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 (ED) pathway in S. elongatus is incomplete, with its key enzyme 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase exhibiting alternative oxaloacetate decarboxylation activity that modulates daytime photosynthesis. This activity allows for the bypassing of the tricarboxylic acid (TCA) 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.

中文翻译：

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磷酸酮醇酶和 KDPG 醛缩酶代谢调节蓝细菌的光合碳产量


蓝细菌贡献了全球净碳固定的大约四分之一。在 diel 光/暗生长过程中，暗呼吸大大降低了蓝藻和其他光养生物的整体光合碳产量。呼吸途径如何参与夜间的碳资源分配以优化夜间生存并支持白天光合作用仍不清楚。在这里，使用蓝藻 Synechococcus elongatus PCC 7942，我们表明磷酸酮醇酶在黑暗中整合到呼吸网络中，以最好地分配碳资源用于氨基酸生物合成，并为光诱导后的光合作用重新启动做准备。此外，我们表明 S. elongatus 中的呼吸 Entner-Doudoroff （ED） 通路是不完整的，其关键酶 2-酮-3-脱氧-6-磷酸葡萄糖酸 （KDPG） 醛缩酶表现出调节白天光合作用的替代草酰乙酸脱羧活性。当用于生物合成的 ATP 和 NADPH 消耗过量且相对于它们通过光反应产生的产生不平衡时，这种活性允许绕过三羧酸 （TCA） 循环，从而防止相对 NADPH 积累并确保最佳光合碳产量。优化这些代谢过程为提高蓝藻和其他光合生物在 diel 光/暗循环下的光合碳产量提供了机会。