Gustatory receptor 28b is necessary for avoiding saponin in Drosophila melanogaster

Abstract

Saponins function as a natural self‐defense mechanism for plants to deter various insects due to their unpleasant taste and their toxicity. Here, we provide evidence that saponin from Quillaja saponaria functions as an antifeedant as well as an insecticide to ward off insects in both the larval and the adult stages. Using a behavioral screen of 26 mutant fly lines, we show that the Gr28b gene cluster plays a role in saponin avoidance in the labellum. The Gr28b mutant does not avoid saponin and exhibits increased lethality when fed saponin‐mixed food. Tissue‐specific rescue experiments with five different Gr28b isoforms revealed that only the Gr28b.c isoform is required for saponin sensation. We propose that in contrast to sensing many other bitter compounds, saponin sensing does not require the function of core taste receptors, such as GR32a, GR33a, and GR66a. Our results reveal a novel role for GR28b in taste. In addition, the ability of saponin to act as insecticides as well as antifeedants suggests its potential application in controlling insect pests.

Evolutionary shifts in taste coding in the fruit pest Drosophila suzukii

“…Although there has been little, if any, previous analysis of the bitter taste system in D. suzukii, bitter taste in D. melanogaster has been studied in detail ( Delventhal and Carlson, 2016 ; Dweck and Carlson, 2020 ; Liman et al, 2014 ; Ling et al, 2014 ; Scott, 2018 ; Weiss et al, 2011 ). Bitter-sensing neurons are housed in taste sensilla in the labellum (one of the mouthparts), the tarsal segments of the legs, and the pharynx ( Chen and Dahanukar, 2017 ; Delventhal and Carlson, 2016 ; Dweck and Carlson, 2020 ; Lee et al, 2010 ; Lee et al, 2015 ; Ling et al, 2014 ; Marella et al, 2006 ; Meunier et al, 2003 ; Moon et al, 2009 ; Poudel and Lee, 2016 ; Rimal et al, 2020 ; Sang et al, 2019 ; Weiss et al, 2011 ). Although there are several kinds of taste receptors, bitter responses depend largely on the Gr (gustatory receptor) family ( Clyne et al, 2000 ; Joseph and Carlson, 2015 ; Liman et al, 2014 ; Scott, 2018 ).…”

“…Although there are several kinds of taste receptors, bitter responses depend largely on the Gr (gustatory receptor) family ( Clyne et al, 2000 ; Joseph and Carlson, 2015 ; Liman et al, 2014 ; Scott, 2018 ). Many Gr genes have been found to be required for response to individual bitter compounds ( Dweck and Carlson, 2020 ; Lee et al, 2010 ; Lee et al, 2015 ; Moon et al, 2009 ; Poudel and Lee, 2016 ; Rimal et al, 2020 ; Sang et al, 2019 ; Weiss et al, 2011 ). Moreover, expression of certain Gr genes in sugar-sensing neurons confers response to bitter compounds ( Dweck and Carlson, 2020 ; Shim et al, 2015 ; Sung et al, 2017 ).…”

A gustatory receptor tuned to the steroid plant hormone brassinolide in Plutella xylostella (Lepidoptera: Plutellidae)

“…Gr33a, Gr66a, and Gr93a participate in the responses to caffeine and umbelliferone (Lee et al, 2009;Moon et al, 2006;Poudel et al, 2015). Gr28b is necessary for avoiding saponin (Sang et al, 2019). However, only a few studies have focused on the function of bitter GRs in phytophagous insects.…”

Scarless engineering of theDrosophilagenome near any site-specific integration site

“…Finally, to test the ability of this technique to create custom deletions, the 7.5 kb Gr28b gene was chosen to be deleted ( Figure 7A and 7C). Gr28b is a complex gustatory receptor locus that encodes 5 different isoforms, and has been shown to have multiple functions such as thermo-preference and toxin avoidance (Ni et al, 2013, Sang et al, 2019. A MiMIC insertion (MI11240) about 300 bp away from the right end of the Gr28b gene was used as the landing site for the targeted deletion ( Figure 7A).…”