University of Calgary, Department of Biological Sciences, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada.
Microbiology (Reading). 2010 Jun;156(Pt 6):1673-1685. doi: 10.1099/mic.0.035386-0. Epub 2010 Mar 4.
In this paper, we describe the regulatory roles of VisN, VisR and Rem in the expression of flagellar, motility and chemotaxis genes in Rhizobium leguminosarum biovar viciae strains VF39SM and 3841. Individual mutations in the genes encoding these proteins resulted in a loss of motility and an absence of flagella, indicating that these regulatory genes are essential for flagellar synthesis and function. Transcriptional experiments involving gusA-gene fusions in wild-type and mutant backgrounds were performed to identify the genes under VisN/R and Rem regulation. Results showed that the chemotaxis and motility genes of R. leguminosarum could be separated into two groups: one group under VisN/R-Rem regulation and another group that is independent of this regulation. VisN and VisR regulate the expression of rem, while Rem positively regulates the expression of flaA, flaB, flaC, flaD, motA, motB, che1 and mcpD. All of these genes except mcpD are located within the main motility and chemotaxis gene cluster of R. leguminosarum. Other chemotaxis and motility genes, which are found outside of the main motility gene cluster (che2 operon, flaH for VF39SM, and flaG) or are plasmid-borne (flaE and mcpC), are not part of the VisN/R-Rem regulatory cascade. In addition, all genes exhibited the same regulation pattern in 3841 and in VF39SM, except flaE and flaH. flaE is not regulated by VisN/R-Rem in 3841 but it is repressed by Rem in VF39SM. flaH is under VisN/R-Rem regulation in 3841, but not in VF39SM. A kinetics experiment demonstrated that a subset of the flagellar genes is continuously expressed in all growth phases, indicating the importance of continuous motility for R. leguminosarum under free-living conditions. On the other hand, motility is repressed under symbiotic conditions. Nodulation experiments showed that the transcriptional activators VisN and Rem are dramatically downregulated in the nodules, suggesting that the symbiotic downregulation of motility-related genes could be mediated by repressing the expression of VisN/R and Rem.
在本文中，我们描述了 VisN、VisR 和 Rem 在根瘤菌属生物变种 viciae 菌株 VF39SM 和 3841 中鞭毛、运动和趋化性基因表达中的调控作用。这些蛋白编码基因的单个突变导致运动性丧失和鞭毛缺失，表明这些调控基因是鞭毛合成和功能所必需的。在野生型和突变体背景下进行了涉及 gusA 基因融合的转录实验，以鉴定 VisN/R 和 Rem 调控的基因。结果表明，根瘤菌的趋化性和运动性基因可分为两组：一组受 VisN/R-Rem 调控，另一组不受此调控。VisN 和 VisR 调节 rem 的表达，而 Rem 正向调节 flaA、flaB、flaC、flaD、motA、motB、che1 和 mcpD 的表达。除了 mcpD 之外，这些基因都位于根瘤菌主要的运动和趋化性基因簇内。其他位于主要运动基因簇之外的趋化性和运动性基因（VF39SM 的 che2 操纵子、flaH 和质粒携带的 flaE 和 mcpC）不属于 VisN/R-Rem 调控级联。此外，除了 flaE 和 flaH，所有基因在 3841 和 VF39SM 中表现出相同的调控模式。flaE 在 3841 中不受 VisN/R-Rem 调控，但在 VF39SM 中受 Rem 抑制。flaH 在 3841 中受 VisN/R-Rem 调控，但在 VF39SM 中不受调控。动力学实验表明，一组鞭毛基因在所有生长阶段持续表达，这表明在自由生活条件下，根瘤菌连续运动的重要性。另一方面，在共生条件下运动受到抑制。结瘤实验表明，转录激活因子 VisN 和 Rem 在根瘤中显著下调，这表明运动相关基因的共生下调可能是通过抑制 VisN/R 和 Rem 的表达来介导的。
