A pair of phospho‐base methyltransferases important for phosphatidylcholine biosynthesis in Arabidopsis

Summary Phosphatidylcholine (PtdCho) is a predominant membrane lipid class in eukaryotes. Phospho‐base N‐methyltransferase (PMT) catalyzes a critical step in PtdCho biosynthesis. However, in Arabidopsis thaliana, the discovery of involvement of the specific PMT isoform in PtdCho biosynthesis remains elusive. Here, we show that PMT1 and PMT3 redundantly play an essential role in phosphocholine (PCho) biosynthesis, a prerequisite for PtdCho production. A pmt1 pmt3 double mutant was devoid of PCho, which affected PtdCho biosynthesis in vivo, showing severe growth defects in post‐embryonic development. PMT1 and PMT3 were both highly expressed in the vasculature. The pmt1 pmt3 mutants had specifically affected leaf vein development and showed pale‐green seedlings that were rescued by exogenous supplementation of PCho. We suggest that PMT1 and PMT3 are the primary enzymes for PCho biosynthesis and are involved in PtdCho biosynthesis and vascular development in Arabidopsis seedlings. Significance Statement This work addressed two methyltransferases crucial for the biosynthesis of phosphatidylcholine, the most predominant phospholipid class in Arabidopsis. Specific vascular defect in the methyltransferase mutant deficient in phosphatidylcholine biosynthesis suggested an emerging role for phosphatidylcholine biosynthesis in vascular development besides its known function as a constituent of cellular membranes.