Screening Of Pathogenicity-Ralated Genes And Function Analysis Of LuxR Gene In Acidovorax Avenae Subsp. Citrulli

Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli,is a serious threat to the watermelon and melon industries. Most economic losses due to BFB have been reported in many parts of the world. In recent years, great economic losses have been caused by BFB in Hami melon-producing regions of Xinjiang.But, most studies on this pathogen related to its distribution and detection, whereas few report focused on its pathogenicity. This study primarily explored the pathogenicity-related genes of A. avenae subsp. citrulli.In order to study of pathogenic related gene, transposon mutagenesis was performed in Acidovorax avenae subsp. citrulli strain xjL12 by transposon Mini-Tn5 and a large-scale mutant library was obtained. In this study,3 strains were mutated using transposon Mini-Tn5 to select the mutants defective in their pathogencity on melons and 1 strain was decreased. By using subclone techonology, the transposon insertion in 4 mutants were identified as pathogencity regulatory gene. Subsequently, one of the four genes deletion mutants were constructed by homologue technology, which was defective in their pathogencity on melons.In addition, the fuction of luxR homologue genes were studied,which were the main component of LuxI/LuxR circus in Quorum Sensing (QS) of Gram negative bacteria. luxR (LuxR family transcriptional regulator), acP (3-oxoacyl-(ACP) synthaseⅢ), acD (acyl-CoA dehydrogenase domain-containing protein) were cloned from Acidovorax avenae subsp. citrulli strain xjL12,which were the related genes of Quorum Sensing.ΔluxR mutant was constructed by homologue technology, which was only defective in the pathogencity on melons. In comparison with the wild-type strain, the luxR deletion mutant(ΔluxR) had a significantly reduced ability to form acyl homoserine lactones (AHLs), which are quorum-sensing molecules. Tolerance to antibiotics were enhanced in theΔluxR than that of the wild-type strain.ΔluxR had reduced virulence on melon plants. RT-PCR indicated that LuxR protein regulated to express of the luxl gene.