Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector AvrRps4

Plant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4 together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thaliana relatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution.113425sciescopu

HopAS1 recognition significantly contributes to Arabidopsis nonhost resistance to Pseudomonas syringae pathogens

Plant immunity is activated by sensing either conserved microbial signatures, called pathogen/microbe-associated molecular patterns (P/MAMPs), or specific effectors secreted by pathogens. However, it is not known why most microbes are nonpathogenic in most plant species. Nonhost resistance (NHR) consists of multiple layers of innate immunity and protects plants from the vast majority of potentially pathogenic microbes. Effector-triggered immunity (ETI) has been implicated in race-specific disease resistance. However, the role of ETI in NHR is unclear. Pseudomonas syringae pv. tomato (Pto) T1 is pathogenic in tomato (Solanum lycopersicum) yet nonpathogenic in Arabidopsis. Here, we show that, in addition to the type III secretion system (T3SS)-dependent effector (T3SE) avrRpt2, a second T3SE of Pto T1, hopAS1, triggers ETI in nonhost Arabidopsis. hopAS1 is broadly present in P.similar to syringae strains, contributes to virulence in tomato, and is quantitatively required for Arabidopsis NHR to Pto T1. Strikingly, all tested P.similar to syringae strains that are pathogenic in Arabidopsis carry truncated hopAS1 variants of forms, demonstrating that HopAS1-triggered immunity plays an important role in Arabidopsis NHR to a broad-range of P.similar to syringae strains.111615sciescopu

A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors

Defense against pathogens in multicellular eukaryotes depends on intracellular immune receptors, yet surveillance by these receptors is poorly understood. Several plant nucleotide-binding, leucinerich repeat (NB-LRR) immune receptors carry fusions with other protein domains. The Arabidopsis RRS1-R NB-LRR protein carries a C-terminal WRKY DNA binding domain and forms a receptor complex with RPS4, another NB-LRR protein. This complex detects the bacterial effectors AvrRps4 or PopP2 and then activates defense. Both bacterial proteins interact with the RRS1 WRKY domain, and PopP2 acetylates lysines to block DNA binding. PopP2 and AvrRps4 interact with other WRKY domain-containing proteins, suggesting these effectors interfere with WRKY transcription factor-dependent defense, and RPS4/RRS1 has integrated a "decoy'' domain that enables detection of effectors that target WRKY proteins. We propose that NB-LRR receptor pairs, one member of which carries an additional protein domain, enable perception of pathogen effectors whose function is to target that domain.11144113sciescopu

SNP markers tightly linked to root knot nematode resistance in grapevine (<i>Vitis cinerea</i>) identified by a genotyping-by-sequencing approach followed by Sequenom MassARRAY validation

<div><p>Plant parasitic nematodes, including root knot nematode <i>Meloidogyne</i> species, cause extensive damage to agriculture and horticultural crops. As <i>Vitis vinifera</i> cultivars are susceptible to root knot nematode parasitism, rootstocks resistant to these soil pests provide a sustainable approach to maintain grapevine production. Currently, most of the commercially available root knot nematode resistant rootstocks are highly vigorous and take up excess potassium, which reduces wine quality. As a result, there is a pressing need to breed new root knot nematode resistant rootstocks, which have no impact on wine quality. To develop molecular markers that predict root knot nematode resistance for marker assisted breeding, a genetic approach was employed to identify a root knot nematode resistance locus in grapevine. To this end, a <i>Meloidogyne javanica</i> resistant <i>Vitis cinerea</i> accession was crossed to a susceptible <i>Vitis vinifera</i> cultivar Riesling and results from screening the F₁ individuals support a model that root knot nematode resistance, is conferred by a single dominant allele, referred as <i>MELOIDOGYNE JAVANICA RESISTANCE1 (MJR1)</i>. Further, <i>MJR1</i> resistance appears to be mediated by a hypersensitive response that occurs in the root apical meristem. Single nucleotide polymorphisms (SNPs) were identified using genotyping-by-sequencing and results from association and genetic mapping identified the <i>MJR1</i> locus, which is located on chromosome 18 in the <i>Vitis cinerea</i> accession. Validation of the SNPs linked to the <i>MJR1</i> locus using a Sequenom MassARRAY platform found that only 50% could be validated. The validated SNPs that flank and co-segregate with the <i>MJR1</i> locus can be used for marker-assisted selection for <i>Meloidogyne javanica</i> resistance in grapevine.</p></div