|HSU, JU-CHUN - National Taiwan University|
|FENG, HAI-TUNG - National Taiwan University|
|WU, WEN-JUR - National Taiwan University|
|MAO, CHING-HUA - National Taiwan University|
|VONTAS, JOHN - University Of Greece - Crete|
Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2012
Publication Date: 10/20/2012
Citation: Hsu, J., Feng, H., Wu, W., Mao, C., Geib, S.M., Vontas, J. 2012. Truncated transcripts of nicotinic acetylcholine subunit gene bdalpha6 are associated with spinosad resistance in Bactrocera dorsalis. Journal of Insect Biochemistry and Molecular Biology. 42(10):806-815.
Interpretive Summary: Spinosad is a biologically derived insecticide that is used for control of Tephritid fruit fly pests, including the oriental fruit fly. A spinosad resistant strain of oriental fruit fly was developed and then the genetic basis for resistance to spinosad was characterized by isolating the nAChR gene transcripts from resistant and susceptible strains of oriental fruit fly. By comparing resistant and susceptible fly gene products, it was found that transcripts from the resistant population are truncated, having deletions that cause the resulting protein to be non-functional. This demonstrates that loss of function of spinosad target variants may be viable and cause strong resistance in certain agricultural pests. While the demonstration of truncated transcripts causing resistance is outlined, the mechanism responsible for generating truncated transcripts remains unknown.
Technical Abstract: We investigated spinosad resistance mechanisms of a Bactocera dorsalis strain from Taiwan. Resistance levels were 901-fold, and there was no cross resistance against imidacloprid or fipronil Combined biochemical and synergistic data indicated that target site insensitivity is the major resistance component. The gene encoding the nAChR subunit alpha 6 (Bda6) from the susceptible strain was isolated by PCR and RACE techniques. The full-length cDNA of Bda6 from spinosadsusceptible strains has an open reading frame of 1467 bp and codes for a typical nAChR subunit with an extracellular ACh-binding domain and four transmembrane domains. Two putative exon isoforms (exon 3 and exon 8) and four alternative full length splicing variants were found in the susceptible lines. In contrast, all transcripts from the spinosad resistant strain were truncated and coded for apparently non functional Bda6. Deletions of exons 4 to 6 or 3 to 6, small insertions and deletions of 2-6 bp in exon 3a, and consequent premature stop codons in exon 7, were associated with the truncated transcripts. The mutations appear to be prime targets for developing RT-PCR diagnostics for detecting spinosad resistance in field populations of B. dorsalis. The association of truncated and mis-spliced transcripts of Bda6 with striking levels of spinosad resistance in B. dorsalis is consistent with a previous studies in Plutella xyllostella (Rinkevich et al., 2010)and confirms that loss of function of spinosad target variants may be viable and cause strong resistance in certain agricultural pests. While the demonstration of truncated transcripts causing resistance is outlined, the mechanism responsible for generating truncated transcripts remains unknown.