Overexpression of a peach defensin gene can enhance the activity of postharvest biocontrol agents

A portion of our research involves developing methods to enhance the activity of yeast biocontrol agents. In the present study, we describe the cloning and characterization of defensin genes from bark tissues of peach and apple. The open reading frame of both genes code for proteins related to the defensins, a family of highly antimicrobial proteins. Sequence comparison of the encoded proteins revealed significant homology between the peach and apple defensins and defensins from other plant species. RNA gel blot analysis and semi-quantitative-PCR indicated that the genes are seasonally-expressed in bark tissues of one-year-old shoots, and the peach defensin is also expressed in early fruit development. A recombinant version of the peach defensin gene, rDFN1 was expressed in the yeast, Pichia pastoris. It was found that rDFN1 inhibited germination of the fungal pathogens Penicillium expansum and Botrytis cinerea. The potential of using defensin genes to enhance biocontrol yeasts is discussed.