Although phytoalexins have long been inferred to be important in the defence of plants against fungal infection, there are few reports showing that they provide resistance to infection. Several plants, including grapevine, synthesize the stilbene-type phytoalexin resveratrol when attacked by pathogens. Stilbenes with fungicidal potential are formed in several unrelated plant species, such as peanut (Arachis hypogaea), grapevine (Vitis vinifera) and pine (Pinus sylvestris). Stilbene biosynthesis only specifically requires the presence of stilbene synthase. Furthermore, the precursor molecules for the formation of hydroxy-stilbenes are malonyl-CoA and p-coumaroyl-CoA, both present in plants. To investigate the potential of stilbene biosynthetic genes in a strategy of engineering pathogen resistance, we isolated stilbene synthase genes from grapevine, where they are expressed at a high level, and transferred them into tobacco. We report here that regenerated tobacco plants containing these genes are more resistant to infection by Botrytis cinerea. This is, to our knowledge, the first report of increased disease resistance in transgenic plants based on an additional foreign phytoalexin.

Twenty independent, petal-specific chalcone synthase (CHS) cDNA clones have been isolated from Petunia hybrida variety Violet 30 (V30). Sequence analysis shows that the largest of these clones contains the entire coding sequence. Using this clone in Southern blot analysis reveals the presence of multiple CHS gene copies in the genome of Petunia hybrida V30. Hybridization and sequence analysis of the CHS cDNA clones shows that they are all copied from a single mRNA species. This indicates the presence of only one transcriptionally active CHS gene in petals. Finally we report the identification, cloning and partial characterization of this gene.

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