Functional Identification Of β-glycosidase Genes In Rice Resistance To Bacterial Leaf Streak And Bacterial Blight

Rice(Oryza sativa)is one of the major subsistence crops widely cultivated.Bacterial leaf streak(BLS)of rice caused by Xanthomonas oryzae pv.oryzicola(Xoc),and rice bacterial blight(BB)caused by X.oryzae pv.oryzae(Xoo),are two important bacterial diseases of rice,occurring both at home and abroad and resulting in loss of production.At present,only two major disease resistance genes and multiple quantitative resistance loci confer resistance to BLS,and 41 resistance genes against BB have been found.Harnessing host resistance through crop breeding offers a more effective and reliable way to combat these two diseases.Genes coding β-glycosidase are ubiquitous in various plant species and has important functions.It is reported that these genes in Arabidopsis,maize,barley and other plants not only participate in their growth and morphogenesis,but also in response to biotic and abiotic stresses.The research of the β-glucosidase genes in rice mainly focuses on the structural analysis and substrate investigation of expression products in vitro.However,little is known about function of these genes in plants.When damaged by insects or microorganisms,plant cells release β-glucosidase hydrolyzing to produce phytoalexin.In this study,the phylogenetic tree analysis of the β-glucosidase in rice showed that the β-glucosidase of rice was not clustered together,but scattered among the three branches.Most β-glycosidase genes are induced by biotic or abiotic stress,indicating that it plays an important role in the stress response,such as AtBGLU23 of Arabidopsis thaliana and VvBG1 of grapes.To investigate the expression changes of β-glycosidase genes in response to the Xoc,the time course experiment was performed for rice leaves.Amongst them,large number of the β-glucosidase genes was induced by pathogenic bacteria significantly.The expression of OsBglu12,Osbglu13 and OsBglu23 maintains high level during RS105 invasion.The T-DNA insertion mutants of OsBglu12 and OsBglu13 were observed to be more-sensitive to Xoc in comparison to the wild type plants.Contrary to mutants inoculated Xoc,whether overexpressing OsBglu12 or OsBglu13 conferring resistance to Xoc.All above experimental results indicate that OsBglu12 and OsBglu13 regulate the resistance of rice to Xoc positively.Besides,we found knockdown OsBglu12 blocked disease to Xoc resistance mediated by MeJA.And,OsBglu13-mediated resistance to Xoc related to gibberellin signaling pathways.To explore whether these two genes are involved in rice-Xoo interaction,interestingly,we found that transcriptional level of both genes was inhibited at 24 hours after Xoo inoculation,speculating whether OsBglu12 and OsBglu13 regulate BB different from BLS.The inoculation results displayed that OsBglu12 and OsBglu13 negatively regulated rice resistance to bacterial blight.In addition to exploring OsBglu12 and OsBglu13,we analyzed the protein sequences of OsBglu19 and OsBglu23 which induced by RS105,and found that these two genes also regulate rice resistance to Xoc,which was related to the expression of diseases resistance-related genes.This study demonstrated that rice β-glucosidase genes respond to biotic stress.Four β-glycosidase genes OsBglu12,OsBglu13,OsBglu19 and OsBglu23 were found to regulate rice disease resistance,providing materials for rice disease resistance breeding.