Functional characterization of genes associated with arabidopsis defence against the two-spotted spider mite feeding

Résumé

Abstract As sessile organisms, plants must cope with multiple and simultaneous stresses in nature. Among them, biotic stresses and specifically pests cause substantial yield losses. In particular, the two-spotted spider mite (Tetranychus urticae) is an extremely polyphagous species found worldwide that feeds on nearly 1,100 documented host plants, including about 150 agronomically important crops. It is considered one of the most significant agricultural threats since it has a short life cycle, high offspring production, and an extraordinary ability to develop pesticide resistance. In addition, T. urticae is a model within chelicerate herbivores because its genome sequenced and a broad range of tools and protocols developed. Mite ability to feed on Arabidopsis thaliana and the wide available toolkits for this plant species have provided an outstanding opportunity for functional studies of plant-mite interaction. In this thesis, we try to elucidate how plants defend themselves against pest attack at different levels of the signal transduction pathway (perception, signaling and final defence molecules). As starting point, a microarray generated with the natural Arabidopsis accessions (Bla-2 and Kon) at the opposite ends of the resistance spectrum against T. urticae was used to search differential expressed genes. This transcriptomic dataset has allowed the identification and selection of candidate genes involved in Arabidopsis defense against spider mites. Thus, genes encoding plant receptors, compounds involved in defense and hormonal signaling and in ROS/RNS balance, and different defensive molecules with acaricide properties directly target the mite phytophagous physiology has been characterized. Besides, Arabidopsis-mite bioassays using over-expressing and silencing plants have demonstrated their defense role against the phytophagous, and the intricate network among these genes developed for the plant survival under suboptimal conditions. Finally, the contra-defences settled by T. urticae against some of these defensive genes have been also studied.