Photosynthetic organisms have evolved photoprotective mechanisms to acclimate to light intensity fluctuations in their natural growth environments. Photosystem (PS) II subunit S (PsbS) and light-harvesting complex (LHC) stress-related proteins (LhcSR) are essential for triggering photoprotection in vascular plants and green algae, respectively. The activity of both proteins is strongly enhanced in the moss Physcomitrella patens under high-light conditions. However, their role in regulating photosynthesis acclimation in P. patens under fluctuating light (FL) conditions is still unknown. Here, we compare the responses of wild-type (WT) P. patens and mutants lacking PsbS (psbs KO) or LhcSR1 and 2 (lhcsr KO) to FL conditions in which the low-light phases were periodically interrupted with high-light pulses. lhcsr KO mutant showed a strong reduction in growth with respect to WT and psbs KO under FL conditions. The lack of LhcSR not only decreased the level of non-photochemical quenching, resulting in an over-reduced plastoquinone pool, but also significantly increased the PSI acceptor limitation values with respect to WT and psbs KO under FL conditions. Moreover, in lhcsr KO mutant, the abundance of PSI core and PSI–LHCI complex decreased greatly under FL conditions compared with the WT and psbs KO. We proposed that LhcSR in P. patens play a crucial role in moss acclimation to dynamic light changes.

光合生物已经进化出光保护机制以适应其自然生长环境中的光强度波动。光系统 (PS) II 亚基 S (PsbS) 和光捕获复合物 (LHC) 应激相关蛋白 (LhcSR) 对于触发维管植物和绿藻的光保护分别是必不可少的。在强光条件下，两种蛋白质的活性在苔藓中都得到了强烈的增强。然而，它们在波动光（FL）条件下调节P. patens光合作用适应中的作用仍然未知。在这里，我们比较了野生型 (WT) P. patens和缺乏 PsbS ( psbs KO) 或 LhcSR1 和 2 ( lhcsrKO) 到 FL 条件，其中低光阶段被高光脉冲周期性地中断。lhcsr KO 突变体在 FL 条件下显示出相对于 WT 和psbs KO 的生长强烈减少。LhcSR 的缺乏不仅降低了非光化学猝灭的水平，导致质体醌池过度减少，而且在 FL 条件下显着增加了 WT 和psbs KO 的 PSI 受体限制值。此外，在lhcsr KO 突变体中，与 WT 和psbs KO相比，在 FL 条件下 PSI 核心和 PSI-LHCI 复合物的丰度大大降低。我们提出P. patens中的 LhcSR在苔藓适应动态光照变化中起着至关重要的作用。