Phosphorylates the second messenger diacylglycerol (DAG) to generate phosphatidic acid (PA), another important signaling molecule (PubMed:32471859). PA is required for plant development and responses to abiotic stress and pathogen attack. May be involved in the accumulation of PA during cold stress (By similarity). Involved in the regulation of PA and phosphatidylcholine biosynthesis in growing pollen tubes (PubMed:30628082). Required for nitric oxide-dependent pollen tube growth and re-orientation responses (PubMed:32220864). Functions together with DGK2 in male gametophyte development and biosynthesis of phosphatidylglycerol and phosphatidylinositol in the endoplasmic reticulum (ER) (PubMed:32471859). Involved in PA production for pollen grain growth, as well as leaf and root growth (PubMed:32471859). Possesses guanylyl cyclase activity in vitro (PubMed:30628082, PubMed:32220864). a 1,2-diacyl-sn-glycerol + ATP = a 1,2-diacyl-sn-glycero-3-phosphate + ADP + H(+) Monomer. Expressed in the cytosol of growing pollen tubes. Highly expressed in pollen grains (PubMed:30628082). Expressed in roots, hypocotyls, leaf vasculature, developing anthers and stigmas, and receptacles of siliques (PubMed:32471859). Reduced plant size with small and curly leaves (PubMed:30628082). Reduced growth rate of pollen tubes and reduced number of seeds (PubMed:30628082). No visible phenotype under normal growth conditions, but the double mutants dgk2 and dgk4 exhibit defective pollen growth and seed development because of non-viable male gametophyte (PubMed:32471859). Belongs to the eukaryotic diacylglycerol kinase family.