Wang Chenzhu's research team revealed that bollworms feel the taste receptors of the plant's bitter substance coumarin

Plant secondary biomass is the product of complex branch metabolic pathways in the plant body, generally has no nutritional value, but constitutes the unique taste of different plants and plays a key role
in plant defense.
The degree to which plant-eating insects prefer plants often depends on the type and content
of secondary biomass.
Although Helicoverpa armigera, an important agricultural pest in China, harms many crops, it has different degrees of preference for different crops, and the degree of harm is also different, among which the existence of "bitter" secondary biomass is a key factor
in determining whether the larvae prefer to feed.

On October 8, 2022, Wang Chenzhu's research team at the Institute of Zoology of the Chinese Academy of Sciences published a report entitled "Functional analysis of a bitter gustatory receptor highly expressed in the larval maxillary galea of Helicoverpa" in the internationally renowned academic journal PLoS Genetics armigera's research paper revealed that the cotton bollworm taste receptor HarmGr180 is a receptor for the bitter substance coumarin, and is also involved in larval feelings
for silyinoside (sinigrin) and strychnine.
The co-first authors of the paper, Chen Yan and Wang Peichao, are doctoral students at the Institute of Zoology of the Chinese Academy of Sciences and the University of Chinese Academy of Sciences, and the supervisor is Professor
Wang Chenzhu.
Chen Yan's doctoral dissertation focused on the function of bitter taste receptors in cotton bollworms, while Wang Peichao's doctoral project focused on the use
of gene editing technology in insect taste.
The laboratory's doctoral students Zhang Shuaishuai and Li Guocheng, postdoctoral Yang Jun, senior engineer Huang Lingqiao and others participated in this study
.

The team's previous transcriptome analysis found that a variety of gustatory receptors (Gr) were expressed on the mouthparts of bollworm larvae, of which HarmGr180 was the most expressed, so the team focused on
this receptor.
When this receptor gene was expressed in the claw toad oocytes, it was recorded with a two-electrode voltage clamp that the cells expressing HarmGr180 specifically had an electrophysiological response to coumarin (Figure 1
).
Next, it was verified whether the taste sensory apparatus on the larval mouthparts had a sensor that reacted to coumarin
.
Using apical recordings, it was found that on the outer jaw leaf of the lower jaw of the larval mouthpiece, a pair of mesothoxycone-receptors had an electrophysiological response to coumarin, and coumarin could inhibit the response
of the other contralateral suppository sensor.

To shed light on the in vivo function of HarmGr180, the research team successfully constructed and obtained the HarmGr180 homozygous mutant (HarmGr180-^/-)
of bollworms using the CRISPR/Cas9 system.
The study found that the suppository cone sensor in the larvae of this mutant lost its response to coumarin, while reducing the response to myrosinin and strychnine, but did not affect the inhibitory effect of coumarin-contralateral suppositosensory (Figure 2).

Further behavioral experiments showed that although coumarin, myrosin, and strychnine still had some feeding containment effects on mutant larvae, the feeding containment index decreased
significantly.

Therefore, the researchers revealed the function of HarmGr180, a bitter taste receptor of bollworm, from multiple angles and levels such as molecular biology, omics, electrophysiology, and behavior, which is of great significance for improving the understanding of the molecular basis of
taste sensation in plant-eating insects and developing pest refusals.
There are an estimated 180 bitter taste receptors in bollworms, the vast majority of which have unexplained
functions.
The study lays the foundation for follow-up research and provides new perspectives
for the taste of other plant-eating insects.

Paper Link: https://journals.
plos.
org/plosgenetics/article?id=10.
1371/journal.
pgen.
1010455

　　Chen Y, Wang P-C, Zhang S-S, Yang J, Li G-C, Huang L-Q & Wang C-Z (2022) Functional analysis of a bitter gustatory receptor highly expressed in the larval maxillary galea of Helicoverpa armigera.
PLoS Genetics 18: e1010455.
doi:10.
1371/journal.
pgen.
1010455.

Figure 1 HarmGr180-expressing claw toad oocytes have a concentration-dependent electrophysiological response to coumarin

Fig.
2 Electrophysiological response of the mid-suppository cone sensory of the larvae of the wild type (WT) and HarmGr180 homozygote mutant (Gr180-^/-) to coumarin, myrosin, and strychnine