Ishihara Seiko, Takabayashi Atsushi, Ido Kunio, Endo Tsuyoshi, Ifuku Kentaro, Sato Fumihiko
Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Plant Physiol. 2007 Nov;145(3):668-79. doi: 10.1104/pp.107.105866. Epub 2007 Sep 7.
PsbP, an extrinsic subunit of photosystem II (PSII), is a nuclear-encoded protein that optimizes the water-splitting reaction in vivo. In addition to PsbP, higher plants have two nuclear-encoded genes for PsbP homologs (PsbP-like proteins [PPLs]) that show significant sequence similarity to a cyanobacterial PsbP homolog (cyanoP); however, the function of PPLs in higher plants has not yet been elucidated. In this study, we characterized Arabidopsis (Arabidopsis thaliana) mutants lacking either of two PPLs, PPL1 and PPL2. Phylogenetic analysis suggests that PPL1 would be an ortholog of cyanoP, and PPL2 and PsbP may have a paralogous relationship with PPL1. Analysis on mRNA expression profiles showed that PPL1 expressed under stress conditions and PPL2 coexpressed with the subunits of chloroplast NAD(P)H dehydrogenase (NDH) complex. Consistent with these suggestions, PSII activity in a ppl1 mutant was more sensitive to high-intensity light than wild type, and the recovery of photoinhibited PSII activity was delayed in ppl1 plants. Therefore, PPL1 is required for efficient repair of photodamaged PSII. Furthermore, the stoichiometric level and activity of the chloroplast NDH complex in thylakoids were severely decreased in a ppl2 mutant, demonstrating that PPL2 is a novel thylakoid lumenal factor required for accumulation of the chloroplast NDH complex. These results suggest that during endosymbiosis and subsequent gene transfer to the host nucleus, cyanoP from ancient cyanobacteria evolved into PPL1, PPL2, and PsbP, and each of them has a distinct role in photosynthetic electron transfer in Arabidopsis.
PsbP是光系统II（PSII）的一种外在亚基，是一种核编码蛋白，可在体内优化水裂解反应。除了PsbP，高等植物还有两个与PsbP同源物（PsbP样蛋白[PPLs]）相关的核编码基因，它们与蓝藻PsbP同源物（cyanoP）具有显著的序列相似性；然而，高等植物中PPLs的功能尚未阐明。在本研究中，我们对拟南芥（Arabidopsis thaliana）中缺失两种PPLs（PPL1和PPL2）之一的突变体进行了表征。系统发育分析表明，PPL1可能是cyanoP的直系同源物，而PPL2和PsbP可能与PPL1具有旁系同源关系。对mRNA表达谱的分析表明，PPL1在胁迫条件下表达，PPL2与叶绿体NAD(P)H脱氢酶（NDH）复合体的亚基共表达。与这些推测一致，ppl1突变体中的PSII活性对高强度光比野生型更敏感，并且ppl1植物中光抑制的PSII活性的恢复延迟。因此，PPL1是光损伤PSII有效修复所必需的。此外，ppl2突变体中类囊体中叶绿体NDH复合体的化学计量水平和活性严重降低，表明PPL2是叶绿体NDH复合体积累所需的一种新型类囊体腔因子。这些结果表明，在共生以及随后的基因转移到宿主细胞核的过程中，古代蓝藻的cyanoP进化成了PPL1、PPL2和PsbP，并且它们各自在拟南芥的光合电子传递中具有不同的作用。
