Evidence That Cytochrome b559 Mediates the Oxidation of Reduced Plastoquinone in the Dark

102

The nuclear atpC1 gene encoding the ␥ subunit of the plastid ATP synthase has been inactivated by T-DNA insertion mutagenesis in Arabidopsis thaliana. In the seedling-lethal dpa1 (deficiency of plastid ATP synthase 1) mutant, the absence of detectable amounts of the ␥ subunit destabilizes the entire ATP synthase complex. The expression of a second gene copy, atpC2, is unaltered in dpa1 and is not sufficient to compensate for the lack of atpC1 expression. However, in vivo protein labeling analysis suggests that assembly of the ATP synthase ␣ and ␤ subunits into the thylakoid membrane still occurs in dpa1. As a consequence of the destabilized ATP synthase complex, photophosphorylation is abolished even under reducing conditions. Further effects of the mutation include an increased light sensitivity of the plant and an altered photosystem II activity. At low light intensity, chlorophyll fluorescence induction kinetics is close to those found in wild type, but non-photochemical quenching strongly increases with increasing actinic light intensity resulting in steady state fluorescence levels of about 60% of the minimal dark fluorescence. Most fluorescence quenching relaxed within 3 min after dark incubation. Spectroscopic and biochemical studies have shown that a high proton gradient is responsible for most quenching. Thylakoids of illuminated dpa1 plants were swollen due to an increased proton accumulation in the lumen. Expression profiling of 3292 nuclear genes encoding mainly chloroplast proteins demonstrates that most organelle functions are down-regulated. On the contrary, the mRNA expression of some photosynthesis genes is significantly up-regulated, probably to compensate for the defect in dpa1.

Section: Discussionsupporting

confidence: 50%

Inactivation of the Chloroplast ATP Synthase γ Subunit Results in High Non-photochemical Fluorescence Quenching and Altered Nuclear Gene Expression in Arabidopsis thaliana

Bosco

Lezhneva

Biehl³

et al. 2004

102

“…Transplastomic tobacco plants that have a mutation in PsbE showed lower associations between PsbP and PSII in the thylakoid membranes (45). It was reported that PsbJ in the vicinity of Cyt b 559 is required for the association of PsbP with PSII and the assembly of PsbR in tobacco (35,46), and that PsbR is required for the stable binding of PsbP and PsbQ in Arabidopsis (36).…”

Section: Discussionmentioning

confidence: 99%

The Conserved His-144 in the PsbP Protein Is Important for the Interaction between the PsbP N-terminus and the Cyt b559 Subunit of Photosystem II

Ido

Kakiuchi

Uno

et al. 2012

Background:PsbP is an extrinsic subunit of photosystem II in green plants. Results: H144A mutation in PsbP alters the chloride requirement and affects the interaction between its N terminus and the PsbE component of photosystem II. Conclusion:The N-and C-terminal domains of PsbP cooperate to support PSII activity. Significance: This provides important information about the binding characteristics of PsbP in green plant PSII.The PsbP protein regulates the binding properties of Ca 2؉ and Cl ؊ , and stabilizes the Mn cluster of photosystem II (PSII); however, the binding site and topology in PSII have yet to be clarified. Here we report that the structure around His-144 and Asp-165 in PsbP, which is suggested to be a metal binding site, has a crucial role for the functional interaction between PsbP and PSII. The mutated PsbP-H144A protein exhibits reduced ability to retain Cl ؊ anions in PSII, whereas the D165V mutation does not affect PsbP function. Interestingly, H144A/D165V double mutation suppresses the effect of H144A mutation, suggesting that these residues have a role other than metal binding. FTIR difference spectroscopy suggests that H144A/D165V restores proper interaction with PSII and induces the conformational change around the Mn cluster during the S 1 /S 2 transition. Cross-linking experiments show that the H144A mutation affects the direct interaction between PsbP and the Cyt b 559 ␣ subunit of PSII (the PsbE protein). However, this interaction is restored in the H144A/D165V mutant. In the PsbP structure, His-144 and Asp-165 form a salt bridge. H144A mutation is likely to disrupt this bridge and liberate Asp-165, inhibiting the proper PsbP-PSII interaction. Finally, mass spectrometric analysis has identified the cross-linked sites of PsbP and PsbE as Ala-1 and Glu-57, respectively. Therefore His-144, in the C-terminal domain of PsbP, plays a crucial role in maintaining proper N terminus interaction. These data provide important information about the binding characteristics of PsbP in green plant PSII.Photosystem II (PSII) 2 consists of both membrane-intrinsic and membrane-extrinsic subunits, and functions as a water/ plastoquinone oxidoreductase (for reviews, Refs. 1-4). On the thylakoid lumenal side of PSII, a metal cluster of four Mn ions, one Ca 2ϩ ion, and five oxo ligands (the Mn cluster) catalyzes the oxygen-evolving reaction. Additionally, two Cl Ϫ ions are bound near to the Mn cluster (5). The membrane-intrinsic subunits of PSII are involved in pigment and/or cofactor binding for photochemical reactions, while the membrane-extrinsic subunits surround the catalytic Mn cluster and play crucial roles in stabilizing the Mn cluster and retaining the PSII cofactor ions (6 -8).X-ray structural analysis of the cyanobacterial PSII complex at atomic resolution has revealed the location of subunits, pigments, and cofactors, including the exact organization of the subunits within PSII (5, 9 -11). However, the crystallographic information gained from the study of cyanobacterial PSII cannot necessarily be...

“…It has been suggested that cytochrome b 559 functions in the re-oxidation of the plastoquinone pool in dark-adapted leaves (65). Therefore, it is conceivable that PsbI also supports this function and that the plastoquinone pool remains predominantly reduced in the dark (Table 1).…”

Section: Transplastomic Psbi Knock-out Mutants In Tobacco Growmentioning

confidence: 99%

PsbI Affects the Stability, Function, and Phosphorylation Patterns of Photosystem II Assemblies in Tobacco

Schwenkert

Umate

Bosco

et al. 2006

Photosystem II (PSII) core complexes consist of CP47, CP43, D1, D2 proteins and of several low molecular weight integral membrane polypeptides, such as the chloroplast-encoded PsbE, PsbF, and PsbI proteins. To elucidate the function of PsbI in the photosynthetic process as well as in the biogenesis of PSII in higher plants, we generated homoplastomic knock-out plants by replacing most of the tobacco psbI gene with a spectinomycin resistance cartridge. Mutant plants are photoautotrophically viable under green house conditions but sensitive to high light irradiation. Antenna proteins of PSII accumulate to normal amounts, but levels of the PSII core complex are reduced by 50%. Bioenergetic and fluorescence studies uncovered that PsbI is required for the stability but not for the assembly of dimeric PSII and supercomplexes consisting of PSII and the outer antenna (PSII-LHCII). Thermoluminescence emission bands indicate that the presence of PsbI is required for assembly of a fully functional Q A binding site. We show that phosphorylation of the reaction center proteins D1 and D2 is light and redoxregulated in the wild type, but phosphorylation is abolished in the mutant, presumably due to structural alterations of PSII when PsbI is deficient. Unlike wild type, phosphorylation of LHCII is strongly increased in the dark due to accumulation of reduced plastoquinone, whereas even upon state II light phosphorylation is decreased in ⌬psbI. These data attest that phosphorylation of D1/D2, CP43, and LHCII is regulated differently.