Photorespiratory metabolism in the cyanobacterial model Synechocystis sp. strain PCC 6803: A systems biology approach

无机碳浓缩机制使蓝藻在低CO2/高O2环境下生长，直到最近才被认为足以抑制蓝藻核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的加氧酶反应。然而，光呼吸代谢和乙醇酸解毒被证明是蓝藻必不可少的，并且都是内共生传递到植物界。我们最近建立了synnechocystis sp. PCC 6803作为蓝藻模型，在低无机碳（Ci）有效性（LC）增强光呼吸的条件下，在转录组、代谢组和荧光组水平上进行系统分析，而高无机碳有效性（HC）则在很大程度上抑制光呼吸反应。这些工具，特别是通量表型，允许使用乙醇酸积累ΔglcD1乙醇酸脱氢酶突变体从HC转变为LC时的光呼吸和光呼吸爆发的正式证明。同样的实验表明，转移到LC条件下可能通过磷酸烯醇丙酮酸(PEP)-羧化酶激活额外/替代CO2同化，这一反应也被高等植物利用。在这里，我们提出通过13c通量探测乙醇酸脱氢酶缺失突变体，结合干扰CCM和固定碳PEP羧化酶途径的基因缺失，研究光呼吸与中心代谢的相互作用。这项研究将揭示两种主要的碳固定途径是否以及如何相互作用。

The inorganic carbon-concentrating mechanism enables cyanobacterial growth in low CO2/high O2 environments and was until recently thought sufficient to suppress the oxygenase reaction of cyanobacterial ribulose-1,5-bisphosphate-carboxylase/-oxygenase (Rubisco). However, photorespiratory metabolism and glycolate detoxification were shown to be essential for cyanobacteria and were both endosymbiontically conveyed into the plant kingdom. We recently established Synechocystis sp. PCC 6803 as a cyanobacterial model for systems analyses at the transcriptome, metabolome and fluxome levels under conditions enhancing photorespiration by low inorganic carbon (Ci) availability (LC), in contrast to high Ci availability (HC), a condition that largely suppresses photorespiratory responses. These tools, specifically the flux phenotyping, allowed the formal demonstration of photorespiration and a photorespiratory burst upon shift from HC to LC using a glycolate accumulating ΔglcD1 glycolate dehydrogenase mutant. The same experiments indicated that transfer to LC conditions activates additional/alternative CO2 assimilation likely via phosphoenolpyruvate (PEP)-carboxylase, a reaction that is also utilized by higher plants. Here we propose to study the interaction of photorespiration with central metabolism by 13C-flux probing of glycolate dehydrogenase deletion mutants in combination with gene deletions that interfere with the CCM and the carbon-fixing PEP carboxylase pathway. The study will reveal, if and how the two main carbon fixing pathways interact.