Nitrogen (N) scarcity frequently constrains global biomass productivity. N deficiency halts cell division, downregulates photosynthetic electron transfer, and enhances carbon storage. However, the molecular mechanism downregulating photosynthesis during N deficiency and its relationship with carbon storage are not fully understood. Proton Gradient Regulator-like 1 (PGRL1) controlling cyclic electron flow (CEF) and Flavodiiron proteins (FLV) involved in pseudo-CEF (PCEF) are major players in the acclimation of photosynthesis. To determine the role of PGRL1 or FLV in photosynthesis under N deficiency, we measured photosynthetic electron transfer, oxygen gas exchange, and carbon storage in Chlamydomonas reinhardtii pgrl1 and flvB knockout mutants. Under N deficiency, pgrl1 maintained higher net photosynthesis and O2 photoreduction rates and higher levels of Cytochrome b6f and PSI compared to the control and flvB. The photosynthetic activity of flvB and pgrl1 flvB double mutants decreased in response to N deficiency, similar to the control strains. Furthermore, the preservation of photosynthetic activity in pgrl1 was accompanied by an increased accumulation of triacylglycerol in certain genetic backgrounds but not others, highlighting the importance of gene-environment interaction in determining traits such as oil content. Our results suggest that in the absence of PGRL1-controlled CEF, FLV-mediated PCEF maintains net photosynthesis at a high level and that CEF and PCEF play antagonistic roles during N deficiency. They further illustrate how a strain's nutrient status and genetic makeup can affect regulation of photosynthetic energy conversion in relation to carbon storage and provide additional strategies for improving lipid productivity in algae.

中文翻译：

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循环和准循环电子途径在莱茵衣藻缺氮过程中起拮抗作用


氮 （N） 稀缺经常限制全球生物质生产力。缺氮会阻止细胞分裂，下调光合电子转移，并增强碳储存。然而，缺氮期间下调光合作用的分子机制及其与碳储存的关系尚不完全清楚。控制循环电子流 （CEF） 的质子梯度调节因子样 1 （PGRL1） 和参与伪 CEF （PCEF） 的黄二铁蛋白 （FLV） 是光合作用驯化的主要参与者。为了确定 PGRL1 或 FLV 在缺氮下光合作用中的作用，我们测量了莱茵衣藻 pgrl1 和 flvB 敲除突变体的光合电子转移、氧气交换和碳储存。在缺氮的情况下，与对照组和 flvB 相比，pgrl1 保持较高的净光合作用和 O2 光还原速率以及更高水平的细胞色素 b6f 和 PSI。flvB 和 pgrl1 flvB 双突变体的光合活性响应 N 缺乏而降低，与对照菌株相似。此外，pgrl1 中光合活性的保留伴随着三酰甘油在某些遗传背景中的积累增加，而在其他遗传背景中没有，这突出了基因-环境相互作用在决定含油量等性状中的重要性。我们的结果表明，在没有 PGRL1 控制的 CEF 的情况下，FLV 介导的 PCEF 将净光合作用维持在高水平，并且 CEF 和 PCEF 在 N 缺乏期间起拮抗作用。它们进一步说明了菌株的营养状况和基因组成如何影响与碳储存相关的光合能量转换的调节，并为提高藻类中的脂质生产力提供了额外的策略。