Plastid Anionic Lipids Are Essential for the Development of Both Photosynthetic and Non-Photosynthetic Organs in Arabidopsis thaliana

The lipid bilayer matrix of the thylakoid membrane of cyanobacteria and chloroplasts of plants and algae is mainly composed of uncharged galactolipids, but also contains anionic lipids sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) as major constituents. The necessity of PG for photosynthesis is evident in all photosynthetic organisms examined to date, whereas the requirement of SQDG varies with species. In plants, although PG and SQDG are also found in non-photosynthetic plastids, their importance for the growth and functions of non-photosynthetic organs remains unclear. In addition, plants synthesize another anionic lipid glucuronosyldiacylglycerol (GlcADG) during phosphorus starvation, but its role in plant cells is not elucidated yet. To understand the functional relationships among PG, SQDG, and GlcADG, we characterized several Arabidopsis thaliana mutants defective in biosynthesis of these lipids. The mutants completely lacking both PG and SQDG biosynthesis in plastids showed developmental defects of roots, hypocotyls, and embryos in addition to leaves, which suggests that these lipids are pleiotropically required for the development of both photosynthetic and non-photosynthetic organs. Furthermore, our analysis revealed that SQDG, but not GlcADG, is essential for complementing the role of PG, particularly in photosynthesis under PG-deficient conditions such as phosphorus starvation.

Automated summary

The thylakoid membrane of cyanobacteria, plants, and algae mainly consists of uncharged galactolipids, but also includes anionic lipids such as sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG). Phosphatidylglycerol (PG) is essential for photosynthesis in all examined organisms, while the importance of SQDG varies. Additionally, plants produce another anionic lipid, glucuronosyldiacylglycerol (GlcADG), under phosphorus starvation, with its role still unclear. Studies on Arabidopsis mutants lacking PG and SQDG biosynthesis in plastids showed developmental defects in both photosynthetic and non-photosynthetic organs, indicating the pleiotropic role of these lipids. SQDG, but not GlcADG, is crucial for complementing PG in photosynthesis under PG-deficient conditions like phosphorus starvation.