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.