Molecular and Global Time-resolved Analysis of a psbSGene Dosage Effect on pH- and Xanthophyll Cycle-dependent Nonphotochemical Quenching in Photosystem II

Abstract

Photosynthetic light harvesting in plants is regulated by a pH-and xanthophyll-dependent nonphotochemical quenching process (qE) that dissipates excess absorbed light energy and requires the psbS gene product. An Arabidopsis thaliana mutant, npq4-1, lacks qE because of a deletion of the psbS gene, yet it exhibits a semidominant phenotype. Here it is shown that the semidominance is due to a psbS gene dosage effect. Diploid Arabidopsis plants containing two psbS gene copies (wild-type), one psbS gene (npq4-1/NPQ4 heterozygote), and no psbS gene (npq4-1/npq4-1 homozygote) were compared. Heterozygous plants had 56% of the wild-type psbS mRNA level, 58% of the wild-type PsbS protein level, and 60% of the wild-type level of qE. Global analysis of the chlorophyll a fluorescence lifetime distributions revealed three components in wild-type and heterozygous plants, but only a single long lifetime component in npq4-1. The short lifetime distribution associated with qE was inhibited by more than 40% in heterozygous plants compared with the wild type. Thus, the extent of qE measured as either the fractional intensities of the PSII chlorophyll a fluorescence lifetime distributions or steady state intensities was stoichiometrically related to the amount of PsbS protein.Absorption of light in excess of photosynthetic capacity necessitates mechanisms to protect plants from photo-oxidative damage (1). Overexcitation of chlorophyll (Chl) 1 and overreduction of the electron transport chain can result in increased generation of reactive intermediates and harmful byproducts of photosynthesis. For example, when excitation energy in singlet-excited Chl ( 1 Chl*) cannot be used to drive electron transport, the lifetime of 1 Chl* increases, resulting in an increased yield of triplet-excited Chl ( 3 Chl*) via intersystem crossing. 3 Chl* can generate singlet O 2 ( 1 O 2 *), which can directly damage pigments, proteins, and lipids in the photosynthetic apparatus. To maintain a short lifetime of 1 Chl* and minimize photo-oxidative damage, a nonphotochemical quenching process, called qE, is induced in excessive light, resulting in deexcitation of 1 Chl* molecules and thermal dissipation of excess absorbed light energy in the light-harvesting antenna of photosystem (PS) II (2, 3). Because it decreases the lifetime of 1 Chl*, qE can be measured easily as a decrease in the maximum yield of Chl fluorescence in isolated chloroplast membranes, algal cells, or intact leaves.qE is induced by a low pH in the thylakoid lumen of chloroplasts during illumination with excessive light (reviewed in Refs. 2-5). Low pH activates the violaxanthin de-epoxidase, which converts violaxanthin, V, into antheraxanthin, A, and then zeaxanthin, Z, as part of a xanthophyll cycle (6 -9). Binding of de-epoxidized xanthophylls (A and Z) and protons (H ϩ ) to undefined PSII proteins is hypothesized to result in a conformational change that effectively switches a PSII unit into a quenched state in which nonphotochemical de-excitation of 1 Chl* is favored (reviewed in Refs....

Chlamydomonas reinhardtii PsbS Protein Is Functional and Accumulates Rapidly and Transiently under High Light

“…S3A). This is similar to the situation in Arabidopsis, where PsbS abundance is also correlated to NPQ levels (Li et al, 2002a(Li et al, , 2002b). …”

“…In Chlamydomonas, the CP24 subunit, which is next to the LHCII-M trimer (Dekker and Boekema, 2005) and that has been suggested to detach from PSII during NPQ induction in a PsbS-dependent phenomenon (Betterle et al, 2009), is lacking and at its place a third LHCII trimer is bound to PSII (Tokutsu et al, 2012;Drop et al, 2014). Even if it is possible that PsbS in Chlamydomonas interacts somehow differently with PSII than in plants, we found that PsbS accumulation has a positive correlation with NPQ capacity as in plants (Li et al, 2002a(Li et al, , 2002b, further supporting a conserved PsbS-dependent NPQ mechanism.…”

Photosynthesis Control: An underrated short-term regulatory mechanism essential for plant viability

“…25,26 Similar results have been reported in pgr5 mutants of rice 37 and Chlamydomonas, 40 but not in mutants devoid of NPQ, such as in the Arabidopsis npq4 plants lacking PsbS protein, 43,45,49 supporting a key and specific role for the PGR5 protein in the Photosynthesis Control mechanism. Clearly, by ensuring the pH-dependent control of PQH 2 oxidation at the level of Cyt b 6 f, PGR5 prevents electrons from flowing freely from PSII to PSI, which would over-reduce the electron carriers on the acceptor side of PSI.…”

Changes in Transcript Abundance in Chlamydomonas reinhardtii following Nitrogen Deprivation Predict Diversion of Metabolism

“…In Arabidopsis (Arabidopsis thaliana), PSBS has been shown to play a critical role in nonphotochemical quenching (Li et al, 2000(Li et al, , 2002, but previous studies in C. reinhardtii have not detected either of the two PSBS proteins in the thylakoids, and nonphotochemical quenching was shown to be independent of these proteins (Bonente et al, 2008). Only rarely have ESTs been found for PSBS transcripts, with the exception of the cDNA stress collection II, which contains RNAs from different stress treatments, including the switch from ammonium to nitrate (Shrager et al, 2003;Bonente et al, 2008).…”