Functional Study On Chitinase MoChil Of Magnaporthe Oryzae And Its Target Lectin OsMBL1 In Rice

Rice blast,caused by the filamentous fungus Pyricularia oryzae syn.Magnaporthe oryzae,is one of the most devastating diseases of rice(Oryza sativa).The fungus also infects other hosts,such as grasses and cereal crops,including barley,wheat and millet.The pathogenesis mechanism of rice blast is still not fully understood.In this study,we characterized the role of the M.oryzae chitinase,MoChil in association with OsMBL1 protein,a Jacalin-related lectin in rice.MoChi1 coded with a GH 18 domain and was proved to be an extracellular endo-chitinase.Deletion of MoChil gene was resulted in reduced growth of mycelia,aerial hyphae and sensitivity to cell wall stress.MoChil deletion mutants were also observed in reducing pathogenicity in rice as inducing the expression of defense-related genes of rice,indicating that MoChil may suppress host immunity to facilitate the infection.Based on in vitro interaction assay in previous study,we further proved that MoChi1 protein was associated with OsMBL1 in vivo by using co-immunoprecipitation and BiFC assays.OsMBL1 encodes a rice Jacalin-like lectin domain.Thirty of genes containing Jacalin-like domain(PF01419.1)were predicted in rice genome.By using RNAseq,it was observed that more than half of rice Jacalin-like genes were strongly induced following M.oyzae infection.OsMBLl along with other seven genes were specifically accumulated at early infectious stage.The realtime PCR showed OsMBL1 gene was induced by plant hormones,PAMPs and M.oryzae,suggesting OsMBL1 gene may have a role in rice immunity.The elevated expression levels of OsMBL1 gene led to activate the expression of defense-related genes and enhance rice resistance to both rice blast and sheath blight.Furthermore,OsMBL1 was localized onto plasma membrane and exhibited the affinity toward to chitin.The competitive binding assay showed that MoChi1 and OsMBL1 proteins inhibit each other in binding chitin.Substitution on C-terminal carbohydrate-binding sites of OsMBL1 protein indicated the recognition of chitin or MoChi1 was independent on these sites.In addition,we found OsMBL1,SalT and Orysata proteins were encoded by the same gene Os01924710 by using multiple alignments,Dotplot and Blast 2 ananlysis.Taken together,we propose that MoChil protein may hijack and degrade chitin to prevent it being recognized by OsMBL1,thereby establishing full pathogenicity.In return,increasing amount of OsMBL1 proteins accumulated on cell membrane then to perceive chitin and initiate chitin-mediated defense.Defense signaling of the host and interference with host signaling by the pathogen help determine the outcome of the interaction.OsMBL1 and MoChil protein may provide one level of cross-talk between the host and pathogen.