Abstract:
Most molecular-genetic studies of plant defense responses to arthropod herbivores have focused on insects. However, plantfeeding
mites are also pests of diverse plants, and mites induce different patterns of damage to plant tissues than do well-studied
insects (e.g. lepidopteran larvae or aphids). The two-spotted spidermite (Tetranychus urticae) is among themost significant mite pests in
agriculture, feeding on a staggering number of plant hosts. To understand the interactions between spider mite and a plant at the
molecular level, we examined reciprocal genome-wide responses of mites and its host Arabidopsis (Arabidopsis thaliana). Despite
differences in feeding guilds, we found that transcriptional responses of Arabidopsis to mite herbivory resembled those observed for
lepidopteran herbivores. Mutant analysis of induced plant defense pathways showed functionally that only a subset of induced
programs, including jasmonic acid signaling and biosynthesis of indole glucosinolates, are central to Arabidopsis’s defense to mite
herbivory. On the herbivore side, indole glucosinolates dramatically increased mite mortality and development times. We identified an
indole glucosinolate dose-dependent increase in the number of differentially expressedmite genes belonging to pathways associated with
detoxification of xenobiotics. This demonstrates that spider mite is sensitive to Arabidopsis defenses that have also been associated with
the deterrence of insect herbivores that are very distantly related to chelicerates. Our findings provide molecular insights into the nature
of, and response to, herbivory for a representative of a major class of arthropod herbivores.
