The GntR-type regulators gtrA and gtrB affect cell growth and nodulation of Sinorhizobium meliloti.
GntR-type transcriptional regulators are involved in the regulation of various biological processes in bacteria, but little is known about their functions in Sinorhizobium meliloti. Here, we identified two GntR-type transcriptional regulator genes, gtrA and gtrB, from S. meliloti strain 1021. Both the gtrA1 mutant and the gtrB1 mutant had lower growth rates and maximal cell yields on rich and minimal media, as well as lower cell motility on swimming plates, than did the wild-type strain. Both mutants were also symbiotically deficient. Alfalfa plants inoculated with wild-type strain 1021 formed pink elongated nodules on primary roots. In contrast, the plants inoculated with the gtrA1 and gtrB1 mutants formed relatively smaller, round, light pink nodules mainly on lateral roots. During the first 3 approximately 4 weeks post-inoculation, the plants inoculated with the gtrA1 and gtrB1 mutants were apparently stunted, with lower levels of nitrogenase activity, but there was a remarkable increase in the number of nodules compared to those inoculated with the wild-type strain. Moreover, the gtrA1 and gtrB1 mutants not only showed delayed nodulation, but also showed markedly reduced nodulation competition. These results demonstrated that both GtrA and GtrB affect cell growth and effective symbiosis of S. meliloti. Our work provides new insight into the functions of GntR-like transcriptional regulators.
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, P R China.
Yi
Y
Wang
Ai-Min
AM
Chen
Ai-Yuan
AY
Yu
Li
L
Luo
Guan-Qian
GQ
Yu
Jia-Bi
JB
Zhu
Yan-Zhang
YZ
Wang
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D015964:Gene Expression Regulation, Bacterial; D000455:Medicago sativa / Q000382:microbiology; D009154:Mutation; D010641:Phenotype; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D016962:Sinorhizobium meliloti / Q000166:cytology* / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D013559:Symbiosis
D001426:Bacterial Proteins; D012097:Repressor Proteins