Abstract
The lipid composition of photosynthetic membranes is highly conserved in organisms performing oxygenic photosynthesis among higher plants and cyanobacteria. However the biosynthetic pathways of the major glycolipid monogalactosyldiacylglycerol (MGDG) are not conserved. Higher plants synthesize MGDG from diacylglycerol (DAG) and UDP-galactose while cyanobacteria produce monoglucosyldiacylglycerol (MGlcDG) from DAG and UDP-glucose followed by the epimerization of the sugar for generating MGDG.
We found that Chlamydomonas, evolutionally positioned between higher plants and cyanobacteria, has genes homologous to those for MGDG synthase and MGlcDG synthase, and confirmed that the two genes were transcriptionally expressed in the cell. To determine the biosynthetic pathway of MGDG in Chlamydomonas, we analyzed glycosyltransferase activities using UDP-galactose or UDP-glucose as a sugar donor after subfractionation of the cell. The result showed that the plant-type MGDG synthesis occurs in the membrane fraction. We will also show the results of the cloning of Chlamyomonas MGDG synthase and the biochemical properties.
