Mechanisms of Carboxylic Acid Attraction in Drosophila melanogaster

Abstract

Sour is one of the fundamental taste modalities that enable taste perception in animals. Chemoreceptors embedded in taste organs are pivotal to discriminate between different chemicals to ensure survival. Animals generally prefer slightly acidic food and avoid highly acidic alternatives. We recently proposed that all acids are aversive at high concentrations, a response that is mediated by low pH as well as specific anions in Drosophila melanogaster . Particularly, some carboxylic acids such as glycolic acid, citric acid, and lactic acid are highly attractive to Drosophila compared with acetic acid. The present study determined that attractive carboxylic acids were mediated by broadly expressed Ir25a and Ir76b , as demonstrated by a candidate mutant library screen. The mutant deficits were completely recovered via wild-type cDNA expression in sweet-sensing gustatory receptor neurons. Furthermore, sweet gustatory receptors such as Gr5a , Gr61a , and Gr64a-f modulate attractive responses. These genetic defects were confirmed using binary food choice assays as well as electrophysiology in the labellum. Taken together, our findings demonstrate that at least two different kinds of receptors are required to discriminate attractive carboxylic acids from other acids.

A molecular mechanism for high salt taste in Drosophila

“…To establish that IR25a, IR76b, and IR7c complex to form a functional high salt receptor, we aimed to reconstitute this receptor in a heterologous GRN type. Thus, we used Gr64f-Gal4 to express IR7c in sweet neurons, which already express IR25a and IR76b 4,13,18,19,21 (Fig. 6A).…”

“…Although there are notable exceptions [14][15][16][17][18] , IR-dependent taste responses typically require both IR25a and IR76b. This includes roles in detecting salts 4 , carbonation 13 , fatty acids 19 , calcium 10 and acids 20,21 . Given the evidence for heteromeric assembly of olfactory IR channels from two co-receptors and a more specific tuning IR subunit, it is likely that each distinct IR25a/IR76b-dependent taste function is mediated by these co-receptors complexing with an additional IR that confers specific tuning 13,19,22 .…”

The taste of vitamin C inDrosophila

“…Vitamin C is also known as ascorbic acid. The ability to taste attractive carboxylic acids requires ionotropic receptors (IRs) and sweet‐sensing GRs (Stanley et al , 2021; Shrestha & Lee, 2021a). We have previously reported that flies are highly attracted to glycolic, citric, and lactic acid and avoid tartaric and propionic acid (Rimal et al , 2019).…”

Protocol for binary food choice assays using Drosophila melanogaster

“…However, labellum and legs are the major taste organs, which mediate a major role in contact chemosensation in insects. The full benefit of this behavioral assay is realized when performed in combination with an electrophysiological assay that measures tastant-induced action potentials in gustatory receptor neurons (tip recordings) ( Aryal et al., 2022 ; Dhakal et al., 2021 ; Shrestha and Lee, 2021a ).…”