Department of Genetics, School of Biological Sciences, Madurai Kamaraj University, Madurai, India.
VIT Bhopal University, Sahore, India.
Biochim Biophys Acta Gene Regul Mech. 2021 Nov-Dec;1864(11-12):194763. doi: 10.1016/j.bbagrm.2021.194763. Epub 2021 Sep 14.
Two-component systems (TCS) are one of the signal transduction mechanisms, which sense physiological/biological restraints and respond to changing environmental conditions by regulating the gene expression. Previously, by employing a forward genetic screen (INSeq), we identified that cbrA gene is essential for the fitness of Pseudomonas aeruginosa PGPR2 during root colonization. Here, we report the functional characterization of cbrAB TCS in PGPR2 during root colonization. We constructed insertion mutants in cbrA and its cognate response regulator cbrB. Genetic characterization revealed drastic down-regultion of sRNA crcZ gene in both mutant strains which play a critical role in carbon catabolite repression (CCR). The mutant strains displayed 10-fold decreased root colonization efficiency when compared to the wild-type strain. On the other hand, mutant strains formed higher biofilm on the abiotic surface, and the expression of pelB and pslA genes involved in biofilm matrix formation was up-regulated. In contrast, the expression of algD, responsible for alginate production, and its associated sigma factor algU was significantly down-regulated in mutant strains. We further analyzed the transcript levels of rsmA, controlled by the algU sigma factor, and found that the expression of rsmA was hampered in both mutants. The ability of mutant strains to swim and swarm was significantly hindered. Also, the expression of genes associated with type III secretion system (T3SS) was dysregulated in mutant strains. Taken together, regulation of gene expression by CbrAB TCS is intricate, and we confirm its role beyond carbon and nitrogen assimilation.
双组份系统（TCS）是一种信号转导机制，可感知生理/生物学限制，并通过调节基因表达对不断变化的环境条件做出反应。此前，我们通过正向遗传筛选（INSeq）发现，cbrA 基因是铜绿假单胞菌 PGPR2 定植根际时适应能力所必需的。在这里，我们报告了 cbrAB TCS 在 PGPR2 定植根际过程中的功能特征。我们构建了 cbrA 和其同源响应调节剂 cbrB 的插入突变体。遗传特征表明，两个突变株中 crcZ 小 RNA 的表达水平急剧下调，crcZ 基因在碳源分解代谢阻遏（CCR）中起着关键作用。与野生型菌株相比，突变株的根际定植效率降低了 10 倍。另一方面，突变株在非生物表面上形成了更高的生物膜，并且与生物膜基质形成有关的 pelB 和 pslA 基因的表达上调。相反，algD 基因（负责产生海藻酸盐）及其相关的 sigma 因子 algU 的表达在突变株中显著下调。我们进一步分析了 algU sigma 因子控制的 rsmA 的转录水平，并发现两个突变株中的 rsmA 表达都受到阻碍。突变株的游泳和群集能力受到严重阻碍。此外，突变株中与 III 型分泌系统（T3SS）相关的基因的表达也失调。综上所述，CbrAB TCS 对基因表达的调控错综复杂，我们证实了它在碳氮同化之外的作用。
