Plant pattern-recognition receptors

Modern Breeding Strategies and Tools for Durable Late Blight Resistance in Potato

Cultivated potato (Solanum tuberosum) is a major crop worldwide. It occupies the second place after cereals (corn, rice, and wheat). This important crop is threatened by the Oomycete Phytophthora infestans, the agent of late blight disease. This pathogen was first encountered during the Irish famine during the 1840s and is a reemerging threat to potatoes. It is mainly controlled chemically by using fungicides, but due to health and environmental concerns, the best alternative is resistance. When there is no disease, no treatment is required. In this study, we present a summary of the ongoing efforts concerning resistance breeding of potato against this devastating pathogen, P. infestans. This work begins with the search for and selection of resistance genes, whether they are from within or from outside the species. The genetic methods developed to date for gene mining, such as effectoromics and GWAS, provide researchers with the ability to identify genes of interest more efficiently. Once identified, these genes are cloned using molecular markers (MAS or QRL) and can then be introduced into different cultivars using somatic hybridization or recombinant DNA technology. More innovative technologies have been developed lately, such as gene editing using the CRISPR system or gene silencing, by exploiting iRNA strategies that have emerged as promising tools for managing Phytophthora infestans, which can be employed. Also, gene pyramiding or gene stacking, which involves the accumulation of two or more R genes on the same individual plant, is an innovative method that has yielded many promising results. All these advances related to the development of molecular techniques for obtaining new potato cultivars resistant to P. infestans can contribute not only to reducing losses in agriculture but especially to ensuring food security and safety.

Subtilisin-like proteases from Fusarium graminearum induce plant cell death and contribute to virulence

Fusarium head blight (FHB), caused by Fusarium graminearum, causes huge annual economic losses in cereal production. To successfully colonize host plants, pathogens secrete hundreds of effectors that interfere with plant immunity and facilitate infection. However, the roles of most secreted effectors of F. graminearum in pathogenesis remain unclear. We analyzed the secreted proteins of F. graminearum and identified 255 candidate effector proteins by liquid chromatography-mass spectrometry (LC-MS). Five subtilisin-like family proteases (FgSLPs) were identified that can induce cell death in Nicotiana benthamiana leaves. Further experiments showed that these FgSLPs induced cell death in cotton (Gossypium barbadense) and Arabidopsis (Arabidopsis thaliana). A signal peptide and light were not essential for the cell death-inducing activity of FgSLPs. The I9 inhibitor domain and the entire C-terminus of FgSLPs were indispensable for their self-processing and cell death-inducing activity. FgSLP-induced cell death occurred independent of the plant signal transduction components BRI-ASSOCIATED KINASE 1 (BAK1), SUPPRESSOR OF BIR1 1 (SOBIR1), ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), and PHYTOALEXIN DEFICIENT 4 (PAD4). Reduced virulence was observed when FgSLP1 and FgSLP2 were simultaneously knocked out. This study reveals a class of secreted toxic proteins essential for F. graminearum virulence.

The soybean plasma membrane GmDR1 protein conferring broad-spectrum disease and pest resistance regulates several receptor kinases and NLR proteins

Overexpression of Glycine max disease resistant 1 (GmDR1) exhibits broad-spectrum resistance against Fusarium virguliforme, Heterodera glycines (soybean cyst nematode), Tetranychus urticae (Koch) (spider mites), and Aphis glycines Matsumura (soybean aphids) in soybean. To understand the mechanisms of broad-spectrum immunity mediated by GmDR1, the transcriptomes of a strong and a weak GmDR1-overexpressor following treatment with chitin, a pathogen- and pest-associated molecular pattern (PAMP) common to these organisms, were investigated. The strong and weak GmDR1-overexpressors exhibited altered expression of 6098 and 992 genes, respectively, as compared to the nontransgenic control following chitin treatment. However, only 192 chitin- and 115 buffer-responsive genes exhibited over two-fold changes in expression levels in both strong and weak GmDR1-overexpressors as compared to the control. MapMan analysis of the 192 chitin-responsive genes revealed 64 biotic stress-related genes, of which 53 were induced and 11 repressed as compared to the control. The 53 chitin-induced genes include nine genes that encode receptor kinases, 13 encode nucleotide-binding leucine-rich repeat (NLR) receptor proteins, seven encode WRKY transcription factors, four ethylene response factors, and three MYB-like transcription factors. Investigation of a subset of these genes revealed three receptor protein kinases, seven NLR proteins, and one WRKY transcription factor genes that are induced following F. virguliforme and H. glycines infection. The integral plasma membrane GmDR1 protein most likely recognizes PAMPs including chitin and activates transcription of genes encoding receptor kinases, NLR proteins and defense-related genes. GmDR1 could be a pattern recognition receptor that regulates the expression of several NLRs for expression of PAMP-triggered immunity and/or priming the effector triggered immunity.

Recognition of the inducible, secretory small protein OsSSP1 by the membrane receptor OsSSR1 and the co-receptor OsBAK1 confers rice resistance to the blast fungus

The plant apoplast, which serves as the frontline battleground for long-term host-pathogen interactions, harbors a wealth of disease resistance resources. However, the identification of the disease resistance proteins in the apoplast is relatively lacking. In this study, we identified and characterized the rice secretory protein OsSSP1 (Oryza sativa secretory small protein 1). OsSSP1 can be secreted into the plant apoplast, and either in vitro treatment of recombinant OsSSP1 or overexpression of OsSSP1 in rice could trigger plant immune response. The expression of OsSSP1 is suppressed significantly during Magnaporthe oryzae infection in the susceptible rice variety Taibei 309, and OsSSP1-overexpressing lines all show strong resistance to M. oryzae. Combining the knockout and overexpression results, we found that OsSSP1 positively regulates plant immunity in response to fungal infection. Moreover, the recognition and immune response triggered by OsSSP1 depend on an uncharacterized transmembrane OsSSR1 (secretory small protein receptor 1) and the key co-receptor OsBAK1, since most of the induced immune response and resistance are lost in the absence of OsSSR1 or OsBAK1. Intriguingly, the OsSSP1 protein is relatively stable and can still induce plant resistance after 1 week of storage in the open environment, and exogenous OsSSP1 treatment for a 2-week period did not affect rice yield. Collectively, our study reveals that OsSSP1 can be secreted into the apoplast and percepted by OsSSR1 and OsBAK1 during fungal infection, thereby triggering the immune response to enhance plant resistance to M. oryzae. These findings provide novel resources and potential strategies for crop breeding and disease control.

Genome-wide characterization of the NBLRR gene family provides evolutionary and functional insights into blast resistance in pearl millet (Cenchrus americanus (L.) Morrone)

MAIN CONCLUSION

The investigation is the first report on genome-wide identification and characterization of NBLRR genes in pearl millet. We have shown the role of gene loss and purifying selection in the divergence of NBLRRs in Poaceae lineage and candidate CaNBLRR genes for resistance to Magnaporthe grisea infection. Plants have evolved multiple integral mechanisms to counteract the pathogens' infection, among which plant immunity through NBLRR (nucleotide-binding site, leucine-rich repeat) genes is at the forefront. The genome-wide mining in pearl millet (Cenchrus americanus (L.) Morrone) revealed 146 CaNBLRRs. The variation in the branch length of NBLRRs showed the dynamic nature of NBLRRs in response to evolving pathogen races. The orthology of NBLRRs showed a predominance of many-to-one orthologs, indicating the divergence of NBLRRs in the pearl millet lineage mainly through gene loss events followed by gene gain through single-copy duplications. Further, the purifying selection (Ka/Ks < 1) shaped the expansion of NBLRRs within the lineage of pear millet and other members of Poaceae. Presence of cis-acting elements, viz. TCA element, G-box, MYB, SARE, ABRE and conserved motifs annotated with P-loop, kinase 2, RNBS-A, RNBS-D, GLPL, MHD, Rx-CC and LRR suggests their putative role in disease resistance and stress regulation. The qRT-PCR analysis in pearl millet lines showing contrasting responses to Magnaporthe grisea infection identified CaNBLRR20, CaNBLRR33, CaNBLRR46 CaNBLRR51, CaNBLRR78 and CaNBLRR146 as putative candidates. Molecular docking showed the involvement of three and two amino acid residues of LRR domains forming hydrogen bonds (histidine, arginine and threonine) and salt bridges (arginine and lysine) with effectors. Whereas 14 and 20 amino acid residues of CaNBLRR78 and CaNBLRR20 showed hydrophobic interactions with 11 and 9 amino acid residues of effectors, Mg.00g064570.m01 and Mg.00g006570.m01, respectively. The present investigation gives a comprehensive overview of CaNBLRRs and paves the foundation for their utility in pearl millet resistance breeding through understanding of host-pathogen interactions.

BRASSINOSTEROID-SIGNALING KINASE1 associates with and is required for cysteine protease RESPONSE TO DEHYDRATION 19-mediated disease resistance in Arabidopsis

The receptor-like cytoplasmic kinase BRASSINOSTEROID-SIGNALING KINASE1 (BSK1) interacts with pattern recognition receptor (PRR) FLAGELLIN SENSING2 (FLS2) and positively regulates plant innate immunity in Arabidopsis thaliana. However, the molecular components involved in BSK1-mediated immune signaling remain largely unknown. To further explore the molecular mechanism underlying BSK1-mediated disease resistance, we screened two cysteine proteases, RESPONSE TO DEHYDRATION 19 (RD19) and RD19-LIKE 2 (RDL2), as BSK1-binding partners. Overexpression of RD19, but not RDL2, displayed an autoimmune phenotype, presenting programmed cell death and enhanced resistance to multiple pathogens. Interestingly, RD19-mediated immune activation depends on BSK1, as knockout of BSK1 in RD19-overexpressing plants rescued their autoimmunity and abolished the increased resistance. Furthermore, we found that BSK1 plays a positive role in maintaining RD19 protein abundance in Arabidopsis. Our results provide new insights into BSK1-mediated immune signaling and reveal a potential mechanism by which BSK1 stabilizes RD19 to promote effective immune output.

Inhibition of PbeXTH1 and PbeSEOB1 is required for the Valsa canker resistance contributed by Wall-associated kinase gene MbWAK1

Wall-associated kinases (WAKs) have been determined to recognize pathogenic signals and initiate plant immune responses. However, the roles of the family members in host resistance against Valsa canker, a serious fungal disease of apples and pears, are largely unknown. Here, we identified MbWAK1 in Malus baccata, a resistant germplasm differentially expressed during infection by Valsa mali (Vm). Over-expression of MbWAK1 enhanced the Valsa canker resistance of apple and pear fruits and 'Duli-G03' (Pyrus betulifolia) suspension cells. A large number of phloem, cell wall, and lipid metabolic process-related genes were differentially expressed in overexpressed suspension cell lines in response to Valsa pyri (Vp) signals. Among these, the expression of xyloglucan endotransglucosylase/hydrolase (XTH) gene PbeXTH1 and sieve element occlusion B-like (SEOB) gene PbeSEOB1 were significantly inhibited. Transient expression of PbeXTH1 or PbeSEOB1 compromised the expressional induction of MbWAK1 and the resistance contributed by MbWAK1. In addition, PbeXTH1 and PbeSEOB1 suppressed the immune response induced by MbWAK1. Our results enriched the molecular mechanisms for MbWAK1 against Valsa canker and resistant breeding.

Coping with alpine habitats: genomic insights into the adaptation strategies of Triplostegia glandulifera (Caprifoliaceae)

How plants find a way to thrive in alpine habitats remains largely unknown. Here we present a chromosome-level genome assembly for an alpine medicinal herb, Triplostegia glandulifera (Caprifoliaceae), and 13 transcriptomes from other species of Dipsacales. We detected a whole-genome duplication event in T. glandulifera that occurred prior to the diversification of Dipsacales. Preferential gene retention after whole-genome duplication was found to contribute to increasing cold-related genes in T. glandulifera. A series of genes putatively associated with alpine adaptation (e.g. CBFs, ERF-VIIs, and RAD51C) exhibited higher expression levels in T. glandulifera than in its low-elevation relative, Lonicera japonica. Comparative genomic analysis among five pairs of high- vs low-elevation species, including a comparison of T. glandulifera and L. japonica, indicated that the gene families related to disease resistance experienced a significantly convergent contraction in alpine plants compared with their lowland relatives. The reduction in gene repertory size was largely concentrated in clades of genes for pathogen recognition (e.g. CNLs, prRLPs, and XII RLKs), while the clades for signal transduction and development remained nearly unchanged. This finding reflects an energy-saving strategy for survival in hostile alpine areas, where there is a tradeoff with less challenge from pathogens and limited resources for growth. We also identified candidate genes for alpine adaptation (e.g. RAD1, DMC1, and MSH3) that were under convergent positive selection or that exhibited a convergent acceleration in evolutionary rate in the investigated alpine plants. Overall, our study provides novel insights into the high-elevation adaptation strategies of this and other alpine plants.

Integrated multi-omics and genetic analyses reveal molecular determinants underlying Arabidopsis snap33 mutant phenotype

The secretory pathway is essential for plant immunity, delivering diverse antimicrobial molecules into the extracellular space. Arabidopsis thaliana soluble N-ethylmaleimide-sensitive-factor attachment protein receptor SNAP33 is a key actor of this process. The snap33 mutant displays dwarfism and necrotic lesions, however the molecular determinants of its macroscopic phenotypes remain elusive. Here, we isolated several new snap33 mutants that exhibited constitutive cell death and H2O2 accumulation, further defining snap33 as an autoimmune mutant. We then carried out quantitative transcriptomic and proteomic analyses showing that numerous defense transcripts and proteins were up-regulated in the snap33 mutant, among which genes/proteins involved in defense hormone, pattern-triggered immunity, and nucleotide-binding domain leucine-rich-repeat receptor signaling. qRT-PCR analyses and hormone dosages supported these results. Furthermore, genetic analyses elucidated the diverse contributions of the main defense hormones and some nucleotide-binding domain leucine-rich-repeat receptor signaling actors in the establishment of the snap33 phenotype, emphasizing the preponderant role of salicylic acid over other defense phytohormones. Moreover, the accumulation of pattern-triggered immunity and nucleotide-binding domain leucine-rich-repeat receptor signaling proteins in the snap33 mutant was confirmed by immunoblotting analyses and further shown to be salicylic acid-dependent. Collectively, this study unveiled molecular determinants underlying the Arabidopsis snap33 mutant phenotype and brought new insights into autoimmunity signaling.

Pull the fuzes: Processing protein precursors to generate apoplastic danger signals for triggering plant immunity

The apoplast is one of the first cellular compartments outside the plasma membrane encountered by phytopathogenic microbes in the early stages of plant tissue invasion. Plants have developed sophisticated surveillance mechanisms to sense danger events at the cell surface and promptly activate immunity. However, a fine tuning of the activation of immune pathways is necessary to mount a robust and effective defense response. Several endogenous proteins and enzymes are synthesized as inactive precursors, and their post-translational processing has emerged as a critical mechanism for triggering alarms in the apoplast. In this review, we focus on the precursors of phytocytokines, cell wall remodeling enzymes, and proteases. The physiological events that convert inactive precursors into immunomodulatory active peptides or enzymes are described. This review also explores the functional synergies among phytocytokines, cell wall damage-associated molecular patterns, and remodeling, highlighting their roles in boosting extracellular immunity and reinforcing defenses against pests.

Interactive transcriptome analyses of Northern Wild Rice (Zizania palustris L.) and Bipolaris oryzae show convoluted communications during the early stages of fungal brown spot development

Fungal diseases, caused mainly by Bipolaris spp., are past and current threats to Northern Wild Rice (NWR) grain production and germplasm preservation in both natural and cultivated settings. Genetic resistance against the pathogen is scarce. Toward expanding our understanding of the global gene communications of NWR and Bipolaris oryzae interaction, we designed an RNA sequencing study encompassing the first 12 h and 48 h of their encounter. NWR activated numerous plant recognition receptors after pathogen infection, followed by active transcriptional reprogramming of signaling mechanisms driven by Ca2+ and its sensors, mitogen-activated protein kinase cascades, activation of an oxidative burst, and phytohormone signaling-bound mechanisms. Several transcription factors associated with plant defense were found to be expressed. Importantly, evidence of diterpenoid phytoalexins, especially phytocassane biosynthesis, among expression of other defense genes was found. In B. oryzae, predicted genes associated with pathogenicity including secreted effectors that could target plant defense mechanisms were expressed. This study uncovered the early molecular communication between the NWR-B. oryzae pathosystem, which could guide selection for allele-specific genes to boost NWR defenses, and overall aid in the development of more efficient selection methods in NWR breeding through the use of the most virulent fungal isolates.

Update on the Basic Understanding of Fusarium graminearum Virulence Factors in Common Wheat Research

Wheat is one of the most important food crops, both in China and worldwide. Wheat production is facing extreme stresses posed by different diseases, including Fusarium head blight (FHB), which has recently become an increasingly serious concerns. FHB is one of the most significant and destructive diseases affecting wheat crops all over the world. Recent advancements in genomic tools provide a new avenue for the study of virulence factors in relation to the host plants. The current review focuses on recent progress in the study of different strains of Fusarium infection. The presence of genome-wide repeat-induced point (RIP) mutations causes genomic mutations, eventually leading to host plant susceptibility against Fusarium invasion. Furthermore, effector proteins disrupt the host plant resistance mechanism. In this study, we proposed systematic modification of the host genome using modern biological tools to facilitate plant resistance against foreign invasion. We also suggested a number of scientific strategies, such as gene cloning, developing more powerful functional markers, and using haplotype marker-assisted selection, to further improve FHB resistance and associated breeding methods.

Transcriptome sequencing and expression analysis in peanut reveal the potential mechanism response to Ralstonia solanacearum infection

BACKGROUND

Bacterial wilt caused by Ralstonia solanacearum severely affects peanut (Arachis hypogaea L.) yields. The breeding of resistant cultivars is an efficient means of controlling plant diseases. Therefore, identification of resistance genes effective against bacterial wilt is a matter of urgency. The lack of a reference genome for a resistant genotype severely hinders the process of identification of resistance genes in peanut. In addition, limited information is available on disease resistance-related pathways in peanut.

RESULTS

Full-length transcriptome data were used to generate wilt-resistant and -susceptible transcript pools. In total, 253,869 transcripts were retained to form a reference transcriptome for RNA-sequencing data analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of differentially expressed genes revealed the plant-pathogen interaction pathway to be the main resistance-related pathway for peanut to prevent bacterial invasion and calcium plays an important role in this pathway. Glutathione metabolism was enriched in wilt-susceptible genotypes, which would promote glutathione synthesis in the early stages of pathogen invasion. Based on our previous quantitative trait locus (QTL) mapping results, the genes arahy.V6I7WA and arahy.MXY2PU, which encode nucleotide-binding site-leucine-rich repeat receptor proteins, were indicated to be associated with resistance to bacterial wilt.

CONCLUSIONS

This study identified several pathways associated with resistance to bacterial wilt and identified candidate genes for bacterial wilt resistance in a major QTL region. These findings lay a foundation for investigation of the mechanism of resistance to bacterial wilt in peanut.

Plant Biostimulant as an Environmentally Friendly Alternative to Modern Agriculture

Ensuring the safety of crop production presents a significant challenge to humanity. Pesticides and fertilizers are commonly used to eliminate external interference and provide nutrients, enabling crops to sustain growth and defense. However, the addition of chemical substances does not meet the environmental standards required for agricultural production. Recently, natural sources such as biostimulants have been found to help plants with growth and defense. The development of biostimulants provides new solutions for agricultural product safety and has become a widely utilized tool in agricultural. The review summarizes the classification of biostimulants, including humic-based biostimulant, protein-based biostimulant, oligosaccharide-based biostimulant, metabolites-based biostimulants, inorganic substance, and microbial inoculant. This review attempts to summarize suitable alternative technology that can address the problems and analyze the current state of biostimulants, summarizes the research mechanisms, and anticipates future technological developments and market trends, which provides comprehensive information for researchers to develop biostimulants.

DGK5β-derived phosphatidic acid regulates ROS production in plant immunity by stabilizing NADPH oxidase

In plant immunity, phosphatidic acid (PA) regulates reactive oxygen species (ROS) by binding to respiratory burst oxidase homolog D (RBOHD), an NADPH oxidase responsible for ROS production. Here, we analyze the influence of PA binding on RBOHD activity and the mechanism of RBOHD-bound PA generation. PA binding enhances RBOHD protein stability by inhibiting vacuolar degradation, thereby increasing chitin-induced ROS production. Mutations in diacylglycerol kinase 5 (DGK5), which phosphorylates diacylglycerol to produce PA, impair chitin-induced PA and ROS production. The DGK5 transcript DGK5β (but not DGK5α) complements reduced PA and ROS production in dgk5-1 mutants, as well as resistance to Botrytis cinerea. Phosphorylation of S506 residue in the C-terminal calmodulin-binding domain of DGK5β contributes to the activation of DGK5β to produce PA. These findings suggest that DGK5β-derived PA regulates ROS production by inhibiting RBOHD protein degradation, elucidating the role of PA-ROS interplay in immune response regulation.

PTI-ETI synergistic signal mechanisms in plant immunity

Plants face a relentless onslaught from a diverse array of pathogens in their natural environment, to which they have evolved a myriad of strategies that unfold across various temporal scales. Cell surface pattern recognition receptors (PRRs) detect conserved elicitors from pathogens or endogenous molecules released during pathogen invasion, initiating the first line of defence in plants, known as pattern-triggered immunity (PTI), which imparts a baseline level of disease resistance. Inside host cells, pathogen effectors are sensed by the nucleotide-binding/leucine-rich repeat (NLR) receptors, which then activate the second line of defence: effector-triggered immunity (ETI), offering a more potent and enduring defence mechanism. Moreover, PTI and ETI collaborate synergistically to bolster disease resistance and collectively trigger a cascade of downstream defence responses. This article provides a comprehensive review of plant defence responses, offering an overview of the stepwise activation of plant immunity and the interactions between PTI-ETI synergistic signal transduction.

Structural and biochemical basis of FLS2-mediated signal activation and transduction in rice

The receptor-like kinase FLAGELLIN-SENSITIVE 2 (FLS2) functions as a bacterial flagellin receptor localized on the cell membrane of plants. In Arabidopsis, the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) cooperates with FLS2 to detect the flagellin epitope flg22, resulting in formation of a signaling complex that triggers plant defense responses. However, the co-receptor responsible for recognizing and signaling the flg22 epitope in rice remains to be determined, and the precise structural mechanism underlying FLS2-mediated signal activation and transduction has not been clarified. This study presents the structural characterization of a kinase-dead mutant of the intracellular kinase domain of OsFLS2 (OsFLS2-KDD1013A) in complex with ATP or ADP, resolved at resolutions of 1.98 Å and 2.09 Å, respectively. Structural analysis revealed that OsFLS2 can adopt an active conformation in the absence of phosphorylation, although it exhibits only weak basal catalytic activity for autophosphorylation. Subsequent investigations demonstrated that OsSERK2 effectively phosphorylates OsFLS2, which reciprocally phosphorylates OsSERK2, leading to complete activation of OsSERK2 and rapid phosphorylation of the downstream substrate receptor-like cytoplasmic kinases OsRLCK176 and OsRLCK185. Through mass spectrometry experiments, we successfully identified critical autophosphorylation sites on OsSERK2, as well as sites transphosphorylated by OsFLS2. Furthermore, we demonstrated the interaction between OsSERK2 and OsFLS2, which is enhanced in the presence of flg22. Genetic evidence suggests that OsRLCK176 and OsRLCK185 may function downstream of the OsFLS2-mediated signaling pathway. Our study reveals the molecular mechanism by which OsFLS2 mediates signal transduction pathways in rice and provides a valuable example for understanding RLK-mediated signaling pathways in plants.

An Oxidoreductase-like Protein is Required for Verticillium dahliae Infection and Participates in the Metabolism of Host Plant Defensive Compounds

Verticillium dahliae, a notorious phytopathogenic fungus, is responsible for vascular wilt diseases in numerous crops. Uncovering the molecular mechanisms underlying pathogenicity is crucial for controlling V. dahliae. Herein, we characterized a putative oxidoreductase-like protein (VdOrlp) from V. dahliae that contains a functional signal peptide. While the expression of VdOrlp was low in artificial media, it significantly increased during host infection. Deletion of VdOrlp had minimal effects on the growth and development of V. dahliae but severely impaired its pathogenicity. Metabolomic analysis revealed significant changes in organic heterocyclic compounds and phenylpropane compounds in cotton plants infected with ΔVdOrlp and V991. Furthermore, VdOrlp expression was induced by lignin, and its deletion affected the metabolism of host lignin and phenolic acids. In conclusion, our results demonstrated that VdOrlp plays an important role in the metabolism of plant phenylpropyl lignin and organic heterocyclic compounds and is required for fungal pathogenicity in V. dahliae.

A perspective on varied fungal virulence factors causing infection in host plants

Pathogenic fungi and their spores are ubiquitously present and invade the tissues of higher living plants causing pathogenesis and inevitably death or retarded growth. A group of fungi kills its hosts and consume the dead tissues (necrotrophs), while others feed on living tissue (biotrophs) or combination of two (hemibiotrophs). A number of virulent factors is used by fungal pathogens to inhabit new hosts and cause illness. Fungal pathogens develop specialized structures for complete invasion into plant organs to regulate pathogenic growth. Virulence factors like effectors, mycotoxins, cell wall degrading enzymes and organic acids have varied roles depending on the infection strategy and assist the pathogens to possess control on living tissues of the plants. Infection strategies employed by fungi generally masks the plant defense mechanism, however necrotrophs are best known to harm plant tissues with their poisonous secretion. Interestingly, the effector chemicals released by Biotrophs reduce plant cell growth and regulate plant metabolism in their advantage causing no direct death. All these virulence tools cause huge loss to the agricultural product of pre- harvest crops and post-harvest yields causing low output leading to huge economic losses. This review focusses on comprehensive study of range of virulence factors of the pathogenic fungi responsible for their invasion inside the healthy tissues of plants. The compiled information would influence researchers to design antidote against all virulence factors of fungi relevant to their area of research which could pave way for protection against plant pathogenesis.

A glycoside hydrolase 30 protein BpXynC of Bacillus paralicheniformis NMSW12 recognized as A MAMP triggers plant immunity response

Bacillus spp. has been widely used as a biocontrol agent to control plant diseases. However, little is known about mechanisms of the protein MAMP secreted by Bacillus spp. Herein, our study reported a glycoside hydrolase family 30 (GH30) protein, BpXynC, produced by the biocontrol bacteria Bacillus paralicheniformis NMSW12, that can induce cell death in several plant species. The results revealed that the recombinant protein triggers cell death in Nicotiana benthamiana in a BAK1-dependent manner and elicits an early defense response, including ROS burst, activation of MAPK cascades, and upregulation of plant immunity marker genes. BpXynC was also found to be a glucuronoxylanase that exhibits hydrolysis activity on xlyan. Two mutants of BpXynC which lost the glucuronoxylanase activity still retained the elicitor activity. The qRT-PCR results of defense-related genes showed that BpXynC induces plant immunity responses via an SA-mediated pathway. BpXynC and its mutants could induce resistance in N. benthamiana against infection by Sclerotinia sclerotiorum and tobacco mosaic virus (TMV). Furthermore, BpXynC-treated tomato fruits exhibited strong resistance to the infection of Phytophthora capsica. Overall, our study revealed that GH30 protein BpXynC can induce plant immunity response as MAMP, which can be further applied as a biopesticide to control plant diseases.

Natural variation in the pattern-triggered immunity response in plants: Investigations, implications and applications

The pattern-triggered immunity (PTI) response is triggered at the plant cell surface by the recognition of microbe-derived molecules known as microbe- or pathogen-associated molecular patterns or molecules derived from compromised host cells called damage-associated molecular patterns. Membrane-localized receptor proteins, known as pattern recognition receptors, are responsible for this recognition. Although much of the machinery of PTI is conserved, natural variation for the PTI response exists within and across species with respect to the components responsible for pattern recognition, activation of the response, and the strength of the response induced. This review describes what is known about this variation. We discuss how variation in the PTI response can be measured and how this knowledge might be utilized in the control of plant disease and in developing plant varieties with enhanced disease resistance.

HvMPK4 phosphorylates HvWRKY1 to enhance its suppression of barley immunity to powdery mildew fungus

Mitogen-activated protein kinase (MAPK) cascades play important roles in disease resistance in model plant species. However, the functions of MAPK signaling pathways in crop disease resistance are largely unknown. Here we report the function of HvMKK1-HvMPK4-HvWRKY1 module in barley immune system. HvMPK4 is identified to play a negative role in barley immune response against Bgh, as virus-induced gene silencing of HvMPK4 results in enhanced disease resistance whilst stably overexpressing HvMPK4 leads to super-susceptibility to Bgh infection. Furthermore, the barley MAPK kinase HvMKK1 is found to specifically interact with HvMPK4, and the activated HvMKK1DD variant specifically phosphorylates HvMPK4 in vitro. Moreover, the transcription factor HvWRKY1 is identified to be a downstream target of HvMPK4 and phosphorylated by HvMPK4 in vitro in the presence of HvMKK1DD. Phosphorylation assay coupled with mutagenesis analyses identifies S122, T284, and S347 in HvWRKY1 as the major residues phosphorylated by HvMPK4. HvWRKY1 is phosphorylated in barley at the early stages of Bgh infection, which enhances its suppression on barley immunity likely due to enhanced DNA-binding and transcriptional repression activity. Our data suggest that the HvMKK1-HvMPK4 kinase pair acts upstream of HvWRKY1 to negatively regulate barley immunity against powdery mildew.

Receptor-like kinases OsRLK902-1 and OsRLK902-2 form immune complexes with OsRLCK185 to regulate rice blast resistance

Receptor-like kinases (RLKs) are major regulators of the plant immune response and play important roles in the perception and transmission of immune signals. RECEPTOR LIKE KINASE 902 (RLK902) is at the key node in leucine-rich repeat receptor-like kinase interaction networks and positively regulates resistance to the bacterial pathogen Pseudomonas syringae in Arabidopsis. However, the function of RLK902 in fungal disease resistance remains obscure. In this study, we found that the expression levels of OsRLK902-1 and OsRLK902-2, encoding two orthologues of RLK902 in rice, were induced by Magnaporthe oryzae, chitin, and flg22 treatment. osrlk902-1 and osrlk902-2 knockout mutants displayed enhanced susceptibility to M. oryzae. Interestingly, the osrlk902-1 rlk902-2 double mutant exhibited similar disease susceptibility, hydrogen peroxide production, and callose deposition to the two single mutants. Further investigation showed that OsRLK902-1 interacts with and stabilizes OsRLK902-2. The two OsRLKs form a complex with OsRLCK185, a key regulator in chitin-triggered immunity, and stabilize it. Taken together, our data demonstrate that OsRLK902-1 and OsRLK902-2, as well as OsRLCK185 function together in regulating disease resistance to M. oryzae in rice.

A new spider mite elicitor triggers plant defence and promotes resistance to herbivores

Herbivore-associated elicitors (HAEs) are active molecules produced by herbivorous insects. Recognition of HAEs by plants induces defence that resist herbivore attacks. We previously demonstrated that the tomato red spider mite Tetranychus evansi triggered defence in Nicotiana benthamiana. However, our knowledge of HAEs from T. evansi remains limited. Here, we characterize a novel HAE, Te16, from T. evansi and dissect its function in mite-plant interactions. We investigate the effects of Te16 on spider mites and plants by heterologous expression, virus-induced gene silencing assay, and RNA interference. Te16 induces cell death, reactive oxygen species (ROS) accumulation, callose deposition, and jasmonate (JA)-related responses in N. benthamiana leaves. Te16-mediated cell death requires a calcium signalling pathway, cytoplasmic localization, the plant co-receptor BAK1, and the signalling components SGT1 and HSP90. The active region of Te16-induced cell death is located at amino acids 114-293. Moreover, silencing Te16 gene in T. evansi reduces spider mite survival and hatchability, but expressing Te16 in N. benthamiana leaves enhances plant resistance to herbivores. Finally, Te16 gene is specific to Tetranychidae species and is highly conserved in activating plant immunity. Our findings reveal a novel salivary protein produced by spider mites that elicits plant defence and resistance to insects, providing valuable clues for pest management.

Comparative transcriptome and metabolome analysis revealed diversity in the response of resistant and susceptible rose (Rosa hybrida) varieties to Marssonina rosae

Rose black spot disease caused by Marssonina rosae is among the most destructive diseases that affects the outdoor cultivation and production of roses; however, the molecular mechanisms underlying the defensive response of roses to M. rosae have not been clarified. To investigate the diversity of response to M. rosae in resistant and susceptible rose varieties, we performed transcriptome and metabolome analyses of resistant (KT) and susceptible (FG) rose varieties and identified differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in response to M. rosae at different time points. In response to M. rosae, DEGs and DAMs were mainly upregulated compared to the control and transcription factors were concentrated in the WRKY and AP2/ERF families. Gene Ontology analysis showed that the DEGs of FG were mainly enriched in biological processes, such as the abscisic acid-activated signaling pathway, cell wall, and defense response, whereas the DEGs of KT were mainly enriched in Golgi-mediated vesicle transport processes. Kyoto Encyclopedia of Genes and Genomes analysis showed that the DEGs of both varieties were concentrated in plant-pathogen interactions, plant hormone signal transduction, and mitogen-activated protein kinase signaling pathways, with the greatest number of DEGs associated with brassinosteroid (BR) in the plant hormone signal transduction pathway. The reliability of the transcriptome results was verified by qRT-PCR. DAMs of KT were significantly enriched in the butanoate metabolism pathway, whereas DAMs of FG were significantly enriched in BR biosynthesis, glucosinolate biosynthesis, and tryptophan metabolism. Moreover, the DAMs in these pathways were significantly positively correlated with the DEGs. Disease symptoms were aggravated when FG leaves were inoculated with M. rosae after 24-epibrassinolide treatment, indicating that the response of FG to M. rosae involves the BR signaling pathway. Our results provide new insights into the molecular mechanisms underlying rose response to M. rosae and lay a theoretical foundation for formulating rose black spot prevention and control strategies and cultivating resistant varieties.

OsLRR-RLP2 Gene Regulates Immunity to Magnaporthe oryzae in Japonica Rice

Rice is an important cereal crop worldwide, the growth of which is affected by rice blast disease, caused by the fungal pathogen Magnaporthe oryzae. As climate change increases the diversity of pathogens, the disease resistance genes (R genes) in plants must be identified. The major blast-resistance genes have been identified in indica rice varieties; therefore, japonica rice varieties with R genes now need to be identified. Because leucine-rich repeat (LRR) domain proteins possess R-gene properties, we used bioinformatics analysis to identify the rice candidate LRR domain receptor-like proteins (OsLRR-RLPs). OsLRR-RLP2, which contains six LRR domains, showed differences in the DNA sequence, containing 43 single-nucleotide polymorphisms (SNPs) in indica and japonica subpopulations. The results of the M. oryzae inoculation analysis indicated that indica varieties with partial deletion of OsLRR-RLP2 showed susceptibility, whereas japonica varieties with intact OsLRR-RLP2 showed resistance. The oslrr-rlp2 mutant, generated using clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), showed increased pathogen susceptibility, whereas plants overexpressing this gene showed pathogen resistance. These results indicate that OsLRR-RLP2 confers resistance to rice, and OsLRR-RLP2 may be useful for breeding resistant cultivars.

Identification of salivary proteins of the cowpea aphid Aphis craccivora by transcriptome and LC-MS/MS analyses

Aphid salivary proteins mediate the interaction between aphids and their host plants. Moreover, these proteins facilitate digestion, detoxification of secondary metabolites, as well as activation and suppression of plant defenses. The cowpea aphid, Aphis craccivora, is an important sucking pest of leguminous crops worldwide. Although aphid saliva plays an important role in aphid plant interactions, knowledge of the cowpea aphid salivary proteins is limited. In this study, we performed transcriptomic and LC-MS/MS analyses to identify the proteins present in the salivary glands and saliva of A. craccivora. A total of 1,08,275 assembled transcripts were identified in the salivary glands of aphids. Of all these assembled transcripts, 53,714 (49.11%) and 53,577 (49.48%) transcripts showed high similarity to known proteins in the Nr and UniProt databases, respectively. A total of 2159 proteins were predicted as secretory proteins from the salivary gland transcriptome dataset, which contain digestive enzymes, detoxification enzymes, previously known effectors and elicitors, and potential proteins whose functions have yet to be determined. The proteomic analysis of aphid saliva resulted in the identification of 171 proteins. Tissue-specific expression of selected genes using RT-PCR showed that three genes were expressed only in the salivary glands. Overall, our results provide a comprehensive repertoire of cowpea aphid salivary proteins from the salivary gland and saliva, which will be a good resource for future effector functional studies and might also be useful for sustainable aphid management.

Evolutionary trajectory of pattern recognition receptors in plants

Cell-surface receptors play pivotal roles in many biological processes, including immunity, development, and reproduction, across diverse organisms. How cell-surface receptors evolve to become specialised in different biological processes remains elusive. To shed light on the immune-specificity of cell-surface receptors, we analyzed more than 200,000 genes encoding cell-surface receptors from 350 genomes and traced the evolutionary origin of immune-specific leucine-rich repeat receptor-like proteins (LRR-RLPs) in plants. Surprisingly, we discovered that the motifs crucial for co-receptor interaction in LRR-RLPs are closely related to those of the LRR-receptor-like kinase (RLK) subgroup Xb, which perceives phytohormones and primarily governs growth and development. Functional characterisation further reveals that LRR-RLPs initiate immune responses through their juxtamembrane and transmembrane regions, while LRR-RLK-Xb members regulate development through their cytosolic kinase domains. Our data suggest that the cell-surface receptors involved in immunity and development share a common origin. After diversification, their ectodomains, juxtamembrane, transmembrane, and cytosolic regions have either diversified or stabilised to recognise diverse ligands and activate differential downstream responses. Our work reveals a mechanism by which plants evolve to perceive diverse signals to activate the appropriate responses in a rapidly changing environment.

From field to plate: How do bacterial enteric pathogens interact with ready-to-eat fruit and vegetables, causing disease outbreaks?

Ready-to-eat fruit and vegetables are a convenient source of nutrients and fibre for consumers, and are generally safe to eat, but are vulnerable to contamination with human enteric bacterial pathogens. Over the last decade, Salmonella spp., pathogenic Escherichia coli, and Listeria monocytogenes have been linked to most of the bacterial outbreaks of foodborne illness associated with fresh produce. The origins of these outbreaks have been traced to multiple sources of contamination from pre-harvest (soil, seeds, irrigation water, domestic and wild animal faecal matter) or post-harvest operations (storage, preparation and packaging). These pathogens have developed multiple processes for successful attachment, survival and colonization conferring them the ability to adapt to multiple environments. However, these processes differ across bacterial strains from the same species, and across different plant species or cultivars. In a competitive environment, additional risk factors are the plant microbiome phyllosphere and the plant responses; both factors directly modulate the survival of the pathogens on the leaf's surface. Understanding the mechanisms involved in bacterial attachment to, colonization of, and proliferation, on fresh produce and the role of the plant in resisting bacterial contamination is therefore crucial to reducing future outbreaks.

Effector-triggered susceptibility by the rice blast fungus Magnaporthe oryzae

Rice blast, the most destructive disease of cultivated rice world-wide, is caused by the filamentous fungus Magnaporthe oryzae. To cause disease in plants, M. oryzae secretes a diverse range of effector proteins to suppress plant defense responses, modulate cellular processes, and support pathogen growth. Some effectors can be secreted by appressoria even before host penetration, while others accumulate in the apoplast, or enter living plant cells where they target specific plant subcellular compartments. During plant infection, the blast fungus induces the formation of a specialized plant structure known as the biotrophic interfacial complex (BIC), which appears to be crucial for effector delivery into plant cells. Here, we review recent advances in the cell biology of M. oryzae-host interactions and show how new breakthroughs in disease control have stemmed from an increased understanding of effector proteins of M. oryzae are deployed and delivered into plant cells to enable pathogen invasion and host susceptibility.

A Sorghum F-Box Protein Induces an Oxidative Burst in the Defense Against Colletotrichum sublineola

The hemibiotrophic fungal pathogen Colletotrichum sublineola is the causal agent of anthracnose in sorghum (Sorghum bicolor), resulting in leaf blight, stalk rot, and head blight in susceptible genotypes, with yield losses of up to 50%. The development of anthracnose-resistant cultivars can reduce reliance on fungicides and provide a more sustainable and economical means for disease management. A previous genome-wide association study of the sorghum association panel identified the candidate resistance gene Sobic.005G172300 encoding an F-box protein. To better understand the role of this gene in the defense against C. sublineola, gene expression following infection with C. sublineola was monitored by RNA sequencing in seedlings of sorghum accession SC110, which harbored the resistance allele, and three accessions that harbored a susceptible allele. Only in SC110 did the expression of Sobic.005G172300 increase during the biotrophic phase of infection. Subsequent transcriptome analysis, gene co-expression networks, and gene regulatory networks of inoculated and mock-inoculated seedlings of resistant and susceptible accessions suggest that the increase in expression of Sobic.005G172300 induces an oxidative burst by lowering the concentration of ascorbic acid during the biotrophic phase of infection. Based on gene regulatory network analysis, the protein encoded by Sobic.005G172300 is proposed to target proteins involved in the biosynthesis of ascorbic acid for polyubiquitination through the SCF E3 ubiquitin ligase, causing their degradation via the proteasome.

Host-pathogen interaction between pitaya and Neoscytalidium dimidiatum reveals the mechanisms of immune response associated with defense regulators and metabolic pathways

BACKGROUND

Understanding how plants and pathogens regulate each other's gene expression during their interactions is key to revealing the mechanisms of disease resistance and controlling the development of pathogens. Despite extensive studies on the molecular and genetic basis of plant immunity against pathogens, the influence of pitaya immunity on N. dimidiatum metabolism to restrict pathogen growth is poorly understood, and how N. dimidiatum breaks through pitaya defenses. In this study, we used the RNA-seq method to assess the expression profiles of pitaya and N. dimidiatum at 4 time periods after interactions to capture the early effects of N. dimidiatum on pitaya processes.

RESULTS

The study defined the establishment of an effective method for analyzing transcriptome interactions between pitaya and N. dimidiatum and to obtain global expression profiles. We identified gene expression clusters in both the host pitaya and the pathogen N. dimidiatum. The analysis showed that numerous differentially expressed genes (DEGs) involved in the recognition and defense of pitaya against N. dimidiatum, as well as N. dimidiatum's evasion of recognition and inhibition of pitaya. The major functional groups identified by GO and KEGG enrichment were responsible for plant and pathogen recognition, phytohormone signaling (such as salicylic acid, abscisic acid). Furthermore, the gene expression of 13 candidate genes involved in phytopathogen recognition, phytohormone receptors, and the plant resistance gene (PG), as well as 7 effector genes of N. dimidiatum, including glycoside hydrolases, pectinase, and putative genes, were validated by qPCR. By focusing on gene expression changes during interactions between pitaya and N. dimidiatum, we were able to observe the infection of N. dimidiatum and its effects on the expression of various defense components and host immune receptors.

CONCLUSION

Our data show that various regulators of the immune response are modified during interactions between pitaya and N. dimidiatum. Furthermore, the activation and repression of these genes are temporally coordinated. These findings provide a framework for better understanding the pathogenicity of N. dimidiatum and its role as an opportunistic pathogen. This offers the potential for a more effective defense against N. dimidiatum.

A novel pectin methylesterase inhibitor, PMEI3, in common bean suggests a key role of pectin methylesterification in Pseudomonas resistance

The mechanisms underlying susceptibility to and defense against Pseudomonas syringae (Pph) of the common bean (Phaseolus vulgaris) have not yet been clarified. To investigate these, 15-day-old plants of the variety Riñón were infected with Pph and the transcriptomic changes at 2 h and 9 h post-infection were analysed. RNA-seq analysis showed an up-regulation of genes involved in defense/signaling at 2 h, most of them being down-regulated at 9 h, suggesting that Pph inhibits the transcriptomic reprogramming of the plant. This trend was also observed in the modulation of 101 cell wall-related genes. Cell wall composition changes at early stages of Pph infection were associated with homogalacturonan methylation and the formation of egg boxes. Among the cell wall genes modulated, a pectin methylesterase inhibitor 3 (PvPMEI3) gene, closely related to AtPMEI3, was detected. PvPMEI3 protein was located in the apoplast and its pectin methylesterase inhibitory activity was demonstrated. PvPMEI3 seems to be a good candidate to play a key role in Pph infection, which was supported by analysis of an Arabidopsis pmei3 mutant, which showed susceptibility to Pph, in contrast to resistant Arabidopsis Col-0 plants. These results indicate a key role of the degree of pectin methylesterification in host resistance to Pph during the first steps of the attack.

Rastonia solanacearum type Ⅲ effectors target host 14-3-3 proteins to suppress plant immunity

14-3-3 proteins play important roles in plant metabolism and stress response. Tomato 14-3-3 proteins, SlTFT4 and SlTFT7, serve as hubs of plant immunity and are targeted by some pathogen effectors. Ralstonia solanacearum with more than 70 type Ⅲ effectors (T3Es) is one of the most destructive plant pathogens. However, little is known on whether R. solanacearum T3Es target SlTFT4 and SlTFT7 and hence interfere with plant immunity. We first detected the associations of SlTFT4/SlTFT7 with R. solanacearum T3Es by luciferase complementation assay, and then confirmed the interactions by yeast two-hybrid approach. We demonstrated that 22 Ralstonia T3Es were associated with both SlTFT4 and SlTFT7, and five among them suppressed the hypersensitive response induced by MAPKKKα, a protein kinase which associated with SlTFT4/SlTFT7. We further demonstrated that suppression of MAPKKKα-induced HR and plant basal defense by the T3E RipAC depend on its association with 14-3-3 proteins. Our findings firstly demonstrate that R. solanacearum T3Es can manipulate plant immunity by targeting 14-3-3 proteins, SlTFT4 and SlTFT7, providing new insights into plant-R. solanacearum interactions.

The Globodera rostochiensis Gr29D09 Effector with a Role in Defense Suppression Targets the Potato Hexokinase 1 Protein

The potato cyst nematode (Globodera rostochiensis) is an obligate root pathogen of potatoes. G. rostochiensis encodes several highly expanded effector gene families, including the Gr4D06 family; however, little is known about the function of this effector family. We cloned four 29D09 genes from G. rostochiensis (named Gr29D09v1/v2/v3/v4) that share high sequence similarity and are homologous to the Hg29D09 and Hg4D06 effector genes from the soybean cyst nematode (Heterodera glycines). Phylogenetic analysis revealed that Gr29D09 genes belong to a subgroup of the Gr4D06 family. We showed that Gr29D09 genes are expressed exclusively within the nematode's dorsal gland cell and are dramatically upregulated in parasitic stages, indicating involvement of Gr29D09 effectors in nematode parasitism. Transgenic potato lines overexpressing Gr29D09 variants showed increased susceptibility to G. rostochiensis. Transient expression assays in Nicotiana benthamiana demonstrated that Gr29D09v3 could suppress reactive oxygen species (ROS) production and defense gene expression induced by flg22 and cell death mediated by immune receptors. These results suggest a critical role of Gr29D09 effectors in defense suppression. The use of affinity purification coupled with nanoliquid chromatography-tandem mass spectrometry identified potato hexokinase 1 (StHXK1) as a candidate target of Gr29D09. The Gr29D09-StHXK1 interaction was further confirmed using in planta protein-protein interaction assays. Plant HXKs have been implicated in defense regulation against pathogen infection. Interestingly, we found that StHXK1 could enhance flg22-induced ROS production, consistent with a positive role of plant HXKs in defense. Altogether, our results suggest that targeting StHXK1 by Gr29D09 effectors may impair the positive function of StHXK1 in plant immunity, thereby aiding nematode parasitism. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Subcritical water extraction of Equisetum arvense biomass withdraws cell wall fractions that trigger plant immune responses and disease resistance

Plant cell walls are complex structures mainly made up of carbohydrate and phenolic polymers. In addition to their structural roles, cell walls function as external barriers against pathogens and are also reservoirs of glycan structures that can be perceived by plant receptors, activating Pattern-Triggered Immunity (PTI). Since these PTI-active glycans are usually released upon plant cell wall degradation, they are classified as Damage Associated Molecular Patterns (DAMPs). Identification of DAMPs imply their extraction from plant cell walls by using multistep methodologies and hazardous chemicals. Subcritical water extraction (SWE) has been shown to be an environmentally sustainable alternative and a simplified methodology for the generation of glycan-enriched fractions from different cell wall sources, since it only involves the use of water. Starting from Equisetum arvense cell walls, we have explored two different SWE sequential extractions (isothermal at 160 ºC and using a ramp of temperature from 100 to 160 ºC) to obtain glycans-enriched fractions, and we have compared them with those generated with a standard chemical-based wall extraction. We obtained SWE fractions enriched in pectins that triggered PTI hallmarks in Arabidopsis thaliana such as calcium influxes, reactive oxygen species production, phosphorylation of mitogen activated protein kinases and overexpression of immune-related genes. Notably, application of selected SWE fractions to pepper plants enhanced their disease resistance against the fungal pathogen Sclerotinia sclerotiorum. These data support the potential of SWE technology in extracting PTI-active fractions from plant cell wall biomass containing DAMPs and the use of SWE fractions in sustainable crop production.

A chitin deacetylase PsCDA2 from Puccinia striiformis f. sp. tritici confers disease pathogenicity by suppressing chitin-triggered immunity in wheat

Plants have the ability to recognize the essential chitin molecule present in the fungal cell wall, which stimulates the immune response. Phytopathogenic fungi have developed various strategies to inhibit the chitin-triggered immune response. Here, we identified a chitin deacetylase of Puccinia striiformis f. sp. tritici (Pst), known as PsCDA2, that was induced during the initial invasion of wheat and acted as an inhibitor of plant cell death. Knockdown of PsCDA2 in wheat enhanced its resistance against Pst, highlighting the significance of PsCDA2 in the host-pathogen interaction. Moreover, PsCDA2 can protect Pst urediniospores from being damaged by host chitinase in vitro. PsCDA2 also suppressed the basal chitin-induced plant immune response, including the accumulation of callose and the expression of defence genes. Overall, our results demonstrate that Pst secretes PsCDA2 as a chitin deacetylase involved in establishing infection and modifying the acetyl group to prevent the breakdown of chitin in the cell wall by host endogenous chitinases. Our research unveils a mechanism by which the fungus suppresses plant immunity, further contributing to the understanding of wheat stripe rust control. This information could have significant implications for the development of suitable strategies for protecting crops against the devastating effects of this disease.

Unraveling the involvement of WRKY TFs in regulating plant disease defense signaling

MAIN CONCLUSION

This review article explores the intricate role, regulation, and signaling mechanisms of WRKY TFs in response to biotic stress, particularly emphasizing their pivotal role in the trophism of plant-pathogen interactions. Transcription factors (TFs) play a vital role in governing both plant defense and development by controlling the expression of various downstream target genes. Early studies have shown the differential expression of certain WRKY transcription factors by microbial infections. Several transcriptome-wide studies later demonstrated that diverse sets of WRKYs are significantly activated in the early stages of viral, bacterial, and fungal infections. Furthermore, functional investigations indicated that overexpression or silencing of certain WRKY genes in plants can drastically alter disease symptoms as well as pathogen multiplication rates. Hence the new aspects of pathogen-triggered WRKY TFs mediated regulation of plant defense can be explored. The already recognized roles of WRKYs include transcriptional regulation of defense-related genes, modulation of hormonal signaling, and participation in signal transduction pathways. Some WRKYs have been shown to directly bind to pathogen effectors, acting as decoys or resistance proteins. Notably, the signaling molecules like salicylic acid, jasmonic acid, and ethylene which are associated with plant defense significantly increase the expression of several WRKYs. Moreover, induction of WRKY genes or heightened WRKY activities is also observed during ISR triggered by the beneficial microbes which protect the plants from subsequent pathogen infection. To understand the contribution of WRKY TFs towards disease resistance and their exact metabolic functions in infected plants, further studies are required. This review article explores the intrinsic transcriptional regulation, signaling mechanisms, and hormonal crosstalk governed by WRKY TFs in plant disease defense response, particularly emphasizing their specific role against different biotrophic, hemibiotrophic, and necrotrophic pathogen infections.

Research Progress in the Mechanisms of Resistance to Biotic Stress in Sweet Potato

Sweet potato (Ipomoea batatas (L.) Lam.) is one of the most important food, feed, industrial raw materials, and new energy crops, and is widely cultivated around the world. China is the largest sweet potato producer in the world, and the sweet potato industry plays an important role in China's agriculture. During the growth of sweet potato, it is often affected by biotic stresses, such as fungi, nematodes, insects, viruses, and bacteria. These stressors are widespread worldwide and have severely restricted the production of sweet potato. In recent years, with the rapid development and maturity of biotechnology, an increasing number of stress-related genes have been introduced into sweet potato, which improves its quality and resistance of sweet potato. This paper summarizes the discovery of biological stress-related genes in sweet potato and the related mechanisms of stress resistance from the perspectives of genomics analysis, transcriptomics analysis, genetic engineering, and physiological and biochemical indicators. The mechanisms of stress resistance provide a reference for analyzing the molecular breeding of disease resistance mechanisms and biotic stress resistance in sweet potato.

MYB44 regulates PTI by promoting the expression of EIN2 and MPK3/6 in Arabidopsis

The plant signaling pathway that regulates pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) involves mitogen-activated protein kinase (MAPK) cascades that comprise sequential activation of several protein kinases and the ensuing phosphorylation of MAPKs, which activate transcription factors (TFs) to promote downstream defense responses. To identify plant TFs that regulate MAPKs, we investigated TF-defective mutants of Arabidopsis thaliana and identified MYB44 as an essential constituent of the PTI pathway. MYB44 confers resistance against the bacterial pathogen Pseudomonas syringae by cooperating with MPK3 and MPK6. Under PAMP treatment, MYB44 binds to the promoters of MPK3 and MPK6 to activate their expression, leading to phosphorylation of MPK3 and MPK6 proteins. In turn, phosphorylated MPK3 and MPK6 phosphorylate MYB44 in a functionally redundant manner, thus enabling MYB44 to activate MPK3 and MPK6 expression and further activate downstream defense responses. Activation of defense responses has also been attributed to activation of EIN2 transcription by MYB44, which has previously been shown to affect PAMP recognition and PTI development. AtMYB44 thus functions as an integral component of the PTI pathway by connecting transcriptional and posttranscriptional regulation of the MPK3/6 cascade.

Molecular mechanisms underpinning quantitative resistance to Phytophthora sojae in Glycine max using a systems genomics approach

Expression of quantitative disease resistance in many host-pathogen systems is controlled by genes at multiple loci, each contributing a small effect to the overall response. We used a systems genomics approach to study the molecular underpinnings of quantitative disease resistance in the soybean-Phytophthora sojae pathosystem, incorporating expression quantitative trait loci (eQTL) mapping and gene co-expression network analysis to identify the genes putatively regulating transcriptional changes in response to inoculation. These findings were compared to previously mapped phenotypic (phQTL) to identify the molecular mechanisms contributing to the expression of this resistance. A subset of 93 recombinant inbred lines (RILs) from a Conrad × Sloan population were inoculated with P. sojae isolate 1.S.1.1 using the tray-test method; RNA was extracted, sequenced, and the normalized read counts were genetically mapped from tissue collected at the inoculation site 24 h after inoculation from both mock and inoculated samples. In total, more than 100,000 eQTLs were mapped. There was a switch from predominantly cis-eQTLs in the mock treatment to an almost entirely nonoverlapping set of predominantly trans-eQTLs in the inoculated treatment, where greater than 100-fold more eQTLs were mapped relative to mock, indicating vast transcriptional reprogramming due to P. sojae infection occurred. The eQTLs were organized into 36 hotspots, with the four largest hotspots from the inoculated treatment corresponding to more than 70% of the eQTLs, each enriched for genes within plant-pathogen interaction pathways. Genetic regulation of trans-eQTLs in response to the pathogen was predicted to occur through transcription factors and signaling molecules involved in plant-pathogen interactions, plant hormone signal transduction, and MAPK pathways. Network analysis identified three co-expression modules that were correlated with susceptibility to P. sojae and associated with three eQTL hotspots. Among the eQTLs co-localized with phQTLs, two cis-eQTLs with putative functions in the regulation of root architecture or jasmonic acid, as well as the putative master regulators of an eQTL hotspot nearby a phQTL, represent candidates potentially underpinning the molecular control of these phQTLs for resistance.

RALF22 promotes plant immunity and amplifies the Pep3 immune signal

Rapid alkalinization factors (RALFs) in plants have been reported to dampen pathogen-associated molecular pattern (PAMP)-triggered immunity via suppressing PAMP-induced complex formation between the pattern recognition receptor (PRR) and its co-receptor BAK1. However, the direct and positive role of RALFs in plant immunity remains largely unknown. Herein, we report the direct and positive roles of a typical RALF, RALF22, in plant immunity. RALF22 alone directly elicited a variety of typical immune responses and triggered resistance against the devastating necrotrophic fungal pathogen Sclerotinia sclerotiorum in a FERONIA (FER)-dependent manner. LORELEI (LRE)-like glycosylphosphatidylinositol (GPI)-anchored protein 1 (LLG1) and NADPH oxidase RBOHD were required for RALF22-elicited reactive oxygen species (ROS) generation. The mutation of cysteines conserved in the C terminus of RALFs abolished, while the constitutive formation of two disulfide bridges between these cysteines promoted the RALF22-elicited ROS production and resistance against S. sclerotiorum, demonstrating the requirement of these cysteines in the functions of RALF22 in plant immunity. Furthermore, RALF22 amplified the Pep3-induced immune signal by dramatically increasing the abundance of PROPEP3 transcript and protein. Supply with RALF22 induced resistance against S. sclerotiorum in Brassica crop plants. Collectively, our results reveal that RALF22 triggers immune responses and augments the Pep3-induced immune signal in a FER-dependent manner, and exhibits the potential to be exploited as an immune elicitor in crop protection.

The rice peroxisomal receptor PEX5 negatively regulates resistance to rice blast fungus Magnaporthe oryzae

The receptor protein PEX5, an important component of peroxisomes, regulates growth, development, and immunity in yeast and mammals. PEX5 also influences growth and development in plants, but whether it participates in plant immunity has remained unclear. Here, we report that knockdown of OsPEX5 enhances resistance to the rice blast fungus Magnaporthe oryzae. We demonstrate that OsPEX5 interacts with the E3 ubiquitin ligase APIP6, a positive regulator of plant immunity. APIP6 ubiquitinates OsPEX5 in vitro and promotes its degradation in vivo via the 26S proteasome pathway. In addition, OsPEX5 interacts with the aldehyde dehydrogenase OsALDH2B1, which functions in growth-defense trade-offs in rice. OsPEX5 stabilizes OsALDH2B1 to enhance its repression of the defense-related gene OsAOS2. Our study thus uncovers a previously unrecognized hierarchical regulatory mechanism in which an E3 ubiquitin ligase targets a peroxisome receptor protein that negatively regulates immunity in rice by stabilizing an aldehyde dehydrogenase that suppresses defense gene expression.

N-hydroxypipecolic acid triggers systemic acquired resistance through extracellular NAD(P)

Systemic acquired resistance (SAR) is a long-lasting broad-spectrum plant defense mechanism induced in distal systemic tissues by mobile signals generated at the primary infection site. Despite the discoveries of multiple potential mobile signals, how these signals cooperate to trigger downstream SAR signaling is unknown. Here, we show that endogenous extracellular nicotinamide adenine dinucleotide (phosphate) [eNAD(P)] accumulates systemically upon pathogen infection and that both eNAD(P) and the lectin receptor kinase (LecRK), LecRK-VI.2, are required in systemic tissues for the establishment of SAR. Moreover, putative mobile signals, e.g., N-hydroxypipecolic acid (NHP), trigger de novo systemic eNAD(P) accumulation largely through the respiratory burst oxidase homolog RBOHF-produced reactive oxygen species (ROS). Importantly, NHP-induced systemic immunity mainly depends on ROS, eNAD(P), LecRK-VI.2, and BAK1, indicating that NHP induces SAR primarily through the ROS-eNAD(P)-LecRK-VI.2/BAK1 signaling pathway. Our results suggest that mobile signals converge on eNAD(P) in systemic tissues to trigger SAR through LecRK-VI.2.

The Imperative Use of Bacillus Consortium and Quercetin Contributes to Suppress Fusarium Wilt Disease by Direct Antagonism and Induced Resistance

Fusarium wilt diseases severely influence the growth and productivity of numerous crop plants. The consortium of antagonistic rhizospheric Bacillus strains and quercetin were evaluated imperatively as a possible remedy to effectively manage the Fusarium wilt disease of tomato plants. The selection of Bacillus strains was made based on in-vitro antagonistic bioassays against Fusarium oxysporum f.sp. lycoprsici (FOL). Quercetin was selected after screening a library of phytochemicals during in-silico molecular docking analysis using tomato LysM receptor kinases "SILKY12" based on its dual role in symbiosis and plant defense responses. After the selection of test materials, pot trials were conducted where tomato plants were provided consortium of Bacillus strains as soil drenching and quercetin as a foliar spray in different concentrations. The combined application of consortium (Bacillus velezensis strain BS6, Bacillus thuringiensis strain BS7, Bacillus fortis strain BS9) and quercetin (1.0 mM) reduced the Fusarium wilt disease index up to 69%, also resulting in increased plant growth attributes. Likewise, the imperative application of the Bacillus consortium and quercetin (1.0 mM) significantly increased total phenolic contents and activities of the enzymes of the phenylpropanoid pathway. Non-targeted metabolomics analysis was performed to investigate the perturbation in metabolites. FOL pathogen negatively affected a range of metabolites including carbohydrates, amino acids, phenylpropanoids, and organic acids. Thereinto, combined treatment of Bacillus consortium and quercetin (1.0 mM) ameliorated the production of different metabolites in tomato plants. These findings prove the imperative use of Bacillus consortium and quercetin as an effective and sustainable remedy to manage Fusarium wilt disease of tomato plants and to promote the growth of tomato plants under pathogen stress conditions.

The glycoside hydrolase 28 member VdEPG1 is a virulence factor of Verticillium dahliae and interacts with the jasmonic acid pathway-related gene GhOPR9

Glycoside hydrolase (GH) family members act as virulence factors and regulate plant immune responses during pathogen infection. Here, we characterized the GH28 family member endopolygalacturonase VdEPG1 in Verticillium dahliae. VdEPG1 acts as a virulence factor during V. dahliae infection. The expression level of VdEPG1 was greatly increased in V. dahliae inoculated on cotton roots. VdEPG1 suppressed VdNLP1-mediated cell death by modulating pathogenesis-related genes in Nicotiana benthamiana. Knocking out VdEPG1 led to a significant decrease in the pathogenicity of V. dahliae in cotton. The deletion strains were more susceptible to osmotic stress and the ability of V. dahliae to utilize carbon sources was deficient. In addition, the deletion strains lost the ability to penetrate cellophane membrane, with mycelia showing a disordered arrangement on the membrane, and spore development was affected. A jasmonic acid (JA) pathway-related gene, GhOPR9, was identified as interacting with VdEPG1 in the yeast two-hybrid system. The interaction was further confirmed by bimolecular fluorescence complementation and luciferase complementation imaging assays in N. benthamiana leaves. GhOPR9 plays a positive role in the resistance of cotton to V. dahliae by regulating JA biosynthesis. These results indicate that VdEPG1 may be able to regulate host immune responses as a virulence factor through modulating the GhOPR9-mediated JA biosynthesis.

Advances in understanding the mechanism of resistance to anthracnose and induced defence response in tea plants

The tea plant (Camellia sinensis) is susceptible to anthracnose disease that causes considerable crop loss and affects the yield and quality of tea. Multiple Colletotrichum spp. are the causative agents of this disease, which spreads quickly in warm and humid climates. During plant-pathogen interactions, resistant cultivars defend themselves against the hemibiotrophic pathogen by activating defence signalling pathways, whereas the pathogen suppresses plant defences in susceptible varieties. Various fungicides have been used to control this disease on susceptible plants, but these fungicide residues are dangerous to human health and cause fungicide resistance in pathogens. The problem-solving approaches to date are the development of resistant cultivars and ecofriendly biocontrol strategies to achieve sustainable tea cultivation and production. Understanding the infection stages of Colletotrichum, tea plant resistance mechanisms, and induced plant defence against Colletotrichum is essential to support sustainable disease management practices in the field. This review therefore summarizes the current knowledge of the identified causative agent of tea plant anthracnose, the infection strategies and pathogenicity of C. gloeosporioides, anthracnose disease resistance mechanisms, and the caffeine-induced defence response against Colletotrichum infection. The information reported in this review will advance our understanding of host-pathogen interactions and eventually help us to develop new disease control strategies.

The Arabidopsis RRM domain proteins EDM3 and IBM2 coordinate the floral transition and basal immune responses

The transition from vegetative to reproductive development (floral transition) is a costly process in annual plants requiring increased investments in metabolic resources. The Arabidopsis thaliana (Arabidopsis) PHD finger protein EDM2 and RRM domain proteins EDM3 and IBM2 are known to form chromatin-associated complexes controlling transcript processing. We are reporting that distinct splice isoforms of EDM3 and IBM2 cooperate in the coordination of the floral transition with basal immune responses. These cooperating splice isoforms, termed EDM3L and IBM2L, control the intensity of basal immunity and, via a separate pathway, the timing of the floral transition. During the developmental phase prior to the floral transition expression of EDM3L and IBM2L strongly and gradually increases, while these isoforms simultaneously down-regulate expression of the floral suppressor gene FLC and promote the transition to reproductive growth. At the same time these accumulating EDM3 and IBM2 splice isoforms gradually suppress basal immunity against the virulent Noco2 isolate of the pathogenic oomycete Hyaloperonospora arabidopsidis and down-regulate expression of a set of defense-associated genes and immune receptor genes. We are providing clear evidence for a functional link between the floral transition and basal immunity in the annual plant Arabidopsis. Coordination of these two biological processes, which compete for metabolic resources, is likely critical for plant survival and reproductive success.

Metabolomics Insight into the Variety-Mediated Responses to Aspergillus carbonarius Infection in Grapevine Berries

Limited knowledge regarding the susceptibility of grape varieties to ochratoxin A (OTA)-producing fungi is available to date. This study aimed to investigate the susceptibility of different grape varieties to Aspergillus carbonarius concerning OTA contamination and modulation at the metabolome level. Six grape varieties were selected, sampled at early veraison and ripening, artificially inoculated with A. carbonarius, and incubated at two temperature regimes. Significant differences were observed across cultivars, with Barbera showing the highest incidence of moldy berries (around 30%), while Malvasia and Ortrugo showed the lowest incidence (about 2%). OTA contamination was the lowest in Ortrugo and Malvasia, and the highest in Croatina, although it was not significantly different from Barbera, Merlot, and Sauvignon Blanc. Fungal development and mycotoxin production changed with grape variety; the sugar content in berries could also have played a role. Unsupervised multivariate statistical analysis from metabolomic fingerprints highlighted cultivar-specific responses, although a more generalized response was observed by supervised OPLS-DA modeling. An accumulation of nitrogen-containing compounds (alkaloids and glucosinolates), phenylpropanoids, and terpenoids, in addition to phytoalexins, was observed in all samples. A broader modulation of the metabolome was observed in white grapes, which were less contaminated by OTA. Jasmonates and oxylipins were identified as critical upstream modulators in metabolomic profiles. A direct correlation between the plant defense machinery and OTA was not observed, but the information was acquired and can contribute to optimizing preventive actions.

Cell specialization and coordination in Arabidopsis leaves upon pathogenic attack revealed by scRNA-seq

Plant defense responses involve several biological processes that allow plants to fight against pathogenic attacks. How these different processes are orchestrated within organs and depend on specific cell types is poorly known. Here, using single-cell RNA sequencing (scRNA-seq) technology on three independent biological replicates, we identified several cell populations representing the core transcriptional responses of wild-type Arabidopsis leaves inoculated with the bacterial pathogen Pseudomonas syringae DC3000. Among these populations, we retrieved major cell types of the leaves (mesophyll, guard, epidermal, companion, and vascular S cells) with which we could associate characteristic transcriptional reprogramming and regulators, thereby specifying different cell-type responses to the pathogen. Further analyses of transcriptional dynamics, on the basis of inference of cell trajectories, indicated that the different cell types, in addition to their characteristic defense responses, can also share similar modules of gene reprogramming, uncovering a ubiquitous antagonism between immune and susceptible processes. Moreover, it appears that the defense responses of vascular S cells, epidermal cells, and mesophyll cells can evolve along two separate paths, one converging toward an identical cell fate, characterized mostly by lignification and detoxification functions. As this divergence does not correspond to the differentiation between immune and susceptible cells, we speculate that this might reflect the discrimination between cell-autonomous and non-cell-autonomous responses. Altogether our data provide an upgraded framework to describe, explore, and explain the specialization and the coordination of plant cell responses upon pathogenic challenge.