Abstract: [Objective] Poplar bacterial canker caused by Lonsdalea quercina subsp. populi is a disease, which is serious harm to poplar industry. In this study, the biological function of the LqHK1 gene in L. quercina subsp. populi was investigated to provide viable knowledge for further understanding the pathogenic mechanism of pathogen.[Method] The bioinformatics method was used to indentify the two component systems LqHK1. The gene deletion mutant strain △LqHK1 was constructed by homologous recombination. Verifying PCR and Southern blot were used to investigate the biological characteristics of the mutant strains and their complementary strains,such as growth rate, motility, biofilm formation, and pathogenicity. At the same time, qRT-PCR was used to test the expression levels of the motility related genes flgB, flgC, flgE, and quantitatively analyze DNA content of poplar tissue pathogen in the vaccination site after pathogen inoculation.[Result] The two-component system gene LqHK1 was identified and the deletion mutant △LqHK1 had been obtained by homologous recombination. Phenotypic analysis showed that pathogenicity test on annual poplar branches was significantly less virulent than wide-type, while the complemented mutant HB LqHK1 restored the virulence to the wild-type level.The mutant had significantly less colonization in host than the wild type strain. Mutant strain had reduced swimming ability compared with the wild-type. The motility related genes flgB, flgC, flgE expression significantly decreased in mutant; forming ability LqHK1 mutant biofilms significantly decreased, but the growth rate of LqHK1 mutant strains had no significant difference from wild type.[Conclusion] Studies indicate that the bacterial poplar canker Lonsdalea quercina subsp.populi two-component signal transduction system LqHK1 gene is closely related to pathogenpathogenicity.

Key words: Lonsdalea quercina subsp.populi, two component system, pathogenicity