Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
Core Research for Environmental Science and Technology, Japan Science and Technology Agency, Tokyo, Japan.
Physiol Plant. 2018 Nov;164(3):337-348. doi: 10.1111/ppl.12723. Epub 2018 Jul 19.
In higher plants, light drives the linear photosynthetic electron transport reaction from H O to electron sinks, which is called the linear electron flow (LEF). LEF activity should be regulated depending on electron sinks; otherwise excess electrons accumulate in the thylakoid membranes and stimulate reactive oxygen species (ROS) production in photosystem I (PSI), which causes oxidative damage to PSI. To prevent ROS production in PSI, PSI should be oxidized during photosynthesis, and PROTON GRADIENT REGULATION 5 (PGR5) and PGR like 1 (PGRL1) are important for this oxidation. PGR5 and PGRL1 are recognized as a component of ferredoxin-dependent cyclic electron flow around PSI (Fd-CEF-PSI), however there is no direct evidence for the significant operation of Fd-CEF-PSI during photosynthesis in wild-type (WT) plants. Thus, electron distribution by PGR5 and PGRL1 between Fd-CEF-PSI and LEF is still elusive. Here, we show direct evidence that Fd-CEF-PSI activity is minor during steady-state photosynthesis by measuring the Fd redox state in vivo in Arabidopsis thaliana. We found that Fd oxidation rate is determined by LEF activity during steady-state photosynthesis in WT. On the other hand, pgr5 and pgrl1 showed lower electron transport efficiency from PSI to electron sinks through Fd during steady-state photosynthesis. These results demonstrate that electrons are exclusively consumed in electron sinks through Fd, and the phenotypes of pgr5 and pgrl1 are likely caused by the disturbance of the LEF between PSI and electron sinks. We suggest that PGR5 and PGRL1 modulate the LEF according to electron sink activities around PSI.
在高等植物中，光驱动从 H2O 到电子受体的线性光合作用电子传递反应，这被称为线性电子流（LEF）。LEF 活性应根据电子受体进行调节；否则，多余的电子会在类囊体膜中积累，并刺激光系统 I（PSI）中活性氧（ROS）的产生，从而对 PSI 造成氧化损伤。为了防止 PSI 中产生 ROS，PSI 应该在光合作用过程中被氧化，而 PROTON GRADIENT REGULATION 5（PGR5）和 PGR 类似蛋白 1（PGRL1）对于这种氧化是重要的。PGR5 和 PGRL1 被认为是 PSI 周围铁氧还蛋白依赖性循环电子流（Fd-CEF-PSI）的一个组成部分，然而，在野生型（WT）植物中，光合作用过程中 Fd-CEF-PSI 的显著作用没有直接证据。因此，PGR5 和 PGRL1 之间的电子分配通过 Fd-CEF-PSI 和 LEF 仍然难以捉摸。在这里，我们通过在活体中测量拟南芥铁氧还蛋白的氧化还原状态，直接证明了 Fd-CEF-PSI 在稳态光合作用过程中的活性较小。我们发现，在 WT 中，稳态光合作用过程中 Fd 氧化速率由 LEF 活性决定。另一方面，pgr5 和 pgrl1 在稳态光合作用过程中从 PSI 到电子受体的电子传递效率较低。这些结果表明，电子通过 Fd 仅在电子受体中消耗，并且 pgr5 和 pgrl1 的表型可能是由于 PSI 和电子受体之间的 LEF 受到干扰所致。我们建议 PGR5 和 PGRL1 根据 PSI 周围电子受体的活性来调节 LEF。
