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Press release.
24/11/2011
Sequencing of first Arachnid genome
An arachnid genome was sequenced for the first time by an international consortium of 33 laboratories, including the University of Western Ontario (Canada), Ghent University (Belgium), the University of Utah (United States) and INRA. The complete sequencing of the spider mite genome was announced in the 24 November 2011 edition of Nature magazine. Tetranychus urticae is a plant-feeding pest. The results open new avenues for understanding evolution trends in arthropods, the largest group of terrestrial animals, and for devising new ways to combat them. The spider mite is notorious for substantial crop damage and for its advanced ability to develop resistance to pesticides.
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Tetranychus urticae
© INRA / Alain Migeon |
Mites belong to the highly diverse Chelicerata arthropod animal group, which also includes spiders, scorpions and marine species such as sea spiders and horseshoe crabs. The group has existed for millions of years. Its ancestors, closely related to trilobites, date back to the Precambrian period, 500 million years ago. Mites, which also include ticks, spread serious diseases in humans, animals and plants. Ticks are the vectors in Lyme disease, dust mites are responsible for several allergies, and Varroa mites are parasites which attack honey bees.
A better understanding of a major agricultural pest
Tetranychus urticae is extremely polyphagous. It feeds on more than 1,100 plant species. Recognizable by two dark spots on its back, the spider mite causes extensive damage in temperate zones, invading tomato crops, beans, melons and cucumbers, as well as beets, carnations, roses, citrus fruits and even household ficus plants. The mites feed on the contents of plant cells and cause spotting on leaves, which sometimes dry and fall off.
The two spotted spider mite owes its name its ability to spin silk threads which it uses to protect itself from predators and to spread from plant to plant.
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Tomato leaf being covered by
T. urticae © INRA / Alexandre Bout |
Spider mites reproduce at a very rapid rate (two generations of aproximately 60 females per month during the summer) which is accelerated in hot weather. Treating mite infestations using pesticides costs nearly $1 billion worldwild annually. The arrival in Europe from South America of Tetranychus evansi and intensifying global warming will promote the development of mites from the Tetranychidae family, making new control strategies - based on a complete understanding of the species’ genome - of crucial importance.
Genome reveals unique characteristics
Past and current heavy use of acaricides, combined with the high reproductive rates of spider mites, has made the species multi-resistant to nearly all classes of existing acaricides. Analysis of the sequenced genome will uncover resistance mechanisms used by the mites, such as feeding on different hosts and detoxification of acaricides.
The complete sequencing of the genome also revealed that while considered small, with only 90 million base pairs, it contains unique genes currently unknown in other arthropods. Some of these genes are the result of lateral gene transfer from fungi and bacteria. Researchers also identified several genes involved in detoxification and digestion which help explain the mite’s unsurpassed resistance to the toxic compounds produced by certain plants as a form of defence. This opens new avenues for developing naturally resistant plants.
Other genes involved in silk production were also identified. The silk of this mite is finer and withstands applied stress better than spider or insect silks. The results could also lead to new developments in medical biotechnology.
Reference :
"The genome of Tetranychus urticae reveals herbivorous pest adaptations"
Nature 479, 487–492 (24 November 2011 ; doi:10.1038/nature10640)
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