Abstract
RNA interference (RNAi) is being developed for the management of pests that destroy crops. The twospotted Spider Mite (TSSM), Tetranychus urticae is a worldwide pest due to its unique physiological and behavioral characteristics including extraordinary ability to detoxify a wide range of pesticides and feed on many host plants. In this study, we conducted experiments to identify target genes that could be used for the development of RNAi-based methods to control TSSM. Leaf disc feeding assays revealed that knockdown in the expression genes coding for proteins involved in the biosynthesis and action of juvenile hormone (JH) and action of ecdysteroids [Methoprene-tolerant (Met), retinoid X receptor β, farnesoic acid O-methyltransferase, and CREB-binding protein] caused 35–56% mortality. Transgenic tobacco plants expressing hairpin dsRNA targeting Met gene were generated and tested. About 48% mortality was observed in TSSM raised on transgenic tobacco plants expressing dsMet. These studies not only broaden our knowledge on understanding hormone action in TSSM but also identified target genes that could be used in RNAi-mediated control of TSSM.
Highlights
In arthropods, crosstalk between ecdysteroids and juvenile hormones regulates growth, differentiation, and reproduction by binding to functional heterodimers of proteins that form receptors for these hormones[4]
The goal of the current study is to identify genes involved in hormone biosynthesis and action and explore their use as RNA interference (RNAi) targets in the twospotted Spider Mite (TSSM)
From the T. urticae genome website, we retrieved sequences of eight genes, including TuMet, TuSRC, and Farnesoic acid O-methyltransferase (FaMet), TuEcR, TuRXR1, TuRXR2, TuRXR β, and TuCBP coding for proteins involved in biosynthesis and action of juvenile hormone (JH) and action of ecdysteroids (Table 1)
Summary
Crosstalk between ecdysteroids and juvenile hormones regulates growth, differentiation, and reproduction by binding to functional heterodimers of proteins that form receptors for these hormones[4]. Due to the lack of CYP306A1 and CYP18A1 genes, which encode the biosynthetic enzymes, C25 hydroxylase, and a C26 hydroxylase/oxidase respectively, it has been suggested that the TSSM may use the ecdysteroid, 25-deoxy-20-hydroxyecdysone (ponasterone A, Pon A), as the major molting hormone. This hypothesis was confirmed by biochemical analysis of TSSM extracts using HPLC, enzyme immunoassay and liquid chromatography/ mass spectrometry (LC-MS)[11]. In TSSM two RNAi methods have been demonstrated far to deliver the double-stranded RNA (dsRNA): an injection into adult females and eggs, and a leaf-disc feeding assay[14,15]. This information helps in understanding TSSM physiology and lays a foundation for the development of RNAi-based methods to control this pest
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