An orphan response regulator Sll0649 involved in cadmium tolerance and metal homeostasis in photosynthetic Synechocystis sp. PCC 6803.
Photosynthetic cyanobacteria are sensitive to toxicity of metal cadmium (Cd(2+)). Although metabolic responses against Cd(2+) exposure have been described, the related regulatory mechanism is still unclear in cyanobacteria. In this study, we identified in Synechocystis sp. PCC 6803 a response regulator (RR)-encoding gene sll0649, whose mutant was more sensitive to Cd(2+) stress. Further phenotypic analysis revealed that ∆sll0649 becomes more sensitive to Cu(2+), Fe(2+), Mn(2+) and Zn(2+) stress as well. Using a quantitative iTRAQ-LC-MS/MS proteomics approach, we showed that a total of 156 and 151 unique proteins were down- and up-regulated for at least 2-fold in the ∆sll0649 mutant grown under Cd(2+) stress, respectively. In addition, electrophoretic mobility shift assays showed that Sll0649 was able to bind directly to the upstream regions of sll1598 and slr0798, which encode an Mn(2+) transporter MntC and a Zn(2+) transporting P-type ATPases ZiaA, respectively, suggesting that Sll0649 was involved in Cd(2+) tolerance by regulating and maintaining intracellular metal homeostasis. The involvement of sll1598 and slr0798 genes in Cd(2+) tolerance was also verified by comparative mutant analyses. The study provided a proteomic description of the Cd(2+) response network mediated by the response regulator Sll0649, and revealed novel insights on the metal-tolerance mechanism in Synechocystis.


CONCLUSIONS
As a major pollutant on earth, Cd(2+) is toxic to both prokaryotic and eukaryotic organisms. It is thus important to obtain a better understanding of cellular response to Cd(2+) and the related regulatory mechanism. In this study, by screening 44 gene knockout mutants of putative RR-encoding genes in Synechocystis for their sensitivity change to Cd(2+) stress, we identified the orphan RR, Slr0649, involved in Cd(2+) tolerance in Synechocystis. The ∆sll0649 mutant was also found to be more sensitive to high-concentration Cu(2+), Fe(2+), Mn(2+) and Zn(2+), when compared with the wild type. Using an iTRAQ-LC-MSMS based quantitative proteomic analysis coupled with EMSAs, we found that, in addition to its positive regulation on genes directly related to Cd(2+) utilization, Sll0649 can also functions as a key positive regulator either directly or indirectly on expression of multiple genes related to transporting and utilization of several other metal ions. The study provided a proteomic description of the Cd(2+) response network mediated by the response regulator Sll0649, and revealed novel insights on the metal-tolerance mechanism in Synechocystis.
Laboratory of Synthetic Microbiology, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, PR China; Key Laboratory of Systems Bioengineering, Ministry of Education of China, Tianjin 300072, PR China; Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China.
Lei
L
Chen
Laboratory of Synthetic Microbiology, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, PR China; Key Laboratory of Systems Bioengineering, Ministry of Education of China, Tianjin 300072, PR China; Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China.
Ye
Y
Zhu
Laboratory of Synthetic Microbiology, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, PR China; Key Laboratory of Systems Bioengineering, Ministry of Education of China, Tianjin 300072, PR China; Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China.
Zhongdi
Z
Song
Laboratory of Synthetic Microbiology, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, PR China; Key Laboratory of Systems Bioengineering, Ministry of Education of China, Tianjin 300072, PR China; Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China.
Jiangxin
J
Wang
Laboratory of Synthetic Microbiology, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, PR China; Key Laboratory of Systems Bioengineering, Ministry of Education of China, Tianjin 300072, PR China; Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China. Electronic address: wwzhang8@tju.edu.cn.
Weiwen
W
Zhang
D001426:Bacterial Proteins / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology*; D004361:Drug Tolerance; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000502:physiology; D006706:Homeostasis; D008670:Metals / Q000378:metabolism / Q000494:pharmacology; D010788:Photosynthesis / Q000235:genetics; D020543:Proteome / Q000378:metabolism; D040901:Proteomics; D013312:Stress, Physiological; D046939:Synechocystis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D008670:Metals; D020543:Proteome; D002104:Cadmium
Cadmium; Proteomics; Response regulator; Synechocystis; Tolerance