Local and systemic transcriptome responses to herbivory and jasmonic acid in Populus

We used DNA microarrays to examine local and systemic transcriptional responses to herbivory by gypsy moth larvae (GM) and exogenous jasmonic acid (JA(trt)) in leaves of Populus nigra L. to identify candidate signaling and defense genes and also to examine primary metabolism, as might relate to tolerance of damage. GM and JA(trt) altered expression of over 800 genes, most of which have putative roles in defense signaling, secondary metabolism, and primary metabolism. Additionally, numerous uncharacterized genes responded to herbivory, providing a rich resource for future studies. There was limited overlap (14%) between the responses to GM and JA(trt). GM did, however, result in strong upregulation of genes involved not only in JA biosynthesis but also abscisic acid biosynthesis and other signaling pathways. GM induced known resistance transcripts, including polyphenolic biosynthetic genes, proteinase inhibitors, and amino acid deaminases. According to GOStats pathway level analysis, GM altered primary metabolism, including aromatic amino acid biosynthesis, fatty acid beta-oxidation, and carbohydrate and organic acid metabolism. These alterations may be related to increased demands for substrate for secondary metabolites or may serve a tolerance-related role. Responses were more intense locally in treated leaves than in untreated (systemic) leaves and systemic responses were mostly a subset of the genes induced locally. A stronger local response might be needed to cope with localized stresses and wound healing. Since Populus in general and this clone in particular are known for their systemic induced resistance, genes induced both locally and systemically may be the highest quality candidates for resistance.