Circular RNA, circ1-3p, is Involved in Cyflumetofen Resistance by Acting as a Competitive RNA against miR-1-3p in Tetranychus cinnabarinus

As a newly recognized type of noncoding RNA, circular RNA can mediate a variety of physiological changes in mammals by regulating the post-transcriptional expression level of genes. However, the function of circRNA in the evolution of pesticide resistance in arthropods is still unknown. In this study, 2546 circRNAs were identified in Tetranychus cinnabarinus by transcriptome sequencing. The differentially expressed gene analysis indicated that 44 circRNAs were overexpressed in a cyflumetofen-resistant strain, of which a circRNA (named circ1-3p) was found to contain the response elements of miR-1-3p, an miRNA that is involved in cyflumetofen resistance by targeting TcGSTm04. The circular structure of circ1-3p was further determined using a divergent primer. The results of different molecular assays in vitro and in vivo showed that circ1-3p can compete with TcGSTm04 in miR-1-3p binding. The colocalization of circ1-3p and miR-1-3p was found using fluorescence in situ hybridization, suggesting that circ1-3p can directly sponge miR-1-3p in T. cinnabarinus. In addition, silencing the expression of circ1-3p resulted in the upregulation of miR-1-3p and the downregulation of TcGSTm04 as well as a significant increase in the sensitivity of T. cinnabarinus to cyflumetofen. All these pieces of evidence indicates that overexpressed circ1-3p promotes the expression of TcGSTm04 through sponging miR-1-3p, thereby involving in the evolution of cyflumetofen resistance in T. cinnabarinus.

Downregulation of carboxylesterase contributes to cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Increased expression or point mutations of carboxyl/cholinesterases (CCEs) have been involved in many cases of insecticide and acaricide resistance. However, it has been only rarely documented that downregulation of CCE genes is associated with resistance, although many insecticides and acaricides need hydrolytic activation in vivo. Previously, expression analysis of a laboratory-selected cyflumetofen-resistant strain of Tetranychus cinnabarinus indicated that resistance was associated with increased expression of a CCE gene of TcCCE04, but also the downregulation of two CCE genes, TcCCE12 and TcCCE23.

RESULTS

Synergism experiments revealed the importance of ester hydrolysis in cyflumetofen toxicity, because treatment with S,S,S-tributylphosphorotrithioate (DEF) caused strong inhibition of cyflumetofen hydrolysis, in both the susceptible and resistant strains. Moreover, silencing expression of TcCCE12 and TcCCE23 via RNAi further decreased the susceptibility of mites to cyflumetofen significantly, suggesting that downregulated CCE genes could be involved in cyflumetofen resistance. In addition, it was shown that recombinant TcCCE12 protein could hydrolyze cyflumetofen effectively.

CONCLUSION

Decreased esterase activity via downregulation of specific CCE genes most likely contributes to cyflumetofen resistance by decreased activation of cyflumetofen to its active metabolite. Mixtures of cyflumetofen and esterase-inhibition acaricides (e.g. organophosphates or carbamates) should be avoided in field applications. © 2019 Society of Chemical Industry.

A microRNA-1 gene, tci-miR-1-3p, is involved in cyflumetofen resistance by targeting a glutathione S-transferase gene, TCGSTM4, in Tetranychus cinnabarinus

microRNA-1 (miR-1) is a well-studied conservative microRNA (miRNA) involved in immune responses in mammals and insects. However, little is known about its role in pesticide resistance in arthropods. In this study, we found that a microRNA belong to miR-1 family (tci-miR-1-3p) was significantly down-regulated in a cyflumetofen-resistant strain (CYR) of Tetranychus cinnabarinus compared with its homologous susceptible strain (SS), indicating an involvement of miR-1 in cyflumetofen resistance in mites. One glutathione S-transferase (GST) gene (TCGSTM4, a mu class GST gene), a candidate target gene of tci-miR-1-3p, was found to be significantly down-regulated when tci-miR-1-3p was over-expressed. The specific interaction between tci-miR-1-3p and the target sequence in the 3' untranslated region of TCGSTM4 was confirmed. A decrease or increase in tci-miR-1-3p abundance through feeding miRNA inhibitors or mimics significantly increased or decreased TCGSTM4 expressions at the mRNA and protein levels, respectively. In addition, an over-expression of tci-miR-1-3p resulted in a decrease in the tolerance of T. cinnabarinus to cyflumetofen in both SS and CYR strains, and vice versa. After decreasing TCGSTM4 transcription via RNA interference, T. cinnabarinus became more sensitive to cyflumetofen in both resistant and susceptible mites, and the change in mortality was greater in CYR than that in SS. Moreover, the recombinant TCGSTM4 could significantly decompose cyflumetofen, indicating that TCGSTM4 is a functional gene responsible for cyflumetofen resistance in mites.