May serve to lubricate the movement of the cellulose microfibrils during cell growth and wall extension and/or may serve to maintain the fluid state of the slug cell wall (By similarity). Overexpression shows aberrant stalk formation. First detectable at the migrating slug stage. Observed throughout slug migration and culmination, and remains present in tip organizer cells. No phenotypic change. Belongs to the expansin family. Expansin A subfamily.