Isolation, characterization and expression of a glycine-rich cell wall protein gene from the rice plant

Structural proteins are one of the major constituents of plant cell walls. In addition to providing mechanical support to the plant cell, cell wall structural proteins may play a role in plant defense. I have isolated a gene coding for a glycine-rich protein (Osgrp-1) from the rice plant (Oryza sativa). The complete nucleotide sequence of this gene was determined, and shown to contain an open reading frame encoding a polypeptide of 165 amino acids. This protein consists of a 23 amino acid signal peptide and a highly repetitive glycine-rich moiety with many (Gly-X)n motifs similar to that of silk fibroin. Osgrp-1 shares over 75% nucleotide sequence identity with glycine-rich cell wall structural protein genes from dicotyledinous plants. The in vitro translation product of Osgrp-1 and proteins extracted from cell walls of the rice plant cross-react with an antiserum against a French bean glycine-rich cell wall structural protein, confirming the identity of the Osgrp-1 gene product as a rice cell wall structural protein. Primer extension analysis identified two transcription initiation sites 34 bp and 273 bp upstream from the translation initiation codon. The expression pattern of Osgrp-1 was examined in transgenic rice plants containing an Osgrp-1-Gus fusion gene. The expression of this gene in transgenic rice plants can be induced by mechanical wounding. The wounding induction is localized at the wounding site. This wound-inducible gene provides a model system for studying the regulation of defense related genes in monocotyledinous plants. Furthermore, the wound-inducible promoter of this gene can be used to introduce pathogen- or insect-resistant genes into crop plants such as rice and maize, since both pathogen infection and insect attack would mechanically damage plant cell walls and thus activate the expression of the resistant genes.