Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
Department of Physics and Astronomy, University of Sheffield, Sheffield, UK.
Nat Plants. 2018 Feb;4(2):116-127. doi: 10.1038/s41477-017-0092-7. Epub 2018 Jan 29.
Upon transition of plants from darkness to light the initiation of photosynthetic linear electron transfer (LET) from HO to NADP precedes the activation of CO fixation, creating a lag period where cyclic electron transfer (CET) around photosystem I (PSI) has an important protective role. CET generates ΔpH without net reduced NADPH formation, preventing overreduction of PSI via regulation of the cytochrome b f (cytb f) complex and protecting PSII from overexcitation by inducing non-photochemical quenching. The dark-to-light transition also provokes increased phosphorylation of light-harvesting complex II (LHCII). However, the relationship between LHCII phosphorylation and regulation of the LET/CET balance is not understood. Here, we show that the dark-to-light changes in LHCII phosphorylation profoundly alter thylakoid membrane architecture and the macromolecular organization of the photosynthetic complexes, without significantly affecting the antenna size of either photosystem. The grana diameter and number of membrane layers per grana are decreased in the light while the number of grana per chloroplast is increased, creating a larger contact area between grana and stromal lamellae. We show that these changes in thylakoid stacking regulate the balance between LET and CET pathways. Smaller grana promote more efficient LET by reducing the diffusion distance for the mobile electron carriers plastoquinone and plastocyanin, whereas larger grana enhance the partition of the granal and stromal lamellae plastoquinone pools, enhancing the efficiency of CET and thus photoprotection by non-photochemical quenching.
当植物从黑暗环境转入光照环境时，HO 到 NADP 的光合线性电子传递（LET）的起始先于 CO2 固定的激活，从而产生一个滞后期，此时围绕光系统 I（PSI）的循环电子传递（CET）具有重要的保护作用。CET 产生ΔpH 而不会净生成还原型 NADPH，通过调节细胞色素 b6f 复合物来防止 PSI 的过度还原，并通过诱导非光化学猝灭来保护 PSII 免受过激发。从黑暗到光照的转变也会引起光捕获复合物 II（LHCII）的磷酸化增加。然而，LHCII 磷酸化与 LET/CET 平衡的调节之间的关系尚不清楚。在这里，我们表明 LHCII 磷酸化的暗至光变化深刻地改变了类囊体膜的结构和光合复合物的大分子组织，而对两个光系统的天线大小没有显著影响。在光照下，基粒直径和每基粒的膜层数减少，而每个叶绿体的基粒数增加，从而在基粒和基质层片之间创造了更大的接触面积。我们表明，这些类囊体堆叠的变化调节了 LET 和 CET 途径之间的平衡。较小的基粒通过减少可移动电子载体质体醌和质体蓝素的扩散距离来促进更有效的 LET，而较大的基粒增强了粒状和基质层片质体醌池的分区，从而提高了 CET 的效率，并通过非光化学猝灭增强了光保护作用。
