The Virulence Function and Regulation of the Metalloprotease Gene in the Plant-Pathogenic Bacterium .

Bacterial panicle blight caused by is a major bacterial disease of rice. Our preliminary RNA-seq study showed that a serine metalloprotease gene, , is regulated in a similar manner to the genes for the biosynthesis and transport of toxoflavin, which is a known major virulence factor of . null mutants of the virulent strain 336gr-1 did not show a detectable extracellular protease activity, indicating that is the solely responsible gene for the extracellular protease activity detected from this bacterium. In addition, inoculation of rice panicles with the mutants resulted in a significant reduction of disease severity compared with the wild-type parent strain, suggesting the requirement of for the full virulence of . A double mutant deficient in both serine metalloprotease and toxoflavin (/) exhibited a further numeric but not statistically significant decrease of disease development compared with the strain. Both the driven extracellular protease activity and the toxoflavin production were dependent on both the / quorum-sensing and the global regulatory gene , indicating the important roles of the two global regulatory factors for the bacterial pathogenesis by this pathogen.