The HCF136 protein is essential for assembly of the photosystem II reaction center in Arabidopsis thaliana

Abstract

Hcf136 encodes a hydrophilic protein localized in the lumen of stroma thylakoids. Its mutational inactivation in Arabidopsis thaliana results in a photosystem II (PHII)-less phenotype. Under standard illumination, PSII is not detectable and the amount of photosystem I (PSI) is reduced, which implies that HCF136p may be required for photosystem biogenesis in general. However, at low light, a comparison of mutants with defects in PSII, PSI, and the cytochrome b 6 f complex reveals that HCF136p regulates selectively biogenesis of PSII. We demonstrate by in vivo radiolabeling of hcf136 that biogenesis of the reaction center (RC) of PSII is blocked. Gel blot analysis and a⁄nity chromatography of solubilized thylakoid membranes suggest that HCF136p associates with a PSII precomplex containing at least D2 and cytochrome b 559 . We conclude that HCF136p is essential for assembly of the RC of PSII and discuss its function as a chaperone-like assembly factor.

PsbN Is Required for Assembly of the Photosystem II Reaction Center in Nicotiana tabacum

“…Also, in this respect, the PSII-specific hcf136 mutant resembles the ΔpsbN phenotype. In contrast with hcf136, PsaA/ PsaB-containing subcomplexes were more strongly labeled at the expense of PSI-LHCI complexes in the wild type (Plücken et al, 2002). Therefore, the effect on the assembly efficiency of PSI can be regarded as a secondary effect when PSII RC assembly is affected and in consequence the thylakoid structure is changed.…”

“…Furthermore, hcf136 and ΔpsbN mutants exhibit a similar phenotype with respect to increased and dense grana stacking as well as photosynthetic performance (Supplemental Figure 4) (Meurer et al, 1998). Both precomplexes, pre-D1 and pre-D2, are assembled in hcf136 and ΔpsbN mutants at wild type-comparable rates but do not form the dimeric RC efficiently ( Figure 7A) (Plücken et al, 2002). The increased efficiency of PSI assembly in the mutants could either be attributed to a direct role of PsbN in PSI assembly or it reflects a secondary effect due to the altered thylakoid ultrastructure (Supplemental Figure 4).…”

“…We hypothesize that these differences arose from the use of more than 5 times higher growth light intensities of 55 µmol photons m 22 s 21 in this work. It has been shown in several studies that these still moderate light intensities are also deleterious to PSI when PSII assembly is primarily abolished (Meurer et al, 1998;Plücken et al, 2002;Swiatek et al, 2003). Furthermore, six hours of photoinhibition induced reduction only of PSII but not of PSI protein levels in the ΔpsbN mutants.…”

“…Although translation rates of PSII proteins in hcf136 were unaffected, their stationary levels were barely detectable, causing seedling lethality. HCF136 is found in the nonappressed stroma lamellae and is essential for early assembly of the PSII RC (Meurer et al, 1998;Plücken et al, 2002). LPA19, a Psb27 homolog, is suggested to facilitate processing of the D1 precursor protein at the C terminus at the lumenal side by the CtpA protease after insertion into the complex to generate mature D1 (Wei et al, 2010;Chi et al, 2012a).…”

Proteomic Analysis of Chloroplast-to-Chromoplast Transition in Tomato Reveals Metabolic Shifts Coupled with Disrupted Thylakoid Biogenesis Machinery and Elevated Energy-Production Components

“…The two proteins have been clearly identified by Peng et al (2006) and Cai et al (2010) but still annotated as unknown gene in The Arabidopsis Information Resource and Solyc databases. Another protein necessary for the assembly of PSII high chlorophyll fluorescence (HCF136, Solyc02g014150; Plücken et al, 2002) decreases continuously. A plastid genome-encoded protein, YCF4 (Solyc01g007360) belonging to the hypothetical chloroplast reading frame family (YCF) decreases strongly between the B and R stages in parallel with the late disassembly of PSI.…”