Virulence Reduction and Differing Regulation of Virulence Genes in rpf Mutants of Xanthomonas oryzae pv. oryzae

Abstract

To define the functions of the rpf genes in Xanthomonas oryzae pv. oryzae (Xoo), which regulates pathogenicity factors in Xanthomonas campestris pv. campestris (Xcc), marker-exchange mutants of each rpf gene were generated. When the mutants were inoculated on a susceptible cultivar, the lesion lengths caused by the rpfB, rpfC, rpfF, and rpfG mutants were significantly smaller than those caused by the wild type, whereas those caused by the rpfA, rpfD, and rpfI mutants were not. Several virulence determinants, including extracellular polysaccharide (EPS) production, xylanase production, and motility, were significantly decreased in the four mutants. However, the cellulase activity in the mutants was unchanged. Complementation of the rpfB and rpfC mutations restored the virulence and the expression of the virulence determinants. Expression analysis of 14 virulence genes revealed that the expression of genes related to EPS production (gumG and gumM), LPS (xanA, xanB, wxoD, and wxoC), phytase (phyA), xylanase (xynB), lipase (lipA), and motility (pitA) were reduced significantly in the mutants rpfB, rpfC, rpfF, and rpfG. In contrast, the expression of genes related to cellulase (eglxob, clsA), cellobiosidase (cbsA), and iron metabolism (fur) was unchanged. The results of this study clearly show that rpfB, rpfC, rpfF, and rpfG are important for the virulence of Xoo KACC10859, and that virulence genes are regulated differently by the Rpfs.