In association with LNG2, regulates leaf morphology by promoting longitudinal polar cell elongation independently of ROT3. Interacts (via C-terminus) with TON1A and TON1B. Expressed in roots, petioles, leaf blades and floral organs. No visible phenotype under normal growth conditions, but the lng1 and lng2 double mutant shows reduced length of cotyledons, rosette leaves, siliques and flowers. The gain-of-function mutant lng1-1D (T-DNA tagging) shows increased elongation of aerial lateral organs, partly due to elongated cells in leaves, petals and siliques.