Rachwał Kamila, Matczyńska Ewa, Janczarek Monika
Department of Genetics and Microbiology, Institute of Microbiology and Biotechnology, Maria Curie-Skłodowska University, Akademicka 19, 20-033, Lublin, Poland.
Department of Mathematics and Computer Science, Institute of Computer Science, Jagiellonian University, Łojasiewicza 6, 30-348, Cracow, Poland.
BMC Genomics. 2015 Dec 29;16:1111. doi: 10.1186/s12864-015-2332-4.
Rhizobium leguminosarum bv. trifolii is a soil bacterium capable of establishing a symbiotic relationship with red clover (Trifolium pratense). The presence of surface polysaccharides and other extracellular components as well as motility and competitiveness are essential traits for both adaptation of this bacterium to changing environmental conditions and successful infection of host plant roots. The R. leguminosarum bv. trifolii rosR gene encodes a protein belonging to the family of Ros/MucR transcriptional regulators, which contain a Cys2His2-type zinc-finger motif and are involved in the regulation of exopolysaccharide synthesis in several rhizobial species. Previously, it was established that a mutation in the rosR gene significantly decreased exopolysaccharide synthesis, increased bacterial sensitivity to some stress factors, and negatively affected infection of clover roots.
RNA-Seq analysis performed for the R. leguminosarum bv. trifolii wild-type strain Rt24.2 and its derivative Rt2472 carrying a rosR mutation identified a large number of genes which were differentially expressed in these two backgrounds. A considerable majority of these genes were up-regulated in the mutant (63.22 %), indicating that RosR functions mainly as a repressor. Transcriptome profiling of the rosR mutant revealed a role of this regulator in several cellular processes, including the synthesis of cell-surface components and polysaccharides, motility, and bacterial metabolism. Moreover, it was established that the Rt2472 strain was characterized by a longer generation time and showed an increased aggregation ability, but was impaired in motility as a result of considerably reduced flagellation of its cells.
The comparative transcriptome analysis of R. leguminosarum bv. trifolii wild-type Rt24.2 and the Rt2472 mutant identified a set of genes belonging to the RosR regulon and confirmed the important role of RosR in the regulatory network. The data obtained in this study indicate that this protein affects several cellular processes and plays an important role in bacterial adaptation to environmental conditions.
三叶草根瘤菌（Rhizobium leguminosarum bv. trifolii）是一种能够与红三叶草（Trifolium pratense）建立共生关系的土壤细菌。表面多糖和其他细胞外成分的存在以及运动性和竞争力是该细菌适应不断变化的环境条件和成功感染宿主植物根部的基本特征。三叶草根瘤菌的rosR基因编码一种属于Ros/MucR转录调节因子家族的蛋白质，该家族含有Cys2His2型锌指基序，并参与多种根瘤菌物种中胞外多糖合成的调控。此前已确定，rosR基因的突变显著降低了胞外多糖的合成，增加了细菌对某些应激因素的敏感性，并对三叶草根部的感染产生负面影响。
对三叶草根瘤菌野生型菌株Rt24.2及其携带rosR突变的衍生物Rt2472进行RNA测序分析，鉴定出大量在这两种背景下差异表达的基因。这些基因中的绝大多数在突变体中上调（63.22%），表明RosR主要作为一种阻遏物发挥作用。rosR突变体的转录组分析揭示了该调节因子在几个细胞过程中的作用，包括细胞表面成分和多糖的合成、运动性和细菌代谢。此外，已确定Rt2472菌株的特征是世代时间更长，聚集能力增强，但由于其细胞鞭毛显著减少而运动性受损。
三叶草根瘤菌野生型Rt24.2和Rt2472突变体的比较转录组分析确定了一组属于RosR调控子的基因，并证实了RosR在调控网络中的重要作用。本研究获得的数据表明，这种蛋白质影响几个细胞过程，并在细菌适应环境条件中发挥重要作用。
