Cloning, sequencing and fuctional study of gacA gene from Xanthomonas oryzae pv. oryzicola

Abstract:

A gacA homologue, designated gacA_Xooc, was cloned from Xanthomonas oryzae pv. oryzicola (Xooc), a bacterium that causes leaf streak of rice, with degenerated primers by polymerase amplification reaction (PCR). NCBI blast search indicated that GacA_Xooc had a similar structure to that of other GacA proteins, and had a CheB（Chemotaxis response regulator containing a CheY-like receiver domain）domain. Sequence comparison showed that the gacA_Xooc was conserved in the Xanthomonas genus. Homology search revealed that the gacA_Xooc was 99.7% similarities to gacA（AY870457, this lab）of Xanthomonas oryzae pv. oryzae (Xoo). A gacA_Xooc disruption mutant was successfully generated by a single cross-over event, and confirmed by PCR and Southern blot. But the mutant still had strong pathogenicity，and its virulence was not obviously different from that of wild type strain. The gacA did not globally regulate metabolism in Xooc, which was different from DC3000 of P. syringae pv. tomato, CHA0 of P. fluorescens and IC1270 of Serratia plymuthica. Chemotaxis to 0.1% tryptone of the mutants was reduced compared to wild type strain. The results suggest that gacA_Xooc is involved chemotaxis of Xooc. Nevertheless, how gacA to regulate chemotaxis of Xooc, transcription and expression of genes involved in regulation still need to be further studied.