Bitter taste receptors confer diverse functions to neurons

Delventhal, Rebecca; Carlson, John R.

doi:10.7554/elife.11181

Cited by 61 publications

(60 citation statements)

References 57 publications

(90 reference statements)

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“…The enhanced responses in Ir25a-/ - moths toward acids could be due to more energy being available to OSNs responding to acids, as these OSNs no longer have to compete with amine-tuned OSNs in the same sensillum. Such a phenomenon has been reported for gustatory receptors (GRs), where sensory neurons in the same sensillum have been shown to interact, exhibiting competition, inhibition or activation 44 .—In conclusion, our results show that IR8a, but neither Orco nor IR25a, is required for acid detection in OSNs of coeloconic sensilla.…”

Section: Resultssupporting

confidence: 79%

The olfactory co-receptor IR8a governs larval-frass mediated competition avoidance in a hawkmoth

Zhang

Bisch-Knaden

Fandino

et al. 2019

Preprint

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12Finding a suitable oviposition site is a challenging task for a gravid female moth. At the same time, it is of 13 paramount importance considering the limited capability of most caterpillars to relocate to alternative host 14 plants. The hawkmoth, Manduca sexta (Sphingidae), oviposits on solanaceous plants. Larvae hatching on 15 a plant that is already attacked by conspecific caterpillars can face food competition, as well as an increased 16 exposure to predators and induced plant defenses. Here, we show that frass from conspecific caterpillars is 17 sufficient to deter a female M. sexta from ovipositing on a plant and that this deterrence is based on the 18 frass-emitted carboxylic acids 3-methylpentanoic acid and hexanoic acid. Using a combination of genome 19 editing (CRISPR/Cas9), electrophysiological recordings, calcium imaging and behavioral analyses we 20 demonstrate that the ionotropic co-receptor IR8a is essential for acid-mediated frass avoidance in 21 ovipositing hawkmoths. 22 (Nicotiana attenuata) and jimson weed (Datura wrightii). It was reported that a single M. sexta caterpillar 57 consumes 1-10 tobacco plants until pupation 31 , resulting in complete defoliation of the plants and 58 accumulation of frass under the plant (Fig. 1 a). Therefore, it is crucial for female M. sexta to find a suitable 59 host plant that is not already occupied by a conspecific larva. 60Volatiles emitted from larval frass have been shown to act as kairomones and attract parasitoids and 61predators [32][33][34][35] . The smell of larval frass, therefore, not only indicates the occupancy of the host plant, and 62 the resulting potential for intra-specific competition, but also an increased susceptibility to parasitization 63 and predation. Hence, female moths should avoid sites that are already occupied by conspecific larvae and 64 could do so by e.g. detecting chemical cues emanating from larval frass. In several insect species, female 65 oviposition has been found to be deterred by conspecific larval frass 36 . Thus, larval frass alone is sufficient 66

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Section: Resultssupporting

confidence: 79%

The olfactory co-receptor IR8a governs larval-frass mediated competition avoidance in a hawkmoth

Zhang

Bisch-Knaden

Fandino

et al. 2019

Preprint

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“…Among these, three GRs, GR32a, GR33a, and GR66a, are expressed in all bitter-sensing GRNs in the labellum and function broadly in the avoidance of various bitter compounds [5,15,16]. In contrast, the other six known bitter-sensing Grs are required for detecting relatively specific bitter compounds [17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

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

2019

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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.

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“…Still, it is difficult to predict the specific function of a neuron from its expression of individual receptor genes. It is rather the combinatorial expression of receptors within one neuron that seems to be crucial for the neuron's specific function (Delventhal & Carlson, ; Knecht et al, ). Therefore, the actual stimuli can only be confirmed by physiological and behavioral tests.…”

Section: Discussionmentioning

confidence: 99%

A map of sensilla and neurons in the taste system of drosophila larvae

Rist

Thum

2017

J of Comparative Neurology

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In Drosophila melanogaster larvae, the prime site of external taste reception is the terminal organ (TO). Though investigation on the TO's implications in taste perception has been expanding rapidly, the sensilla of the TO have been essentially unexplored. In this study, we performed a systematic anatomical and molecular analysis of the TO. We precisely define morphological types of TO sensilla taking advantage of volume electron microscopy and 3D image analysis. We corroborate the presence of five external types of sensilla: papilla, pit, spot, knob, and modified papilla. Detailed 3D analysis of their structural organization allowed a finer discrimination into subtypes. We classify three subtypes of papilla and pit sensilla, respectively, and two subtypes of knob sensilla. Further, we determine the repertoire of receptor genes for each sensillum by analyzing GAL4 driver lines of Ir, Gr, Ppk, and Trp receptor genes. We construct a map of the TO, in which the receptor genes are mapped to neurons of individual sensilla. While modified papillum and spot sensilla are not labeled by any GAL4 driver, neurons of the pit, papilla, and knob type are labeled by partially overlapping but different subsets of GAL4 driver lines of the Ir, Gr, and Ppk gene family. The results suggest that pit, papilla and knob sensilla act in contact chemosensation. However, they likely do these employing different stimulus transduction mechanisms to sense the diverse chemicals of their environment.

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Bitter taste receptors confer diverse functions to neurons

Cited by 61 publications

References 57 publications

The olfactory co-receptor IR8a governs larval-frass mediated competition avoidance in a hawkmoth

The olfactory co-receptor IR8a governs larval-frass mediated competition avoidance in a hawkmoth

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

A map of sensilla and neurons in the taste system of drosophila larvae

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