Thioredoxin A regulates protein synthesis to maintain carbon and nitrogen partitioning in cyanobacteria

Abstract

Thioredoxins play an essential role in regulating enzyme activity in response to environmental changes, especially in photosynthetic organisms. They are crucial for metabolic regulation in cyanobacteria, but the key redox-regulated central processes remain to be determined. Physiological, metabolic, and transcriptomic characterization of a conditional mutant of the essential Synechocystis sp. PCC 6803 thioredoxin trxA gene (STXA2) revealed that decreased TrxA levels alter cell morphology and induce a dormant-like state. Furthermore, 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 EF-Tu elongation factor. Transcriptomic analysis of TrxA depletion in STXA2 revealed a robust transcriptional response. Down-regulated genes formed a large cluster directly related to photosynthesis, ATP synthesis, and CO2 fixation. In contrast, up-regulated genes were grouped into different clusters related to respiratory electron transport, carotenoid biosynthesis, amino acid metabolism, and protein degradation, among others. These findings highlight the complex regulatory mechanisms that govern cyanobacterial metabolism, where TrxA acts as a critical regulator that orchestrates the transition from anabolic to maintenance metabolism and regulates carbon and nitrogen balance.

From ubiquity to specificity: The diverse functions of bacterial thioredoxin systems

“…For Cyanobacteria, the essentiality of the m-type Trx is due to the reduction of the FBP/SBPase, which is essential for photoautotrophic growth (Mallén-Ponce et al, 2021). Moreover, the m-type Trx plays a crucial role in protein synthesis in Synechocystis, mainly through the control of the redox state of the EF-Tu elongation factor (Mallén-Ponce et al, 2024). Some classes of RNRs, the enzymes for de novo synthesis and repair of DNA, are Trx-dependent and are essential in some organisms (Torrents, 2014).…”