水稻细菌性条斑病菌中一个调控致病性的DNA结合蛋白负调控胞外酶活性

原核革兰氏阴性菌稻黄单胞菌稻生致病变种(又称水稻细菌性条斑病菌,Xanthomonas oryzae pv.oryzicola,Xoc)是引起水稻细菌性条斑病的病原物,该病是水稻粮食生产中的严重病害之一.我们的前期工作对广西农科院分离到的Xoc菌株GX01进行基因组序列分析,发现一个编号为gx01_0566的基因可能编...

A DNA-binding protein required for virulence negatively regulates the activity of extracellular enzymes in Xanthomonas oryzae pv. oryzicola

The prokaryotic Gram-negative bacterium Xanthomonas oryzae pv. oryzicola (Xoc) is the causal agent of bacterial leaf streak disease of rice. In our previous work, a scanning of the genome sequence of the Xoc wild type strain GX01 isolated from Guangxi, China, revealed that a gene named gx01_0566 might encode a DNA-binding protein belonging to the Fis family. To facilitate the characterization of gx01_0566, a deletion mutant was constructed by using the suicide vector pK18mobsacB and complemented in trans. Phenotypic analysis revealed that the virulence of the gx01_0566 mutant in the host plant Japonica cultivar Nipponbare was greatly reduced compared with wild-type, while the exopolysaccharide production of the gx01_0566 mutant is comparable to that of the wild-type. Interestingly, activities of the exoenzymes such as the endoglucanase increased greatly in the gx01_0566 mutant strain compared with the wild-type. To further investigate the role of the gx01_0566 gene in regulation of the endoglucanase activity, gx01_0566 protein was overproduced and purified. Electrophoresis mobility shift assays indicated that gx01_0566 protein binds to the promoter of certain endoglucanases-encoding genes such as gx01_0026 and gx01_4282. Furthermore, quantitative real-time PCR revealed that the expression level of several endoglucanase-encoding genes was enhanced greatly in the mutant compared with the wild-type, implying that the gx01_0566 protein represses the expression of these endoglucanases encoding genes via directly binding to their promoters.