Abstract
Sulfoquinovosyldiacylglycerol (SQDG) is a sulfur-containing glycolipid and one of the component of thylakoid membrane. Recently, it was reported that plastidic UDP-glucose pyrophosphorylase (UGP3) which catalyzes glcose-1-phosphate (G1P) to UDP-glucose is essential for SQDG biosynthesis in Arabidopsis. In Chlamydomonas reinhardtii, AtUGP3 homolog is important for growth under phosphate or/and sulfate limitation. Therefore, we analyzed growth and lipid composition of UGP3 overexpression mutant in comparison with wild type and ugp3 under nutrient stress. As the results, differences between wild type and the mutants were not observed, suggesting that the function of UGP3 is different between higher plants and green alga. In plastids, phosphoglucose isomerase (PGI) is involved in G1P synthesis followed by starch synthesis. Indeed, pgi mutants contains significantly less starch than wild type. Therefore, to clarify if the G1P pool is shared between starch biosynthesis and SQDG synthesis, we analyzed lipid composition of pgi mutant. As the result, we found that the lipid composition of pgi is similar to wild type, suggesting that another G1P pool is involved in SQDG biosynthesis.
