Identification Of The Pattern Recognition Receptor And Signaling Components Required For XEG1-Mediated Plant Immunity

Root rot of soybean caused by Phytophthora sojae is one of the most destructive diseases in soybean production in the world.The disease causes extremely significant economic losses every year.P.sojae is an oomycete pathogen,which form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms,related to diatoms.Chemicals used in controlling fungi are not very effective to control the disease caused by oomycetes.Under selection pressure,the rapid evoulution of avirulence genes in P.sojae makes problems for resistance breeding.The control of disease caused by P.sojae is one of the most important problems in soybean production.Innate immunity is the first line of defense against invading microorganisms in plants.PAMPs are the classical activators of immune responses.These alarm signal molecules are perceived as 'nonself' by plant pattern recognition receptors(PRRs)to switch on the plant immune responses.PTI improves the non-host resistance of plants against pathogen and PTI is a durable broad-spectrum resistance.There are several PRRs of bacteria PAMPs that have been identified.In previous study in our lab,a novel apoplastic elicitor from P.sojae,XEG1,has been identified function as a PAMP.So identification of XEG1-receptors will provide theoretical basis for developing new resistant cultivars.Therefore,this research focuses on the mechanism of the plant recognition of XEG1.The main results and conclusions are shown as follows:Identification of plant pattern recognition receptors required for XEG1 recognition.Recently,XEG1 was identified as a PAMP and can induce cell death in Nicotiana benthamiana.But XEG1 can not induce cell death in BAK1-slienced N.benthamiana indicating XEG1 induced cell death depends on BAK1-mediated receptor recognition.The results suggest that XEG1-receptors belong to leucine rich repeat(LRR)subfamily of PRRs.114 LRR genes were silenced in N.benthamiana by Virus-induced Gene Silencing(VIGS).PsXEG1 was transiently expressed in the gene-slienced N.benthamiana.PsXEG1 did not trigger cell death in both RXEG1A-and RXEG1B-slienced N.benthamiana.RXEG1A overexpression in N.benthamiana leaves enhanced the resistance to Phytophthora parasitica.Identification of the signaling components required for XEG1-triggerred plant immunity.PAMPs are perceived by plants as danger signals and these signals activates signaling systems transduce defense responses.Previous study reveals that RXEG1 function as the receptor of XEG1 and we want to know how the signals were transmitted into cell activating defense responses.XEG1 co-expressed with BAK1 in N.benthamiana and the Co-IP assay reverals that XEG1 can associate with BAK1.In previous study,BAK1 and SOBIR1 were used as baits to find the components required for XEG1-triggerred plant immunity signaling pathway.From the MS(Mass spectrometry)results,we got 2 candidate proteins named R1 and R2,respectively.When R1 or R2 was silenced in N.benthamiana,the cell death and the activation of defense-related gene CYP71D20 induced by PsXEG1 were significantly influenced.Co-IP assays revealed that both R1 and R2 in N.benthamiana can associate with BAK1.Mitogen-activated protein kinase cascade is a very important signal pathway in PTI.When MEK2,SIPK or NTF6 was silenced in N.benthamiana,the cell death induced by PsXEG1 was influenced.When MEK2 or WIPK was silenced in N.benthamiana,the activation of defense-related gene CYP71D20 induced by XEG1 was influenced.