(1st Place) Plant prophylaxis: Tall goldenrod (Solidago altissima L.) alters its transcriptome after detecting the emission of a gall-inducing herbivore

Plants can use environmental olfactory cues to sense nearby herbivores. When plants perceive a chemical associated with an herbivore, they can induce chemical defenses in preparation for a possible challenge. This phenomenon, called “priming”, enables a rapid defense response to later herbivory. Priming mediates interactions of tall goldenrod (Solidago altissima L., Asteraceae) and the goldenrod gall fly (Eurosta solidaginis Fitch, Diptera: Tephritidae). While perching on goldenrod, male gall flies emit a volatile pheromone to attract mates. Mated females then lay eggs in apical buds of S. altissima, and E. solidaginis larvae feed and induce galls. The male pheromone primes nearby S. altissima plants, conferring resistance to galling and feeding by some co-occurring herbivore species. Although the chemical ecology of the goldenrod gall system is well described, the molecular underpinnings of priming are still poorly understood. Our study appears to be the first to use transcriptomic tools in this ecological model system. We exposed S. altissima plants to E. solidaginis pheromone and subjected them to herbivory from a generalist caterpillar for 48 hours. We harvested damaged plant tissue at five time points during that period for Illumina RNAseq and performed differential gene expression (DGE) analysis using the Trinity pipeline. Our DGE results highlight key differences in gene expression patterns between primed and unexposed plants, including a suite of defense pathways like wounding response and jasmonic acid induction. Our study illustrates the influence of a co-evolved specialist on generalist herbivory and sheds valuable light on the molecular signatures of priming in plants.