Photorespiratory glycolate oxidase is essential for the survival of the red alga Cyanidioschyzon merolae under ambient CO2 conditions.
Photorespiratory glycolate oxidase is essential for the survival of the red alga Cyanidioschyzon merolae under ambient CO2 conditions.
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DOI：
10.1093/jxb/erw118
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发表时间：
2016-05
影响因子：
6.9
通讯作者：
Weber AP
中科院分区：
文献类型：
--
作者：
Rademacher N;Kern R;Fujiwara T;Mettler-Altmann T;Miyagishima SY;Hagemann M;Eisenhut M;Weber AP
Cyanidioschyzon 中的乙醇酸氧化酶敲除揭示了红藻拥有类似植物的光呼吸途径。这表明使用过氧化物酶体乙醇酸氧化酶的光呼吸途径是古老的并且不是最近才进化的。光呼吸对于所有进行氧气光合作用的生物体都是必不可少的。光呼吸代谢的进化始于蓝细菌，并导致植物中形成高度分隔的途径。对真核藻类（如灰藻、红藻和叶绿藻）光呼吸的分子理解对于揭示这一途径的进化至关重要。然而，红藻光呼吸途径的机制细节很少。单细胞红藻 Cyanidioschyzon merolae 代表了红色谱系的模型。其基因组已完全测序，并且可以使用用于靶向基因工程的工具。为了研究红藻光呼吸的功能和重要性，我们选择乙醇酸氧化酶（GOX）作为靶标。 GOX 催化乙醇酸转化为乙醛酸，同时产生过氧化氢作为副产物。来自 C. merolae 的候选 GOX 的功能通过以下事实得到验证：重组 GOX 更喜欢乙醇酸而不是 L-乳酸作为底物。黄色荧光蛋白-GOX 融合蛋白表明 GOX 靶向 C. merolae 中的过氧化物酶体。 GOX 敲除突变株系在环境空气条件下表现出高碳需求表型，与野生型相比，生长减少且光合活性降低。代谢分析显示，从高二氧化碳条件转移到环境空气后，突变细胞中乙醇酸和甘氨酸积累。总之，结果表明光呼吸代谢对于红藻至关重要。过氧化物酶体 GOX 的使用表明高光呼吸通量是所有光合真核生物的祖先特征。
Glycolate oxidase knockouts in Cyanidioschyzon reveal that red algae harbour a plant-like photorespiratory pathway. This suggests that a photorespiratory pathway employing peroxisomal glycolate oxidase is ancient and not recently evolved. Photorespiration is essential for all organisms performing oxygenic photosynthesis. The evolution of photorespiratory metabolism began among cyanobacteria and led to a highly compartmented pathway in plants. A molecular understanding of photorespiration in eukaryotic algae, such as glaucophytes, rhodophytes, and chlorophytes, is essential to unravel the evolution of this pathway. However, mechanistic detail of the photorespiratory pathway in red algae is scarce. The unicellular red alga Cyanidioschyzon merolae represents a model for the red lineage. Its genome is fully sequenced, and tools for targeted gene engineering are available. To study the function and importance of photorespiration in red algae, we chose glycolate oxidase (GOX) as the target. GOX catalyses the conversion of glycolate into glyoxylate, while hydrogen peroxide is generated as a side-product. The function of the candidate GOX from C. merolae was verified by the fact that recombinant GOX preferred glycolate over L-lactate as a substrate. Yellow fluorescent protein-GOX fusion proteins showed that GOX is targeted to peroxisomes in C. merolae. The GOX knockout mutant lines showed a high-carbon-requiring phenotype with decreased growth and reduced photosynthetic activity compared to the wild type under ambient air conditions. Metabolite analyses revealed glycolate and glycine accumulation in the mutant cells after a shift from high CO2 conditions to ambient air. In summary, or results demonstrate that photorespiratory metabolism is essential for red algae. The use of a peroxisomal GOX points to a high photorespiratory flux as an ancestral feature of all photosynthetic eukaryotes.