Bacterial origin of insect chemosensory proteins

What is it about?

It has long been thought that insect "Chemosensory Proteins" (CSPs) play a role in delivering tastant or odorant molecules to chemosensory receptors. These proteins would be necessary to detect the scents emitted by plants and stimulate insects' sense of smell. I discovered this family of proteins ("CSPs") in bacteria. I was able to date the genesis of this protein back to a billion years ago, before the diversity of prokaryotes emerged, because I found them in several different bacterial species (Actinomycetes, Firmicutes, and Proteobacteria). I believe that "CSP" was obtained by the insects via horizontal gene transfer. Is it possible for this distant heritage to play a part in chemosensing? The acquisition of an olfactory function for this gene is still a long way off. It most likely stems from the origin of life (protobiont).

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Photo by National Institute of Allergy and Infectious Diseases on Unsplash

Photo by National Institute of Allergy and Infectious Diseases on Unsplash

Why is it important?

"CSPs" are confusingly expressed in a number of other organs and probably have functions other than chemosensing. I discovered that CSPs are found in bacteria as well as insects and other arthropods by searching microbial and crustacean protein databases. I concluded that CSPs are unlikely to have only chemosensory functions because they are expressed in a wide variety of tissues and are found in everything from prokaryotes to insects and arthropods. This is in line with the majority of current research in the field of insect "olfactory" proteins, where it has been shown that odorant-binding proteins (OBPs) and CSPs serve non-olfactory purposes (see Guo et al. 2021 Frontiers in Insect Physiology). The overall physiology of bacterial and arthropod cells is supported by CSPs and OBPs. The following elements of genetics and evolutionary genetics depend on the analysis of CSP genes in bacteria and crustaceans: 1) The discovery of gene structures in prokaryotes and arthropods supports the "late intron" theory; 2) Despite millions of years of evolution, CSP's initial function of binding lipids returns to the majority of primordial cell activity; 3) Certain proteins can be conserved from bacteria to insects; 4) CSP remains unchanged in the host gut, The analysis of CSP genes in bacteria and crustaceans, revealed here, is important for multiple aspects related to genetics and evolutionary genetics: 1) The identification of gene structures in prokaryotes and arthropods validate the theory of "late intron", 2) the original function of CSP (binding lipids) returns to most primordial cell activity, this activity has been maintained despite millions years of evolution, 3) there can be proteins so conserved from bacteria to insects, 4) CSP does not change once in the host intestine, 5) CSPs from free-living bacteria exhibit greater diversity; 6) CSP can be found in a formin-like structure in bacteria, indicating that formin is not a eukaryotic innovation because it was present in prokaryotes; and 7) CSP can be found in an immunoglobulin-like structure in bacteria, indicating that immunoglobulin (antibody) is not a eukaryotic innovation because it was present in bacteria (see Picimbon, 2026). Anemopods, branchiopods, copepods, and decapods are among the 21 species of crustaceans whose CSP genes have been studied. The results show that CSP expression is widely distributed throughout various organs, from gills to the hepatopancreas. From a genetic perspective, it demonstrates: 1) highly specific splicing mechanisms that were present in the earliest arthropods; 2) highly specific editing mechanisms; 3) +Cysteine mutations, which may be an adaptation mechanism of crustaceans to the marine environment; 4) "widespread RNA editing would support the mutation-driven evolution, that is mutation occurs before evolution, speciation, and adaptation, in contrast to Darwin's theory (descent with modification); 5) there is no random mutation.

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