Involved in determining the orientation of cell expansion, probably by playing an important role in cellulose deposition. May act by recruiting cellulose synthesizing complexes to discrete positions on the cell surface. Located on the longitudinal sides of the cell rather than on the apical or basal sides. Expressed in roots, stems, leaves, flowers and siliques. Up-regulated in the root zone of rapid longitudinal expansion. A partial protein missing the N-terminal signal peptide was reported to complement a yeast mutant defective in phytochelatin synthesis. It is therefore possible that COBRA binds divalent metals. Belongs to the COBRA family.