Plants respond to pathogens through an orchestration of signaling events that coordinate modifications to transcriptional profiles and physiological processes. Resistance to necrotrophic pathogens often requires
jasmonic acid, which antagonizes the
salicylic acid dependent biotrophic defense response. Recently, myo-
inositol has been shown to negatively impact
salicylic acid (SA) levels and signaling, while
galactinol enhances
jasmonic acid (JA)-dependent induced systemic resistance to necrotrophic pathogens. To investigate the function of these compounds in biotrophic pathogen defense, we characterized the defense response of Populus alba × grandidentata overexpressing Arabidopsis
GALACTINOL SYNTHASE3 (AtGolS) and Cucumber sativus
RAFFINOSE SYNTHASE (CsRFS) challenged with Melampsora aecidiodes, a causative agent of poplar leaf rust disease. Relative to wild-type leaves, the overexpression of AtGolS3 and CsRFS increased accumulation of
galactinol and
raffinose and led to increased leaf rust
infection. During the resistance response, inoculated wild-type leaves displayed reduced levels of
galactinol and repressed transcript abundance of two endogenous GolS genes compared to un-inoculated wild-type leaves prior to the up-regulation of NON-EXPRESSOR OF PR1 and PATHOGENESIS-RELATED1. Transcriptome analysis and qRT-PCR validation also revealed the repression of genes participating in
calcium influx,
phosphatidic acid biosynthesis and signaling, and
salicylic acid signaling in the transgenic lines. In contrast, enhanced tolerance to H2O2 and up-regulation of
antioxidant biosynthesis genes were exhibited in the overexpression lines. Thus, we conclude that overexpression of AtGolS and CsRFS antagonizes the defense response to poplar leaf rust disease through repressing
reactive oxygen species and attenuating
calcium and
phosphatidic acid signaling events that lead to SA defense.