Functional Analysis Of Hrp Gene Cluster HrcJ、HrpX And HrpY Genes In Lonsdalea Quercina N-5-1

Poplar bacterial canker caused by Lonsdalea quercina subsp. populi N-5-1 was a disease that was a seriously harm to poplar industry and there is no effective control measures. In order to further clarify the factors associated with the pathogenicity process and provide a theoretical basis for disease control, in this study, we analyzed the function of the hrp gene cluster based on an understanding of Ⅲ secretion system and the function of individual genes measured. The host bioassay of the hrcJ gene was tested on branches of poplar varieties and the function of the hrp gene cluster of the bacterium associated with the regulation of type Ⅲ secretion system was analyzed. At the same time, the culture conditions of bacteria have been optimized. The results are shown below.Culture conditions in vitro study of Ⅰ. quercina N-5-1 showed that 30-34 ℃ is the most suitable growth temperature and 6-7 is the most suitable pH. In order to clarify the function of the hrcJ gene in the pathogenesis of L.quercina N-5-1, the hrcJ gene inserted mutant was constructed by homologous recombination and confirmed by PCR and Southern blot. Pathogenicity test on annual branches indicated that the hrcJ gene mutant was significantly less virulent than wide-type,while the complementary mutant HBhrcJ restored the virulence to the wild-type level. Growth analysis results showed that growth capacity of hrcJ gene mutant had no significant change compared with the wide-type. N-5-1, △hrcJand HBhrcJ were able to form biofilms, and their OD570 were similar. Motility test results showed that the motility of hrcJ gene mutant was decreased by 21 percent compared with that of wide-type.hrpX and hrpY gene mutants of L. quercina N-5-1 were also obtained. The hrpX and hrpY gene mutation of L. quercina N-5-1 have no effect on the growth of L. quercina N-5-1, but motility and the formation of biofilm of the mutants reduced. Pathogenicity tests showed that the disease index of △hrpX and △ hrpY decreased by 52.1%and 75.5%compared with the strain L. quercina N-5-1.The construction of the hrpX and hrpY gene insertion mutants laid a solid basis for understanding the function of adjustment of the hrp gene cluster.