Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, UK.
Nat Plants. 2021 Jan;7(1):87-98. doi: 10.1038/s41477-020-00828-3. Epub 2021 Jan 11.
TAP38/STN7-dependent (de)phosphorylation of light-harvesting complex II (LHCII) regulates the relative excitation rates of photosystems I and II (PSI, PSII) (state transitions) and the size of the thylakoid grana stacks (dynamic thylakoid stacking). Yet, it remains unclear how changing grana size benefits photosynthesis and whether these two regulatory mechanisms function independently. Here, by comparing Arabidopsis wild-type, stn7 and tap38 plants with the psal mutant, which undergoes dynamic thylakoid stacking but lacks state transitions, we explain their distinct roles. Under low light, smaller grana increase the rate of PSI reduction and photosynthesis by reducing the diffusion distance for plastoquinol; however, this beneficial effect is only apparent when PSI/PSII excitation balance is maintained by state transitions or far-red light. Under high light, the larger grana slow plastoquinol diffusion and lower the equilibrium constant between plastocyanin and PSI, maximizing photosynthesis by avoiding PSI photoinhibition. Loss of state transitions in low light or maintenance of smaller grana in high light also both bring about a decrease in cyclic electron transfer and over-reduction of the PSI acceptor side. These results demonstrate that state transitions and dynamic thylakoid stacking work synergistically to regulate photosynthesis in variable light.
TAP38/STN7 依赖的光捕获复合物 II（LHCII）的磷酸化/去磷酸化调节光系统 I 和 II（PSI、PSII）的相对激发率（状态转变）和类囊体垛叠的大小（动态类囊体堆叠）。然而，目前尚不清楚改变垛叠大小如何有益于光合作用，以及这两种调节机制是否独立发挥作用。在这里，通过比较拟南芥野生型、stn7 和 tap38 植株与 psal 突变体，该突变体经历动态类囊体堆叠但缺乏状态转变，我们解释了它们的不同作用。在低光下，较小的垛叠通过减少质体醌的扩散距离来增加 PSI 还原和光合作用的速率；然而，当 PSI/PSII 激发平衡通过状态转变或远红光维持时，这种有益的效果才明显。在高光下，较大的垛叠会减缓质体醌的扩散，并降低质体蓝素与 PSI 之间的平衡常数，通过避免 PSI 光抑制来最大限度地提高光合作用。在低光下丧失状态转变或在高光下维持较小的垛叠也会导致循环电子传递减少和 PSI 受体侧的过度还原。这些结果表明，状态转变和动态类囊体堆叠协同作用以调节可变光照下的光合作用。
