Spider mites in the genomic era: The Tetranychus urticae genome project and beyond

The two-spotted spider mite Tetranychus urticae is among the first acari to benefit from the completion of a whole-genome sequencing project, which has been taken in charge by an international consortium of 5 teams. Several features of T. urticae make this species an excellent candidate to become a genetic model among the Chelicerata. This mite has the smallest genome of any arthropod determined so far (90 Mbp – 30 times smaller than that of Ixodes scapularis (2.3 Gbp), has only 3 chromosomes, has a rapid development and is easily reared in the laboratory. In addition, spider mites are major agricultural pests and are therefore of substantial economic importance and significance for the biotechnology of pest control. Among the wealth of studies that become accessible with the new resources produced by the sequence of T. urticae we discuss here questions of special importance related to: i) Plant- pest interaction: a genetic dissection of mite-plant interactions would provide insights into the signalling and transcriptional basis of direct and indirect defences used against herbivores and pest interaction. In addition, genome-wide sequences of pest organisms lend to analysis transcriptome’s responses to climate stress, host plant defensive compounds and any number of phenomena affecting the pest status of arthropods; ii) Ecology and biodiversity studies: the availability of the T. urticae genome but also the production of sequences of closely related species by the so called Next Generation Sequencing techniques, will aid in finding new genetic markers for molecular species diagnosis, ranging from security against invasions by exotic pests and monitoring of insecticide. The genome sequence will provide fine-scale mapping of genes involved in these processes. We show that genomic approaches have great promise for understanding the interaction of mites with their plant hosts.