Sinorhizobium Meliloti, Sinorhizobium Meliloti, The Function Of The Lysr Family Of Transcription Factors

The development of alfalfa (Medicago sativa) nodules induced by its symbiotic partner, Sinorhizobium meliloti, depends on the timely expression of nodulation genes that are controlled by LysR-type regulators, NodDs. Ninety putative genes coding for LysR-type transcriptional regulators were identified in S. meliloti Rm1021 genome. After all putative lysR genes were mutagenized using plasmid insertions and then examined their phenotypes, two new LysR-type Symbiosis Regulator genes, lsrA and lsrB, were found to be essential for symbiosis. The lsrA mutant is defective in symbiosis and elicited only white nodules that exhibited no nitrogenase activity, and the bacteriods senesced early. The lsrB mutant is deficient in symbiosis and elicited a mixture of pink and white nodules on alfalfa plants, which exhibited lower overall nitrogenase activity than those elicited by wild type strain. Secondly, we identified and characterized the oxyR gene of S. meliloti. The oxyR mutant was more sensitive and less adaptive to H2O2 than the wild type strain. However, the activities of KatA and KatB of oxyR mutant were higher than the parental strain when it grown in the absence of H2O2, indicating that reduced OxyR repressed the expression katA and katB. Third, the six LysR family regulator genes from S.meliloti Rm1021 were designated as LrhA subfamily genes since they showed similar identity (30%) of amino acid sequences, located at one clade of evolutional tree, and shared higher homology with LrhA from E.coli. One of LrhA subfamily genes, espR mutants increased the secretion of unknown extracelluar proteins. In a conclusion, lsrA...