Thirty years of resistance: Zig-zag through the plant immune system

Expression characteristics of CsPG23 in citrus and analysis of its interacting protein

Exploring the resistance genes of citrus to Huanglongbing (HLB) is the foundation and key to citrus disease-resistant breeding. Through the analysis of comparative transcriptome data, we identified six cell wall degradation genes that respond to citrus infection with CaLas. We selected one of the genes with high differential expression levels and cloned it, naming it CsPG23. The subcellular localization results of tobacco indicated that the CsPG23 protein is localized in the nucleus, cytoplasm, and cell membrane. Real-time fluorescence quantitative PCR (RT-qPCR) analysis showed that the expression of CsPG23 is related to variety tolerance, tissue location, and symptom development. In addition, we constructed overexpression and silencing vectors for CsPG23 and obtained CsPG23 silencing plants, overexpression and silencing hairy roots, and analyzed the expression characteristics of CsPG23 in response to SA, JA, MeSA and H2O2 induction through RT-qPCR. Using Protein-Protein Interaction (PPI) to predict and screen for a citrus protein CsAGD8 that may interact with CsPG23, and preliminarily verifying its interaction with CsPG23 protein through Yeast Two-hybrid (Y2H). We constructed overexpression and silencing vectors for CsAGD8 and obtained CsAGD8 overexpression and silencing hairy roots. In summary, it is indicated that CsPG23 may interact with CsAGD8 in response to CaLas infection.

Salicylic acid and jasmonic acid in plant immunity

Salicylic acid (SA) and jasmonic acid (JA) are the two most important phytohormones in plant immunity. While SA plays pivotal roles in local and systemic acquired resistance (SAR) against biotrophic pathogens, JA, on the other hand, contributes to defense against necrotrophic pathogens, herbivores, and induced systemic resistance (ISR). Over the past 30 years, extensive research has elucidated the biosynthesis, metabolism, physiological functions, and signaling of both SA and JA. Here, we present an overview of signaling pathways of SA and JA and how they interact with each other to fine-tune plant defense responses.

Overexpression of the lectin receptor-like kinase gene OsLecRK-S.7 inhibits plant growth and enhances disease resistance in rice

Lectin receptor-like kinases (LecRKs) are a critical class of plant proteins that play essential roles in plant development as well as in responses to both biotic and abiotic stresses. In this study, we found that overexpression of the L-type Lectin receptor kinase gene OsLecRK-S.7 severely inhibits plant growth and triggers spontaneous cell death. Meanwhile, immune responses, including pathogenesis-related (PR) gene expression and reactive oxygen species (ROS) accumulation, were elevated in OsLecRK-S.7 overexpressing plants. Kinase inactivation experiments demonstrated that kinase activity was essential for OsLecRK-S.7-mediated constitutive immunity. Infection assays further demonstrated that overexpression of OsLecRK-S.7 enhances rice resistance to bacterial blight. Additionally, bimolecular fluorescence complementation (BiFC) and pull-down experiments identified interactions between OsLecRK-S.7 and receptor-like cytoplasmic kinases (RLCKs) OsRLCK118, OsRLCK185, and OsRLCK107 that are involved in immune signaling. These findings suggest that OsLecRK-S.7 is a significant regulator of plant immunity, likely promoting cell death and immune responses through its interactions with OsRLCK118, OsRLCK185, and OsRLCK107.

The cell death-inducing protein BcPlp1 from Botrytis cinerea contributes to pathogenicity and modulates plant resistance

Botrytis cinerea is a necrotrophic plant pathogen fungus with a broad host range, causing grey mould and rot diseases in many important crops, leading to significant economic losses in agriculture. Cell death-inducing proteins (CDIPs) secreted by necrotrophic phytopathogens promote plant tissue death and play important roles in infection. However, the mechanisms by which CDIPs induce cell death in B. cinerea-plants interactions remain unclear. Here, we demonstrate that the B. cinerea CDIP BcPlp1 is secreted into the plant apoplast where it induces cell death. BcPlp1 is a cysteine-rich protein, and four out of the 8 cysteine residues and a conserved N-terminal α-helix structure are essential for its cell death-inducing activity. A purified GST-tagged BcPlp1 fusion protein triggered cell death in multiple plant species, up-regulated expression of defense-related genes and enhanced plant resistance to B. cinerea. Additionally, the cell death-inducing activity of BcPlp1 was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Furthermore, BcPlp1 was not necessary for colony morphology, conidial production, growth rate, and stress tolerance. Although deletion of BcPlp1 did not affect virulence, its overexpression led to larger disease lesion, highlighting its contribution to B. cinerea pathogenicity when upregulated.

Regeneration and defense: unveiling the molecular interplay in plants

In both plants and animals, tissue or organ regeneration typically follows wounding, which also activates defense responses against pathogenic microbes and herbivores. Both intrinsic and environmental cues guide the molecular decisions between regeneration and defense. In animal studies, extensive research has highlighted the role of various microbes - including pathogenic, commensal, and beneficial species - in influencing the signaling interplay between immunity and regeneration. Conversely, most plant regeneration studies are conducted under sterile conditions, which leaves a gap in our understanding of how plant innate immunity influences regeneration pathways. Recent findings have begun to elucidate the roles of key defense pathways in modulating plant regeneration and the crosstalk between these two processes. These studies also explore how microbes might influence the molecular choice between defense and regeneration in plants. This review examines the molecular mechanisms governing the balance between plant regeneration and innate immunity, with a focus on the emerging role of aging and microbial interactions in shaping these processes.

A well-annotated genome of Apium graveolens var. dulce cv. Challenger, a celery with resistance to Fusarium oxysporum f. sp. apii race 2

Celery (Apium graveolens var. dulce) production can be limited by the fungal pathogen Fusarium oxysporum f. sp. apii (Foa), particularly at temperatures above 22°C. Because celery has a narrow genetic base, an intraspecific admixture of Apium graveolens was developed into cv. Challenger, which is resistant to Foa race 2, the causal agent of Fusarium yellows, but susceptible to Foa race 4, a relatively unrelated causal agent of Fusarium wilt. We assembled a high-quality, chromosome-level physical map of Challenger with 40 464 RNA-based, protein-coding gene models in 3.3 Gbp and anchored it with a genetic map. Although there is high gene density and higher recombination at the ends of the chromosomes, an average of 56% of the genes/chromosome are in lower recombination zones (<0.025 cM/Mb). We identified Challenger's nucleotide-binding and leucine-rich repeat receptors (NLRs) and pattern recognition receptors (PRRs), the two gene families that encode most resistance (R) genes. In three treatment groups (mock-infested or infested with either Foa race 2 or race 4), 243 NLRs and 445 PRRs were quantified in the celery crowns via Quant-Seq 3' mRNA-Seq (Tag-Seq). We compared the genomes of Challenger with that of the previously published cv. Ventura, which is moderately susceptible to Foa race 2. We present a toolbox for genome-assisted breeding for celery that includes annotated gene models, a protocol for genotype-by-sequencing, documentation of the expression of NLRs and PRRs, and a straightforward strategy for introgressing selected NLR superclusters, 83% of which are in higher recombination regions.

Elevated CO2 alters soybean physiology and defense responses, and has disparate effects on susceptibility to diverse microbial pathogens

Increasing atmospheric CO2 levels have a variety of effects that can influence plant responses to microbial pathogens. However, these responses are varied, and it is challenging to predict how elevated CO2 (eCO2) will affect a particular plant-pathogen interaction. We investigated how eCO2 may influence disease development and responses to diverse pathogens in the major oilseed crop, soybean. Soybean plants grown in ambient CO2 (aCO2, 419 parts per million (ppm)) or in eCO2 (550 ppm) were challenged with bacterial, viral, fungal, and oomycete pathogens. Disease severity, pathogen growth, gene expression, and molecular plant defense responses were quantified. In eCO2, plants were less susceptible to Pseudomonas syringae pv. glycinea (Psg) but more susceptible to bean pod mottle virus, soybean mosaic virus, and Fusarium virguliforme. Susceptibility to Pythium sylvaticum was unchanged, although a greater loss in biomass occurred in eCO2. Reduced susceptibility to Psg was associated with enhanced defense responses. Increased susceptibility to the viruses was associated with reduced expression of antiviral defenses. This work provides a foundation for understanding how future eCO2 levels may impact molecular responses to pathogen challenges in soybean and demonstrates that microbes infecting both shoots and roots are of potential concern in future climatic conditions.

Genetic and physical localization of a leaf rust susceptibility gene in barley

KEY MESSAGE

Fine mapping of the leaf rust susceptibility gene Sph1 identified a receptor-like kinase-encoding gene as a candidate and provided user-friendly markers for barley breeding. Caused by the biotrophic fungal pathogen Puccinia hordei, leaf rust is one of the important foliar diseases in barley. Although a few dominant genes for leaf rust resistance have been identified and cloned in barley, resistance conferred by major genes has been frequently defeated by the pathogen. A recessive resistance was identified in a spring barley accession using the P. hordei isolate VA90-34 which is virulent to most of major resistance genes. To localize this recessive resistance (hereafter named Susceptibility to P. hordei 1 or Sph1 indicating that the dominant allele confers disease susceptibility), we conducted fine mapping with an F2 population and molecular markers in the present study. The Sph1 gene was anchored near the telomere of the short arm of chromosome 3H, delimited within an ⁓560 kb region in the dominant parent. Of the six predicted genes in the Sph1 region, a gene encoding putative receptor-like kinase was selected as a candidate for functional validation. Therefore, our study provides a high-resolution genetic map and candidate for Sph1, building a foundation for the cloning of this important gene.

An integrated transcriptomic and metabolomic analysis of black spot disease in Jinggang honey pomelo reveals underlying resistance mechanisms

Introduction

The Jinggang honey pomelo is recognized as one of the three major fruit industry brands in Jiangxi Province. However, the crop's growth and yield have been significantly affected by the black spot disease caused by Diaporthe citri. Despite this impact, the defense mechanisms and underlying molecular responses of the Jinggang honey pomelo to the disease remain poorly understood.

Methods

In this study, we utilized UPLC-MS/MS and RNA-Seq to conduct a comparative analysis of differentially abundant metabolites (DAMs) and differentially expressed genes (DEGs) in uninfected and D. citri-infected Jinggang honey pomelo fruits 13 days post-infection (dpi) in vivo.

Results

Our analysis yielded 1,744, 1,616, and 1,325 DAMs, as well as 3,403, 1,767, and 453 DEGs from the respective varieties, with 426 DAMs and 66 DEGs common across all three. Kyoto Encyclopedia of Genes and Genomes enrichment analysis demonstrated significant enrichment of these DAMs and DEGs in phenylpropanoid and flavonoid biosynthesis pathways. We also discovered that transcription factors (TFs), specifically MYB and bHLH, related to these pathways, were highly expressed. Our elucidation of the phenylpropanoid and flavonoid biosynthesis pathways surmises that genes (4CL, F5H, HCT, CCR, and CAD) and metabolites (p-coumaryl acetate, pinocembrin, naringin, and neohesperidin) could significantly contribute to the resistivity of Jinggang honey pomelo against D. citri.

Discussion

Our findings suggest that Jinggang honey pomelo activates phenylpropanoid and flavonoid biosynthesis pathways, leading to the accumulation of flavonoid compounds that resist D. citri invasion. This study lays the groundwork for further research into the molecular mechanisms and breeding of Jinggang honey pomelo resistant to black spot disease.

The battle within: Discovering new insights into phytopathogen interactions and effector dynamics

Phytopathogen interactions are complicated and constantly evolving, driven by a never-ending war amongst the host's immune defenses and the pathogen's virulence strategies. This comprehensive review examines the intricate mechanisms of effector-triggered immunity (ETI) and how pathogen effectors use host cellular progressions to promote infection. This review article investigates the modification of Phytopathogen effectors and plant resistance proteins, highlighting the role of meta-population dynamics and rapid adaptation. Additionally, it highlights the influence of environmental impact and climate change on host-pathogen interactions, describing their significant impact on disease dynamics and pathogen evolution. Effector proteins are crucial in sabotaging plant immunity, with bacterial, fungal, oomycete, and nematode effectors targeting common host protein networks and phytohormone pathways. Additionally, the review discusses advanced approaches for classifying effector targets, such as bioinformatics and single-cell transcriptomics, highlighting their importance in developing effective disease management strategies. Further insights are described into how effectors control phytohormone pathways, shedding light on how pathogens exploit host signaling. This review covers structural studies and protein modeling that have advanced effector prediction and our understanding of their functions and evolution, while providing an overview of phytopathogen interactions and future directions for effector research.

Genomic structure of yellow lupin (Lupinus luteus): genome organization, evolution, gene family expansion, metabolites and protein synthesis

Yellow lupin (Lupinus luteus) gives valuable high-quality protein and has good sustainability due to its ability in nitrogen fixation and exudation of organic acids, which reduces the need for chemical-based phosphate fertilization in acid soils. However, the crop needs further improvements to contribute in a major way to sustainable agriculture and food security.In this study, we present the first chromosome-level genome assembly of L. luteus. The results provide insights into its genomic organization, evolution, and functional attributes. Using integrated genomic approaches, we unveil the genetic bases governing its adaptive responses to environmental stress, delineating the intricate interplay among alkaloid biosynthesis, mechanisms of pathogen resistance, and secondary metabolite transporters. Our comparative genomic analysis of closely related species highlights recent speciation events within the Lupinus genus, exposing extensive synteny preservation alongside notable structural alterations, particularly chromosome translocations. Remarkable expansions of gene families implicated in terpene metabolism, stress responses, and conglutin proteins were identified, elucidating the genetic basis of L. luteus' superior nutritional profile and defensive capabilities. Additionally, a diverse array of disease resistance-related (R) genes was uncovered, alongside the characterization of pivotal enzymes governing quinolizidine alkaloid biosynthesis, thus shedding light on the molecular mechanisms underlying "bitterness" in lupin seeds.This comprehensive genomic analysis serves as a valuable resource to improve this species in terms of resilience, yield, and seed protein levels to contribute to food and feed to face the worldwide challenge of sustainable agriculture and food security.

Selenium: The Toxicant for Pathogen and Pest but the Guardian of Soil and Crop

Selenium (Se) is an essential micronutrient for higher organisms and plays a beneficial role in plant growth and development. In recent years, there has been growing interest in the using of Se to enhance plant resilience, particularly in mitigating the effects of diseases and pests in agricultural systems. This review offers a comprehensive analysis of the sources and chemical forms of Se in soil, investigates the mechanisms of plant uptake and metabolism of different Se forms, and evaluates the physical and chemical inhibition of pathogens by various Se forms, as well as the role of Se in enhancing plant systemic resistance for crop protection. Additionally, we summarize current research on the role of Se in pest and disease control and explore potential future research directions, with a focus on integrating Se into sustainable agricultural practices. The insights presented in this review seek to establish a solid scientific foundation for Se-based approaches to pest control and emphasize its potential application in sustainable agriculture.

Lettuce immune responses and apoplastic metabolite profile contribute to reduced internal leaf colonization by human bacterial pathogens

BACKGROUND

Human bacterial pathogens such as Salmonella enterica and Escherichia coli can colonize the apoplast of leafy greens, where they may evade standard sanitization measures and persist until produce consumption. Bacterial survival in this niche is influenced by plant immune responses that may vary according to bacterial species and plant genotypes. The variability in immune responses has been associated with differences in pathogen persistence capacity within the phyllosphere. In addition, emerging evidence suggests that preexisting and inducible plant metabolites contribute to either restricting or facilitating colonization of human pathogens in plant tissues. Identifying the molecular mechanisms underlying these interactions is crucial for developing strategies to mitigate contamination in fresh produce.

RESULTS

We characterized whole-leaf transcriptome and apoplast metabolome profiles of three lettuce cultivars upon exposure to the human pathogenic bacteria S. enterica ser. Typhimurium 14028s and E. coli O157:H7. The lettuce genotypes Lollo Rossa and Green Towers exhibited stronger transcriptional modulation, primarily associated with defense-related processes and showed reduced bacterial survival in their apoplast. Surprisingly, Green Towers did not generate callose deposition or reactive oxygen species burst responses at levels comparable to that of Lollo Rossa, suggesting it has distinct modifications in the apoplastic conditions that restrict pathogen persistence. Apoplastic metabolomic profiling revealed specific compounds alterations in Green Towers linked to bacterial survival, indicating their potential role in this genotype's defense mechanism. In contrast, the lettuce cultivar Red Tide exhibited minimal transcriptional and metabolic modulation, lack of robust defense activation, which was accompanied by apoplastic bacterial survival.

CONCLUSIONS

This study provides evidence that lettuce cultivars exhibit distinct molecular responses that may influence the persistence of human bacterial pathogens in the leaf apoplast. The results indicate that both immune response activation and metabolite composition may contribute to restrict apoplastic bacterial persistence or growth. These findings offer novel insights into the genetic and biochemical factors shaping lettuce-pathogen interactions, which might inform breeding programs and agronomic practices aimed at enhancing food safety.

Ferroptosis in plant immunity

Plant cell death is mediated by calcium, iron, and reactive oxygen species (ROS) signaling in plant immunity. The reconstruction of a nucleotide-binding leucine-rich-repeat receptor (NLR) supramolecular structure, called the resistosome, is intimately involved in the hypersensitive response (HR), a type of cell death involved in effector-triggered immunity (ETI). Iron is a crucial redox catalyst in various cellular reactions. Ferroptosis is a regulated, non-apoptotic form of iron- and ROS-dependent cell death in plants. Pathogen infections trigger iron accumulation and ROS bursts in plant cells, leading to lipid peroxidation via the Fenton reaction and subsequent ferroptosis in plant cells similar to that in mammalian cells. The small-molecule inducer erastin triggers iron-dependent lipid ROS accumulation and glutathione depletion, leading to HR cell death in plant immunity. Calcium (Ca2+) is another major mediator of plant immunity. Cytoplasmic Ca2+ influx through calcium-permeable channels, the resistosomes, mediates iron- and ROS-dependent ferroptotic cell death under reduced glutathione reductase (GR) expression levels in the ETI response. Acibenzolar-S-methyl (ASM), a plant defense activator, enhances Ca2+ influx, ROS and iron accumulation, and lipid peroxidation to trigger ferroptotic cell death. These breakthroughs suggest a potential role for Ca2+ signaling in ferroptosis and its coordination with iron and ROS signaling in plant immunity. In this review, we highlight the essential roles of calcium, iron, and ROS signaling in ferroptosis during plant immunity and discuss advances in the understanding of how Ca2+-mediated ferroptotic cell death orchestrates effective plant immune responses against invading pathogens.

LRR Receptor-like Protein in Rapeseed Confers Resistance to Sclerotinia sclerotiorum Infection via a Conserved SsNEP2 Peptide

Brassica napus is one of the most extensively cultivated oilseed crops in China, but its yield is significantly impacted by stem rot caused by Sclerotinia sclerotiorum. Receptor-like proteins (RLPs) and receptor-like kinases (RLKs) play essential roles in plant-pathogen interactions; however, their regulatory mechanisms remain largely unknown in B. napus. In this study, we investigated the function of the leucine-rich repeat receptor-like protein BnaRLP-G13-1 in Brassica napus immunity. Previous observations indicated that B. napus plants expressing BnaRLP-G13-1 exhibited enhanced resistance to Sclerotinia sclerotiorum. We hypothesized that BnaRLP-G13-1 mediates pathogen recognition and immune signaling. To test this, we employed mitogen-activated protein kinase (MAPK) activity assays, transgenic overexpression analyses, and pathogen infection assays. Our results demonstrated that BnaRLP-G13-1 recognizes the conserved necrosis- and ethylene-inducing peptide Ssnlp24SsNEP2 derived from S. sclerotiorum, triggering MAPK cascades and subsequent immune responses. Furthermore, protein interaction studies revealed that BnaRLP-G13-1 physically interacts with the receptor-like kinase BnaSOBIR1, which is essential for full antifungal defense activation. These results elucidate the molecular basis of BnaRLP-G13-1-mediated immunity, providing insights into improving disease resistance in oilseed crops.

The resistance awakens: Diversity at the DNA, RNA, and protein levels informs engineering of plant immune receptors from Arabidopsis to crops

Plants rely on germline-encoded, innate immune receptors to sense pathogens and initiate the defense response. The exponential increase in quality and quantity of genomes, RNA-seq datasets, and protein structures has underscored the incredible biodiversity of plant immunity. Arabidopsis continues to serve as a valuable model and theoretical foundation of our understanding of wild plant diversity of immune receptors, while expansion of study into agricultural crops has also revealed distinct evolutionary trajectories and challenges. Here, we provide the classical context for study of both intracellular nucleotide-binding, leucine-rich repeat receptors and surface-localized pattern recognition receptors at the levels of DNA sequences, transcriptional regulation, and protein structures. We then examine how recent technology has shaped our understanding of immune receptor evolution and informed our ability to efficiently engineer resistance. We summarize current literature and provide an outlook on how researchers take inspiration from natural diversity in bioengineering efforts for disease resistance from Arabidopsis and other model systems to crops.

Identification of a Papain-like Cysteine Protease Functioning as an Avirulence Factor in Striga-Cowpea Interactions

While most cowpea cultivars are susceptible to parasitism by the root parasitic weed Striga gesnerioides (Willd.) Vatke, cultivar B301 is resistant to all Striga races except for SG4z. Resistance to Striga parasitism is manifested by the elicitation of a hypersensitive response (HR) at the site of parasite attachment on the host root followed by rapid death of the attached parasite. We isolated a papain-like cysteine protease (PLCP) designated SGCP1 that is highly expressed in the haustoria of S. gesnerioides race SG3 at the time of parasite attachment to the host root. SGCP1 contains an apoplast-targeting signal peptide, a Cathepsin pro-peptide inhibitory domain, a papain family cysteine protease domain, and a granulin domain. Full-length SGCP1 and a variant lacking the signal peptide (SGCP∆SP) were expressed in the roots of composite B301 plants. Expression of SGCP1 and SGCP∆SP resulted in activation of host innate immune responses exemplified by increased frequency of HR and decreased levels of parasite cotyledon expansion (CE), indicative of successful host parasitism, in transgenic compared to wild-type B301 roots parasitized by SG4z. These data indicate that SGCP1 functions as an avirulence factor capable of activating host innate immunity and furthers our understanding of how compatible and incompatible host-parasite interactions are controlled.

Physiological and molecular profiling unveils oat (Avena sativa L.) defense mechanisms against powdery mildew

Oat powdery mildew, caused by Blumeria graminis f. sp. avenae (Bga), poses a serious threat to oat production, yet the underlying resistance mechanisms remain largely unclear. In this study, we investigated early-stage defense responses in resistant (BY642) and susceptible (BY119) oat varieties following Bga inoculation using cytological observations, physiological and hormonal measurements, and transcriptomic analysis. Microscopy revealed that Bga penetrates oat tissues directly through epidermal cells rather than stomata. BY642 exhibited a rapid and robust defense characterized by reactive oxygen species (ROS) accumulation and hypersensitive response, tightly regulated by an efficient antioxidant system to prevent cellular damage. Hormone profiling indicated a salicylic acid (SA)-dominated signaling pathway in BY642, accompanied by suppression of jasmonic acid (JA) responses. Transcriptome profiling showed early activation of photosynthesis-related pathways, metabolic reprogramming, and immune-related networks, including MAPK cascades and WRKY transcription factors. Hub genes such as AsGSTU6 and AsWRKY50 were identified as key contributors to resistance. These findings suggest that BY642 employs a coordinated defense strategy integrating ROS dynamics, SA signaling, and transcriptional regulation, providing novel insights into the molecular basis of powdery mildew resistance and potential targets for oat breeding.

A virulence protein activates SERK4 and degrades RNA polymerase IV protein to suppress rice antiviral immunity

Rice, a major global food staple, is threatened by viral infections that hinder its growth and yield. We have recently shown that the virulence protein P3 of rice grassy stunt virus promotes pathogenesis by inducing proteasome-controlled degradation of the rice RNA polymerase IV (RNA Pol IV) protein NRPD1a controlled by the P3-interacting E3 ubiquitin ligase P3IP1. However, the underlying mechanisms remain elusive. In this study, we show that P3 acts as a virus-encoded transcription activator-like effector to upregulate transcription of somatic embryogenesis receptor kinase 4 (SERK4) by directly binding to its promoter. SERK4 phosphorylates P3IP1 and enhances RNA Pol IVa (NRPD1a) degradation following P3IP1-controlled ubiquitination, leading to attenuated antiviral defense in rice. Thus, our study finds a critical viral virulence strategy by encoding a transcription factor-like protein that activates a host kinase to promote proteasome-controlled degradation of NRPD1a, thereby disarming RNA-directed DNA methylation (RdDM) antiviral defense.

Interdependence of plasma membrane nanoscale dynamics of a kinase and its cognate substrate underlies Arabidopsis response to viral infection

Plant viruses represent a risk to agricultural production and as only a few treatments exist, it is urgent to identify resistance mechanisms and factors. In plant immunity, plasma membrane (PM)-localized proteins play an essential role in sensing the extracellular threat presented by bacteria, fungi, or herbivores. Viruses are intracellular pathogens and as such the role of the plant PM in detection and resistance against viruses is often overlooked. We investigated the role of the partially PM-bound Calcium-dependent protein kinase 3 (CPK3) in viral infection and we discovered that it displayed a specific ability to hamper viral propagation over CPK isoforms that are involved in immune response to extracellular pathogens. More and more evidence supports that the lateral organization of PM proteins and lipids underlies signal transduction in plants. We showed here that CPK3 diffusion in the PM is reduced upon activation as well as upon viral infection and that such immobilization depended on its substrate, Remorin (REM1.2), a scaffold protein. Furthermore, we discovered that the viral infection induced a CPK3-dependent increase of REM1.2 PM diffusion. Such interdependence was also observable regarding viral propagation. This study unveils a complex relationship between a kinase and its substrate that contrasts with the commonly described co-stabilisation upon activation while it proposes a PM-based mechanism involved in decreased sensitivity to viral infection in plants.

Microtubule-mediated defence reaction of grapevine to Neofusicoccum parvum via the transcription factor VrWRKY22 promoting the kinesin-like protein VrKIN10C

Grapevine Trunk Diseases (GTDs) are among the most destructive diseases in viticulture due to global climate change. Some causal agents like Neofusicoccum parvum can be latent endophytic and become pathogenic under abiotic stress. Microtubules (MTs) have been found to play a role in mediating the pathogen-related signaling in grapevine. In this study, a novel transcription factor VrWRKY22 was identified and cloned from the native American grapevine Vitis rupestris. Leaves of the table grape variety 'Kyoho' (V. vinifera × V. labrusca L.) overexpressing VrWRKY22 showed less necroses after N. parvum Bt-67 inoculation and activated signaling pathways. VrWRKY22 interacted with VrMPK3 and then bounded to the TTGACC motif in the promoter of VrKIN10C, which was confirmed by Y2H and Y1H assays. Since VrKIN10C is one of the important kinesin-like proteins associated with MTs, a grapevine MT marker line overexpressing VrWRKY22 was generated to test the responses of grapevine cells to N. parvum Bt-67. An increased number of prompt movement proteins can be traced within the peri-nuclear MTs and along the cortical MTs. The skewness and thickness of both central and cortical MTs were significantly increased. Moreover, a prominent (resulting from both the number and the rate) accumulation of speckles appeared in the nucleus and cortical MTs. A significant reduction in cell mortality and a stronger antioxidant capacity were detected. This study demonstrates that VrWRKY22 plays positive roles during N. parvum Bt-67 invasion by rapidly increasing the concentration and dynamics of MTs in the peri-nuclear and cortical regions via VrKIN10, and will facilitate the interpretation of the results of further GTD mitigation studies.

Fusarium oxysporum NAD+ hydrolase FonNADase1 is essential for pathogenicity and inhibits plant immune responses

Plants use nicotinamide adenine dinucleotide (NAD+) as a key signaling molecule to activate immune responses. However, whether pathogens secrete specific NAD+ hydrolases (NADases) to affect plant NAD+ levels for infection remains unclear. Here, we report the function and possible mechanism of fungal NADases in watermelon Fusarium wilt fungus Fusarium oxysporum f. sp. niveum (Fon) pathogenicity. Fon secretes two NADases, FonNADase1 and FonNADase2, both of which harbor a secretory signal peptide and an NADase-active tuberculosis necrotizing toxin (TNT) domain. FonNADase1 and FonNADase2 are not involved in the growth, development, or stress responses of Fon. Moreover, only FonNADase1 is essential for Fon pathogenicity, and FonNADase1 deletion results in decreased invasive growth and spread within watermelon plants. FonNADase1 and FonNADase2 are functional NADases capable of decreasing plant NAD+ levels and FonNADase1 inhibits INF1- and BAX-induced cell death and chitin-triggered immune responses in Nicotiana benthamiana leaves in an NADase activity-dependent manner. Furthermore, FonNADase1 inhibited INF1- and BAX-induced expression of defense genes, such as NbPR1a, NbPR2, NbLOX, NbERF1, NbHIN1, and NbHSR203J, in N. benthamiana leaves and affected the expression of a set of immunity-associated genes in watermelon plants. These findings suggest that FonNADase1 plays a key role in Fon pathogenicity by affecting fungal invasive growth and spread within plants as well as modulating host immune responses, thus highlighting the critical role of fungal NADases in pathogenicity.

Do guard cells have single or multiple defense mechanisms in response to flg22?

Bacterial flagellin (flg22) induces rapid and permanent stomatal closure. However, its local and systemic as well as tissue- and cell-specific effects are less understood. Our results show that flg22 induced local and systemic stomatal closure in intact tomato plants, which was regulated by reactive oxygen- and nitrogen species, and also affected the photosynthetic activity of guard cells but not of mesophyll cells. Interestingly, rapid and extensive local expression of Ethylene response factor 1 was observed after exposure to flg22, whereas the relative transcript levels of Defensin increased only after six hours, especially in systemic leaves. Following local and systemic ethylene emission already after one and six hours, jasmonic acid levels increased in the local leaves after six hours of flg22 treatment. Using immunohistochemical methods, significant defensin accumulation was found in the epidermis and stomata of flg22-treated leaves and above them. Immunogold labelling revealed significant levels of defensins in the cell wall of the mesophyll parenchyma and guard cells. Furthermore, single cell qRT-PCR confirmed that guard cells are able to synthesise defensins. It can be concluded that guard cells are not only involved in the first line of plant defense by regulating stomatal pore size, but can also defend themselves and the plant by producing and accumulating antimicrobial defensins where phytopathogens can penetrate.

Single-Cell and Spatial Transcriptomics Reveals a Stereoscopic Response of Rice Leaf Cells to Magnaporthe oryzae Infection

Infection by the fungal pathogen Magnaporthe oryzae elicits dynamic responses in rice. Utilizing an integrated approach of single-cell and spatial transcriptomics, a 3D response is uncovered within rice leaf cells to M. oryzae infection. A comprehensive rice leaf atlas is constructed from 236 708 single-cell transcriptomes, revealing heightened expression of immune receptors, namely Pattern Recognition Receptors (PRRs) and Nucleotide-binding site and leucine-rich repeat (NLRs) proteins, within vascular tissues. Diterpene phytoalexins biosynthesis genes are dramatically upregulated in procambium cells, leading to an accumulation of these phytoalexins within vascular bundles. Consistent with these findings, microscopic observations confirmed that M. oryzae is prone to target leaf veins for invasion, yet is unable to colonize further within vascular tissues. Following fungal infection, basal defenses are extensively activated in rice cells, as inferred from trajectory analyses. The spatial transcriptomics reveals that rice leaf tissues toward leaf tips display stronger immunity. Characterization of the polarity gene OsHKT9 suggests that potassium transport plays a critical role in resisting M. oryzae infection by expression along the longitudinal axis, where the immunity is stronger toward leaf tip. This work uncovers that there is a cell-specific and multi-dimensional (local and longitudinal) immune response to a fungal pathogen infection.

Overexpression of FvGCN5 enhances the resistance of woodland strawberry against Botrytis cinerea

Epigenetic modifications mediated by histone acetylation play essential roles in plant development and stress response. However, the mechanism of regulating biotic stress through histone acetyltransferase GCN5 in strawberry is still unclear. In this study, we isolated FvGCN5 from woodland strawberry and found that FvGCN5 may form the conserved SAGA (Spt-Ada-Gcn5 acetyltransferase) complex through interaction with FvADA2a and FvADA2b. In addition, we found that FvGCN5 could be significantly induced by the infection of fungal pathogen Botrytis cinerea, and that the transgenic strawberry plants overexpressing FvGCN5 exhibited enhanced resistance against B. cinerea. Further RNA-seq-based transcriptome and quantitative PCR analysis indicated that several disease-resistant genes such as FvMYC2 and, FvPR1 were significantly upregulated in FvGCN5 overexpression lines. Taken together, our study indicates that FvGCN5 plays important roles in the resistance against B. cinerea in woodland strawberry through activating disease-resistant genes.

Autophagy in Plant Health and Disease

Autophagy has emerged as an essential quality control pathway in plants that selectively and rapidly removes damaged or unwanted cellular components to maintain cellular homeostasis. It can recycle a broad range of cargoes, including entire organelles, protein aggregates, and even invading microbes. It involves the de novo biogenesis of a new cellular compartment, making it intimately linked to endomembrane trafficking pathways. Autophagy is induced by a wide range of biotic and abiotic stress factors, and autophagy mutant plants are highly sensitive to stress, making it an attractive target for improving plant stress resilience. Here, we critically discuss recent discoveries related to plant autophagy and highlight open questions and future research areas.

PRIMER cells: immune hotspots in plants

Advances in single-cell and spatial biology have transformed the study of plant immunity, revealing distinct immune cell states such as primary immune responder (PRIMER) cells and offering a deeper understanding of defense mechanisms. These insights offer opportunities for the development of advanced strategies for crop protection and disease resistance.

Verticillium dahliae effector Vd06254 disrupts cotton defence response by interfering with GhMYC3-GhCCD8-mediated hormonal crosstalk between jasmonic acid and strigolactones

Verticillium dahliae is among the most destructive plant pathogens, posing a significant threat to global cotton production. Cotton plants have developed sophisticated immune networks to inhibit V. dahliae colonization. Ingeniously, V. dahliae employs numerous virulent effectors to surmount plant immune responses. However, the pathogenic mechanisms of V. dahliae-derived effectors remain elusive. In this study, we demonstrate that the Vd06254 effector from V. dahliae disrupts the synergistic interaction between jasmonic acid (JA) and strigolactones (SL), thereby suppressing cotton immunity. Ectopic expression of Vd06254 enhanced susceptibility to both viral and V. dahliae infections in Nicotiana benthamiana and cotton, respectively. Vd06254 directly interacts with the JA pathway regulator GhMYC3. The nuclear localization signal (NLS) was found to be essential for the virulence of Vd06254 and its interaction with GhMYC3. Additionally, overexpression and knockout of GhMYC3 in cotton modified the plant's resistance to V. dahliae. Our findings further reveal that GhMYC3 inhibits the expression of GhCCD8 by binding to its promoter, potentially regulating SL homeostasis in cotton through a negative feedback loop. This repression was enhanced by Vd06254, highlighting its crucial role in modulating cotton immunity and illustrating how V. dahliae effectors reprogram cotton transcription to disrupt this regulatory mechanism.

Discovery of Novel Inhibitors Targeting Fungal Chitin Deacetylase via Virtual Screening for Plant Disease Control

Fungal chitin deacetylase (CDA) plays a crucial role in pathogen-plant interactions, which is regarded as an innovative and promising target for fungicides. In this study, a pharmacophore-based virtual screening strategy was employed to identify compounds VS-24 and VS-25 as potent inhibitors against Puccinia striiformis f. sp. tritici CDA (PstCDA). Further bioassays demonstrated that VS-24 exhibited a protective effect of 61.2% against rice blast at 100 μg/mL, while VS-25 showed a superior protective effect of 45.5% against corn rust at 5 μg/mL, both superior to the reported CDA inhibitor benzohydroxamic acid (BHA). Molecular dynamics simulations revealed that multiple key interactions involving the Zn2+ ion and residues His207 and Tyr152 of PstCDA are critical for the binding of VS-24 or VS-25, with electrostatic interactions contributing most significantly to the binding free energy. Finally, toxicity predictions confirmed the potential biosafety of VS-24 and VS-25. Overall, this study identified two promising lead compounds targeting fungal CDA to control plant diseases.

Two pathogen-inducible UDP-glycosyltransferases, UGT73C3 and UGT73C4, catalyze the glycosylation of pinoresinol to promote plant immunity in Arabidopsis

UDP-glycosyltransferases (UGTs) constitute the largest glycosyltransferase family in the plant kingdom, regulating many metabolic processes by transferring sugar moieties onto various small molecules. However, their physiological significance in plants remains largely unknown. Here, we reveal the functions and mechanisms of two Arabidopsis UGT genes, UGT73C3 and UGT73C4, which are strongly induced by Pseudomonas syringae pv. tomato (Pst) DC3000. Overexpression of these genes significantly enhanced plant immune response, whereas their loss of function in double mutants led to increased sensitivity to pathogen infections. However, single mutants showed no obvious alteration in pathogen resistance. To further investigate the regulatory mechanisms of UGT73C3/C4 in plant immunity, we conducted comprehensive secondary metabolome analyses and glycoside quantification. Overexpression lines accumulated higher levels of pinoresinol diglucosides than wild-type plants, both before and after Pst DC3000 treatment, whereas double mutants accumulated lower levels. Furthermore, in vitro and in vivo experiments demonstrated that UGT73C3 and UGT73C4 can glycosylate pinoresinol to form pinoresinol monoglucoside and diglucoside. Moreover, pinoresinol glycosylation promotes the plant immune response by increasing reactive oxygen species production and callose deposition. Additionally, the transcription factor HB34 was found to activate UGT73C3 and UGT73C4 transcription and play a key role in plant immunity. Overall, this study reveals a novel pathway in which UGT73C3/C4-mediated pinoresinol glycosylation, regulated by HB34, enhances the plant immune response.

A Novel Effector FoUpe9 Enhances the Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4 by Inhibiting Plant Immunity

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is the most destructive disease of the banana. Effectors play a crucial role in Foc TR4-banana interaction; however, only a few effectors have been functionally characterized. Our previous secretome studies on Foc TR4 highlighted an uncharacterized protein without any conserved domains (named FoUpe9), which was predicted to be a candidate effector. Herein, bioinformatics analysis showed that FoUpe9 was highly conserved among Fusarium species. FoUpe9 was highly induced during the early infection stages in the banana. A yeast signal sequence trap assay showed that FoUpe9 is a secretory protein. FoUpe9 could inhibit cell death and ROS accumulation triggered by BAX through the Agrobacterium-mediated Nicotiana benthamiana expression system. Subcellular location showed that FoUpe9 was located in the nucleus and cytoplasm of N. benthamiana cells. Deletion of the FoUpe9 gene did not affect mycelial growth, conidiation, sensitivity to cell-wall integrity, or osmotic and oxidative stress, but significantly attenuated fungal virulence. FoUpe9 deletion diminished fungal colonization and induced ROS production and expression of SA-related defense genes in banana plants. These results suggest that FoUpe9 enhances Foc TR4 virulence by inhibiting host immune responses and provide new insights into the functions of the uncharacterized proteins, further enhancing our understanding of effector-mediated Foc TR4 pathogenesis.

A Ralstonia solanacearum effector regulates plant cell death by disrupting the homeostasis of the BPA1-ACD11 complex

Effectors secreted by phytopathogenic bacteria can suppress ETI responses induced by avirulence effectors, thereby overcoming crop resistance. However, the detailed mechanisms remain largely unknown. We report that the effector RipD from Ralstonia solanacearum regulates plant cell death in a protein abundance-dependent manner. RipD targets Arabidopsis BPA1, which directly interacts with the key cell death negative regulator ACD11. RipD competes with ACD11 for binding to BPA1, leading to the selective degradation of BPA1 via autophagy, sparing ACD11. A lower dose of RipD promotes BPA1 degradation but leads to ACD11 accumulation, thereby inhibiting RipAA-induced cell death. Conversely, higher levels of RipD degrade both BPA1 and ACD11, resulting in autophagy-dependent cell death. Visualization of RipD delivery by R. solanacearum indicated that it reaches levels sufficient to promote ACD11 accumulation and inhibit cell death. Our study reveals a novel mechanism by which an effector inhibits ETI and, for the first time, highlights the critical role of protein abundance in its function.IMPORTANCER. solanacearum infects major economic crops, notably tomato, potato, and tobacco, leading to substantial yield reductions and economic losses. This pathogen utilizes various type III effectors to suppress host resistance, often resulting in weakened or lost resistance. However, the underlying mechanisms remain largely unknown. Here, we reveal a novel mechanism by which RipD targets the BPA1-ACD11 complex, which is involved in host immunity and cell death. RipD regulates ACD11 protein homeostasis in a dose-dependent manner by competitively binding and activating autophagy, thereby modulating plant cell death. Importantly, visualization analysis revealed that the amount of RipD secreted by R. solanacearum into host cells is sufficient to inhibit Avr effector-induced cell death. Our study highlights for the first time the critical role of effector dosage, deepening the understanding of how R. solanacearum suppresses host ETI-related cell death and providing guidance and resources for breeding bacterial wilt resistance.

Plant PAQR-like sensors activate heterotrimeric G proteins to confer resistance against multiple pathogens

Human adiponectin receptors (AdipoRs) and membrane progestin receptors (mPRs, members of the progestin and adipoQ receptor [PAQR] family) are seven-transmembrane receptors involved in the regulation of metabolism and cancer development, which share structural similarities with G protein-coupled receptors. Plant PAQR-like sensors (PLSs) are homologous to human PAQRs but their molecular functions remain unclear. In this study, we found that PLSs associate with cell surface receptor-like kinases through KIN7 and positively regulate plant immune responses, stomatal defense, and disease resistance. Moreover, PLSs activate heterotrimeric G proteins (Gαβγ) to transduce immune signals and regulate the exchange of GDP for GTP on GPA1. Further analyses revealed that the immune function of PLSs is conserved in rice and soybean and contributes to resistance against multiple diseases. Notably, heterologous expression of human AdipoRs in Arabidopsis replicates the immune functions of PLSs. Collectively, our findings demonstrate that PLSs are key modulators of plant immunity via the G-protein pathway and highlight the potential application of human genes in enhancing plant disease resistance.

Evolutionary characteristics, expression patterns of wheat receptor-like kinases and functional analysis of TaCrRLK1L16

Reverse genetics research in complex hexaploid wheat often encounters challenges in determining the priority of gene functional characterization. This study aims to systematically analyze the wheat (Triticum aestivum) receptor-like kinase (TaRLK) gene family and develop an effective strategy to identify key candidate genes for further investigation. We identified 3,424 TaRLKs using bioinformatics methods and analyzed the diverse and conserved evolutionary relationships of RLKs among Arabidopsis, rice and wheat. Based on publicly available and our laboratory's transcriptome data, we comprehensively analyzed the transcriptional expression patterns of TaRLKs in response to various stresses, particularly Puccinia striiformis f. sp. tritici (Pst). The TaCrRLK1L16, which is upregulated during Pst infection and triggered cell death in Nicotiana benthamiana, has been identified as a key candidate gene for further functional characterization. Furthermore, our results suggested that the transgenic wheat overexpressing TaCrRLK1L16 significantly enhanced resistance to Pst. This study will provide valuable insights into understanding the evolutionary characteristics and expression patterns of TaRLKs while offering a novel strategy for determining the priority of key candidate TaRLKs.

Comparative single-nucleus RNA-seq analysis revealed localized and cell type-specific pathways governing root-microbiome interactions

Roots can recognize and differentially respond to beneficial and pathogenic microbes, which are fundamental for maintaining root microbiome homeostasis, plasticity, and plant fitness. Meanwhile, roots are highly heterogeneous tissues with complex cell-type compositions and spatially distinct developmental stages. We found that beneficial microbe specifically induces the expression of translation-related genes in the proximal meristem cells, and diverse ribosome proteins and translation regulators are necessary for beneficial microbe-mediated growth promotion. Notably, the root maturation zone can still mount localized immune responses to root pathogens, including genes related to camalexin and triterpene biosynthesis. A triterpene biosynthesis mutant blocked the microbiome reshaping process upon GMI1000 infection. Our results indicate roots may have specialized immune responses in the maturation zone, and provide important insights and vital resources for further elucidating regulators of root-microbe interactions and microbiome reshaping.

Plant ubiquitin E2 enzymes UBC32, UBC33, and UBC34 are involved in ERAD and function in host stress tolerance

BACKGROUND

Endoplasmic reticulum (ER)-associated protein degradation (ERAD) is a critical component of the ER-mediated protein quality control (ERQC) system and plays a vital role in plant stress responses. However, the ubiquitination machinery underlying plant ERAD-particularly the ubiquitin-conjugating enzymes (E2s)-and their contributions to stress tolerance remain poorly understood.

RESULTS

In this study, we identified UBC32, UBC33, and UBC34 as ER-localized ubiquitin E2 enzymes involved in ERAD and demonstrated their roles in biotic and abiotic stress tolerance in tomato (Solanum lycopersicum) and Arabidopsis (Arabidopsis thaliana). In response to biotic stress, UBC33 and UBC34 collectively contribute more substantially than UBC32 to plant immunity against Pseudomonas syringae pv. tomato (Pst). Under abiotic stress and ER stress induced by tunicamycin (TM), all three E2s play important roles. Notably, mutation of UBC32 enhances tolerance to TM-induced ER stress, whereas the loss of function in UBC33 or UBC34 suppresses this response. Additionally, UBC32, UBC33, and UBC34 act synergistically in Arabidopsis seed germination under salt stress and abscisic acid (ABA) treatment. While the single mutants atubc32, atubc33, and atubc34 exhibit germination rates comparable to Col-0 under salt stress or ABA treatment, the double mutants atubc32/33, atubc32/34, and atubc33/34 show a significantly greater reduction in germination rate. Interestingly, the atubc32/33/34 triple mutant exhibits a seed germination rate under salt stress and ABA treatment, as well as a level of host immunity to Pst, comparable to that of the atubc33/34 and atubc32/34 double mutants.

CONCLUSIONS

Our findings establish UBC32, UBC33, and UBC34 as key components of the plant ERAD machinery, contributing to plant tolerance to both abiotic and biotic stress. Despite their close phylogenetic relationship, these E2 enzymes exhibit redundant, synergistic, or antagonistic roles depending on the specific stress response pathway, underscoring the complexity of their functional interactions.

Turnip mosaic virus infection cleaves MEDIATOR SUBUNIT16 in plants increasing plant susceptibility to the virus and its aphid vector Myzus persicae

Plant viruses both trigger and inhibit host plant defense responses, including defenses that target their insect vectors, such as aphids. Turnip mosaic viru (TuMV) infection and its protein, NIa-Pro (nuclear inclusion protease a), suppress aphid-induced plant defenses, however the mechanisms of this suppression are still largely unknown. In this study, we determined that NIa-Pro's protease activity is required to increase aphid performance on host plants and that 40 transcripts with predicted NIa-Pro cleavage sequences are regulated in Arabidopsis plants challenged with aphids and/or virus compared to healthy controls. One of the candidates, MEDIATOR 16 (MED16), regulates the transcription of ethylene (ET)/jasmonic acid (JA)-dependent defense responses against necrotrophic pathogens. We show that a nuclear localization signal is removed from MED16 by specific proteolytic cleavage in virus-infected plants and in plants overexpressing NIa-Pro in the presence of aphids. Although some cleavage was occasionally detected in the absence of virus infection, it occurred at a much higher rate in plants that were virus-infected or overexpressing NIa-Pro, especially when aphids were also present. This suggests MED16 functions in the nucleus may be impacted in virus infected plants. Consistent with this, induction of the MED16-dependent transcript of PLANT DEFENSIN 1.2 (PDF1.2), was reduced in virus-infected plants and in plants expressing NIa-Pro compared to controls, but not in plants expressing NIa-Pro C151A that lacks its protease activity. Finally, we show the performance of both the virus and the aphid vector was enhanced on med16 mutant Arabidopsis compared to controls. Overall, this study demonstrates MED16 regulates defense responses against both the virus and the aphid and provides insights into the mechanism by which TuMV suppresses anti-virus and anti-herbivore defenses.

Tomato B-cell lymphoma2 (Bcl2)-associated athanogene 5 (SlBAG5) contributes negatively to immunity against necrotrophic fungus Botrytis cinerea through interacting with SlBAP1 and modulating catalase activity

The evolutionarily conserved and multifunctional B-cell lymphoma2 (Bcl2)-associated athanogene proteins (BAGs), serving as co-chaperone regulators, play a pivotal role in orchestrating plant stress responses. In this study, the possible involvement of tomato SlBAG genes in resistance to Botrytis cinerea was examined. The SlBAG genes respond with different expression change patterns to B. cinerea and defense signaling hormones. SlBAG proteins are individually differentially localized to the nucleus, mitochondria, cytoplasm, endoplasmic reticulum (ER), or vacuole. Silencing of SlBAG5 enhanced immunity to B. cinerea, while overexpression weakened it, affecting Botrytis-induced JA/ET defense gene expression and JA levels. Chitin-induced ROS burst and expression of PTI marker genes SlPTI5 and SlLRR22 were strengthened in SlBAG5-silenced plants but were weakened in SlBAG5-overexpressing plants (SlBAG5-OE) plants. SlBAG5 interacts with BON1 ASSOCIATED PROTEIN 1 (SlBAP1) through its BAG domain, and the stability of SlBAP1 depends on the presence of SlBAG5. Silencing of SlBAP1 conferred increased resistance to B. cinerea through increased expression of JA/ET signaling and defense genes. SlBAP1 functions by recruiting and boosting SlCAT3 activity to remove H2O2. The findings suggest that SlBAG5 suppresses tomato immunity to B. cinerea by stabilizing SlBAP1, which modulates ROS scavenging and acts as a negative regulator of immunity.

Genome-wide screening for virulent candidate secreted effector protein macromolecules in Magnaporthe oryzae

Rice blast, caused by Magnaporthe oryzae (M. oryzae), is a severe threat to rice production globally. The pathogen counters rice immunity by secreting effectors that disrupt host defenses. In this study, we conducted a comprehensive genome-wide screening to identify candidate secreted effector proteins (CSEPs) in M. oryzae. Using a new bioinformatics pipeline, we predicted 577 CSEPs and analyzed their sequence features and functional annotations. We found that these effectors have distinct sequence signatures, such as high cysteine content, and are involved in infection and immune suppression. Phylogenetic analysis revealed M. oryzae's close relationship with other pathogenic fungi and the conservation of certain CSEPs across species. Expression analysis during infection indicated a role of CSEPs in the pathogenic process and the ability to inhibit plant necrosis. Finally, we validated the function of three candidate effector proteins through gene disruption mutant analysis including pathogenesis testing in rice. This study provides a foundation for understanding M. oryzae pathogenicity and may aid in developing resistance strategies against rice blast.

Helper NLR immune protein NRC3 evolved to evade inhibition by a cyst nematode virulence effector

Parasites can counteract host immunity by suppressing nucleotide binding and leucine-rich repeat (NLR) proteins that function as immune receptors. We previously showed that a cyst nematode virulence effector SPRYSEC15 (SS15) binds and inhibits oligomerisation of helper NLR proteins in the expanded NRC1/2/3 clade by preventing intramolecular rearrangements required for NRC oligomerisation into an activated resistosome. Here we examined the degree to which NRC proteins from multiple Solanaceae species are sensitive to suppression by SS15 and tested hypotheses about adaptive evolution of the binding interface between the SS15 inhibitor and NRC proteins. Whereas all tested orthologs of NRC2 were inhibited by SS15, some natural variants of NRC1 and NRC3 are insensitive to SS15 suppression. Ancestral sequence reconstruction combined with functional assays revealed that NRC3 transitioned from an ancestral suppressed form to an insensitive one over 19 million years ago. Our analyses revealed the evolutionary trajectory of an NLR immune receptor against a parasite inhibitor, identifying key evolutionary transitions in helper NLRs that counteract this inhibition. This work reveals a distinct type of gene-for-gene interaction between parasite or pathogen immunosuppressors and host immune receptors that contrasts with the coevolution between AVR effectors and immune receptors.

Plant pattern recognition receptors: from evolutionary insight to engineering

The plant immune system relies on germline-encoded pattern recognition receptors (PRRs) that sense foreign and plant-derived molecular patterns, and signal health threats. Genomic and pangenomic data sets provide valuable insights into the evolution of PRRs and their molecular triggers, which is furthering our understanding of plant-pathogen co-evolution and convergent evolution. Moreover, in silico and in vivo methods of PRR identification have accelerated the characterization of receptor-ligand complexes, and advances in protein structure prediction algorithms are revealing novel PRR sensor functions. Harnessing these recent advances to engineer PRRs presents an opportunity to enhance plant disease resistance against a broad spectrum of pathogens, enabling more sustainable agricultural practices. This Review summarizes both established and innovative approaches to leverage genomic data and translate resulting evolutionary insights into engineering PRR recognition specificities.

A Necrotrophic Phytopathogen-Derived GPI-Anchored Protein Functions as an Elicitor to Activate Plant Immunity and Enhance Resistance

GPI-anchored proteins are widely distributed in eukaryotic cells. However, their functions are still poorly understood in necrotrophic pathogenic fungi. Here, based on Agrobacterium tumefaciens-mediated transient expression screening, a novel secreted GPI-anchored protein, SsGP1, that induces plant cell death was characterised in Sclerotinia sclerotiorum. The homologues of SsGP1 are broadly distributed among ascomycetes. SsGP1 can activate plant immune responses, including reactive oxygen species (ROS) burst and the up-regulated expression of immunity genes, in a manner that is dependent on BAK1 but independent of SOBIR1. Treatment of plants with SsGP1 protein enhanced the resistance of Nicotiana benthamiana and Arabidopsis thaliana to S. sclerotiorum. Our findings reveal that SsGP1 functions as a pathogen-associated molecular pattern (PAMP) and is recognised by plants in a BAK1-dependent manner.

Pan-analysis of intra- and inter-species diversity reveals a group of highly variable immune receptor genes in rice

Plant immune receptors and their natural variations play a central role in combating disease-causing pathogens. These immune receptors include intracellular nucleotide-binding leucine-rich repeat (LRR) receptors (NLRs) and cell-surface pattern recognition receptors (PRRs) that can be further classified as receptor-like proteins (RLPs) and receptor-like kinases (RLKs). Although the NLRome has been characterized, the repertoire and extent of diversity of PRRome remain undetermined in rice. In this study, we examined the diversity of immune receptor genes using high-quality genomes of 309 rice accessions from 8 species within the genus Oryza. A total of 376 310 immune receptor genes were identified, including 149 592 NLR-coding genes and 226 718 PRR coding genes. Shannon entropy analysis revealed a set of immune receptors that display significant intra-species and inter-species diversity in rice. In general, RLPs are more variable than RLKs, while NLRs and LRR-RLPs are more variable than LRR-RLKs. Additionally, NLR and PRR genes exhibit contrasting shoot/root expression patterns, with NLRs generally skewed towards root expression. Furthermore, we found that the size of the LRR-RLK gene families correlates with local annual precipitation, suggesting a stronger selection pressure on LRR-RLK genes in rice accessions grown under wet conditions than dry conditions. In sum, this pan-genomic analysis not only reveals the extensive diversity of the immune receptor repertoires in rice but also provides potential target genes for improving disease resistance in rice.

Time-course dual RNA-seq analyses and gene identification during early stages of plant-Phytophthora infestans interactions

Late blight caused by Phytophthora infestans is a major threat to global potato and tomato production. Sustainable management of late blight requires the development of resistant crop cultivars. This process can be facilitated by high-throughput identification of functional genes involved in late blight pathogenesis. In this study, we generated a high-quality transcriptomic time-course dataset focusing on the initial 24 h of contact between P. infestans and 3 solanaceous plant species, tobacco (Nicotiana benthamiana), tomato (Solanum lycopersicum), and potato (Solanum tuberosum). Our results demonstrate species-specific transcriptional regulation in early stages of the infection. Transient silencing of putative RIBOSE-5-PHOSPHATE ISOMERASE and HMG-CoA REDUCTASE genes in N. benthamiana lowered plant resistance against P. infestans. Furthermore, heterologous expression of a putative tomato Golgi-localized nucleosugar transporter-encoding gene exacerbated P. infestans infection of N. benthamiana. In comparison, bioassays using transgenic tomato lines showed that the quantitative disease resistance genes were required but insufficient for late blight resistance; genetic knock-out of the susceptibility gene enhanced resistance. The same RNA-seq dataset was exploited to examine the transcriptional landscape of P. infestans and revealed host-specific gene expression patterns in the pathogen. This temporal transcriptomic diversity, in combination with genomic distribution features, identified the P. infestans IPI-B family GLYCINE-RICH PROTEINs as putative virulence factors that promoted disease severity or induced plant tissue necrosis when transiently expressed in N. benthamiana. These functional genes underline the effectiveness of functional gene-mining through a time-course dual RNA-seq approach and provide insight into the molecular interactions between solanaceous plants and P. infestans.

A wheat tandem kinase activates an NLR to trigger immunity

The role of nucleotide-binding leucine-rich repeat (NLR) receptors in plant immunity is well studied, but the function of a class of tandem kinases (TKs) that confer disease resistance in wheat and barley remains unclear. In this study, we show that the SR62 locus is a digenic module encoding the Sr62TK TK and an NLR (Sr62NLR), and we identify the corresponding AvrSr62 effector. AvrSr62 binds to the N-terminal kinase 1 of Sr62TK, triggering displacement of kinase 2, which activates Sr62NLR. Modeling and mutation analysis indicated that this is mediated by overlapping binding sites (i) on kinase 1 for binding AvrSr62 and kinase 2 and (ii) on kinase 2 for binding kinase 1 and Sr62NLR. Understanding this two-component resistance complex may help engineering and breeding plants for durable resistance.

A wheat tandem kinase and NLR pair confers resistance to multiple fungal pathogens

Tandem kinase proteins underlie the innate immune systems of cereal plants, but how they initiate plant immune responses remains unclear. This report identifies wheat protein wheat tandem NBD 1 (WTN1), a noncanonical nucleotide-binding leucine-rich repeat (NLR) receptor featuring tandem nucleotide binding adaptor shared by APAF-1, plant R proteins, and CED-4 (NB-ARC) domains, required for WTK3-mediated disease resistance. Both WTK3 and its allelic variant Rwt4-known for conferring resistance to wheat powdery mildew and blast, respectively-are capable of recognizing the blast effector PWT4. They activate WTN1 to form calcium-permeable channels, akin to ZAR1 and Sr35. Thus, tandem kinase proteins and their associated NLRs operate as "sensor-executor" pairs against fungal pathogens. Additionally, evolutionary analyses reveal a coevolutionary trajectory of the tandem kinase-NLR module, highlighting their cooperative role in triggering plant immunity.

Cell wall bricks of defence: the case study of oligogalacturonides

The plant cell wall (CW) is more than a structural barrier; it serves as the first line of defence against pathogens and environmental stresses. During pathogen attacks or physical damage, fragments of the CW, known as CW-derived Damage-Associated Molecular Patterns (CW-DAMPs), are released. These molecular signals play a critical role in activating the plant's immune responses. Among CW-DAMPs, oligogalacturonides (OGs), fragments derived from the breakdown of pectin, are some of the most well-studied. This review highlights recent advances in understanding the functional and signalling roles of OGs, beginning with their formation through enzymatic CW degradation during pathogen invasion or mechanical injury. We discuss how OGs perception triggers intracellular signalling pathways that enhance plant defence and regulate interactions with microbes. Given that excessive OG levels can negatively impact growth and development, we also examine the regulatory mechanisms plants use to fine-tune their responses, avoiding immune overactivation or hyper- immunity. As natural immune modulators, OGs (and more generally CW-DAMPs), offer a promising, sustainable alternative to chemical pesticides by enhancing crop resilience without harming the environment. By strengthening plant defences and supporting eco-friendly agricultural practices, OGs hold great potential for advancing resilient and sustainable farming systems.

A PRA-Rab trafficking machinery modulates NLR immune receptor plasma membrane microdomain anchoring and blast resistance in rice

Nucleotide-binding leucine-rich repeat (NLR) receptors mediate pathogen effector-triggered immunity (ETI) in plants, and a subclass of NLRs are hypothesized to function at the plasma membrane (PM). However, how NLR traffic and PM delivery are regulated during immune responses remains largely unknown. The rice NLR PigmR confers broad-spectrum resistance to the blast fungus Magnaporthe oryzae. Here, we report that a PRA (Prenylated Rab acceptor) protein, PIBP4 (PigmR-INTERACTING and BLAST RESISTANCE PROTEIN 4), interacts with both PigmR and the active form of the Rab GTPase, OsRab5a, thereby loads a portion of PigmR on trafficking vesicles that target to PM microdomains. Microdomain-localized PigmR interacts with and activates the small GTPase OsRac1, which triggers reactive oxygen species signaling and hypersensitive response, leading to immune responses against blast infection. Thus, our study discovers a previously unknown mechanism that deploys a PRA-Rab protein delivering hub to ensure ETI, linking the membrane trafficking machinery with NLR function and immune activation in plants.