Genome of Tetranychus urticae reveals herbivorous pest adaptations

Mites belong to the Chelicerata, the second largest group of terrestrial animals. Chelicerates represent a basal branch of arthropods with the most diverse chelicerate clade, with 40,000+ described species exhibiting tremendous variations in lifestyle, ranging from parasitic to predatory to plant-feeding. Some are of major concern to human health and include allergy-causing dust mites, scabies mites and mite vectors of scrub typhus. Here we present the completely sequenced and annotated Tetranychus urticae spider mite genome, representing the first complete chelicerate genome to date.  At 90 Mb T. urticae has the smallest sequenced arthropod genome and shows unique changes in hormonal milieu, organization of the Hox complex, and evolution of silk used to establish colonial micro-habitats, protecting it against abiotic agents or predators, but also for communication via pheromones or providing a vehicle for dispersion. On the genome, we identified 18,414 protein coding gene models, of which 84% (15,397) are supported by: EST (8,243), protein homology (11,433) and/or RNA-seq data (14,545). We found strong signatures of polyphagy and detoxification in gene families associated with feeding including new gene families acquired by lateral gene transfer.   T. urticae is a cosmopolitan agricultural pest with an extensive host plant range and an extreme record of pesticide resistance, being one of the most polyphagous arthropod herbivores, feeding on more than 1,100 plant species in over 140 different plant families.  Deep transcriptome analysis of mites feeding on different plants shows for the first time how this pest responds to a changing host environment. The T. urticae genome thus offers new insights into arthropod evolution and plant-herbivore interactions, and provides unique opportunities for developing novel plant protection strategies.