Non-specific phospholipases C, NPC2 and NPC6, are required for root growth in Arabidopsis

Mutants in lipid metabolism often show a lethal phenotype during reproduction that prevents investigating a specific role of the lipid during different developmental processes. We focused on two non-specific phospholipases C, NPC2 and NPC6, whose double knock-out causes a gametophyte-lethal phenotype. To investigate the role of NPC2 and NPC6 during vegetative growth, we produced transgenic knock-down mutant lines that circumvent the lethal effect during gametogenesis. Despite no defect observed in leaves, root growth was significantly retarded, with abnormal cellular architecture in root columella cells. Furthermore, the short root phenotype was rescued by exogenous supplementation of phosphocholine, a product of non-specific phospholipase C (NPC) -catalyzed phosphatidylcholine hydrolysis. The expression of phospho-base N-methyltransferase 1 (PMT1), which produces phosphocholine and is required for root growth, was induced in the knock-down mutant lines and was attenuated after phosphocholine supplementation. These results suggest that NPC2 and NPC6 may be involved in root growth by producing phosphocholine via metabolic interaction with a PMT-catalyzed pathway, which highlights a tissue-specific role of NPC enzymes in vegetative growth beyond the gametophyte-lethal phenotype.