Abstract
Induced plant responses to insect herbivores are well studied, but we know very little about responses to gastropod feeding. We aim to identify the temporal dynamics of signalling- and defence-related plant responses after slug feeding in relation to induced resistance. We exposed Solanum dulcamara plants to feeding by the grey field slug (GFS; Deroceras reticulatum) for different periods and tested discs of local and systemic leaves in preference assays. Induced responses were analysed using metabolomics and transcriptomics. GFS feeding induced local and systemic responses. Slug feeding for 72h more strongly affected the plant metabolome than 24h feeding. It increased the levels of a glycoalkaloid (solasonine), phenolamides, anthocyanins, and trypsin protease inhibitors as well as polyphenol oxidase activity. Phytohormone and transcriptome analyses revealed that jasmonic acid, abscisic acid and salicylic acid signalling were activated. GFS feeding upregulated more genes than that it downregulated. The response directly after feeding was more than five times higher than after an additional 24h without feeding. Our research showed that GFS, like most chewing insects, triggers anti-herbivore defences by activating defence signalling pathways, resulting in increased resistance to further slug feeding. Slug herbivory may therefore impact other herbivores in the community.
Overall design Four seed batches were selected from S. dulcamara populations in the Netherlands (Goeree and Friesland) and Germany (Erkner and Siethen). Plants were randomly assigned to one of four treatments (n = 16 plants / population / treatment). Leaf number 10 from the apex was exposed to feeding by GFS for 24h or fitted with an empty clip cage for the same time period (undamaged control). Harvest took place directly (0h) after removing the slugs or after an additional 24h without exposure to GFS. RNA from four plants of a single plant population at each time point were pooled, resulting in four total RNA samples per treatment (control or induced) for both time points.
