Biological Sciences Department, Dartmouth College, Hanover, NH, USA.
Mol Plant Microbe Interact. 2012 Jan;25(1):119-28. doi: 10.1094/MPMI-07-11-0188.
Alternative sigma (σ) factors, proteins that recruit RNA polymerase core enzyme to target promoters, are one mechanism by which bacteria transcriptionally regulate groups of genes in response to environmental stimuli. A class of σ(70) proteins, termed extracytoplasmic function (ECF) σ factors, are involved in cellular processes such as bacterial stress responses and virulence. Here, we describe an ECF16 σ factor, EcfS (Blr4928) from the gram-negative soil bacterium Bradyrhizobium japonicum USDA110, that plays a critical role in the establishment of a functional symbiosis with soybean. Nonpolar insertional mutants of ecfS form immature nodules that do not fix nitrogen, a defect that can be successfully complemented by expression of ecfS. Overexpression of the cocistronic gene, tmrS (blr4929), phenocopies the ecfS mutant in planta and, therefore, we propose that TmrS is a negative regulator of EcfS, a determination consistent with the prediction that it encodes an anti-σ factor. Microarray analysis of the ecfS mutant and tmrS overexpressor was used to identify 40 transcripts misregulated in both strains. These transcripts primarily encode proteins of unknown and transport-related functions and may provide insights into the symbiotic defect in these strains.
替代 sigma（σ）因子是一种能够招募 RNA 聚合酶核心酶到靶启动子的蛋白质，是细菌在应对环境刺激时转录调控基因群的一种机制。一类 σ(70) 蛋白，称为细胞外功能（ECF）σ 因子，参与细胞过程，如细菌应激反应和毒力。在这里，我们描述了一种来自革兰氏阴性土壤细菌根瘤菌（Bradyrhizobium japonicum）USDA110 的 ECF16 σ 因子 EcfS（Blr4928），它在与大豆建立功能性共生关系中起着关键作用。ecfS 的非极性插入突变体形成不成熟的根瘤，不能固定氮，这一缺陷可以通过表达 ecfS 成功补偿。tmrS（blr4929）的共转录基因的过表达在植物体内模拟了 ecfS 突变体，因此，我们提出 TmrS 是 EcfS 的负调控因子，这一结论与它编码反 σ 因子的预测一致。对 ecfS 突变体和 tmrS 过表达菌株的微阵列分析用于鉴定在两种菌株中都失调的 40 个转录本。这些转录本主要编码未知和运输相关功能的蛋白质，可能为这些菌株的共生缺陷提供见解。
