Microalgae contribute to about half of global net photosynthesis, which converts sunlight into the chemical energy (ATP and NADPH) used to transform CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required to sustain CO2 fixation. However, the relative importance of each alternative pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic and chloroplast-to-mitochondria electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that (i) each alternative pathway can provide sufficient additional energy to sustain high CO2 fixation rates, (ii) the alternative pathways exhibit cross-compensation, and (iii) the activity of at least one of the three alternative pathways is necessary to sustain photosynthesis. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast–mitochondria interaction being the most efficient. Overall, our data lay bioenergetic foundations for biotechnological strategies to improve CO2 capture and fixation.

中文翻译：

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光合作用的替代电子途径为绿藻捕获二氧化碳提供动力

微藻贡献了全球约一半的净光合作用，将阳光转化为化学能（ATP 和 NADPH），用于将二氧化碳转化为生物质。已经提出了光合作用的替代电子途径来产生维持二氧化碳固定所需的额外 ATP。然而，每种替代途径的相对重要性仍然难以捉摸。在这里，我们剖析并量化了循环、伪循环和叶绿体到线粒体电子流对微藻莱茵衣藻维持净光合作用的能力的贡献。我们表明（i）每个替代途径可以提供足够的额外能量来维持高二氧化碳固定率，（ii）替代途径表现出交叉补偿，（iii）三个替代途径中至少一个的活性对于维持高二氧化碳固定率是必要的。维持光合作用。我们进一步表明，所有途径在激发二氧化碳固定方面具有非常不同的效率，其中叶绿体-线粒体相互作用是最有效的。总体而言，我们的数据为改善二氧化碳捕获和固定的生物技术策略奠定了生物能基础。