How do glycolytic routes and especially the newly discovered Entner-Doudoroff pathway contribute to the central carbon metabolism in cyanobacteria and do they play an essential role for carbon fixation and photosynthesis?

我们最近发现，蓝藻和植物除了Emden-Meyerhof-Parns(EMP)和氧化戊糖磷酸(OPP)途径之外，还有一个以前被忽视的第三条糖酵解途径：Entner-Doudoroff(ED)途径(Chen等人)。2016年，PNAS)。ED途径的缺失会导致在混合营养(葡萄糖和光)条件下和暗/光循环(12小时暗/12小时光)下的生长减弱。尽管这些观察表明ED途径在蓝藻中具有生理重要性，但它并没有量化这一途径的份额。因此，通量分析对于发现其对蓝藻中心碳代谢的真正贡献是绝对必要的。ED和OPP途径的阻断导致了一个在混合营养和自养条件下生长极差的突变株(未发表)。这一结果令人惊讶，清楚地表明糖酵解途径在自养条件下是必不可少的。到目前为止，光自养植物糖酵解途径、固碳和光合作用之间的相互作用还没有得到令人满意的研究，因为糖酵解途径之一是未知的。这项建议旨在量化在混合营养、异养和自养条件下所有糖酵解途径和固定CO2的Calvin-Benson-Bassham(CBB)循环的通量。我们的重点是研究糖酵解途径、固碳和光合作用之间的相互联系。我们特别想验证这一假说，如果糖酵解途径是补充光中固定二氧化碳的CBB循环所必需的，以及它们是否需要平衡光合作用电子传递。对于这种方法，需要结合通量分析、选定的缺失突变体的特征和生理测量。

We could recently show that both cyanobacteria and plants possess a previously overlooked third glycolytic route beside Emden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (OPP) pathway: the Entner-Doudoroff (ED) pathway (Chen et al. 2016, PNAS). Deletion of the ED pathway results in diminished growth both under mixotrophic (glucose and light) conditions and in a dark/light cycle (12h dark/12h light). Even though these observations indicate that the ED pathway is of physiological importance in cyanobacteria it does not quantify the share of this pathway. Therefore, flux analyses are absolutely essential to discover its true contribution to the central carbon metabolism in cyanobacteria. Interruption of both ED and OPP pathway results in a mutant with extremely poor growth under both mixotrophic and autotrophic conditions (unpublished). This result came as a surprise and clearly shows that glycolytic routes are essential under autotrophic conditions. The interplay between glycolytic routes, carbon fixation and photosynthesis could not be studied satisfactory in photoautotrophs until now, as one of the glycolytic routes was unknown. This proposal aims to quantify the fluxes through all glycolytic routes and the Calvin-Benson-Bassham (CBB) cycle of CO2 fixation under mixotrophic, heterotrophic and autotrophic conditions. Our main emphasis is to study the interconnection between glycolytic routes, carbon fixation and photosynthesis. We especially want to test the hypothesis, if glycolytic routes are essential to replenish the CBB cycle of CO2 fixation in the light and whether they are required to balance the photosynthetic electron transport. For this approach a combination of flux analyses, characterization of selected deletion mutants and physiological measurements are needed.