Mekala Nageswara Rao, Suorsa Marjaana, Rantala Marjaana, Aro Eva-Mari, Tikkanen Mikko
Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014 Turku, Finland.
Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014 Turku, Finland
Plant Physiol. 2015 Jun;168(2):721-34. doi: 10.1104/pp.15.00488. Epub 2015 Apr 22.
Photosystem II (PSII) core and light-harvesting complex II (LHCII) proteins in plant chloroplasts undergo reversible phosphorylation upon changes in light intensity (being under control of redox-regulated STN7 and STN8 kinases and TAP38/PPH1 and PSII core phosphatases). Shift of plants from growth light to high light results in an increase of PSII core phosphorylation, whereas LHCII phosphorylation concomitantly decreases. Exactly the opposite takes place when plants are shifted to lower light intensity. Despite distinct changes occurring in thylakoid protein phosphorylation upon light intensity changes, the excitation balance between PSII and photosystem I remains unchanged. This differs drastically from the canonical-state transition model induced by artificial states 1 and 2 lights that concomitantly either dephosphorylate or phosphorylate, respectively, both the PSII core and LHCII phosphoproteins. Analysis of the kinase and phosphatase mutants revealed that TAP38/PPH1 phosphatase is crucial in preventing state transition upon increase in light intensity. Indeed, tap38/pph1 mutant revealed strong concomitant phosphorylation of both the PSII core and LHCII proteins upon transfer to high light, thus resembling the wild type under state 2 light. Coordinated function of thylakoid protein kinases and phosphatases is shown to secure balanced excitation energy for both photosystems by preventing state transitions upon changes in light intensity. Moreover, proton gradient regulation5 (PGR5) is required for proper regulation of thylakoid protein kinases and phosphatases, and the pgr5 mutant mimics phenotypes of tap38/pph1. This shows that there is a close cooperation between the redox- and proton gradient-dependent regulatory mechanisms for proper function of the photosynthetic machinery.
植物叶绿体中的光系统II（PSII）核心蛋白和捕光复合物II（LHCII）蛋白会在光照强度变化时发生可逆磷酸化（受氧化还原调节的STN7和STN8激酶以及TAP38/PPH1和PSII核心磷酸酶的控制）。植物从生长光转移到高光下会导致PSII核心磷酸化增加，而LHCII磷酸化则随之减少。当植物转移到较低光照强度时，情况正好相反。尽管类囊体蛋白磷酸化在光照强度变化时会发生明显改变，但PSII和光系统I之间的激发平衡保持不变。这与由人工状态1和状态2光诱导的典型状态转换模型有很大不同，在该模型中，PSII核心蛋白和LHCII磷酸化蛋白分别会同时发生去磷酸化或磷酸化。对激酶和磷酸酶突变体的分析表明，TAP38/PPH1磷酸酶对于防止光照强度增加时的状态转换至关重要。实际上，tap38/pph1突变体在转移到高光下时，PSII核心蛋白和LHCII蛋白都会发生强烈的同时磷酸化，因此类似于处于状态2光下的野生型。类囊体蛋白激酶和磷酸酶的协同作用表明，通过防止光照强度变化时的状态转换，可以确保两个光系统获得平衡的激发能。此外，质子梯度调节蛋白5（PGR5）是类囊体蛋白激酶和磷酸酶正常调节所必需的，pgr5突变体模拟了tap38/pph1的表型。这表明，在光合机构的正常功能中，氧化还原和质子梯度依赖性调节机制之间存在密切合作。
