Postharvest Fumigation of (E)-2-Hexenal on Kiwifruit (Actinidia chinensis cv. ‘Haegeum’) Enhances Resistance to Botrytis cinerea

(E)-2-Hexenal is a reactive electrophile species released by green plants upon herbivory or pathogenic infection and induces various defense responses. In this study, (E)-2-hexenal was used as a natural alternative to artificial fumigants to prevent postharvest pathogenic infection of the 'Haegeum' kiwifruit (Actinidia chinensis). Integrated transcriptome-metabolome analyses were performed to investigate its effect on the induction of plant defense responses. When kiwifruit was fumigated with 100 μmol L-1 (E)-2-hexenal for 24 h at 20 °C and then inoculated with fungal pathogen Botrytis cinerea, the disease severity, as assessed by necrotic lesion size and B. cinerea biomass, was reduced compared to the control, distilled water-treated fruit. (E)-2-Hexenal treatment also led to upregulated expression of genes encoding pattern recognition receptors, signal transducer proteins, and pathogenesis-related proteins, including chitinase. Furthermore, treatment led to increased jasmonic acid and flavonoid biosynthesis. (E)-2-Hexenal fumigation therefore enhanced the resistance of kiwifruit to B. cinerea infection, presumably by facilitating the signaling network from pathogen recognition to defense gene expression and enabling the accumulation of secondary metabolites, such as flavonoids. The present study not only suggests an optimal concentration of (E)-2-hexenal fumigation for controlling postharvest disease of kiwifruit, but also broadens our understanding of the underlying molecular mechanism by which (E)-2-hexenal enhances plant resistance.