ACTIVATION OF A TOBACCO GLYCINE-RICH PROTEIN GENE BY A FUNGAL GLUCAN PREPARATION

A Phytophthora megasperma f.sp. glycinea cell wall glucan preparation was previously shown to protect tobacco plants against viral infection . Eleven plant defense-related genes were assayed for elevated mRNA ac cumulation levels in response to glucan treatment of tobacco plants. T he expression of only one of these genes, a glycine-rich protein (GRP) gene, was induced by glucan application. Elevated GRP gene mRNA level s could be detected within 15 min of glucan treatment and reached maxi mum levels at 4 h post-treatment followed by a slow decline to 8 h. Th e maximum induction of the GRP gene was approximately ninefold above H 2O-treated control plants. Northern blot analysis showed that a single mRNA species of 1.4 kb was responding to the glucan treatment. GRP ge nes occur in tobacco as members of a multigene family, but only one sp ecific GRP gene was induced by the glucan treatment. A genomic copy of this responding GRP gene was cloned and sequenced. This tobacco GRP g ene is homologous to the petunia ptGRP1 gene and the French bean GRP1. 8 gene, but is not closely related to the French bean GRP1.0 gene. GRP gene expression has previously been associated with disease resistanc e in plants, but it remains to be determined whether beta-glucan activ ation of the tobacco GRP gene results in the observed resistance to vi rus.