Ito Ryo, Endo Mizuki, Aoki Motohide, Fujiwara Shoko, Sato Norihiro
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan.
Front Plant Sci. 2025 Mar 24;16:1569038. doi: 10.3389/fpls.2025.1569038. eCollection 2025.
Plastoquinone plays a crucial role in the photosynthetic electron transport system as an electron carrier, transferring electrons from photosystem II to cytochrome bf complexes. Certain cyanobacteria acylate plastoquinone derivatives, plastoquinol, the reduced form of plastoquinone, and/or plastoquinone-C, the hydroxylated form of plastoquinone to synthesize newly found cyanobacterial lipids, acylplastoquinol and acylplastoquinone-C, the latter of which is known as plastoquinone-B in seed plants. The cyanobacterial genes, in sp. PCC 6803 and its ortholog in sp. PCC 7002, encode a bifunctional acyltransferase for the synthesis of both acylplastoquinol and plastoquinone-B. Despite conservation of orthologs across a wide range of cyanobacteria, only four cyanobacterial strains, including the two mentioned above, have been identified as producing acylplastoquinol and/or plastoquinone-B. Moreover, the extent to which acylplastoquinone species are distributed in eukaryotic photosynthetic organisms that lack orthologs remains largely unknown. Using LC-MS/MS analysis of total cellular lipids, this study demonstrates that acylplastoquinol and plastoquinone-B are conserved not only in cyanobacteria with orthologs but also in eukaryotic photosynthetic organisms lacking these orthologs, including primary and secondary endosymbiotic algae, and a seed plant. Notably, in eukaryotic photosynthetic organisms as well as in cyanobacteria, these acylplastoquinone species are predominantly esterified with saturated fatty acids. The evolutionary conservation of these acylplastoquinone species suggests replacement of orthologs by alternative gene(s) responsible for their synthesis at least once after the primary endosymbiotic event in the evolution of photosynthetic organisms. The persistent conservation of acylplastoquinone species throughout the evolution likely reflects their critical physiological roles.
质体醌作为电子载体在光合电子传递系统中起着关键作用，它将电子从光系统II转移到细胞色素bf复合体。某些蓝细菌会使质体醌衍生物、质体醌醇（质体醌的还原形式）和/或质体醌-C（质体醌的羟基化形式）发生酰化反应，以合成新发现的蓝细菌脂质——酰基质体醌醇和酰基质体醌-C，后者在种子植物中被称为质体醌-B。集胞藻属PCC 6803菌株及其在聚球藻属PCC 7002中的直系同源基因编码一种双功能酰基转移酶，用于合成酰基质体醌醇和质体醌-B。尽管在广泛的蓝细菌中直系同源基因具有保守性，但只有包括上述两种在内的四个蓝细菌菌株被鉴定为能产生酰基质体醌醇和/或质体醌-B。此外，酰基质体醌种类在缺乏直系同源基因的真核光合生物中的分布程度在很大程度上仍不清楚。本研究通过对总细胞脂质进行液相色谱-串联质谱分析表明，酰基质体醌醇和质体醌-B不仅在具有直系同源基因的蓝细菌中保守，而且在缺乏这些直系同源基因的真核光合生物中也保守，包括初级和次级内共生藻类以及一种种子植物。值得注意的是，在真核光合生物以及蓝细菌中，这些酰基质体醌种类主要与饱和脂肪酸酯化。这些酰基质体醌种类的进化保守性表明，在光合生物进化过程中的初级内共生事件之后，负责其合成的直系同源基因至少被替代基因取代过一次。酰基质体醌种类在整个进化过程中的持续保守可能反映了它们关键的生理作用。
