Primary Research Of Regulatory Mechanism Of The GntR-like Transcriptional Regulator GtrA In Sinorhizobium Meliloti Rm1021

Our previous researches show the mutant gtrA1, constructed by mutangenizing gtrA gene in Sinorhizobium Meliloti Rm1021, has defect phenotypes in free-living and symbiotic condition. In this paper,we reported the preliminary results of the regulatory mechanism of the GntR-like transcription regulator GtrA.Bioinformatics analysis showed that GtrA has 64% identity to MatR from Rhizobium leguminosarum bv. Trifolii. Four consecutive genes upstream of gtrA gene are SMa0157,SMa0155,SMa0151and SMa0150,whose orthologues were found from other bacteria. SMa0151and SMa0150 has highly identity to MatA(60%) and MatB(67%) from Rhizobium leguminosarum bv. Trifolii, respectively. SMa0157 and SMa0151 has the identity to TRAP transporters DctP(23%) and DctM(31%) from Rhodobacter capsulatus. In R.trifolii, matABC operon participates in malonate metabolism, and regulated by GntR transcription regulator MatR. We designated these four genes upstream of gtrA as matP(SMa0157), matQ(SMa0157), matMA(SMa0157), and matB(SMa0157).We speculated that matPQMAB may form an operon involved in malonate transportation and utilization, and regulated by GtrA in Sinorhizobium Meliloti Rm1021.In order to confirm this hypothesis, we first fused the predicted matPQMAB promoter to lacZ reporter gene, and then assayed theβ-galactosidase activity in the wildtype Rm1021 and mutant gtrA1 background in free-living and symbiotic condition. The results showed that matP could be induced to express in free-living and symbiotic condition, and malonate as an inducer. The mutants of matP,matQ,matMA and matB can not grow in M9 minimum mediun with sodium malonate as a sole carbon source, but the wild type Rm1021 can grow. These results show that matPQMAB is involved in malonate metabolism, and is one and only pathways in Sinorhizobium melilote Rm1021.