. Our data indicated that TaMYB391 is induced by Pst infection and exogenous application of salicylic acid (SA) and abscisic acid (ABA). TaMYB391 is localized in the nucleus of both wheat and Nicotiana benthamiana. Transient overexpression of TaMYB391 in N. benthamiana triggered HR-related PCD accompanied by increased electrolyte leakage, high accumulation of reactive oxygen species (ROS), and transcriptional accumulation of SA defense-related genes and HR-specific marker genes. Overexpression of TaMYB391 in wheat significantly enhanced wheat resistance to stripe rust fungus through the induction of pathogenesis-related (PR) genes, ROS accumulation and hypersensitive cell death. On the other hand, RNAi-mediated silencing of TaMYB391 decreased the resistance of wheat to Pst accompanied by enhanced growth of the pathogen. Together our findings demonstrate that TaMYB391 acts as a positive regulator of HR-associated cell death and positively contributes to the resistance of wheat to the stripe rust fungus by regulating certain PR genes, possibly through SA signaling pathways. [ABSTRACT FROM AUTHOR]

The necrotrophic pathogen Valsa mali (Vm) resulting Valsa canker of apple is considered one of the most destructing fungal diseases. To study the resistance mechanism, we investigated gene expression profiles of suspension cells from resistant varieties 'Dongbeishanjingzi' (DS, Malus baccata) and susceptible varieties 'Gala' (GL, Malus × domestica) in response to Vm metabolism (VmM) using RNA sequencing (RNA-seq). Functional enrichment showed that differentially expressed genes (DEGs) were widely involved in multiple metabolisms or signals, such as "Lipid metabolic process", "plant hormone signal transduction" and "plant-pathogen interaction". Further expressional patterns exhibited that induction of genes related to "xyloglucan biosynthetic process" and "cell wall biogenesis" was beneficial for cell wall integrity and tolerance of DS cells. In brassinosteroid signaling, we identified that TCH4 gene MbTCH4-1 positively regulated Vm resistance of 'Fuji' fruit, but BSK gene MdBSK1 negatively regulated the resistance. In contrast, cell death associated with hypersensitive response caused by up-regulation of CNGCs and CDPK genes is an important cause of weakened tolerance in GL cells. Our results provide a new insight direction for the molecular mechanism of apple against Valsa canker. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Meile et al. (2023), 238: 1562–1577. [ABSTRACT FROM AUTHOR]

During pathogenesis, effector proteins are secreted from the pathogen to the host plant to provide virulence activity for invasion of the host. However, once the host plant recognizes one of the delivered effectors, effector‐triggered immunity activates a robust immune and hypersensitive response (HR). In planta, the effector AvrRps4 is processed into the N‐terminus (AvrRps4N) and the C‐terminus (AvrRps4C). AvrRps4C is sufficient to trigger HR in turnip and activate AtRRS1/AtRPS4‐mediated immunity in Arabidopsis; on the other hand, AvrRps4N induces HR in lettuce. Furthermore, AvrRps4N‐mediated HR requires a conserved arginine at position 112 (R112), which is also important for full‐length AvrRps4 (AvrRps4F) processing. Here, we show that effector processing and effector recognition in lettuce are uncoupled for the AvrRps4 family. In addition, we compared effector recognition by lettuce of AvrRps4 and its homologues, HopK1 and XopO. Interestingly, unlike for AvrRps4 and HopK1, mutation of the conserved R111 in XopO by itself was insufficient to abolish recognition. The combination of amino acid substitutions arginine 111 to leucine with glutamate 114 to lysine abolished the XopO‐mediated HR, suggesting that AvrRps4 family members have distinct structural requirements for perception by lettuce. Together, our results provide an insight into the processing and recognition of AvrRps4 and its homologues. [ABSTRACT FROM AUTHOR]

Recognition of a pathogen by the plant immune system often triggers a form of regulated cell death traditionally known as the hypersensitive response (HR). This type of cell death occurs precisely at the site of pathogen recognition, and it is restricted to a few cells. Extensive research has shed light on how plant immune receptors are mechanistically activated. However, two central key questions remain largely unresolved: how does cell death zonation take place, and what are the mechanisms that underpin this phenomenon? Consequently, bona fide transcriptional indicators of HR are lacking, which prevents deeper insight into its mechanisms before cell death becomes macroscopic and precludes early or live observation. In this study, to identify the transcriptional indicators of HR we used the paradigmatic Arabidopsis thaliana – Pseudomonas syringae pathosystem and performed a spatiotemporally resolved gene expression analysis that compared infected cells that will undergo HR upon pathogen recognition with bystander cells that will stay alive and activate immunity. Our data revealed unique and time-dependent differences in the repertoire of differentially expressed genes, expression profiles, and biological processes derived from tissue undergoing HR and that of its surroundings. Furthermore, we generated a pipeline based on concatenated pairwise comparisons between time, zone, and treatment that enabled us to define 13 robust transcriptional HR markers. Among these genes, the promoter of an uncharacterized AAA-ATPase was used to obtain a fluorescent reporter transgenic line that displays a strong spatiotemporally resolved signal specifically in cells that will later undergo pathogen-triggered cell death. This valuable set of genes can be used to define cells that are destined to die upon infection with HR-triggering bacteria, opening new avenues for specific and/or high-throughput techniques to study HR processes at a single-cell level. This work provides a detailed analysis of the spatiotemporal transcriptomic landscape of the hypersensitive response (HR), a form of plant-specific immune cell death. A set of robust transcriptional marker genes for cells that will undergo HR is identified. [ABSTRACT FROM AUTHOR]

EPS66A was derived from an unidentified Streptomyces sp. HL-66 by chemical fraction and disease-resistance assays. It was identified as a polysaccharide through a series of chemical characterization, including infrared spectrum analysis, methylation, gas chromatography–mass spectrometry, nuclear magnetic resonance, and high-performance gel permeation chromatography. To determine its effect in plant, EPS66A was applied to tobacco leaves infected with TMV, resulting in the plant with enhanced systemic resistance with a significant reduction of TMV severity. Plant defense was confirmed by early responses, including hypersensitive response (HR) indicated by programed cell death, moderate alkalization, oxidative burst, increase in nitric oxide (NO) and salicylic acid (SA). Furthermore, EPS66A induced callose deposition to form defense barriers against pathogen invasion and the expression of pathogenesis-related (PR) genes, which confirmed the second level of plant defense. Therefore, EPS66A served as a resistance inducer, which was reorganized by tobacco cells that triggered the production of signal molecules. The signals moved in long distance and systemically in plant, which coordinated the expression of defense responses. The study provided a new perspective in understanding the mechanism of EPS66A in regulating plants on environmental adaptability and provided a theoretical foundation for designing safe and sustainable pesticides. [ABSTRACT FROM AUTHOR]

Background: The study of the regulatory mechanisms of evolutionarily conserved Nucleotide-binding leucine-rich repeat (NLR) resistance (R) proteins in animals and plants is of increasing importance due to understanding basic immunity and the value of various crop engineering applications of NLR immune receptors. The importance of temperature is also emerging when applying NLR to crops responding to global climate change. In particular, studies of pathogen effector recognition and autoimmune activity of NLRs in plants can quickly and easily determine their function in tobacco using agro-mediated transient assay. However, there are conditions that should not be overlooked in these cell death-related assays in tobacco. Results: Environmental conditions play an important role in the immune response of plants. The system used in this study was to establish conditions for optimal hypertensive response (HR) cell death analysis by using the paired NLR RPS4/RRS1 autoimmune and AvrRps4 effector recognition system. The most suitable greenhouse temperature for growing plants was fixed at 22 °C. In this study, RPS4/RRS1-mediated autoimmune activity, RPS4 TIR domain-dependent cell death, and RPS4/RRS1-mediated HR cell death upon AvrRps4 perception significantly inhibited under conditions of 65% humidity. The HR is strongly activated when the humidity is below 10%. Besides, the leaf position of tobacco is important for HR cell death. Position #4 of the leaf from the top in 4–5 weeks old tobacco plants showed the most effective HR cell death. Conclusions: As whole genome sequencing (WGS) or resistance gene enrichment sequencing (RenSeq) of various crops continues, different types of NLRs and their functions will be studied. At this time, if we optimize the conditions for evaluating NLR-mediated HR cell death, it will help to more accurately identify the function of NLRs. In addition, it will be possible to contribute to crop development in response to global climate change through NLR engineering. [ABSTRACT FROM AUTHOR]

A general investigation on the mechanism of stochastic resonance is reported in a time-delay fractional Langevin system, which endues a nonlinear form multiplicative colored noise and fractional Gaussian noise. In terms of theoretical analysis, both the expressions of output steady-state amplitude and that of the first moment of system response are obtained by utilizing stochastic averaging method, fractional Shapiro and Laplace methods. Due to the presence of trichotomous colored noise, the excitation frequency can induce fresh multimodal Bona fide stochastic resonance, exhibiting much more novel dynamical behaviors than the non-disturbance case. It is verified that multimodal pattern only appears with small noise switching rate and memory damping order. The explicit expressions of critical noise intensity corresponding to the generalized stochastic resonance are given for the first time, by which it is determined that nonlinear form colored noise induces much more of a comprehensive resonant phenomena than the linear form. In the case of slow transfer rate noise, a newfangled phenomenon of double hypersensitive response induced by a variation in noise intensity is discovered and verified for the first time, with the necessary range of parameters for this phenomenon given. In terms of numerical scheme, an efficient and feasible algorithm for generating trichotomous noise is proposed, by which an algorithm based on the Caputo fractional derivative are applied. The numerical results match well with the analytical ones. [ABSTRACT FROM AUTHOR]

• The study identifies wild potato genotypes, AC1 of Solanum chacoense and AC4 of Solanum sparsipilum, and cultivar , Kufri Girdhari of Solanum tuberosum as highly resistant to late blight disease. • At field level, resistant genotypes AC4 and AC1 exhibit a novel mechanism of shedding infected leaves with a concomitant up-regulation of a systemic immune response. • The resistant genotypes exhibit robust hydrogen peroxide production, prolonged heightened SOD activity, cell death, high phenolic and flavonoid content and callose deposition at the site of infection, thus collectively arresting progression of disease. • The susceptible check Kufri Jyoti (earlier released as a resistant cultivar) has several of downstream resistant mechanisms in place, but shows a weak hypersensitive response, rendering it susceptible. • Hypersensitive response is paramount in resistance of potato species against late blight. Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most devastating disease causing colossal yield losses in potato globally. With the goal of identifying resistant potato genotypes and understanding the underlying mechanisms, nine potato genotypes comprising of wild species Solanum chacoense (AC1, AC2), Solanum sparsipilum (AC3, AC4, AC5) and Solanum spegzinii (AC6) and three potato cultivars (Kufri Jyoti [KJ], Kufri Chandramuki [KC] and Kufri Girdhari [KG]), were evaluated for their response to late blight in field, in vitro detached leaf assays and assessed by biochemical analyses. The study identified genotypes, AC1, of Solanum chacoense and AC4 of Solanum sparsipilum, and cultivar , Kufri Girdhari as highly resistant, and genotype AC6, of Solanum spegzinii as the most susceptible genotype in this study. At field level, resistant genotypes AC4 and AC1 exhibited a novel mechanism of shedding infected leaves with a concomitant up-regulation of a systemic immune response. At the cellular level, all the potato genotypes exhibited a generalized response to infection with increase in peroxidase activity and calcium- dependent protein kinase accumulation. However, the resistant genotypes exhibited robust hydrogen peroxide production, cell death and callose deposition at the site of infection, thus arresting the progression of disease. With the initial infection, AC4 and AC1 showed significant induction of peroxidase and superoxide dismutase (SOD) enzyme activities and accumulation of phenolics and flavonoids, while resistant cultivar KG, exhibited relatively high basal SOD activity. All the three resistant genotypes exhibited prolonged heightened SOD activity even towards the end of the cropping season. The study implicates hypersensitive response as paramount in resistance of potato species against late blight. The popular and susceptible cultivar Kufri Jyoti, which was introduced initially as a resistant cultivar, was found to have some of the resistance mechanisms in place, however, showed subdued hypersensitive response. [ABSTRACT FROM AUTHOR]

The Sw5 gene cluster furnishes robust resistance to Tomato spotted wilt virus in tomato, which has led to its widespread applicability in agriculture. Among the five orthologs, Sw5b functions as a resistance gene against a broad-spectrum tospovirus and is linked with tospovirus resistance. However, its paralog Sw5a has been recently implicated in providing resistance against Tomato leaf curl New Delhi virus, broadening the relevance of the Sw5 gene cluster in promoting defense against plant viruses. We propose that plants have established modifications within the homologs of R genes that permit identification of different effector proteins and provide broad and robust resistance against different pathogens through activation of the hypersensitive response and cell death. [ABSTRACT FROM AUTHOR]

Key message: In Rosaceae, tandem duplication caused the drastic expansion of CNGC gene family Group I. The members MdCN11 and MdCN19 negatively regulate Valsa canker resistance. Apple (Malus domestica) and pear (Pyrus bretschneideri and P. communis) are important fruit crops in Rosaceae family but are suffering from threats of Valsa canker. Cyclic nucleotide-gated ion channels (CNGCs) take crucial roles in plant immune responses. In the present study, a total of 355 CNGCs was identified from 8 Rosaceae plants. Based on phylogenetic analysis, 540 CNGCs from 18 plants (8 in Rosaceae and 10 others) could be divided into four groups. Group I was greatly expanded in Rosaceae resulted from tandem duplications. A large number of cis-acting regulatory elements (cis-elements) responsive to signals from multiple stresses and hormones were identified in the promoter regions of CNGCs in Malus spp. and Pyrus spp. Expressions of most Group I members were obviously up-regulated in Valsa canker susceptible varieties but not in the resistant ones. Furthermore, overexpression of the MdCN11 and MdCN19 in both apple fruits and 'Duli' (P. betulifolia) suspension cells compromised Valsa canker resistance. Overexpression of MdCN11 induced expression of hypersensitive response (HR)-related genes. In conclusion, tandem duplication resulted in a drastic expansion of CNGC Group I members in Rosaceae. Among these, MdCN11 and MdCN19 negatively regulate the Valsa canker resistance via inducting HR. [ABSTRACT FROM AUTHOR]

In plants, the reactive oxygen species (ROS) formed during normal conditions are essential in regulating several processes, like stomatal physiology, pathogen immunity and developmental signaling. However, biotic and abiotic stresses can cause ROS over-accumulation leading to oxidative stress. Therefore, a suitable equilibrium is vital for redox homeostasis in plants, and there have been major advances in this research arena. Salicylic acid (SA) is known as a chief regulator of ROS; however, the underlying mechanisms remain largely unexplored. SA plays an important role in establishing the hypersensitive response (HR) and systemic acquired resistance (SAR). This is underpinned by a robust and complex network of SA with Non-Expressor of Pathogenesis Related protein-1 (NPR1), ROS, calcium ions (Ca2+), nitric oxide (NO) and mitogen-activated protein kinase (MAPK) cascades. In this review, we summarize the recent advances in the regulation of ROS and antioxidant defense system signalling by SA at the physiological and molecular levels. Understanding the molecular mechanisms of how SA controls redox homeostasis would provide a fundamental framework to develop approaches that will improve plant growth and fitness, in order to meet the increasing global demand for food and bioenergy. [Display omitted] • Reactive oxygen species display duality in plants, as they act as signalling molecules under normal conditions, whereas they act as oxidant molecules under adverse conditions thereby leading to altered redox status. • Salicylic acid plays a key role in plant immunity by regulating the redox signalling and the antioxidant defence system. • SA induces the hypersensitive response and systemic acquired resistance (SAR). • It involves multifaceted network of the SA receptor Non-Expressor of Pathogenesis Related protein-1, reactive oxygen species, calcium ions, nitric oxide and mitogen-activated protein kinase cascades. [ABSTRACT FROM AUTHOR]

SUMMARY: Plant defense against melon necrotic spot virus (MNSV) is triggered by the viral auxiliary replicase p29 that is targeted to mitochondrial membranes causing morphological alterations, oxidative burst and necrosis. Here we show that MNSV coat protein (CP) was also targeted to mitochondria and mitochondrial‐derived replication complexes [viral replication factories or complex (VRC)], in close association with p29, in addition to chloroplasts. CP import resulted in the cleavage of the R/arm domain previously implicated in genome binding during encapsidation and RNA silencing suppression (RSS). We also show that CP organelle import inhibition enhanced RSS activity, CP accumulation and VRC biogenesis but resulted in inhibition of systemic spreading, indicating that MNSV whole‐plant infection requires CP organelle import. We hypothesize that to alleviate the p29 impact on host physiology, MNSV could moderate its replication and p29 accumulation by regulating CP RSS activity through organelle targeting and, consequently, eluding early‐triggered antiviral response. Cellular and molecular events also suggested that S/P domains, which correspond to processed CP in chloroplast stroma or mitochondrion matrix, could mitigate host response inhibiting p29‐induced necrosis. S/P deletion mainly resulted in a precarious balance between defense and counter‐defense responses, generating either cytopathic alterations and MNSV cell‐to‐cell movement restriction or some degree of local movement. In addition, local necrosis and defense responses were dampened when RSS activity but not S/P organelle targeting was affected. Based on a robust biochemical and cellular analysis, we established that the mitochondrial and chloroplast dual targeting of MNSV CP profoundly impacts the viral infection cycle. [ABSTRACT FROM AUTHOR]

Calcium (Ca2+) signalling regulates salicylic acid (SA)‐mediated immune response through calmodulin‐meditated transcriptional activators, AtSRs/CAMTAs, but its mechanism is not fully understood. Here, we report an AtSR1/CAMTA3‐mediated regulatory mechanism involving the expression of the SA receptor, NPR1. Results indicate that the transcriptional expression of NPR1 was regulated by AtSR1 binding to a CGCG box in the NPR1 promotor. The atsr1 mutant exhibited resistance to the virulent strain of Pseudomonas syringae pv. tomato (Pst), however, was susceptible to an avirulent Pst strain carrying avrRpt2, due to the failure of the induction of hypersensitive responses. These resistant/susceptible phenotypes in the atsr1 mutant were reversed in the npr1 mutant background, suggesting that AtSR1 regulates NPR1 as a downstream target during plant immune response. The virulent Pst strain triggered a transient elevation in intracellular Ca2+ concentration, whereas the avirulent Pst strain triggered a prolonged change. The distinct Ca2+ signatures were decoded into the regulation of NPR1 expression through AtSR1's IQ motif binding with Ca2+‐free‐CaM2, while AtSR1's calmodulin‐binding domain with Ca2+‐bound‐CaM2. These observations reveal a role for AtSR1 as a Ca2+‐mediated transcription regulator in controlling the NPR1‐mediated plant immune response. Calcium signalling regulates salicylic acid (SA)‐mediated immune response through calmodulin‐meditated transcriptional activators, AtSRs/CAMTAs, but its mechanism is not clearly understood. Here, we report an AtSR1/CAMTA3‐mediated regulatory mechanism involving the expression of the SA receptor, NPR1. These observations reveal an additional mechanism for controlling the NPR1‐mediated plant immune response. A better understanding of plant immunity should help in modern agriculture. Hence, this topic is of major interest to plant scientists. The Arabidopsis thaliana lines used in this study are wild‐type (WT) Columbia (Col‐0) and loss‐of‐function atsr1 mutant (Salk_001152C). [ABSTRACT FROM AUTHOR]

Marigold (Tagetes erecta) is an Asteraceae plant commonly used as an ornamental and ceremonial flower during the fall season in Mexico. Marigold plants cultivated in the field presented bacterial leaf spot disease symptoms. A bacterial strain that potentially causes spot disease was isolated. The main goal of this research was to classify this bacterium and assess its pathogenicity towards marigold and other plant species. The biochemical profiling identified this strain as Pseudomonas syringae LF2012. The phylogenetic analysis of the 16S rRNA gene revealed a close relation with Pseudomonas genomospecies. The I-CeuI macro-restriction profile of the chromosomal confirmed its high degree of similarity with distinct P. syringae pathovars. P. syringae LF2012 causes spot disease when inoculated by spray in marigold leaves. Infection assays towards plants from other families (Asteraceae, Brassicaceae, Amaranthaceae, Poaceae y Solanaceae) suggested that disease might be limited to marigold plants. Furthermore, this strain causes hypersensitive-like responses in Nicotiana tabacum leaves. [ABSTRACT FROM AUTHOR]

Several attempts have been made to identify antiviral genes against Tomato leaf curl New Delhi virus (ToLCNDV) and related viruses. This has led to the recognition of Ty genes (Ty1-Ty6), which have been successful in developing virus-resistant crops to some extent. Owing to the regular appearance of resistance-breaking strains of these viruses, it is important to identify genes related to resistance. In the present study, we identified a ToLCNDV resistance (R) gene, SlSw5a, in a ToLCNDV-resistant tomato cultivar, H-88-78-1, which lacks the known Ty genes. The expression of SlSw5a is controlled by the transcription factor SlMyb33, which in turn is regulated by microRNA159 (sly-miR159). Virus-induced gene silencing of either SlSw5a or SlMyb33 severely increases the disease symptoms and viral titer in leaves of resistant cultivar. Moreover, in SlMyb33-silenced plants, the relative messenger RNA level of SlSw5a was reduced, suggesting SlSw5a is downstream of the sly-miR159-SlMyb33 module. We also demonstrate that SlSw5a interacts physically with ToLCNDV-AC4 (viral suppressor of RNA silencing) to trigger a hypersensitive response (HR) and generate reactive oxygen species at infection sites to limit the spread of the virus. The "RTSK" motif in the AC4 C terminus is important for the interaction, and its mutation completely abolishes the interaction with Sw5a and HR elicitation. Overall, our research reports an R gene against ToLCNDV and establishes a connection between the upstream miR159-Myb33 module and its downstream target Sw5a to activate HR in the tomato, resulting in geminivirus resistance. [ABSTRACT FROM AUTHOR]

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]

The plant hypersensitive response (HR), a rapid cell death at the point of pathogenesis, is mediated by nucleotide‐binding site, leucine‐rich repeat (NLR) resistance proteins (R‐proteins) that recognize the presence of specific pathogen‐derived proteins. Rp1‐D21 is an autoactive maize NLR R‐protein that triggers HR spontaneously. We previously mapped loci associated with variation in the strength of HR induced by Rp1‐D21. Here we identify the E3 ligase ZmMIEL1 as the causal gene at a chromosome 10 modifier locus. Transient ZmMIEL1 expression in Nicotiana benthamiana reduced HR induced by Rp1‐D21, while suppression of ZmMIEL1 expression in maize carrying Rp1‐D21 increased HR. ZmMIEL1 also suppressed HR induced by another autoactive NLR, the Arabidopsis R‐protein RPM1D505V, in N. benthamiana. We demonstrated that ZmMIEL1 is a functional E3 ligase and that the effect of ZmMIEL1 was dependent on the proteasome but also that levels of Rp1‐D21 and RPM1D505V were not reduced when coexpressed with ZmMIEL1 in the N. benthamiana system. By comparison to a similar system in Arabidopsis, we identify ZmMYB83 as a potential target of ZmMIEL1. Suppression of ZmMYB83 expression in maize lines carrying Rp1‐D21 suppressed HR. Suppression of ZmMIEL1 expression caused an increase in ZmMYB83 transcript and protein levels in N. benthamiana and maize. Using coimmunoprecipitation and bimolecular fluorescence complementation assays, we demonstrated that ZmMIEL1 and ZmMYB83 physically interacted. Additionally, ZmMYB83 and ZmMIEL1 regulated the expression of a set of maize very long chain fatty acid (VLCFA) biosynthetic genes that may be involved in regulating HR. [ABSTRACT FROM AUTHOR]

The innate immune system of plants is crucial in defining the fate of a plant cell during plant–pathogen interactions. This response is often accompanied by a hypersensitive reaction leading to the death of a plant cell and restricted pathogen growth. Plant mitochondria, in this case, play a key role by maintaining a balance between cell respiration and reactive oxygen species formation. One of the key features of the hypersensitive response is the shift of the normal plant respiratory pathway to a special 'alternative' pathway. Plants contain an enzyme, alternative oxidase, for maintaining metabolic homeostasis of the cell. This energy dissipating respiration provides a branch in normal respiration by using ubiquinone to form water and heat, thus maintaining the energy status of the cell. Alternative oxidase is thought to minimize production of reactive oxygen species and can also function in 'anti‐apoptotic' machinery in plant cells. In this mini review, we briefly describe the alternative respiratory pathway and explain the role of alternative oxidase in important cellular processes, such as programmed cell death and the hypersensitive response. [ABSTRACT FROM AUTHOR]

Most plant intracellular immune receptors belong to nucleotide‐binding, leucine‐rich repeat (NLR) proteins. The recognition between NLRs and their corresponding pathogen effectors often triggers a hypersensitive response (HR) at the pathogen infection sites. The nicotinate N‐methyltransferase (NANMT) is responsible for the conversion of nicotinate to trigonelline in plants. However, the role of NANMT in plant defence response is unknown. In this study, we demonstrated that the maize ZmNANMT, but not its close homolog ZmCOMT, an enzyme in the lignin biosynthesis pathway, suppresses the HR mediated by the autoactive NLR protein Rp1‐D21 and its N‐terminal coiled‐coil signalling domain (CCD21). ZmNANMT, but not ZmCOMT, interacts with CCD21, and they form a complex with HCT1806 and CCoAOMT2, two key enzymes in lignin biosynthesis, which can also suppress the autoactive HR mediated by Rp1‐D21. ZmNANMT is mainly localized in the cytoplasm and nucleus, and either localization is important for suppressing the HR phenotype. These results lay the foundation for further elucidating the molecular mechanism of NANMTs in plant disease resistance. [ABSTRACT FROM AUTHOR]

In the present study, genes encoding for six major classes of enzymatic antioxidants, namely superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), Peroxidase (Prx) and glutathione S -transferase (GST) are identified in tomato. Their expression was studied in tomato cultivars contrastingly tolerant to ToLCNDV during virus infection and different hormone treatments. Significant upregulation of SlGR3 , SlPrx25 , SlPrx75 , SlPrx95 , SlGST44, and SlGST96 was observed in the tolerant cultivar during disease infection. Virus-induced gene silencing of SlGR3 in the tolerant cultivar conferred disease susceptibility to the knock-down line, and higher accumulation (~80%) of viral DNA was observed in the tolerant cultivar. Further, subcellular localization of SlGR3 showed its presence in cytoplasm, and its enzymatic activity was found to be increased (~65%) during ToLCNDV infection. Knock-down lines showed ~3- and 3.5-fold reduction in GR activity, which altogether underlines that SlGR3 is vital component of the defense mechanism against ToLCNDV infection. • A total of 281 genes encoding for ROS detoxifying enzymes were identified in tomato. • Phylogenetic analysis and chromosomal positioning of the identified genes were performed. • SlGR3 , SlPrx25 , SlPrx75 , SlPrx95 , SlGST44 and SlGST96 showed significant upregulation during virus infection. • Virus-induced gene silencing of SlGR3 turned tolerant cultivar to susceptible. • Enhanced accumulation of viral DNA was observed in knock-out line. [ABSTRACT FROM AUTHOR]

Although emerging evidence indicates that bacteria extracellularly export many cytoplasmic proteins referred to as nonclassically secreted proteins (ncSecPs) for their own benefit, the mechanisms and functional significance of the ncSecPs in the extracellular milieu remain elusive. "Candidatus Liberibacter asiaticus" (CLas) is a fastidious Gram-negative bacterium that causes Huanglongbing (HLB), the most devastating citrus disease globally. In this study, using the SecretomeP program coupled with an Escherichia coli alkaline phosphatase assay, we identified 27 ncSecPs from the CLas genome. Further, we demonstrated that 10 of these exhibited significantly higher levels of gene expression in citrus than in psyllid hosts and particularly suppressed hypersensitive response (HR)-based cell death and H2O2 overaccumulation in Nicotiana benthamiana, indicating their opposing effects on early plant defenses. However, these proteins also dramatically enhanced the gene expression of pathogenesis-related 1 protein (PR-1), PR-2, and PR-5, essential components of plant defense mechanisms. Additional experiments disclosed that the increased expression of these PR genes, in particular PR-1 and PR-5, could negatively regulate HR-based cell death development and H2O2 accumulation. Remarkably, CLas infection clearly induced gene expression of PR-1, PR-2, and PR-5 in both HLB-tolerant and HLB-susceptible species of citrus plants. Taking together these data, we hypothesized that CLas has evolved an arsenal of ncSecPs that function cooperatively to overwhelm the early plant defenses by inducing host PR genes. [ABSTRACT FROM AUTHOR]

Pathogens and their hosts are engaged in an evolutionary arms race. Pathogen-derived effectors promote virulence by targeting components of a host's innate immune system, while hosts have evolved proteins that sense effectors and trigger a pathogen-specific immune response. Many bacterial effectors are translocated into host cells using type III secretion systems. Type III effector proteases irreversibly modify host proteins by cleavage of peptide bonds and are prevalent among both plant and animal bacterial pathogens. In plants, the study of model effector proteases has yielded important insights into the virulence mechanisms employed by pathogens to overcome their host's immune response, as well as into the mechanisms deployed by their hosts to detect these effector proteases and counteract their effects. In recent years, the study of a larger number of effector proteases, across a wider range of pathogens, has yielded novel insights into their functions and recognition. One key limitation that remains is the lack of methods to detect protease cleavage at the proteome-wide level. We review known substrates and mechanisms of plant pathogen type III effector proteases and compare their functions with those of known type III effector proteases of mammalian pathogens. Finally, we discuss approaches to uncover their function on a system-wide level. [ABSTRACT FROM AUTHOR]

Secreted proteases act at the front line of defence and play pivotal roles in disease resistance. However, the criteria for apoplastic immune proteases are not always defined and followed. Here, we critically reviewed 46 apoplastic proteases that function in plant defence. We found that most apoplastic immune proteases are induced upon infection, and 17 proteases are genetically required for the immune response. Proteolytic activity has been confirmed for most of the proteases but is rarely shown to be required for biological function, and the apoplastic location of proteases can be subjective and dynamic. Pathogen-derived inhibitors have only been described for cysteine and serine proteases, and the selection pressure acting on immune proteases is rarely investigated. We discuss six different mechanisms by which these proteases mediate plant immunity and summarize the challenges for future research. [ABSTRACT FROM AUTHOR]

Successful plant defence against microbial pathogens is based on early recognition and fast activation of inducible responses. Key mechanisms include detection of microbe-associated molecular patterns by membrane-localized pattern recognition receptors that induce a basal resistance response. A well-described model of such responses to pathogens involves the interactions between Solanaceae plants and proteinaceous elicitors secreted by oomycetes, called elicitins. It has been hypothesized that the formation of oligomeric structures by elicitins could be involved in their recognition and activation of defensive transduction cascades. In this study, we tested this hypothesis using several approaches, and we observed differences in tobacco plant responses induced by the elicitin β-cryptogein (β-CRY) and its homodimer, β-CRYDIM. We also found that the C-terminal domain of elicitins of other ELI (true-elicitin) clades plays a significant role in stabilization of their oligomeric structure and restraint in the cell wall. In addition, covalently cross-linking β-CRYDIM impaired the formation of signalling complexes, thereby reducing its capacity to elicit the hypersensitive response and resistance in the host plant, with no significant changes in pathogenesis-related protein expression. By revealing the details of the effects of β-CRY dimerization on recognition and defence responses in tobacco, our results shed light on the poorly understood role of elicitins' oligomeric structures in the interactions between oomycetes and plants. [ABSTRACT FROM AUTHOR]

Summary: Evolutionary arms‐races between plants and insect herbivores have long been proposed to generate key innovations such as plant toxins and detoxification mechanisms that can drive diversification of the interacting species. A novel front‐line of plant defence is the killing of herbivorous insect eggs.We test whether an egg‐killing plant trait has an evolutionary basis in such a plant–insect arms‐race. Within the crucifer family (Brassicaceae), some species express a hypersensitive response (HR)‐like necrosis underneath butterfly eggs (Pieridae) that leads to eggs desiccating or falling off the plant. We studied the phylogenetic distribution of this trait, its egg‐killing effect on and elicitation by butterflies, by screening 31 Brassicales species, and nine Pieridae species.We show a clade‐specific induction of strong, egg‐killing HR‐like necrosis mainly in species of the Brassiceae tribe including Brassica crops and close relatives. The necrosis is strongly elicited by pierid butterflies that are specialists of crucifers. Furthermore, HR‐like necrosis is linked to PR1 defence gene expression, accumulation of reactive oxygen species and cell death, eventually leading to egg‐killing.Our findings suggest that the plants' egg‐killing trait is a new front on the evolutionary arms‐race between Brassicaceae and pierid butterflies beyond the well‐studied plant toxins that have evolved against their caterpillars. [ABSTRACT FROM AUTHOR]