Wang Yi, Chen Ai-Min, Yu Ai-Yuan, Luo Li, Yu Guan-Qian, Zhu Jia-Bi, Wang Yan-Zhang
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.
J Microbiol. 2008 Apr;46(2):137-45. doi: 10.1007/s12275-007-0145-0. Epub 2008 Jun 11.
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.
GntR 型转录调节因子参与细菌中各种生物学过程的调控，但对其在苜蓿中华根瘤菌中的功能了解甚少。在此，我们从苜蓿中华根瘤菌 1021 菌株中鉴定出两个 GntR 型转录调节因子基因，gtrA 和 gtrB。与野生型菌株相比，gtrA1 突变体和 gtrB1 突变体在丰富培养基和基本培养基上的生长速率和最大细胞产量均较低，在游动平板上的细胞运动性也较低。这两个突变体在共生方面也存在缺陷。接种野生型菌株 1021 的苜蓿植株在主根上形成粉红色细长根瘤。相比之下，接种 gtrA1 和 gtrB1 突变体的植株主要在侧根上形成相对较小、圆形、浅粉红色的根瘤。在接种后的大约前 3 至 4 周内，接种 gtrA1 和 gtrB1 突变体的植株明显生长受阻，固氮酶活性水平较低，但与接种野生型菌株的植株相比，根瘤数量显著增加。此外，gtrA1 和 gtrB1 突变体不仅结瘤延迟，而且结瘤竞争能力明显降低。这些结果表明，GtrA 和 GtrB 都影响苜蓿中华根瘤菌的细胞生长和有效共生。我们的工作为 GntR 样转录调节因子的功能提供了新的见解。
