The identification of the yeastphosphatidate phosphohydrolase(PAH1) gene encoding an enzyme with phosphatidate phosphatase (PAP; 3-sn-phosphati-date phosphohydrolase, EC ) activity led to the discovery of mam-malianLipinsand subsequently to homologous genes from plants. In the present study, we describe the functional characterization ofArabidopsis and Brassica napushomologs ofPAH1.