Causes loosening and extension of plant cell walls by disrupting non-covalent bonding between cellulose microfibrils and matrix glucans. No enzymatic activity has been found. Required for normal plant growth. May be required for rapid internodal elongation in deepwater rice during submergence. Expressed in lateral root primordia, adventitious root primordia, coleoptiles, shoot apex, leaf primordia, very young leaves, panicles and flowers. By gibberellin (GA3), submergence and wounding. Plants are smaller. Belongs to the expansin family. Expansin A subfamily.