Abstract
Monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in thylakoid membranes of chloroplasts. In Arabidopsis, three MGDG synthase genes are encoded on the genome (atMGD1, atMGD2 and atMGD3). MGD1 is localized to the inner envelope membranes of chloroplasts and would mainly contribute to thylakoid membrane construction. In this study, we newly isolated a mgd1 knockout mutant, which showed severe growth defect during seedling development and no chlorophyll accumulation. Lipid analysis revealed that not only MGDG but also digalactosyldiacylglycerol (DGDG) greatly decreased in mgd1, suggesting the necessity of MGD1 in galactolipid biosynthesis. Moreover, MGDG in this mutant possessed no 16:3 fatty acids, which indicates complete defect in prokaryotic MGDG biosynthesis. These data demonstrate that MGD1 is necessary for galactolipid biosynthesis via prokaryotic pathway. Furthermore, MGD1 knockout causes abnormal embryogenesis, suggesting that MGD1 plays an important role in embryo development in addition to seedling growth.
