Expression of the grapevine stilbene synthase gene VST1 in papaya provides increased resistance against diseases caused by Phytophthora palmivora

The phytoalexin resveratrol (trans-3,5,4'-trihydroxystilbene), a natural component of resistance to fungal diseases in many plants, is synthesized by the enzyme trihydroxystilbene synthase ( stilbene synthase, EC 2.3.1.95), which appears to be deficient or lacking in susceptible plants. Earlier workers isolated a stilbene synthase gene (Vst1) from grapevine ( Vitis vinifera L.), which has subsequently been introduced as a transgene into a range of species to increase resistance of hosts to pathogens to which they were originally susceptible. Papaya ( Carica papaya L.) is susceptible to a variety of fungal diseases, including root, stem, and fruit rot caused by the pathogen Phytophthora palmivora. Since resveratrol at 1.0 mM inhibited mycelium growth of P. palmivora in vitro, we hypothesized that papaya resistance to this pathogen might be increased by transformation with the grapevine stilbene synthase construct pVst1, containing the Vst1 gene and its pathogen-inducible promoter. Multiple transformed lines were produced, clonally propagated, and evaluated with a leaf disk bioassay and whole plant response to inoculation with P. palmivora. RNA transcripts of stilbene synthase and resveratrol glycoside were induced in plant lines transformed with the grapevine pVst1 construct shortly after pathogen inoculation, and the transformed papaya lines exhibited increased resistance to P. palmivora. The immature transformed plants appear normal and will be advanced to field trials to evaluate their utility.