Schwenkert Serena, Umate Pavan, Dal Bosco Cristina, Volz Stefanie, Mlçochová Lada, Zoryan Mikael, Eichacker Lutz A, Ohad Itzhak, Herrmann Reinhold G, Meurer Jörg
Department Biology I, Botany, Ludwig-Maximilians-University Munich, Menzingerstrasse 67, 80638 Munich, Germany.
J Biol Chem. 2006 Nov 10;281(45):34227-38. doi: 10.1074/jbc.M604888200. Epub 2006 Aug 18.
Photosystem II (PSII) core complexes consist of CP47, CP43, D1, D2 proteins and of several low molecular weight integral membrane polypeptides, such as the chloroplast-encoded PsbE, PsbF, and PsbI proteins. To elucidate the function of PsbI in the photosynthetic process as well as in the biogenesis of PSII in higher plants, we generated homoplastomic knock-out plants by replacing most of the tobacco psbI gene with a spectinomycin resistance cartridge. Mutant plants are photoautotrophically viable under green house conditions but sensitive to high light irradiation. Antenna proteins of PSII accumulate to normal amounts, but levels of the PSII core complex are reduced by 50%. Bioenergetic and fluorescence studies uncovered that PsbI is required for the stability but not for the assembly of dimeric PSII and supercomplexes consisting of PSII and the outer antenna (PSII-LHCII). Thermoluminescence emission bands indicate that the presence of PsbI is required for assembly of a fully functional Q(A) binding site. We show that phosphorylation of the reaction center proteins D1 and D2 is light and redox-regulated in the wild type, but phosphorylation is abolished in the mutant, presumably due to structural alterations of PSII when PsbI is deficient. Unlike wild type, phosphorylation of LHCII is strongly increased in the dark due to accumulation of reduced plastoquinone, whereas even upon state II light phosphorylation is decreased in delta psbI. These data attest that phosphorylation of D1/D2, CP43, and LHCII is regulated differently.
光系统II（PSII）核心复合物由CP47、CP43、D1、D2蛋白以及几种低分子量整合膜多肽组成，如叶绿体编码的PsbE、PsbF和PsbI蛋白。为了阐明PsbI在高等植物光合作用过程以及PSII生物发生中的功能，我们通过用壮观霉素抗性盒替换大部分烟草psbI基因，构建了同核敲除植物。突变体植物在温室条件下可进行光合自养生长，但对高光照射敏感。PSII的天线蛋白积累量正常，但PSII核心复合物的水平降低了50%。生物能量和荧光研究发现，PsbI对于二聚体PSII以及由PSII和外周天线（PSII-LHCII）组成的超复合物的稳定性是必需的，但对于其组装并非必需。热发光发射带表明，PsbI的存在是组装完全功能性Q(A)结合位点所必需的。我们发现，在野生型中，反应中心蛋白D1和D2的磷酸化受光和氧化还原调节，但在突变体中磷酸化被消除，这可能是由于PsbI缺失时PSII的结构改变所致。与野生型不同，由于还原型质体醌的积累，LHCII在黑暗中的磷酸化强烈增加，而在ΔpsbI中，即使在状态II光照下磷酸化也会降低。这些数据证明，D1/D2、CP43和LHCII的磷酸化受到不同的调节。
