Inducible Sesquiterpene Synthase and a Phenylpropanoid Phytoalexin of Eggplants (Solanum melongena) Synergistically Promote Nonhost Resistance against Phytophthora infestans

Late blight caused by Phytophthora infestans is a devastating disease on potatoes (Solanum tuberosum) and tomatoes (Solanum lycopersicum). By contrast, eggplants (Solanum melongena) are a nonhost species of late blight, though the mechanisms underlying their resistance remain elusive. In this study, comparative transcriptomics analyses revealed that a sesquiterpene synthase-encoding SmTPS28 could enhance potato resistance against late blight when expressed as a transgene. Further targeted metabolomics analyses showed that syringaldehyde, a phenylpropanoid phytoalexin in eggplant leaves, could induce immune-related gene expression and protect potatoes from late blight when exogenously applied prior to pathogen exposure. Intriguingly, syringaldehyde exhibited a greater protective efficiency on SmTPS28-overexpressing potato plants than on their wild-type progenitors, suggesting functional synergism between these two components of nonhost resistance. These findings reveal novel perspectives of the nonhost resistance mechanisms of eggplants against late blight, and could facilitate the development of new tools and technologies for sustainable late blight management.