Department Biology I, Ludwig-Maximilians-University Munich (LMU), Plant Molecular Biology (Botany), Großhaderner Strasse 2, Planegg-Martinsried, Germany.
Planta. 2013 Feb;237(2):541-58. doi: 10.1007/s00425-012-1775-y. Epub 2012 Oct 21.
Reversible phosphorylation of LHCII, the light-harvesting complex of photosystem II, controls its migration between the two photosystems (state transitions), and serves to adapt the photosynthetic machinery of plants and green algae to short-term changes in ambient light conditions. The thylakoid kinase STN7 is required for LHCII phosphorylation and state transitions in vascular plants. Regulation of STN7 levels occurs at the post-translational level, depends on the thylakoid redox state, and might involve reversible autophosphorylation. Here, we have analysed the effects of different light conditions and chemical inhibitors on the abundance of STN7 transcripts and their products. This analysis was performed in wild-type Arabidopsis thaliana plants, in several photosynthetic mutants, and in lines overexpressing STN7 (oeSTN7) or expressing mutant variants of STN7 carrying single or double cysteine-serine exchanges. It was found that accumulation of the STN7 protein is also controlled at the level of transcript abundance. Under certain conditions, exposure to high light or far-red light treatment, the relative decreases in LHCII phosphorylation can be attributed to decreases in STN7 abundance. Nevertheless, inhibitor experiments showed that redox control of LHCII kinase activity persists in oeSTN7 plants. STN7 dimers were found in oeSTN7 plants and in lines with single cysteine-serine exchanges, indicating that dimerisation involves disulphide bridges. We speculate that transient STN7 dimerisation is required for STN7 activity, and that the altered dimerisation behaviour of oeSTN7 plants might be responsible for the unusually high phosphorylation of LHCII in the dark found in this genotype.
LHCII 的可逆磷酸化是光系统 II 的光捕获复合物，控制其在两个光系统之间的迁移（状态转换），并使植物和绿藻的光合作用机器适应环境光条件的短期变化。类囊体激酶 STN7 是 LHCII 磷酸化和血管植物状态转换所必需的。STN7 水平的调节发生在翻译后水平，依赖于类囊体的氧化还原状态，可能涉及可逆自磷酸化。在这里，我们分析了不同光照条件和化学抑制剂对 STN7 转录物及其产物丰度的影响。这项分析是在野生型拟南芥植物、几种光合作用突变体以及过表达 STN7（oeSTN7）或表达携带单个或双半胱氨酸-丝氨酸交换的突变体的系中进行的。结果发现，STN7 蛋白的积累也受到转录物丰度的控制。在某些条件下，暴露于高光或远红光处理下，LHCII 磷酸化的相对减少可归因于 STN7 丰度的降低。然而，抑制剂实验表明，LHCII 激酶活性的氧化还原控制在 oeSTN7 植物中仍然存在。在 oeSTN7 植物和具有单个半胱氨酸-丝氨酸交换的系中发现了 STN7 二聚体，表明二聚化涉及二硫键。我们推测，STN7 活性需要瞬时 STN7 二聚化，并且 oeSTN7 植物改变的二聚化行为可能是导致该基因型在黑暗中 LHCII 异常高磷酸化的原因。
