Abstract:

RsmA is a highly conservative global regulator in Pseudomonas, which could affect mRNA stability or control the translation of the target gene, and then to affect protine expression by combining mRNA of the target gene. In nitrogen-fixing Pseudomonas stutzeri A1501, there were one rsmA homologus gene and one non\|coding small RNA gene rsmZ that might regulate RsmA activity. The evolution of RsmA and RsmZ in A1501 and conducted additional studies on their expression indicated that RsmA of A1501 shared 98% genetic similarity with RsmA of Pseudomonas aeruginosa PAO1 and RsmZ contained 4 RsmA binding sites. The real\|time PCR results showed that the rsmA transcription level was high in early growing period and drops down in the exponential growing and stable phases. The expression of rsmZ did not change significantly during the whole growing period. Under carbon starvation conditions,  rsmA and rsmZ genes showed a significantly reduced level of transcription. The mutation of rpoS did not affect rsmA expression; however, rsmZ transcription was enhanced by 30\|fold, indicating that rsmZ was negatively regulated by rpoS. Further study indicated that there were no changes in the expression of rsmA and rsmZ in gacA mutant. Based on the above experiments, the regulatory model of rsmA and rsmZ in A1501 was different from other Pseudomonas, such as Pseudomonas fluorescens CHAO and Pseudomonas aeruginosa PAO1. This paper has laid a theoretical foundation for further studying rsmA function and its regulatory mechanism under spesific condition.

Key words: Pseudomonas stutzeri A1501, nitrogen fixation, rsmA, rsmZ, transcriptional regulation

摘要：

RsmA是假单胞菌属高度保守的全局性调控因子，该蛋白可通过与靶基因的mRNA结合影响其稳定性或者抑制靶基因的翻译影响蛋白表达。固氮施氏假单胞菌A1501中发现一个rsmA同源基因及一个可能参与rsmA活性调节的非编码小RNA rsmZ基因。对A1501菌中RsmA及RsmZ的分子进化及表达特性进行了研究。分析结果表明，RsmA与铜绿假单胞菌同源性可达98%，RsmZ具有4个RsmA的结合位点。实时定量RT\|PCR结果显示，rsmA在生长初期具有高表达量，而在指数生长期以及平台稳定期表达量下降。非编码RNA rsmZ的转录水平在整个生长时期未发生显著变化。在碳匮乏条件下，rsmA和rsmZ的表达量都显著下调。在一般胁迫σ因子rpoS突变株中，rsmA的表达未受影响，但rsmZ表达上调了30多倍，说明rsmZ的表达受rpoS的负调控。进一步发现，A1501菌中，rsmA和rsmZ的转录不受转录调控因子gacA突变的影响，这与荧光假单胞菌CHAO和铜绿假单胞菌PAO1的调控模式区别，表明RsmA的转录调控模式在固氮施氏假单胞菌A1501中有其独特性。该结果为进一步探索固氮施氏假单胞中RsmA的功能及其特定条件下的调控机制奠定了理论基础。

关键词: 施氏假单胞菌A1501；生物固氮；rsmA；rsmZ；转录调控