Preliminary Study On Phar Gene Of Xanthomonas Oryzae PV. Oryzae PXO99~A

Xanthomonas oryzae pv.oryzae (Xoo) causes rice bacterial disease, which largely affects rice production. In the genome of Xoo, there is a PhaR gene which encodes a kind of protein associated with PHAs granule. PHAs (polyhydroxyalkanoates) is an intracellular carbon and energy storage material. Under certain conditions, a variety of microorganisms can accumulate PHAs as intracellular carbon and energy storage material. PHAs are more generally found in microorganisms than glycogen, poly phosphoric acid and fatty acids.In this study, a PhaR gene deletion mutant of PXO99was constructed using overlap extention PCR. The biological phenotype and pathogenicity of the mutant was tested.Construct of pMDPhaRF1F2containing flanking fragments of phaR on both ends and kanamycin gene in the center was made by overlap PCR. The constructed plasmid of pMDPhaRF1F2was then electroporated into the cells of PXO99.The transformants grown on kanamycin containing medium plate were selected and patched on ampicilin plate. The colonies with kanamycin resistance and ampicilin sensitivity were selected as phaR knockout mutant, which is named as PXOâ–³PhaR. The phaR knock out mutant was verified by colony PCR.PXOâ–³PhaR is different from the wildtype PXO99on colony morphology, the swimming, growth rate and EPS production have been reduced all. Both PXO99and PXOâ–³PhaR can induce HR on tobacco leaves after infiltration. However, PXOâ–³PhaR has reduced pathogenicity when inoculated on rice.Tobacco HR inducing analysis and determination of pathogenicity of rice showed that, PXOâ–³PhaR have the ability of stimulating HR induction, but the pathogenicity has been weakened. The above results show that the mutation of PhaR gene affects the colony morphology of Xanthomonas and growth rate, and it also affects the pathogenicity. As how does PhaR gene affect the infection of Xoo remains to be further elucitated.