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Regulation of cysteine residues in LsrB proteins from Sinorhizobium meliloti under free‐living and symbiotic oxidative stress
Author(s) -
Tang Guirong,
Xing Shenghui,
Wang Sunjun,
Yu Liangliang,
Li Xuan,
Staehelin Christian,
Yang Menghua,
Luo Li
Publication year - 2017
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.13992
Subject(s) - sinorhizobium meliloti , biology , biochemistry , cysteine , mutant , oxidative stress , gene , nitrogen fixation , glutathione , reactive oxygen species , microbiology and biotechnology , genetics , bacteria , enzyme
Summary The development of legume nitrogen‐fixing nodules is regulated by reactive oxygen species (ROS) produced by symbionts. Several regulators from Rhizobium are involved in ROS sensing. In a previous study, we found that Sinorhizobium meliloti LsrB regulates lipopolysaccharide production and is associated with H 2 O 2 accumulation in alfalfa ( Medicago sativa ) nodules. However, its underlying regulatory mechanism remains unclear. Here, we report that the cysteine residues in LsrB are required for adaptation to oxidative stress, gene expression, alfalfa nodulation and nitrogen fixation. Moreover, LsrB directly activated the transcription of lrp3 and gshA (encoding γ‐glutamylcysteine synthetase, responsible for glutathione synthesis) and this regulation required the cysteine (Cys) residues in the LsrB substrate‐binding domain. The Cys residues could sense oxidative stress via the formation of intermolecular disulfide bonds, generating LsrB dimers and LsrB‐DNA complexes. Among the Cys residues, C238 is a positive regulatory site for the induction of downstream genes, whereas C146 and C275 play negative roles in the process. The lsrB mutants with Cys‐to‐Ser substitutions displayed altered phenotypes in respect to their adaptation to oxidative stress, nodulation and nitrogen fixation‐related plant growth. Our findings demonstrate that S. meliloti LsrB modulates alfalfa nodule development by directly regulating downstream gene expression via a post‐translational strategy.