Minimized Dark Consumption of Calvin Cycle Intermediates Facilitates the Initiation of Photosynthesis in Synechocystis sp. PCC 6803.

This article focuses on the regulation of downstream glycolytic metabolites of the Calvin–Benson–Bassham (CBB) cycle in the cyanobacterium Synechocystis sp. PCC 6803 during dark and light conditions. The study demonstrates that low activity of pyruvate kinase (Pyk) during darkness maintains the accumulation of glycolytic intermediates necessary for efficient photosynthesis initiation upon light exposure, while overexpression of Pyk reduces these intermediates and impairs photosynthetic oxygen evolution. Similarly, overexpression of phosphoenolpyruvate carboxylase (PepC) decreases glycolytic intermediates but leads to accumulation of sugar phosphates, partially offsetting photosynthetic decline. These findings highlight the importance of balanced cataplerotic flux—defined here as the consumption pathways of CBB cycle intermediates—in supporting photosynthetic reactivation and adaptation to dark stress in cyanobacteria.