title: Knockdown of the PsbP protein does not prevent assembly of the dimeric PSII core complex but impairs accumulation of photosystem II supercomplexes in tobacco.
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 Q(A) 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, S(2)/Q(A)(-). 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.
authors.affiliation: Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Ido
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ifuku
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Seiko
authors.initials: S
authors.lastname: Ishihara
authors.forename: Akio
authors.initials: A
authors.lastname: Murakami
authors.forename: Keiji
authors.initials: K
authors.lastname: Takabe
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Sato
mesh_terms: D002736:Chloroplasts / Q000648:ultrastructure; D019281:Dimerization; D017353:Gene Deletion; D008954:Models, Biological; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000648:ultrastructure; D030821:Plants, Genetically Modified; D021122:Protein Subunits / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D034622:RNA Interference; D020524:Thylakoids / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D021122:Protein Subunits; C075419:photosystem II, psbL subunit