Modulates cell morphogenesis by regulating cell wall formation and assembly, and/or growth polarization. Expressed in roots, leaves and flowers. Observed in emerging secondary roots and young leaves. During flower development, restricted to carpels, stamen filament, and the abscission zone of the floral whorls. Hydroxylated on proline residues in the S-P-P-P-P repeat. O-glycosylated on hydroxyprolines.