Chenzhu Wang's research team revealed that the deletion of the Orco gene led to severe olfactory dysfunction of the important agricultural pest cotton bollworm

Insects live in a complex and changeable environment with various odors, so the sense of smell is essential
for their life activities.
There are three main types of olfactory receptor proteins for insects: (1) odorant receptor (OR), (2) ionic receptor (IR), and (3) partial taste receptor (GR
).
Among them, the study of OR is the most prominent
.
Each OR functions
by the odor receptor Or, which is responsible for binding the ligand, by binding to the odor receptor coreceptor (Orco) to form an heterologous multimer.
There are many varieties of Ors in one type of insect, but there is only one Orco, so Orco is the most important target gene
to study the overall function of insect odor receptors.

On September 30, 2022, the research team of Chenzhu Wang, Institute of Zoology, Chinese Academy of Sciences, published a report in BMC Biology titled "Mutagenesis of the odorant receptor co-receptor (Orco) reveals severe olfactory defects in the crop pest moth.
" Helicoverpa armigera's research paper reveals that Orco-mediated olfactory pathways play a vital role
in bollworm reproduction, egg laying selection, sexual pheromonic communication, and larval chemotaxis behavior.

Wang Chenzhu's research team has been working to explore the chemical communication mechanism
of important agricultural pests in China.
Cotton bollworm is a typical polyphagic insect, widely distributed in China and around the world, harming many crops including wheat, cotton, corn, tomatoes, soybeans, peanuts, green peppers, etc.
, causing huge economic losses
all year round.
The team, supported by a key project of the National Natural Science Foundation of China, tried to find new ways
to control insects by regulating their sense of smell.
There is still a great deal of uncertainty about the olfactory receptor function of bollworms, with more than 60 Ors expressed in the antennae of its main olfactory organ, and only a few Or's ligands have been identified
so far.
The aim of the study was to clarify the role
of Orco-mediated olfactory pathways in bollworm behavior and reproduction.

The team used the gene-editing technology CRISPR/Cas9 system to successfully construct and obtain Orco^-/-homozygous mutants
in bollworms.
It was found that neither the mutant's inbreeding nor the mutant male's cross-breeding with wild-type females yielded offspring, while mutant females mated with wild-type males to obtain normal offspring
.
The results of antennal transcriptome experiments showed that in the antennae of Orco-^/-homozygous mutants, although the expression of some sexual pheromone receptor (PR) genes was found to change significantly, most other Or, Ir, Gr There was no significant
change in expression patterns of genes and other related olfactory pathways.
Histochemical experiments on the antennal lobes of the primary olfactory processing center in the adult brain found that Occo deletion had no significant effect on
the structure and number of neurofibrous spheres encoding odor signals.
The researchers used the antennal potential (EAG) technique to detect the electrophysiological response of the antennae of Orco-^/-homozygous mutant adults to 27 different types of important odor compounds, and found that the absence of Orco led to a significant decrease in the response of adult antennae to most of the detected compounds.
Further using the single sensor recording (SSR) technique, it was found that the hair-type sensors, three types of susceptible pheromones, on the male antennae of the mutant, had significantly reduced
the electrophysiological response of the six sex pheromones-related components.
In wind tunnel behavioral experiments, almost all mutant males lost their tendency, landing, and mating behaviors
toward sexual pheromone sources.
The results of the ovi-laying behavior experiment showed that the mutant female lost its ovio-laying preference for the host plant, green pepper.
At the same time, the chemotaxis behavior of the larvae showed that the mutant larvae also lost their chemotaxis on green peppers
.
In this study, the researchers explored the function of Orco-mediated olfactory pathway in bollworm from multiple angles and levels such as genetics, omics, histochemistry, electrophysiology, and behavior, and provided sufficient evidence for regulating the behavior of bollworm by regulating odor substances (Figure 1).

The sense of smell is the oldest way
of feeling in the animal kingdom.
The olfactory system of insects has something in common with other animals, including humans, among others
.
Mammals and humans have also been of much concern
for sensing odor substances in their environments primarily through Orco-mediated olfactory receptors.
The results of this study are also of reference value for the study of the olfactory sense of other animals and the olfactory sense of humans
.

The first author of the paper, Dr.
Fan Xiaobin, is a postdoctoral fellow at the Institute of Zoology, Chinese Academy of Sciences, and the co-supervisor is Professor
Wang Chenzhu.
Huang Lingqiao, Guo Hao, Mo Baotong, Li Guocheng and Gong Xinlin participated in the research work
.

Paper Link: https://bmcbiol.
biomedcentral.
com/articles/10.
1186/s12915-022-01411-2

Figure 1.
Deletion of the Orco gene leads to olfactory dysfunction produced by bollworms