TrxA-mediated regulation of protein synthesis contributes to the maintenance of carbon and nitrogen balance in cyanobacteria.
Thioredoxins play an essential role in regulating enzyme activity upon response to environmental changes, especially in photosynthetic organisms. These are crucial for the regulation of metabolism in cyanobacteria, but the key central processes redox-regulated remain to be determined. Physiological, metabolic and transcriptomic characterization of a conditional mutant of the essential trxA gene in Synechocystis (STXA2) revealed that reduced TrxA levels alter cell morphology and enter in a dormant-like state. TrxA depletion in the STXA2 strain inhibited protein synthesis and led to changes in amino acid pools and nitrogen/carbon reserve polymers, accompanied by oxidation of the Elongation Factor EF-Tu. Transcriptomic analysis of TrxA depletion in STXA2 showed a robust transcriptional response. Genes that responded negatively were grouped in a large cluster and were directly related to photosynthesis, ATP synthesis and CO2 fixation, while genes that responded positively were grouped in different clusters and related to respiratory electron transport, carotenoids synthesis, amino acid metabolism and protein degradation, among others. Regulation of cyanobacterial metabolism is complex and fine-tuned, our results link TrxA to the switch from anabolic to maintenance metabolism in cyanobacteria, regulating carbon and nitrogen balance. Overall design: To investigate a possible function of TrxA in central cellular processes, we established a mutant strain (STXA2) in which the trxA gene has been knocked down