The Chloroplast Gene ycf9 Encodes a Photosystem II (PSII) Core Subunit, PsbZ, That Participates in PSII Supramolecular Architecture

Abstract

We have characterized the biochemical nature and the function of PsbZ, the protein product of a ubiquitous open reading frame, which is known as ycf9 in Chlamydomonas and ORF 62 in tobacco, that is present in chloroplast and cyanobacterial genomes. After raising specific antibodies to PsbZ from Chlamydomonas and tobacco, we demonstrated that it is a bona fide photosystem II (PSII) subunit. PsbZ copurifies with PSII cores in Chlamydomonas as well as in tobacco. Accordingly, PSII mutants from Chlamydomonas and tobacco are deficient in PsbZ. Using psbZ-targeted gene inactivation in tobacco and Chlamydomonas, we show that this protein controls the interaction of PSII cores with the light-harvesting antenna; in particular, PSII-LHCII supercomplexes no longer could be isolated from PsbZ-deficient tobacco plants. The content of the minor chlorophyll binding protein CP26, and to a lesser extent that of CP29, also was altered substantially under most growth conditions in the tobacco mutant and in Chlamydomonas mutant cells grown under photoautotrophic conditions. These PsbZ-dependent changes in the supramolecular organization of the PSII cores with their peripheral antennas cause two distinct phenotypes in tobacco and are accompanied by considerable modifications in (1) the pattern of protein phosphorylation within PSII units, (2) the deepoxidation of xanthophylls, and (3) the kinetics and amplitude of nonphotochemical quenching. The role of PsbZ in excitation energy dissipation within PSII is discussed in light of its proximity to CP43, in agreement with the most recent structural data on PSII.

Differential accumulation ofLhcbgene products in thylakoid membranes ofZea maysplants grown under contrasting light and temperature conditions

“…Fluorescence analyses on intact leaves were performed using a home-made digital video imaging system. Maximal fluorescence (F m ) was measured on dark-adapted leaves with a homemade video-imaging apparatus previously described [22]…”

Structural and functional studies on Ycf12 (Psb30) and PsbZ-deletion mutants from a thermophilic cyanobacterium

“…In cyanobacteria, this complex consists of 17 membrane-spanning subunits, three extrinsic proteins, and more than 70 cofactors including chlorophylls (Chls), carotenoids, plastoquinones, pheophytins, manganese atoms, non-heme iron, calcium, chlorides, and heme groups, with a total molecular weight of around 350 kDa for a monomer. Among the 17 trans-membrane subunits, 13 have molecular weight lower than 10 kDa, and are termed low molecular weight (LMW) subunits. Twelve LMW subunits have single trans-membrane helix, and only PsbZ has two trans-membrane helices.…”

Chlamydomonas raudensis (UWO 241), Chlorophyceae, exhibits the capacity for rapid D1 repair in response to chronic photoinhibition at low temperature1

“…However, there is significant support for the specific role of the PSII subunit, PsbS, in regulating NPQ in terrestrial plants (Niyogi et al 2005). Swiatek et al (2001) reported that another photosystem subunit, PsbZ, regulates NPQ in C. reinhardtii. Thus, the precise molecular role of PsbS in regulating NPQ remains equivocal.…”