Role of sulfoquinovosyl diacylglycerol for the maintenance of photosystem II in Chlamydomonas reinhardtii

Abstract

The physiological role of sulfoquinovosyl diacylglycerol (SQDG) in photosynthesis was investigated with a SQDG defective mutant (hf-2) of Chlamydomonas reinhardtii that did not have any detectable amount of SQDG. The mutant showed a lower rate of photosystem II (PSII) activity by 40% and also a lower growth rate than those of the wildtype. Results of genetical analysis of hf-2 strongly suggest that the SQDG defect and the lowered PSII activity are due to a single gene mutation. The supplementation of SQDG to hf-2 cells restored the lowered PSII activity to the same level as that of wild-type cells, and also enabled the mutant to grow even in the presence of 135 nM 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Moreover, the incubation of isolated thylakoid membranes of hf-2 with SQDG raised the lowered PSII activity. Chemical modifications of SQDG impaired the recovery of PSII activity. The results suggest that SQDG is indispensable for PSII activity in Chlamydomonas by maintaining PSII complexes in their proper state.Keywords: sulfoquinovosyl diacylglycerol; photosystem II; Chlamydomonas; thylakoid membrane; glycolipid.The primary process in photosynthesis occurs in thylakoid membranes. Protein complexes such as photosystem (PS) I and PSII play a role of energy conversion from excitation energy to redox potential. As autotrophic organisms obtain energy by photosynthesis, its efficiency is a matter of survival. Thylakoid membranes consist of four glycerolipids; monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), phosphatidylglycerol (PtdG) and sulfoquinovosyl diacylglycerol (SQDG). The lipophilic matrix may promote the efficiency of the reaction by organized pigment protein complexes [1][2][3]. Thylakoid membranes adapt to environmental conditions such as the unsaturation of lipids under low temperatures [4,5]. Thus, it is important to investigate the participation of thylakoid lipids in photosynthesis.Of all known thylakoid membrane lipids, SQDG is a unique acidic glycolipid due to an unusual head group, sulfoquinovose, and is likely to be present almost exclusively in thylakoid membranes [6]. In anoxygenic photosynthetic bacteria, it is localized in the Proteobacteria a-subgroup except for Rhodopseudomonas viridis whose photosystem resembles the PSII complex of higher plants [7]. Additionally, SQDG is present in organisms that perform oxygenic photosynthesis from cyanobacteria to higher plants, except for Gloeobacter violaceus PCC7421, which is considered as one of the ancient cyanobacteria and lacks thylakoid membranes [8,9].SQDG-null mutants of Rhodobacter sphaeroides and Synechococcus sp. PCC7942 did not show any effect on the photosynthetic apparatus [10,11]. By separation of the PSII complex using detergents, it can be shown that SQDG is associated with the PSII complex in thylakoid membranes [1,[12][13][14][15]. In contrast to the SQDG-null mutants of bacteria, the SQDG-defective mutant (hf-2) obtained by UV irradiation in Chlamydomonas reinhardtii showed a slightly slower growth rate and...

Decrease in the efficiency of the electron donation to tyrosine Z of photosystem II in an SQDG‐deficient mutant of Chlamydomonas

“…2). Under high light condition, hf-2 was slightly more sensitive to photoinhibition, and the recovery was a little slower than in the wild-type [12]. The D1 polypeptide of the reaction center in PSII seems to be one of the most severely modi¢ed subunits in hf-2.…”

“…In fact, the incubation of thylakoid membranes of hf-2 with SQDG on ice resulted in an increase of the PSII activity without de novo protein synthesis [5]. We will propose the hypothesis that SQDG is indispensable for maximum PSII activity in Chlamydomonas.…”

Impairment in Sulfite Reductase Leads to Early Leaf Senescence in Tomato Plants

“…However, SQD1 activity in SIR Ri plants was apparently insufficient to protect chloroplasts from sulfite. The increased SQDG level in the upper leaves of SIR Ri plants might be also related to additional stabilization of PSII (Minoda et al, 2002(Minoda et al, , 2003 required during enhanced sulfite production.…”

The Marine Microalga, Heterosigma akashiwo, Converts Industrial Waste Gases into Valuable Biomass

“…Enhanced synthesis of these fatty acids in the presence of high CO 2 and NO (Figure 3) likely functioned to support an increase in thylakoid number or surface area as suggested by a significant 17% increase in chlorophyll content (Benning, 1998;Minoda et al, 2002). This subsequently explains the increase in C14:0, which is linked to the fatty acid synthase enzyme prior to the two carbon elongation cycle that produces C16:0, where C16:0 is then released from fatty acid synthase as the precursor to long chain saturated and unsaturated fatty acid synthesis.…”