The Effects Of Amino Acid Biosynthesis On The Virulence Of Xanthomonas Oryzae Pv.oryzae

Xanthomonas oryzae pv.oryzae(Xoo)is the causal agent of rice bacterial blight disease,which causes a large reduction in rice production.The successful interaction of pathogens and plants requires a particular nutrient environment that allows pathogen growth and the initiation of both pathogen and host responses.Many findings suggest that amino acid synthesis is important for bacteria and fungi to successfully infect hosts.However,the roles of most amino acids in the Xoo–rice interaction remain unclear.In this study,genes encoding key enzymes for amino acid biosynthesis(leu B,leu C,leu D,ilv C,thr C,his D,trp C,arg H,met B and asp C)were screened according to the KEGG biosynthesis pathway,and these genes were systematically deleted.Then we tested the growth of wild-type and related amino acid deletion mutants on M4 N plates containing different concentrations of the corresponding amino acids.The results showed that leu B,thr C,his D,trp C,arg H and met B are essential for the synthesis of the corresponding amino acids.We analyzed the effects of these mutations on Xoo virulence.Our results showed that leucine,isoleucine,valine,threonine,histidine,tryptophan,arginine and cysteine syntheses are essential to Xoo infection.Then,we detected the growth of the Xoo strains in media supplemented with raw amino acids extracts from rice leaves.Our results illustrate that free amino acids in rice leaves tightly influence Xoo growth.Growth curve data showed that leucine and arginine auxotrophic strains had slower growth than wild type strain even at high amino acid concentrations,which may be the reason that these auxotrophic strains had a worse inflectional ability compared with that of the wild-type strain.As some amino acids can function as nutrients as well as regulatory molecules in higher organisms,we further studied the role of leucine in the interaction between pathogens and hosts.Results of RNA-Seq,q PCR and promoter activity assays suggest that leucine can regulate the expression of genes involved in chemotaxis and type VI secretion system,and crosstalk with the biosynthesis pathways of other amino acids.Our findings highlight that amino acids not only act as nutrients for bacterial growth but also play essential roles in the Xoo-rice interaction.The study may deepen our understanding of the interaction between pathogenic bacteria and rice,and provide more new ideas for the prevention and control of rice diseases.