Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China.
Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
J Biol Chem. 2022 Apr;298(4):101783. doi: 10.1016/j.jbc.2022.101783. Epub 2022 Mar 2.
Photosynthetic organisms have evolved light-harvesting antennae over time. In cyanobacteria, external phycobilisomes (PBSs) are the dominant antennae, whereas in green algae and higher plants, PBSs have been replaced by proteins of the Lhc family that are integrated in the membrane. Red algae represent an evolutionary intermediate between these two systems, as they employ both PBSs and membrane LHCR proteins as light-harvesting units. Understanding how red algae cope with light is not only interesting for biotechnological applications, but is also of evolutionary interest. For example, energy-dependent quenching (qE) is an essential photoprotective mechanism widely used by species from cyanobacteria to higher plants to avoid light damage; however, the quenching mechanism in red algae remains largely unexplored. Here, we used both pulse amplitude-modulated (PAM) and time-resolved chlorophyll fluorescence to characterize qE kinetics in the red alga Porphyridium purpureum. PAM traces confirmed that qE in P. purpureum is activated by a decrease in the thylakoid lumen pH, whereas time-resolved fluorescence results further revealed the quenching site and ultrafast quenching kinetics. We found that quenching exclusively takes place in the photosystem II (PSII) complexes and preferentially occurs at PSII's core antenna rather than at its reaction center, with an overall quenching rate of 17.6 ± 3.0 ns. In conclusion, we propose that qE in red algae is not a reaction center type of quenching, and that there might be a membrane-bound protein that resembles PsbS of higher plants or LHCSR of green algae that senses low luminal pH and triggers qE in red algae.
光合生物随着时间的推移进化出了光捕获天线。在蓝细菌中，外部藻胆体（PBS）是主要的天线，而在绿藻和高等植物中，PBS 已被整合在膜中的 Lhc 家族蛋白所取代。红藻是这两个系统之间的进化中间体，因为它们既使用 PBS 又使用膜 LHCR 蛋白作为光捕获单元。了解红藻如何应对光照不仅对生物技术应用具有重要意义，而且对进化也具有重要意义。例如，能量依赖的淬灭（qE）是一种广泛存在于从蓝细菌到高等植物的物种中的重要光保护机制，以避免光损伤；然而，红藻的淬灭机制在很大程度上仍未得到探索。在这里，我们使用脉冲幅度调制（PAM）和时间分辨叶绿素荧光来表征红藻 Porphyridium purpureum 中的 qE 动力学。PAM 迹线证实，P. purpureum 中的 qE 是由类囊体腔 pH 下降激活的，而时间分辨荧光结果进一步揭示了淬灭位点和超快淬灭动力学。我们发现淬灭仅发生在光系统 II（PSII）复合物中，并且优先发生在 PSII 的核心天线而不是其反应中心，整体淬灭速率为 17.6 ± 3.0 ns。总之，我们提出红藻中的 qE 不是反应中心类型的淬灭，可能存在一种类似于高等植物的 PsbS 或绿藻的 LHCSR 的膜结合蛋白，它能感知低腔 pH 值并触发红藻中的 qE。
