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 (By similarity). Target of the transcriptional activator LBD18. Regulated by LBD18 to promote lateral root formation (PubMed:22974309). Expressed during lateral root development. By auxin. Belongs to the expansin family. Expansin A subfamily.