Xie Ningdong, Sharma Chetna, Rusche Katherine, Wang Xin
Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA.
Department of Microbiology, Miami University, Oxford, OH 45056, USA.
Plant Cell. 2024 Dec 23;37(1). doi: 10.1093/plcell/koae291.
Cyanobacteria contribute to roughly a quarter of global net carbon fixation. During diel light/dark growth, dark respiration substantially lowers the overall photosynthetic carbon yield in cyanobacteria and other phototrophs. How respiratory pathways participate in carbon resource allocation at night to optimize dark survival and support daytime photosynthesis remains unclear. Here, using the cyanobacterium Synechococcus elongatus PCC 7942, we show that phosphoketolase integrates into a respiratory network in the dark to best allocate carbon resources for amino acid biosynthesis and to prepare for photosynthesis reinitiation upon photoinduction. Moreover, we show that the respiratory Entner-Doudoroff pathway in S. elongatus is incomplete, with its key enzyme 2-keto-3-deoxy-6-phosphogluconate aldolase exhibiting alternative oxaloacetate decarboxylation activity that modulates daytime photosynthesis. This activity allows for the bypassing of the tricarboxylic acid cycle when ATP and NADPH consumption for biosynthesis is excessive and imbalanced relative to their production by the light reactions, thereby preventing relative NADPH accumulation and ensuring optimal photosynthetic carbon yield. Optimizing these metabolic processes offers opportunities to enhance photosynthetic carbon yield in cyanobacteria and other photosynthetic organisms under diel light/dark cycles.
蓝藻对全球净碳固定的贡献约为四分之一。在昼夜光/暗生长过程中，暗呼吸显著降低了蓝藻和其他光合生物的总体光合碳产量。呼吸途径如何在夜间参与碳资源分配以优化暗生存并支持白天的光合作用仍不清楚。在这里，我们使用聚球藻属蓝藻（Synechococcus elongatus）PCC 7942表明，磷酸酮醇酶在黑暗中整合到呼吸网络中，以便为氨基酸生物合成最佳地分配碳资源，并为光诱导后光合作用的重新启动做好准备。此外，我们表明聚球藻属蓝藻中的呼吸型Entner-Doudoroff途径是不完整的，其关键酶2-酮-3-脱氧-6-磷酸葡萄糖酸醛缩酶表现出替代的草酰乙酸脱羧酶活性，该活性调节白天的光合作用。当生物合成所需的ATP和NADPH消耗相对于光反应产生的ATP和NADPH过多且不平衡时，这种活性允许绕过三羧酸循环，从而防止相对NADPH积累并确保最佳的光合碳产量。优化这些代谢过程为在昼夜光/暗循环下提高蓝藻和其他光合生物的光合碳产量提供了机会。
