Autophagy delivers cellular cargoes for degradation and plays an important role in nutrient recycling under nutrient limitation. A critical component in autophagy is the lipidation of phosphatidylethanolamine (PE) to autophagy-related protein 8 (ATG8) to form ATG8-PE. Here we show that phospholipase Dε (PLDε) in Arabidopsis cells interacts with ATG8 and hydrolyzes ATG8-PE conjugates. In response to nitrogen deficiency, the transcript and protein levels of PLDε increase and additionally, an increasing amount of PLDε became associated with intracellular membranes compared with its primary plasma membrane association under sufficient nitrogen in Arabidopsis seedlings. PLDε-knockout (KO) plants have a lower number, whereas PLDε-overexpressing (OE) plants have a higher number of autophagosomes than that in wild-type plants during nitrogen starvation. The level of ATG8-PE is lower in PLDε-KO, but higher in PLDε-OE plants than in wild-type plants. PLDε-KO and PLDε-OE Arabidopsis seedlings display accelerated and delayed leaf senescence, respectively, during nitrogen limitation. The results suggest that PLDε promotes autophagy in the plant response to nitrogen deficiency. The multifaceted effects of PLDε activity and interaction with ATG8 on autophagic processes are discussed.
Keywords: ATG8-PE conjugates; autophagy; lipid regulation; nitrogen responses; phospholipase D.