A gene encoding a novel glycine-rich structural protein of petunia

Abstract

The proteinaceous material of the cell wall of some plant species is composed of 20% or more hydroxyproline residues¹. In 1965, Lamport¹ suggested that this imino acid is derived from a hydroxyproline-rich glycoprotein (HRGP) present in cell walls. HRGP was thought to give the cell wall plasticity, thereby allowing it to grow by extension. But the cell walls of some plant species and/or organs contain very little hydroxyproline, and instead contain large amounts of glycine^2–4, suggesting that HRGP cannot be the only protein molecule in cell walls responsible for plasticity, and that there could be a glycine-rich cell-wall protein. Here we report the cloning and sequencing of an expressed gene from petunia, grp-1, the product of which is likely to function as a cell-wall structural protein in plants. The predicted amino-acid sequence of the grp-1 gene product contains 67% glycine residues. The predicted protein structure includes a 27 amino-acid signal sequence for transport out of the cytoplasm and a 314 amino-acid region in which 90% of the residues are capable of forming a β-pleated sheet composed of 8 anti-parallel strands.