Abstract
Monogalactosyldiacylglycerol (MGDG) is not only the most abundant lipid of thylakoid membrane in chloroplast but also has an important role in photosynthesis. In Arabidopsis, MGDG synthases are classified into two types, type A (MGD1) and type B (MGD2 and 3). MGD1 is expressed in photosynthetic tissues, whereas MGD2 and 3 are expressed in nonphotosynthetic tissues such as roots and inflorescences. A knockout mutant of MGD1 shows a disruption of thylakoid membranes and no chlorophyll accumulation, demonstrating that MGD1 has an indispensable role in chloroplast biogenesis.
Since light and cytokinin substantially up-regulate the MGD1 gene expression, we used mutants for light and cytokinin receptors in Arabidopsis and investigated the regulatory mechanism for galactolipid biosynthesis. Lipid analysis indicated that cytokinin signals are important for light-dependent galactolipid accumulation during early seedling growth. The results suggest that the regulation of MGDG synthesis by light and cytokinin is important for chloroplast biogenesis.
