An NBS-LRR protein in the Rpp1 locus negates the dominance of Rpp1-mediated resistance against Phakopsora pachyrhizi in soybean.

The soybean Rpp1 locus confers resistance to Phakopsora pachyrhizi, causal agent of rust, and resistance is usually dominant over susceptibility. However, dominance of Rpp1-mediated resistance is lost when a resistant genotype (Rpp1 or Rpp1b) is crossed with susceptible line TMG06_0011, and the mechanism of this dominant susceptibility (DS) is unknown. Sequencing the Rpp1 region reveals that the TMG06_0011 Rpp1 locus has a single nucleotide-binding site leucine-rich repeat (NBS-LRR) gene (DS-R), whereas resistant PI 594760B (Rpp1b) is similar to PI 200492 (Rpp1) and has three NBS-LRR resistance gene candidates. Evidence that DS-R is the cause of DS was reflected in virus-induced gene silencing of DS-R in Rpp1b/DS-R or Rpp1/DS-R heterozygous plants with resistance partially restored. In heterozygous Rpp1b/DS-R plants, expression of Rpp1b candidate genes was not significantly altered, indicating no effect of DS-R on transcription. Physical interaction of the DS-R protein with candidate Rpp1b resistance proteins was supported by yeast two-hybrid studies and in silico modeling. Thus, we conclude that suppression of resistance most likely does not occur at the transcript level, but instead probably at the protein level, possibly with Rpp1 function inhibited by binding to the DS-R protein. The DS-R gene was found in other soybean lines, with an estimated allele frequency of 6% in a diverse population, and also found in wild soybean (Glycine soja). The identification of a dominant susceptible NBS-LRR gene provides insight into the behavior of NBS-LRR proteins and serves as a reminder to breeders that the dominance of an R gene can be influenced by a susceptibility allele.

Biocontrol potential of plant growth-promoting rhizobacteria against plant disease and insect pest.

Biological control is a promising approach to enhance pathogen and pest control to ensure high productivity in cash crop production. Therefore, PGPR biofertilizers are very suitable for application in the cultivation of tea plants (Camellia sinensis) and tobacco, but it is rarely reported so far. In this study, production of a consortium of three strains of PGPR were applied to tobacco and tea plants. The results demonstrated that plants treated with PGPR exhibited enhanced resistance against the bacterial pathogen Pseudomonas syringae (PstDC3000). The significant effect in improving the plant's ability to resist pathogen invasion was verified through measurements of oxygen activity, bacterial colony counts, and expression levels of resistance-related genes (NPR1, PR1, JAZ1, POD etc.). Moreover, the application of PGPR in the tea plantation showed significantly reduced population occurrences of tea green leafhoppers (Empoasca onukii Matsuda), tea thrips (Thysanoptera:Thripidae), Aleurocanthus spiniferus (Quaintanca) and alleviated anthracnose disease in tea seedlings. Therefore, PGPR biofertilizers may serve as a viable biological control method to improve tobacco and tea plant yield and quality. Our findings revealed part of the mechanism by which PGPR helped improve plant biostresses resistance, enabling better application in agricultural production.

Dynamic localization of a helper NLR at the plant-pathogen interface underpins pathogen recognition.

Plants employ sensor-helper pairs of NLR immune receptors to recognize pathogen effectors and activate immune responses. Yet, the subcellular localization of NLRs pre- and postactivation during pathogen infection remains poorly understood. Here, we show that NRC4, from the "NRC" solanaceous helper NLR family, undergoes dynamic changes in subcellular localization by shuttling to and from the plant-pathogen haustorium interface established during infection by the Irish potato famine pathogen Phytophthora infestans. Specifically, prior to activation, NRC4 accumulates at the extrahaustorial membrane (EHM), presumably to mediate response to perihaustorial effectors that are recognized by NRC4-dependent sensor NLRs. However, not all NLRs accumulate at the EHM, as the closely related helper NRC2 and the distantly related ZAR1 did not accumulate at the EHM. NRC4 required an intact N-terminal coiled-coil domain to accumulate at the EHM, whereas the functionally conserved MADA motif implicated in cell death activation and membrane insertion was dispensable for this process. Strikingly, a constitutively autoactive NRC4 mutant did not accumulate at the EHM and showed punctate distribution that mainly associated with the plasma membrane, suggesting that postactivation, NRC4 may undergo a conformation switch to form clusters that do not preferentially associate with the EHM. When NRC4 is activated by a sensor NLR during infection, however, NRC4 forms puncta mainly at the EHM and, to a lesser extent, at the plasma membrane. We conclude that following activation at the EHM, NRC4 may spread to other cellular membranes from its primary site of activation to trigger immune responses.

Phosphatases: Decoding the Role of Mycorrhizal Fungi in Plant Disease Resistance.

Mycorrhizal fungi, a category of fungi that form symbiotic relationships with plant roots, can participate in the induction of plant disease resistance by secreting phosphatase enzymes. While extensive research exists on the mechanisms by which mycorrhizal fungi induce resistance, the specific contributions of phosphatases to these processes require further elucidation. This article reviews the spectrum of mycorrhizal fungi-induced resistance mechanisms and synthesizes a current understanding of how phosphatases mediate these effects, such as the induction of defense structures in plants, the negative regulation of plant immune responses, and the limitation of pathogen invasion and spread. It explores the role of phosphatases in the resistance induced by mycorrhizal fungi and provides prospective future research directions in this field.

HISS: Snakemake-based workflows for performing SMRT-RenSeq assembly, AgRenSeq and dRenSeq for the discovery of novel plant disease resistance genes.

BACKGROUND: In the ten years since the initial publication of the RenSeq protocol, the method has proved to be a powerful tool for studying disease resistance in plants and providing target genes for breeding programmes. Since the initial publication of the methodology, it has continued to be developed as new technologies have become available and the increased availability of computing power has made new bioinformatic approaches possible. Most recently, this has included the development of a k-mer based association genetics approach, the use of PacBio HiFi data, and graphical genotyping with diagnostic RenSeq. However, there is not yet a unified workflow available and researchers must instead configure approaches from various sources themselves. This makes reproducibility and version control a challenge and limits the ability to perform these analyses to those with bioinformatics expertise. RESULTS: Here we present HISS, consisting of three workflows which take a user from raw RenSeq reads to the identification of candidates for disease resistance genes. These workflows conduct the assembly of enriched HiFi reads from an accession with the resistance phenotype of interest. A panel of accessions both possessing and lacking the resistance are then used in an association genetics approach (AgRenSeq) to identify contigs positively associated with the resistance phenotype. Candidate genes are then identified on these contigs and assessed for their presence or absence in the panel with a graphical genotyping approach that uses dRenSeq. These workflows are implemented via Snakemake, a python-based workflow manager. Software dependencies are either shipped with the release or handled with conda. All code is freely available and is distributed under the GNU GPL-3.0 license. CONCLUSIONS: HISS provides a user-friendly, portable, and easily customised approach for identifying novel disease resistance genes in plants. It is easily installed with all dependencies handled internally or shipped with the release and represents a significant improvement in the ease of use of these bioinformatics analyses.

The secret password: Cell death-inducing proteins in filamentous phytopathogens - As versatile tools to develop disease-resistant crops.

Cell death-inducing proteins (CDIPs) are some of the secreted effector proteins manifested by filamentous oomycetes and fungal pathogens to invade the plant tissue and facilitate infection. Along with their involvement in different developmental processes and virulence, CDIPs play a crucial role in plant-pathogen interactions. As the name implies, CDIPs cause necrosis and trigger localised cell death in the infected host tissues by the accumulation of higher concentrations of hydrogen peroxide (H2O2), oxidative burst, accumulation of nitric oxide (NO), and electrolyte leakage. They also stimulate the biosynthesis of defense-related phytohormones such as salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and ethylene (ET), as well as the expression of pathogenesis-related (PR) genes that are important in disease resistance. Altogether, the interactions result in the hypersensitive response (HR) in the host plant, which might confer systemic acquired resistance (SAR) in some cases against a vast array of related and unrelated pathogens. The CDIPs, due to their capability of inducing host resistance, are thus unique among the array of proteins secreted by filamentous plant pathogens. More interestingly, a few transgenic plant lines have also been developed expressing the CDIPs with added resistance. Thus, CDIPs have opened an interesting hot area of research. The present study critically reviews the current knowledge of major types of CDIPs identified across filamentous phytopathogens and their modes of action in the last couple of years. This review also highlights the recent breakthrough technologies in studying plant-pathogen interactions as well as crop improvement by enhancing disease resistance through CDIPs.

Evolution of antimicrobial cysteine-rich peptides in plants.

KEY MESSAGE: We analyzed the evolutionary pattern of cysteine-rich peptides (CRPs) to infer the relationship between CRP copy number and plant ecotype, and the origin of bi-domains CRPs. Plants produce cysteine-rich peptides (CRPs) that have long-lasting broad-spectrum antimicrobial activity to protect themselves from various groups of pathogens. We analyzed 240 plant genomes, ranging from algae to eudicots, and discovered that CRPs are widely distributed in plants. Our comparative genomics results revealed that CRP genes have been amplified through both whole genome and local tandem duplication. The copy number of these genes varied significantly across lineages and was associated with the plant ecotype. This may be due to their resistance to changing pathogenic environments. The conserved and lineage-specific CRP families contribute to diverse antimicrobial activities. Furthermore, we investigated the unique bi-domain CRPs that result from unequal crossover events. Our findings provide a unique evolutionary perspective on CRPs and insights into their antimicrobial and symbiosis characteristics.

An atypical N-ethylmaleimide sensitive factor enables the viability of nematode-resistant Rhg1 soybeans.

N-ethylmaleimide sensitive factor (NSF) and α-soluble NSF attachment protein (α-SNAP) are essential eukaryotic housekeeping proteins that cooperatively function to sustain vesicular trafficking. The "resistance to Heterodera glycines 1" (Rhg1) locus of soybean (Glycine max) confers resistance to soybean cyst nematode, a highly damaging soybean pest. Rhg1 loci encode repeat copies of atypical α-SNAP proteins that are defective in promoting NSF function and are cytotoxic in certain contexts. Here, we discovered an unusual NSF allele (Rhg1-associated NSF on chromosome 07; NSFRAN07 ) in Rhg1+ germplasm. NSFRAN07 protein modeling to mammalian NSF/α-SNAP complex structures indicated that at least three of the five NSFRAN07 polymorphisms reside adjacent to the α-SNAP binding interface. NSFRAN07 exhibited stronger in vitro binding with Rhg1 resistance-type α-SNAPs. NSFRAN07 coexpression in planta was more protective against Rhg1 α-SNAP cytotoxicity, relative to WT NSFCh07 Investigation of a previously reported segregation distortion between chromosome 18 Rhg1 and a chromosome 07 interval now known to contain the Glyma.07G195900 NSF gene revealed 100% coinheritance of the NSFRAN07 allele with disease resistance Rhg1 alleles, across 855 soybean accessions and in all examined Rhg1+ progeny from biparental crosses. Additionally, we show that some Rhg1-mediated resistance is associated with depletion of WT α-SNAP abundance via selective loss of WT α-SNAP loci. Hence atypical coevolution of the soybean SNARE-recycling machinery has balanced the acquisition of an otherwise disruptive housekeeping protein, enabling a valuable disease resistance trait. Our findings further indicate that successful engineering of Rhg1-related resistance in plants will require a compatible NSF partner for the resistance-conferring α-SNAP.

Distinct modes of derepression of an Arabidopsis immune receptor complex by two different bacterial effectors.

Plant intracellular nucleotide-binding leucine-rich repeat (NLR) immune receptors often function in pairs to detect pathogen effectors and activate defense. The Arabidopsis RRS1-R-RPS4 NLR pair recognizes the bacterial effectors AvrRps4 and PopP2 via an integrated WRKY transcription factor domain in RRS1-R that mimics the effector's authentic targets. How the complex activates defense upon effector recognition is unknown. Deletion of the WRKY domain results in an RRS1 allele that triggers constitutive RPS4-dependent defense activation, suggesting that in the absence of effector, the WRKY domain contributes to maintaining the complex in an inactive state. We show the WRKY domain interacts with the adjacent domain 4, and that the inactive state of RRS1 is maintained by WRKY-domain 4 interactions before ligand detection. AvrRps4 interaction with the WRKY domain disrupts WRKY-domain 4 association, thus derepressing the complex. PopP2-triggered activation is less easily explained by such disruption and involves the longer C-terminal extension of RRS1-R. Furthermore, some mutations in RPS4 and RRS1 compromise PopP2 but not AvrRps4 recognition, suggesting that AvrRps4 and PopP2 derepress the complex differently. Consistent with this, a "reversibly closed" conformation of RRS1-R, engineered in a method exploiting the high affinity of colicin E9 and Im9 domains, reversibly loses AvrRps4, but not PopP2 responsiveness. Following RRS1 derepression, interactions between domain 4 and the RPS4 C-terminal domain likely contribute to activation. Simultaneous relief of autoinhibition and activation may contribute to defense activation in many immune receptors.

Multiple functional self-association interfaces in plant TIR domains.

The self-association of Toll/interleukin-1 receptor/resistance protein (TIR) domains has been implicated in signaling in plant and animal immunity receptors. Structure-based studies identified different TIR-domain dimerization interfaces required for signaling of the plant nucleotide-binding oligomerization domain-like receptors (NLRs) L6 from flax and disease resistance protein RPS4 from Arabidopsis Here we show that the crystal structure of the TIR domain from the Arabidopsis NLR suppressor of npr1-1, constitutive 1 (SNC1) contains both an L6-like interface involving helices αD and αE (DE interface) and an RPS4-like interface involving helices αA and αE (AE interface). Mutations in either the AE- or DE-interface region disrupt cell-death signaling activity of SNC1, L6, and RPS4 TIR domains and full-length L6 and RPS4. Self-association of L6 and RPS4 TIR domains is affected by mutations in either region, whereas only AE-interface mutations affect SNC1 TIR-domain self-association. We further show two similar interfaces in the crystal structure of the TIR domain from the Arabidopsis NLR recognition of Peronospora parasitica 1 (RPP1). These data demonstrate that both the AE and DE self-association interfaces are simultaneously required for self-association and cell-death signaling in diverse plant NLRs.

Characterization of Phn15.1, a Newly Identified Phytophthora nicotianae Resistance QTL in Nicotiana tabacum.

Phytophthora nicotianae is an oomycete that causes black shank, one of the most economically important diseases affecting tobacco production worldwide. Identification and introgression of novel genetic variability affecting partial genetic resistance to this pathogen is important because of the increased durability of partial resistance over time as compared with genes conferring immunity. A previous mapping study identified a quantitative trait locus (QTL), hereafter designated as Phn15.1, with a major effect on P. nicotianae resistance in tobacco. In this research, we describe significantly improved resistance of nearly isogenic lines (NILs) of flue-cured tobacco carrying the introgressed Phn15.1 region derived from highly resistant cigar tobacco cultivar Beinhart 1000. The Phn15.1 region appeared to act in an additive or partially dominant manner to positively affect resistance. To more finely resolve the position of the gene or genes underlying the Phn15.1 effect, the QTL was mapped with an increased number of molecular markers (single-nucleotide polymorphisms) identified to reside within the region. Development and evaluation of subNILs containing varying amounts of Beinhart 1000-derived Phn15.1-associated genetic material permitted the localization of the QTL to a genetic interval of approximately 2.7 centimorgans. Importantly, we were able to disassociate the Beinhart 1000 Phn15.1 resistance alleles from a functional NtCPS2 allele(s) which contributes to the accumulation of a diterpene leaf surface exudate considered undesirable for flue-cured and burley tobacco. Information from this research should be of value for marker-assisted introgression of Beinhart 1000-derived partial black shank resistance into flue-cured and burley tobacco breeding programs.

Update on Cuticular Wax Biosynthesis and Its Roles in Plant Disease Resistance.

The aerial surface of higher plants is covered by a hydrophobic layer of cuticular waxes to protect plant tissues against enormous environmental challenges including the infection of various pathogens. As the first contact site between plants and pathogens, the layer of cuticular waxes could function as a plant physical barrier that limits the entry of pathogens, acts as a reservoir of signals to trigger plant defense responses, and even gives cues exploited by pathogens to initiate their infection processes. Past decades have seen unprecedented proceedings in understanding the molecular mechanisms underlying the biosynthesis of plant cuticular waxes and their functions regulating plant-pathogen interactions. In this review, we summarized the recent progress in the molecular biology of cuticular wax biosynthesis and highlighted its multiple roles in plant disease resistance against bacterial, fungal, and insect pathogens.

Redox-Dependent Structural Modification of Nucleoredoxin Triggers Defense Responses against Alternaria brassicicola in Arabidopsis.

In plants, thioredoxin (TRX) family proteins participate in various biological processes by regulating the oxidative stress response. However, their role in phytohormone signaling remains largely unknown. In this study, we investigated the functions of TRX proteins in Arabidopsis thaliana. Quantitative polymerase chain reaction (qPCR) experiments revealed that the expression of ARABIDOPSIS NUCLEOREDOXIN 1 (AtNRX1) is specifically induced by the application of jasmonic acid (JA) and upon inoculation with a necrotrophic fungal pathogen, Alternaria brassicicola. The AtNRX1 protein usually exists as a low molecular weight (LMW) monomer and functions as a reductase, but under oxidative stress AtNRX1 transforms into polymeric forms. However, the AtNRX1M3 mutant protein, harboring four cysteine-to-serine substitutions in the TRX domain, did not show structural modification under oxidative stress. The Arabidopsisatnrx1 null mutant showed greater resistance to A. brassicicola than wild-type plants. In addition, plants overexpressing both AtNRX1 and AtNRX1M3 were susceptible to A. brassicicola infection. Together, these findings suggest that AtNRX1 normally suppresses the expression of defense-responsive genes, as if it were a safety pin, but functions as a molecular sensor through its redox-dependent structural modification to induce disease resistance in plants.

OsExo70B1 Positively Regulates Disease Resistance to Magnaporthe oryzae in Rice.

The exocyst, an evolutionarily conserved octameric protein complex, mediates tethering of vesicles to the plasma membrane in the early stage of exocytosis. Arabidopsis Exo70, a subunit of the exocyst complex, has been found to be involved in plant immunity. Here, we characterize the function of OsExo70B1 in rice. OsExo70B1 mainly expresses in leaf and shoot and its expression is induced by pathogen-associated molecular patterns (PAMPs) and rice blast fungus Magnaporthe oryzae (M. oryzae). Knocking out OsExo70B1 results in significantly decreased resistance and defense responses to M. oryzae compared to the wild type, including more disease lesions and enhanced fungal growth, downregulated expression of pathogenesis-related (PR) genes, and decreased reactive oxygen species accumulation. In contrast, the exo70B1 mutant does not show any defects in growth and development. Furthermore, OsExo70B1 can interact with the receptor-like kinase OsCERK1, an essential component for chitin reception in rice. Taken together, our data demonstrate that OsExo70B1 functions as an important regulator in rice immunity.

Oxathiapiprolin, a Novel Chemical Inducer Activates the Plant Disease Resistance.

Oxathiapiprolin was developed as a specific plant pathogenic oomycete inhibitor, previously shown to have highly curative and protective activities against the pepper Phytophthora blight disease under field and greenhouse tests. Therefore, it was hypothesized that oxathiapiprolin might potentially activate the plant disease resistance against pathogen infections. This study investigated the potential and related mechanism of oxathiapiprolin to activate the plant disease resistance using the bacterium Pseudomonas syringae pv tomato (Pst) and plant Arabidopsis interaction as the targeted system. Our results showed that oxathiapiprolin could activate the plant disease resistance against Pst DC3000, a non-target pathogen of oxathiapiprolin, in Arabidopsis, tobacco, and tomato plants. Our results also showed the enhanced callose deposition and H2O2 accumulation in the oxathiapiprolin-treated Arabidopsis under the induction of flg22 as the pathogen-associated molecular pattern (PAMP) treatment. Furthermore, increased levels of free salicylic acid (SA) and jasmonic acid (JA) were detected in the oxathiapiprolin-treated Arabidopsis plants compared to the mock-treated ones under the challenge of Pst DC3000. Besides, the gene expression results confirmed that at 24 h after the infiltration with Pst DC3000, the oxathiapiprolin-treated Arabidopsis plants had upregulated expression levels of the respiratory burst oxidase homolog D (RBOHD), JA-responsive gene (PDF1.2), and SA-responsive genes (PR1, PR2, and PR5) compared to the control. Taken together, oxathiapiprolin is identified as a novel chemical inducer which activates the plant disease resistance against Pst DC3000 by enhancing the callose deposition, H2O2 accumulation, and hormone SA and JA production.

Genome-wide in silico identification of LysM-RLK genes in potato (Solanum tuberosum L.).

The receptor like kinases (RLKs) belong to the RLK/Pelle superfamily, one of the largest gene families in plants. RLKs play an important role in plant development, as well as in response to biotic and abiotic stresses. The lysine motif receptor like kinases (LysM-RLKs) are a subfamily of RLKs containing at least one lysine motif (LysM) that are involved in the perception of elicitors or pathogen-associated molecular patterns (PAMPs). In the present study, 77 putative RLKs genes and three receptor like proteins were identified in potato (Solanum tuberosum) genome, following a genome-wide search. The 77 potato RLK proteins are classified into two major phylogenetic groups based on their kinase domain amino acid sequence similarities. Out of 77 RLKs, 10 proteins had at least one LysM. Among them three RLP proteins were found in potato genome with either 2 or three tandem LysM but these lacked a cytoplasmic kinase domain. Expression analyses of a potato LysM-RLKs (StLysM-RLK05) was carried out by a Real time RT-PCR, following inoculation of potato leaves and immature tubers with late blight and common scab pathogens, respectively. The expression was significantly higher in resistant than in susceptible following S. scabies inoculation. The StLysM-RLK05 sequence was verified and it was polymorphic in scab susceptible cultivar. The present study provides an overview of the StLysM-RLKs gene family in potato genome. This information is helpful for future functional analysis of such an important protein family, in Solanaceae species.

Disease resistance through impairment of α-SNAP-NSF interaction and vesicular trafficking by soybean Rhg1.

α-SNAP [soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein] and NSF proteins are conserved across eukaryotes and sustain cellular vesicle trafficking by mediating disassembly and reuse of SNARE protein complexes, which facilitate fusion of vesicles to target membranes. However, certain haplotypes of the Rhg1 (resistance to Heterodera glycines 1) locus of soybean possess multiple repeat copies of an α-SNAP gene (Glyma.18G022500) that encodes atypical amino acids at a highly conserved functional site. These Rhg1 loci mediate resistance to soybean cyst nematode (SCN; H. glycines), the most economically damaging pathogen of soybeans worldwide. Rhg1 is widely used in agriculture, but the mechanisms of Rhg1 disease resistance have remained unclear. In the present study, we found that the resistance-type Rhg1 α-SNAP is defective in interaction with NSF. Elevated in planta expression of resistance-type Rhg1 α-SNAPs depleted the abundance of SNARE-recycling 20S complexes, disrupted vesicle trafficking, induced elevated abundance of NSF, and caused cytotoxicity. Soybean, due to ancient genome duplication events, carries other loci that encode canonical (wild-type) α-SNAPs. Expression of these α-SNAPs counteracted the cytotoxicity of resistance-type Rhg1 α-SNAPs. For successful growth and reproduction, SCN dramatically reprograms a set of plant root cells and must sustain this sedentary feeding site for 2-4 weeks. Immunoblots and electron microscopy immunolocalization revealed that resistance-type α-SNAPs specifically hyperaccumulate relative to wild-type α-SNAPs at the nematode feeding site, promoting the demise of this biotrophic interface. The paradigm of disease resistance through a dysfunctional variant of an essential gene may be applicable to other plant-pathogen interactions.

Roq1 mediates recognition of the Xanthomonas and Pseudomonas effector proteins XopQ and HopQ1.

Xanthomonas spp. are phytopathogenic bacteria that can cause disease on a wide variety of plant species resulting in significant impacts on crop yields. Limited genetic resistance is available in most crop species and current control methods are often inadequate, particularly when environmental conditions favor disease. The plant Nicotiana benthamiana has been shown to be resistant to Xanthomonas and Pseudomonas due to an immune response triggered by the bacterial effector proteins XopQ and HopQ1, respectively. We used a reverse genetic screen to identify Recognition of XopQ 1 (Roq1), a nucleotide-binding leucine-rich repeat (NLR) protein with a Toll-like interleukin-1 receptor (TIR) domain, which mediates XopQ recognition in N. benthamiana. Roq1 orthologs appear to be present only in the Nicotiana genus. Expression of Roq1 was found to be sufficient for XopQ recognition in both the closely-related Nicotiana sylvestris and the distantly-related beet plant (Beta vulgaris). Roq1 was found to co-immunoprecipitate with XopQ, suggesting a physical association between the two proteins. Roq1 is able to recognize XopQ alleles from various Xanthomonas species, as well as HopQ1 from Pseudomonas, demonstrating widespread potential application in protecting crop plants from these pathogens.

The tomato I gene for Fusarium wilt resistance encodes an atypical leucine-rich repeat receptor-like protein whose function is nevertheless dependent on SOBIR1 and SERK3/BAK1.

We have identified the tomato I gene for resistance to the Fusarium wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol) and show that it encodes a membrane-anchored leucine-rich repeat receptor-like protein (LRR-RLP). Unlike most other LRR-RLP genes involved in plant defence, the I gene is not a member of a gene cluster and contains introns in its coding sequence. The I gene encodes a loopout domain larger than those in most other LRR-RLPs, with a distinct composition rich in serine and threonine residues. The I protein also lacks a basic cytosolic domain. Instead, this domain is rich in aromatic residues that could form a second transmembrane domain. The I protein recognises the Fol Avr1 effector protein, but, unlike many other LRR-RLPs, recognition specificity is determined in the C-terminal half of the protein by polymorphic amino acid residues in the LRRs just preceding the loopout domain and in the loopout domain itself. Despite these differences, we show that I/Avr1-dependent necrosis in Nicotiana benthamiana depends on the LRR receptor-like kinases (RLKs) SERK3/BAK1 and SOBIR1. Sequence comparisons revealed that the I protein and other LRR-RLPs involved in plant defence all carry residues in their last LRR and C-terminal LRR capping domain that are conserved with SERK3/BAK1-interacting residues in the same relative positions in the LRR-RLKs BRI1 and PSKR1. Tyrosine mutations of two of these conserved residues, Q922 and T925, abolished I/Avr1-dependent necrosis in N. benthamiana, consistent with similar mutations in BRI1 and PSKR1 preventing their interaction with SERK3/BAK1.