A Pair of Arabidopsis Diacylglycerol Kinases Essential for Gametogenesis and Endoplasmic Reticulum Phospholipid Metabolism in Leaves and Flowers.

Phosphatidic acid (PA) is a key phospholipid in glycerolipid metabolism and signaling. Diacylglycerol kinase (DGK) produces PA by phosphorylating diacylglycerol, a crucial step in PA metabolism. Although DGK activity is known to be involved in plant development and stress response, how specific DGK isoforms function in development and phospholipid metabolism remains elusive. Here, we showed that Arabidopsis (Arabidopsis thaliana) DGK2 and DGK4 are crucial for gametogenesis and biosynthesis of phosphatidylglycerol and phosphatidylinositol in the endoplasmic reticulum (ER). With comprehensive transcriptomic data of seven DGKs and genetic crossing, we found that dgk2-1/- dgk4-1/- plants were gametophyte lethal, although parental single homozygous plants were viable. The dgk2-1/+ dgk4-1/+ double heterozygote showed defective pollen tube growth and seed development because of nonviable mutant gametes. DGK2 and DGK4 were localized to the ER and were involved in PA production for pollen tube growth. Transgenic knockdown lines of DGK2 and DGK4 confirmed the gametophyte defect and also revealed defective leaf and root growth. Glycerolipid analysis in the knockdown lines showed that phosphatidylglycerol and phosphatidylinositol metabolism was affected differently in floral buds and leaves. These results suggest that DGK2 and DGK4 are essential during gametogenesis and are required for ER-localized phospholipid metabolism in vegetative and reproductive growth.