The Virulence Function and Regulation of the Metalloprotease Gene <i>prtA</i> in the Plant-Pathogenic Bacterium <i>Burkholderia glumae</i>

Abstract

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