Lysophosphatidylcholine homeostasis via the Lands cycle regulates root growth in Arabidopsis

Lysophosphatidylcholine acyltransferase (LPCAT) is a key enzyme in the Lands cycle that mediates the interconversion of phosphatidylcholine (PC) and lysophosphatidylcholine (LPC). A proper balance between LPC and PC is essential for phospholipid turnover and membrane homeostasis. In this study, we show that the Arabidopsis lpcat double mutant exhibits an altered LPC/PC ratio in root tissues, reflecting a compromised Lands cycle. Using a chemical phenocopying strategy, we found that root growth in the lpcat mutant was more sensitive than that the wild type to lyso-platelet-activating factor (lysoPAF), which is a structural analog of LPC. This growth defect was largely rescued when the lysoPAF treatment was combined with ONO-RS-082, which is a phospholipase A2 inhibitor. Subcellular localization using green fluorescent protein (GFP) fusions demonstrated that both LPCAT1 and LPCAT2 localize to the endoplasmic reticulum (ER) membrane. Furthermore, an RNA-seq analysis of root tissues from the lpcat mutant revealed transcriptional changes indicative of an unfolded protein response in the ER and altered endomembrane trafficking. Together, our results demonstrate that ER-localized LPCATs play a pivotal role in maintaining root growth when plants encounter conditions that require adjustments in lipid homeostasis.