Abstract
RNA interference (RNAi) can be used for the protection against agricultural pests through the silencing of genes required for pest fitness. To assess the potential of RNAi approaches in the two-spotted spider mite, Tetranychus urticae, we compared 5 methods for the delivery of double-stranded RNA (dsRNA). These methods include mite feeding on either (i) leaves floating on a dsRNA solution, (ii) dsRNA-expressing plants, (iii) artificial diet supplemented with dsRNA, or (iv) dsRNA-coated leaves, and (v) mite soaking in a dsRNA solution. In all cases, the gene targeted for method validation was the Vacuolar-type H+-ATPase (TuVATPase), encoding a constitutively expressed ATP-driven proton pump located in the membrane. Down-regulation of TuVATPase increased mortality and/or reduced fecundity in all methods, but with variable efficiency. The most efficient methods for dsRNA delivery were direct soaking of mites in the dsRNA solution and mite feeding on dsRNA-coated leaves that mimics dsRNA application as a sprayable pesticide. Both resulted in a dark-body phenotype not observed in mites treated with a control dsRNA. Although with lower efficiency, dsRNA designed for TuVATPase silencing and expressed in transgenic Arabidopsis plants impacted the fitness of mites feeding on these plants. RNAi may thus be a valuable strategy to control spider mite populations, either as a sprayable pesticide or through transgenic crops. This comparative methodological study focusing on the induction of RNAi-based gene silencing in T. urticae paves the way for reverse genetics approaches in this model chelicerate system and prepares large-scale systematic RNAi screens as a first step towards the development of specific RNA-based pesticides. Such alternative molecules may help control spider mites that cause significant damages to crops and ornamental plant species, as well as other chelicerates detrimental to agriculture and health.
Highlights
The chelicerates represent the second largest group of terrestrial animals after insects [1]
We describe several methods for double-stranded RNA (dsRNA) delivery into spider mites towards the development of reverse genetics platforms: soaking, which may be applicable to high-throughput screens; leaf coating, that mimics the application of dsRNA as a sprayable pesticide; and artificial diet for the administration of quantifiable amounts of dsRNA to two spotted spider mite (TSSM)
The efficiency of these methods was compared to the floating leaf disc assay, with the same dsRNA-TuVATPase fragment and concentration previously reported by Kwon et al [18]
Summary
The chelicerates represent the second largest group of terrestrial animals after insects [1] This basal lineage of the phylum Arthropoda includes horseshoe crabs, scorpions, spiders, mites and ticks that display a plethora of different lifestyles and include economically important species for human health and agriculture. The two spotted spider mite (TSSM), Tetranychus urticae (Koch), is the first chelicerate whose complete genome was sequenced and annotated [5]. It is a compact genome of 90 Mbp (54% of which is protein coding sequence), with simple gene structure, complemented with several transcriptome databases. Because it is a major agricultural herbivorous pest, a strong research community supports the emergence of T. urticae as a versatile chelicerate model organism [6]
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