Abstract
In nature, plants are frequently subjected to multiple biotic and abiotic stresses, resulting in a convergence of adaptive responses. We hypothesized that hormonal signalling regulating defences to different herbivores may interact with drought response, causing distinct resistance phenotypes. To test this, we studied hormonal and transcriptomic responses of Solanum dulcamara subjected to drought and herbivory by the generalist Spodoptera exigua (BAW) or the specialist Leptinotarsa decemlineata (CPB). Bioassays showed that plants under drought became more resistant to BAW, but not to CPB. While drought did not alter BAW-induced hormonal responses, it enhanced CPB-induced accumulation of jasmonic acid and salicylic acid (SA) as well as supressed ethylene (ET) emission. Microarray analyses showed that under drought BAW herbivory enhanced several herbivore-induced responses, including cell-wall remodelling and metabolism of carbohydrates, lipids and secondary metabolites. In contrast, CPB herbivory enhanced several photosynthesis-related and pathogen responses in drought-stressed plants. This may divert resources away from the production of effective defences and increase tissue nutritive value. In conclusion, while BAW suffers from the drought-enhanced defences, CPB may benefit from effects of the enhanced SA and reduced ET signalling. This suggests that the fine-tuned interaction between the plant and its specialist herbivore is sustained under drought.
Overall design 24 samples for 8 treatment groups (3 replicate each) were analysed. Leaves of plants under control watering regime (CON) or drought treatment (DRY) were either undamaged (NO) or fed upon by Spodoptera exigua (BAW2) or Leptinotarsa decemlineata (CPB2) for 48 h. Samples from plants under control watering regime that were fed by S. exigua (BAW1) and L. decemlineata (CPB1) for 24h were also included.
