Functional analysis of an upregulated calmodulin gene related to the acaricidal activity of curcumin againstTetranychus cinnabarinus(Boisduval)

BACKGROUND Curcumin is a promising botanical acaricidal compound with activity againstTetranychus cinnabarinus. Calmodulin (CaM) is a key calcium ion (Ca2+) sensor that plays a vital role in calcium signaling. Overexpression of theCaMgene with inducible character occurs in curcumin-treated mites, but its functional role remains to be further analyzed by RNA interference (RNAi) and protein expression. RESULTS A CaM gene was cloned fromT.cinnabarinus(designatedTcCaM).TcCaMwas upregulated and the protein was activated in mites by curcumin. The susceptibility of mites to curcumin was decreased after inhibitingCaMfunction with anti-CaM drug trifluoperazine (TFP) and silencingCaMtranscription with RNAi, suggesting that theCaMgene is involved in the acaricidal activity of curcumin against mites. Moreover, the TFP pre-treated Sf9 cells were resistant to curcumin-mediated increase in [Ca2+]i levels, indicating that CaM-mediated Ca(2+)homeostasis was disturbed by curcumin.TcCaMwas then re-engineered for heterologous expression inEscherichia coli. Strikingly, our results showed that the recombinant CaM protein was directly activated by curcumin via inducing its conformational changes, its half-maximal effective concentration (EC50) value is 0.3 mu mol L(-1)in vitro, which is similar to curcumin against CaM-expressing Sf9 cells (0.76 mu mol L-1)in vivo. CONCLUSION These results confirm that the overexpressedCaMgene is involved in the acaricidal activity of curcumin, and the mode of action of curcumin may be via activating CaM function, and thereby disrupting Ca(2+)homeostasis inT.cinnabarinus. This study highlights the novel target mechanism of new acaricides, promoting our understanding of the molecular mechanism of CaM-mediated acaricide targets in mites.

Automated summary

The study reveals that curcumin disrupts calcium homeostasis in Tetranychus cinnabarinus by activating the expression of the CaM gene, thereby exhibiting acaricidal activity against the mites. The findings suggest a novel target mechanism for new acaricides and enhance understanding of the molecular mechanisms of CaM-mediated acaricide targets in mites.