Comparison of Solanum dulcamara transcriptome after real and simulated herbivory

Plants are attacked by diverse herbivores and respond with manifold defense responses. To study transcriptional and other early regulation events of these plant responses, herbivory is often mimicked to standardize the temporal and spatial dynamics that vary tremendously for natural herbivory. Yet to what extent such mimics of herbivory are able to elicit the same plant response as real herbivory remains largely undetermined. We examined the transcriptional response of a new model plant to herbivory by a lepidopteran larva and to a commonly used herbivory mimic by applying the larvae’s oral secretions to standardized wounds. We designed a microarray for Solanum dulcamara and showed that the transcriptional response to real and to simulated herbivory by Spodoptera exigua overlapped moderately by about 40%. Interestingly, certain responses were mimicked better than others; 60% of the genes up-regulated but not even a quarter of the genes down-regulated by herbivory were similarly affected by application of oral secretions to wounds. While the regulation of genes involved in signaling, defense and water stress were mirrored well by the herbivory mimic, most of the genes related to photosynthesis, carbohydrate- and lipid metabolism were exclusively regulated by real herbivory. Thus, wounding and elicitor application decently mimics herbivory-induced defense responses but likely not the re-allocation of primary metabolites induced by real herbivory. Four treatment groups were analyzed in S. dulcamara clones from different locations (Siethen, Erkner, Grunewald, and Mehrow, all in the vicinity of Berlin, Germany). Leaves were either undamaged controls (control), fed upon by S. exigua (spodo) caterpillars for 24 h or damaged with a pattern wheel and treated with S. exigua oral secretions (w+os) and harvested either after 1 h or 24 h.