Storti Mattia, Segalla Anna, Mellon Marco, Alboresi Alessandro, Morosinotto Tomas
Department of Biology, University of Padova, Padova, 35121, Italy.
New Phytol. 2020 Nov;228(4):1316-1326. doi: 10.1111/nph.16643. Epub 2020 Jun 18.
Photosynthetic electron transport is regulated by cyclic and pseudocyclic electron flow (CEF and PCEF) to maintain the balance between light availability and metabolic demands. CEF transfers electrons from photosystem I to the plastoquinone pool with two mechanisms, dependent either on PGR5/PGRL1 or on the type I NADH dehydrogenase-like (NDH) complex. PCEF uses electrons from photosystem I to reduce oxygen and in many groups of photosynthetic organisms, but remarkably not in angiosperms, it is catalyzed by flavodiiron proteins (FLVs). In this study, Physcomitrella patens plants depleted in PGRL1, NDH and FLVs in different combinations were generated and characterized, showing that all these mechanisms are active in this moss. Surprisingly, in contrast to flowering plants, Physcomitrella patens can cope with the simultaneous inactivation of PGR5- and NDH-dependent CEF but, when FLVs are also depleted, plants show strong growth reduction and photosynthetic activity is drastically reduced. The results demonstrate that mechanisms for modulation of photosynthetic electron transport have large functional overlap but are together indispensable to protect photosystem I from damage and they are an essential component for photosynthesis in any light regime.
光合电子传递受循环和伪循环电子流（CEF和PCEF）调节，以维持光能供应与代谢需求之间的平衡。CEF通过两种机制将电子从光系统I转移到质体醌库，一种依赖于PGR5/PGRL1，另一种依赖于I型NADH脱氢酶样（NDH）复合体。PCEF利用光系统I的电子来还原氧气，在许多光合生物类群中存在，但被子植物中明显不存在，它由黄素二铁蛋白（FLV）催化。在本研究中，构建并表征了不同组合缺失PGRL1、NDH和FLV的小立碗藓植株，结果表明所有这些机制在这种苔藓中均有活性。令人惊讶的是，与开花植物不同，小立碗藓能够应对PGR5和NDH依赖的CEF同时失活的情况，但是，当FLV也缺失时，植株生长显著减缓，光合活性急剧降低。结果表明，光合电子传递的调节机制具有很大的功能重叠，但共同作用对于保护光系统I免受损伤不可或缺，并且它们是任何光照条件下光合作用的重要组成部分。
