Thioredoxin pathway in Anabaena sp. PCC 7120: activity of NADPH-thioredoxin reductase C.

To understand the physiological role of NADPH-thioredoxin reductase C (NTRC) in cyanobacteria, we investigated an NTRC-deficient mutant strain of Anabaena sp., PCC 7120, cultivated under different regimes of nitrogen supplementation and light exposure. The deletion of ntrC did not induce a change in the cell structure and metabolic pathways. However, time-dependent changes in the abundance of specific proteins and metabolites were observed. A decrease in chlorophyll a was correlated with a decrease in chlorophyll a biosynthesis enzymes and photosystem I subunits. The deletion of ntrC led to a deregulation of nitrogen metabolism, including the NtcA accumulation and heterocyst-specific proteins while nitrate ions were available in the culture medium. Interestingly, this deletion resulted in a redox imbalance, indicated by higher peroxide levels, higher catalase activity and the induction of chaperones such as MsrA. Surprisingly, the antioxidant protein 2-CysPrx was downregulated. The deficiency in ntrC also resulted in the accumulation of metabolites such as 6-phosphogluconate, ADP and ATP. Higher levels of NADP+ and NADPH partly correlated with higher G6PDH activity. Rather than impacting protein expression levels, NTRC appears to be involved in the direct regulation of enzymes, especially during the dark-to-light transition period.