Responsible for plasticity of the cell wall. Expressed during cell expansive growth and decreases during lignification (at protein level). This protein contains 67% glycine residues. 90% of the mature protein residues are capable of forming a beta-pleated sheet composed of 8 anti-parallel strands. The glycine-rich region is comprised of two related families of repeats, F1 and F2, each repeat containing about 40 AA.