Arabidopsis endoplasmic reticulum-localized acyltransferase LPAT2 interacts with ATI1/2 and mediates lipid droplet proliferation

Lipid droplet (LD) biogenesis from the endoplasmic reticulum (ER) is accompanied by conversion of phospholipids to triacylglycerol and expansion of phospholipid monolayer surface. The determinants of this process are largely unknown in plants. Here, we demonstrate that the Arabidopsis thaliana lysophosphatidic acid acyltransferase, LPAT2, and its product phosphatidic acid (PA), are critical lipid-based cues for LD proliferation. RNAi suppression of LPAT2 decrease PA accumulation at the monolayer surface of LDs, consequently compromising dark- or stress-induced LD biogenesis, whereas overexpression of LPAT2 exhibits opposite effects. Furthermore, LPAT2 physically interacts with ATG8-interacting protein 1/2 (ATI1/2), which serve as autophagy cargo receptors. Mutations of ATI1/2 drastically disrupted LPAT2 translocation from the ER to the forming LDs. Our data suggest that the LPAT2-ATI1/2 complex is the core protein machinery that facilitates LD biogenesis to mediate plant responses to developmental and environmental stimuli.