Host plant adaptation of a polyphagous herbivore shapes transcriptome of both herbivore and host

In an experimental evolutionary set-up, we transferred a genetically diverse strain of the spider mite Tetranychus urticae from its common host bean to tomato where replicated populations were allowed to adapt. By sampling the transcriptomes of non-adapted and adaptes mites feeding on bean and tomato, we identified gene-expression changes in the spider mite affiliated with tomato adaptation. Transcriptional analysis revealed that both constitutive gene-expression levels as well as the transcriptional plasticity of genes were affected. Specifically, tomato adaptation resulted in a large set of constitutively down-regulated genes of unknown function in adapted mites compared to non-adapted mites. Additionally, upon tomato exposure, adapted mites exhibited an increased transcriptional plasticity of genes coding for detoxifying enzymes and xenobiotic transporters. Remarkably, adapted mites further exhibited a differential effect on host plant physiology compared to non-adapted mites. Adapted mites induced a greater chlorotic area on tomato leaves and triggered attenuated induced responses relative to those induced by non-adapted mites. 12 comparisons were investigated; 3 biological replicates for 4 conditions: (1) NonAdapted-Induced (non-adapted 24 hrs on tomato vs non-adapted on bean); (2) Adapted-Tomato (adapted on tomato vs non-adapted on bean); (3) Adapted-2G Bean (adapted 2 generations on bean vs non-adapted on bean); (4) Adapted-2G Bean-Induced (adapted 2 generations on bean, 24 hrs on tomato vs non-adapted on bean).