Structural component which strengthens the primary cell wall. Experimental confirmation may be lacking for some isoforms. Predominantly expressed in the roots. Not detected in the leaves, nor in flowers or flower buds. Wounding reverses this pattern, turning on the gene in the leaves and repressing it in the roots. Early expressed in the whole plant. Detected in the leaves of 2 and 4 weeks old rosettes, but not in 6-weeks-old rosettes. Detected specifically in roots from the mature plant (6-weeks old). By wounding, water and cold stresses; in response to plant hormones 2,4-D, BAP, GA3, SA, MeJA and ABA treatment; in response to L-Ser, Hyp and L-Pro treatment. Extensins contain a characteristic repeat of the pentapeptide Ser-Pro(4). For this particular extensin, a typical repeat of Ser-Pro(3) is found. In both cases, the proline residues are hydroxylated and then O-glycosylated (arabinosylation). Synthetised as soluble proteins which become insolubilised in the cell wall through the intermolecular cross-linking of Tyr on adjacent monomers. Isodityrosine (IDT) stabilizes and makes rigid the part of the polypeptide where IDT functional sites are present. Belongs to the extensin family. In cv. Landsberg erecta, absence of several repeats.