Poster: Photosynthesis

Abs # 378: Diversity of the function of sulfoquinovosyl diacylglycerol in cyanobacteria

Presenter:	Aoki, Motohide , s99701@educ.ls.toyaku.ac.jp
Authors	Aoki, Motohide  (A)   Sato, Norihiro  (A)   Meguro, Ayano  (A)   Tsuzuki, Mikio  (A)
Affiliations:	(A): School of Life Science, Tokyo University of Pharmacy and Life Science

Sulfoquinovosyl diacylglycerol (SQDG) is present in the thylakoid membranes of most photosynthetic organisms. We produced a disruptant of a cyanobacterium Synechocystis PCC6803 as to an ORF, the deduced amino acid sequence of which is homologous to those of sqdB gene products responsible for SQDG synthesis in Rhodobacter sphaeroides and Synechococcus PCC7942. The disruptant, designated as SD1, required SQDG supplementation for its growth. After SD1 pregrown in the presence of SQDG was transferred to SQDG-free conditions, net photosynthetic and photosystem II (PSII) activities on chlorophyll (Chl) basis decreased with SQDG content declining. Moreover, the sensitivity of PSII activity to DCMU and atrazine increased in SD1. However, SD1 maintained normal amounts of cytochrome b₅₅₉ and D1 protein, subunits constructing PSII core complex, on Chl basis, indicating the content of PSII reaction center was little changed irrespective of a decrease in SQDG content. Thus, SQDG would play a role of maintenance of PSII function in PCC6803, as was proposed for Chlamydomonas reinhardtii through an analysis of its SQDG-deficient mutant. In contrast, the SQDG-null mutant of PCC7942 we produced could grow without SQDG-supplementation, as was reported previously for another SQDG-null mutant of PCC7942 (Güler et al., 1996, J.Biol.Chem. 271, 7501), and showed the normal properties of PSII. Therefore, the difference exists for SQDG requirement of PSII and growth between these cyanobacterial species, suggesting that PSII core complex is diverse in relation to SQDG even in unicellular cyanobacteria. These cyanobacterial mutants would also provide us with a clue for elucidation of mechanism how SQDG interacts with PSII complex at the molecular level in PCC6803 and C. reinhardtii.