Phosphorylates the second messenger diacylglycerol (DAG) to generate phosphatidic acid (PA), another important signaling molecule (PubMed:30887532). PA is required for plant development and responses to abiotic stress (Probable). May play a role in disease resistance responses to pathogen attack (Probable). Modulates root architecture by regulating the ratio of DAG and PA, which have opposite effect on the promotion or suppression of lateral roots vs seminal roots (PubMed:30887532). Suppresses lateral root number, but promotes seminal root and crown root thickness (PubMed:30887532). a 1,2-diacyl-sn-glycerol + ATP = a 1,2-diacyl-sn-glycero-3-phosphate + ADP + H(+) Monomer. Highly expressed in roots. Induced by infection with the rice blast fungus Magnaporthe oryzae, and the inducer of plant defense responses benzothiadiazole (BTH). Increased number and density of lateral roots and decreased thickness of seminal roots. Plants overexpressing DGK1 exhibit decreased density of lateral roots and increased thickness of seminal roots. Belongs to the eukaryotic diacylglycerol kinase family.