The Fuction Of Transcriptional Regulators Belonging To GntR Family In Sinorhizobium Meliloti Rm1021

Sinorhizobium meliloti Rm1021, whose genome has been sequenced in 2001, is the model bacterium to study the relationship between Rhizobium and legume.GntR family tracriptional regulators are the second tracriptional regulator family in Rm1021. GntR-type tracriptional regulators are ubiquitous in prokaryota , regulating various important metabolism pathways.Thay are essential to the growth and development of the cell. Some GntR-type tracriptional regulators in other bacterium have been well known, but still remain dark in S.meliloti Rm1021. In order to shed light on the fuction of GntR-type tracriptional regulators in S.meliloti Rm1021., we analysed the genome sequence . 55 putative GntR-type tracriptional regulators were identified. According to amino acid identity,these transcriptional regulators were classified into 4 subamilies .All gntR genes were mutagenized using plasmid insertion and examined the free-living and symbiotic phenotyes .On symbiotic phenotypes, all 55 gntR mutant can induce effective nodules in the roots of alfafa, and the inoculated plants appeared to growth normally. Whether these mutants show differences in nodulation competition and nodulation kinetics with wild-type strain needs to be further studied.On free-living phenotypes, all these mutants appear no differnce in exopolysaccharide with wild-type strain. In the case of swarming ability, two mutants gtrA1 and gtrB1 swarm slower than the wild type,and their maximal cell yield decrease in stationary phase.Further studies indicated that they can infect plant and form nodules normally,but the nitrogenase activity reduced slightly and decreased greatly in nodulation competition compared with wild type .The regulatory mechanism of GtrA and GtrB will be further investigated..