Mutation Analysis On The Main Putative Pathogenetic System Genes In Xanthomonas Oryzae Pathovar Oryzicola Strain GX01

Xanthomonas oryzae pv. oryzicola, the causal agent of Bacterial leaf streak (BLS), is belong to y-Proteus xanthomonas that infects rice. Xoc enters into the plant via stomata or wound, and multiplies in mesophyll tissue. Depending on the rice cultivar and climate condition, the loss in rice production caused by BLS can attain20%-50%. In some cases, the pathogen on infected leaves could be spread all over the field by wind and rain. In this work, studies have been focused on the candidate virulence-related genes in a quasi-fully sequenced Xoc strain GX01.Based on the known pathogenic system of Xcc8004,15genes of GX01, including genes encoding HrcC and HrcV, which are parts of the injectisome of type â…¢ secretion system (XOC4122, XOC4132); gene encoding protein involved in secretion via type â…¡ section system (XOC3508); five genes encoding extracellular protease (XOC0172, XOC1023, XOC1545, XOC2796, XOC3520); a extracellular polysaccharide secretion-related gene (XOC1701); genes encoding the RpfG/RpfC two component regulatory system (XOC2054and XOC2055); gene encoding c-di-GMP phosphodiesterase A(XOC2153); gene encoding RsmA (which is also referred as CsrA)(XOC2555); gene encoding a virulence regulator (XOC3268) were selected for functional analysis. Mutagenesis by homologous recombination was carried out for all the genes listed above. The phenotyping revealed that twelve mutants exhibit reduced virulence on susceptible rice culfivar Nippontare, mutants NK1701, NK2054, NK3508, NK4122, NK2555had almost completely lost their virulence. NK4132, NK1545, NK2796, NK3268, NK2055, NK2063, NK2153had found that its full virulence. These results indicated that twelve of the putative pathogenic genes are essential for the virulence of Xoc (pathogenic analysis of the mutants affected genes XOC0172, XOC1023and XOC3520are still in progress). Genes XOC1545and XOC3508showed that the mutant had almost lost the ability to extracellular protease; NK2153and NK4132had showed that significantly lower extracellular protease activity; mutants NK1701and NK2054produced significantly smaller the extracellular endoglucanase, however, NK1701and NK2054produced significantly higher extracellular protease activity; NK2055, NK2063, NK3508produced smaller the extracellular endoglucanase; In addition, NK1545, NK1701, NK2054, NK2055, K2153, NK2796, NK3508, NK4122had showed very significantly smaller motility in the extreme, and NK2063, NK3268, NK4132had showed significantly smaller motility.Mutant NK1545showed dramatically reduced extracellular protease activity compared to the mutants affected in other extracellular protease-encoding genes, and the phenotypes of mutant NK1545can be fully restored by complementation. Previous studies showed that Xcc8004requires an extracellular protease PrtA for its full virulence, however, any of extracellular protease-encoding genes homologous of prtAXoc. Instead, XOC1545was found to be responsible for the major extracellular protease activity of Xoc and its full virulence.