Knockdown of the PsbP protein does not prevent assembly of the dimeric PSII core complex but impairs accumulation of photosystem II supercomplexes in tobacco.
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.
Ido
Kunio
K
Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Ifuku
Kentaro
K
Yamamoto
Yumiko
Y
Ishihara
Seiko
S
Murakami
Akio
A
Takabe
Keiji
K
Miyake
Chikahiro
C
Sato
Fumihiko
F
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*
D045332:Photosystem II Protein Complex; D021122:Protein Subunits; C075419:photosystem II, psbL subunit