Ifuku Kentaro, Yamamoto Yumiko, Ono Taka-Aki, Ishihara Seiko, Sato Fumihiko
Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Plant Physiol. 2005 Nov;139(3):1175-84. doi: 10.1104/pp.105.068643. Epub 2005 Oct 21.
PsbP and PsbQ proteins are extrinsic subunits of photosystem II (PSII) and participate in the normal function of photosynthetic water oxidation. Both proteins exist in a broad range of the oxygenic photosynthetic organisms; however, their physiological roles in vivo have not been well defined in higher plants. In this study, we established and analyzed transgenic tobacco (Nicotiana tabacum) plants in which the levels of PsbP or PsbQ were severely down-regulated by the RNA interference technique. A plant that lacked PsbQ showed no specific phenotype compared to a wild-type plant. This suggests that PsbQ in higher plants is dispensable under the normal growth condition. On the other hand, a plant that lacked PsbP showed prominent phenotypes: drastic retardation of growth, pale-green-colored leaves, and a marked decrease in the quantum yield of PSII evaluated by chlorophyll fluorescence. In PsbP-deficient plant, most PSII core subunits were accumulated in thylakoids, whereas PsbQ, which requires PsbP to bind PSII in vitro, was dramatically decreased. PSII without PsbP was hypersensitive to light and rapidly inactivated when the repair process of the damaged PSII was inhibited by chloramphenicol. Furthermore, thermoluminescence studies showed that the catalytic manganese cluster in PsbP-deficient leaves was markedly unstable and readily disassembled in the dark. The present results demonstrated that PsbP, but not PsbQ, is indispensable for the normal PSII function in higher plants in vivo.
PsbP和PsbQ蛋白是光系统II（PSII）的外在亚基，参与光合水氧化的正常功能。这两种蛋白存在于广泛的产氧光合生物中；然而，它们在高等植物体内的生理作用尚未得到很好的界定。在本研究中，我们建立并分析了通过RNA干扰技术使PsbP或PsbQ水平严重下调的转基因烟草（Nicotiana tabacum）植株。与野生型植株相比，缺乏PsbQ的植株没有表现出特定的表型。这表明在正常生长条件下，高等植物中的PsbQ是可有可无的。另一方面，缺乏PsbP的植株表现出显著的表型：生长严重迟缓、叶片呈淡绿色，以及通过叶绿素荧光评估的PSII量子产率显著降低。在缺乏PsbP的植株中，大多数PSII核心亚基积累在类囊体中，而在体外需要PsbP才能结合到PSII上的PsbQ则显著减少。当受损PSII的修复过程被氯霉素抑制时，没有PsbP的PSII对光高度敏感并迅速失活。此外，热发光研究表明，缺乏PsbP的叶片中的催化锰簇明显不稳定，在黑暗中容易分解。目前的结果表明，在高等植物体内，PsbP而非PsbQ对于正常的PSII功能是不可或缺的。
