The Transient Receptor Potential Ankyrin 1 (TRPA1) cation channels function as broadly-tuned sensors of noxious chemicals in many species. Recent studies identified four functional TRPA1 isoforms in Drosophila melanogaster (dTRPA1(A) to (D)), but their responses to non-electrophilic chemicals are yet to be fully characterized. Methods: We determined the behavioral responses of adult flies to the mammalian TRPA1 non-electrophilic activators citronellal and menthol, and characterized the effects of these compounds on all four dTRPA1 channel isoforms using intracellular Ca2+ imaging and whole-cell patch-clamp recordings. Results: Wild type flies avoided citronellal and menthol in an olfactory test and this behavior was reduced in dTrpA1 mutant flies. Both compounds activate all dTRPA1 isoforms in the heterologous expression system HEK293T, with the following sensitivity series: dTRPA1(C) = dTRPA1(D) > dTRPA1(A) ≫ dTRPA1(B) for citronellal and dTRPA1(A) > dTRPA1(D) > dTRPA1(C) > dTRPA1(B) for menthol. Conclusions: dTrpA1 was required for the normal avoidance of Drosophila melanogaster towards citronellal and menthol. All dTRPA1 isoforms are activated by both compounds, but the dTRPA1(B) is consistently the least sensitive. We discuss how these findings may guide further studies on the physiological roles and the structural bases of chemical sensitivity of TRPA1 channels.

Lemon oils are amongst the highest volume and most frequently traded of the flavour and fragrance essential oils. Citronellal and citral are considered the key components responsible for the lemon note with citral (neral + geranial) preferred. Of the myriad of sources of citral, the Australian myrtaceous tree, Backhousia citriodora, is considered superior. This review examines the history, natural occurrence, the cultivation, the taxonomy, the chemistry, the biological activity, the toxicology, standardisation and the commercialisation of Backhousia citriodora especially in relation to its essential oil.