مشخصات پژوهش

The redox regulation has shown to be important for symbiosis efficiency. This implies that the activity of bacterial transcriptional regulators may be modulated by ROS/RNS to regulate the expression of gene(s) involved in response to changes in redox environment. Our objective was to identify the mechanism (s) by which a transcriptional regulator of S. meliloti, Sma2020, likely acts in redox regulation during symbiosis. The role of various ROS/RNS on the activity of Sma2020 was investigated. Firstly, we identified targets of the Sma2020 by comparing the expression of genes located in close vicinity of Sma2020 gene, by RT-qPCR, in wild type and mutant backgrounds. Secondly, we quantified the expression of target genes in cultures treated with different ROS/RNS. The expression of Sma2020 target gene, Sma2023, was up-regulated in bacteria treated with H2O2, Tert-butyl or NaOCl. The inactivation of Sma2020 did not affect symbiosis and nitrogen fixation, suggesting that there is an additional enzymatic activity in this strain. Both Sma2020 and Sma2023 are expressed in nodules that indicate they are involved in nitrogen fixation. In accordance to the in silico analyses, electrophoretic mobility shift (gel retardation) assay using purified Sma2020 and intergenic space fragment between the genes Sma2020 and Sma2023 showed that Sma2020 binds specifically to two palindrome regions in the intergenic region. In addition to, the oxidation increased the dimerization of Sma2020, which in turn prevented Sma2020 from binding to the promoter regions, which was reversed by addition of a reducing agent, DTT. Accordingly, the study of redox signaling helps to get better understanding how bacteria behave when modulated by ROS / RNS production during coexistence or pathogenesis. This research will generally lead to a better understanding of the mechanisms by which a host plant or animal can control its bacterial population.