PARENT SESSION
Posters P7B Evolution of photosynthesis. Abstracts (579-591)

The roles of sulfolipid, sulfoquinovosyl diacylglycerol, in photosynthetic organisms. Motohide Aoki^*,1, Norihiro Sato¹, Ayano Meguro¹, Mikio Tsuzuki¹, ¹ Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo, Japan

ABSTRACT- Interestingly, there are differences in the degree of the contribution of SQDG to photosynthesis even in cyanobacteria. The SQDG-deficient mutant of Synechococcus sp. PCC7942, distinct from SQDG-deficient mutants of Synechocystis sp. PCC6803 and a green alga, Chlamydomonas reinhardtii, showed no deleterious effect of the SQDG defect on PSII activity or its sensitivity to the herbicides. We consider that the PSII complex of Synechocystis sp. PCC6803 is more evolved than that of Synechococcus sp. PCC7942, since SQDG is not required for functioning the photosystem of Rhodobacter sphaeroides, the prototype of the PSII complex, but is responsible for that of the PSII complex of C. reinhardtii. It was also suggested that Synechococcus sp. PCC7942 was closely related to alpha-group bacteria rather than Synechocystis sp. PCC6803, since Synechococcus sp. PCC7942 was positioned in the same cluster as R. sphaeroides apart from other cyanobacteria in the phylogenetic tree for known UDP-sulfoquinovose synthases and, contrary to Synechocystis sp. PCC6803, did not have some fatty acid desaturases or the tocopherols synthesizing ability [refer to the poster by N. Sato et al. in this congress; Sato et al. (2003) DNA Res. 10, 229-237; Riekhof et al. (2003) Plant Physiol. 133, 864-874]. Therefore, the interaction of SQDG with PSII might appear in cyanobacteria during the evolution. It was suggested that the effective quantum yield of PSII was slightly but significantly reduced in SQDG-deficient mutants of a higher plant Arabidopsis thaliana [Yu et al. (2002) Proc. Natl. Acad. Sci. USA 99, 5732-5737]. It is considered that a cyanobacterium is origin of the chloroplast of the eukaryotic photosynthesis organisms. Taken together, it was proposed that in the process for the evolution, which reaches higher plant from photosynthetic bacteria, the interaction of SQDG with PSII appeared in cyanobacteria such as Synechocystis sp. PCC6803 and has been conserved to higher plant. Thus, the PSII complex may have evolved along with the interaction of SQDG as one of the factors to define the properties of the complex.

KEY WORDS: sulfoquinovosyl diacylglycerol, sulfolipid, photosystem II, cyanobacteria