Knockdown of the PsbP protein does not prevent assembly of the dimeric PSII core complex but impairs accumulation of photosystem II supercomplexes in tobacco |
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Authors: | Kunio Ido Yumiko Yamamoto Seiko Ishihara Keiji Takabe Fumihiko Sato |
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Institution: | a Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan b Kobe University Research Center for Inland Seas, Awaji, Hyogo 656-2401, Japan c Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan d Research Institute of Innovative Technology for the Earth (RITE), Kyoto 619-0292, Japan |
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Abstract: | The PsbP protein is an extrinsic subunit of photosystem II (PSII) specifically found in land plants and green algae. Using PsbP-RNAi tobacco, we have investigated effects of PsbP knockdown on protein supercomplex organization within the thylakoid membranes and photosynthetic properties of PSII. In PsbP-RNAi leaves, PSII dimers binding the extrinsic PsbO protein could be formed, while the light-harvesting complex II (LHCII)-PSII supercomplexes were severely decreased. Furthermore, LHCII and major PSII subunits were significantly dephosphorylated. Electron microscopic analysis showed that thylakoid grana stacking in PsbP-RNAi chloroplast was largely disordered and appeared similar to the stromally-exposed or marginal regions of wild-type thylakoids. Knockdown of PsbP modified both the donor and acceptor sides of PSII; In addition to the lower water-splitting activity, the primary quinone QA in PSII was significantly reduced even when the photosystem I reaction center (P700) was noticeably oxidized, and thermoluminescence studies suggested the stabilization of the charged pair, S2/QA−. These data indicate that assembly and/or maintenance of the functional MnCa cluster is perturbed in absence of PsbP, which impairs accumulation of final active forms of PSII supercomplexes. |
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Keywords: | Extrinsic proteins LHCII-PSII supercomplex Nicotiana tabacum Oxygen-evolving complex Photosystem II PsbP |
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