American biologists believe that hallucinogenic fungi have acquired clusters of genes that make psychedelic psilocybin, as a result of horizontal transfer. The researchers came to this conclusion by analyzing several species of fungi from different families. According to the authors, mushrooms produce psilocybin to scare off insects that either eat them, or compete with them for food.
Psilocybin synthesizes more than 200 species of fungi, which belong to several families lamellar. In its structure, this substance is similar to serotonin and the hallucinogenic effect that it has on humans is due to the stimulation of 5-HT2A serotonin receptors. The substance serves as a secondary metabolite, which in different organisms can perform transport or protective functions. Although the role of psilocybin for the life of fungi is still unknown, it presumably serves to regulate the behavior of multicellular organisms.
Fungi produce psilocybin from the amino acid tryptophan in the process of multistage biosynthesis, which involves a number of enzymes. Accordingly, they are encoded by several genes, apparently forming a cluster in the fungal genome. The authors of the new study, led by Jason Slot of the University of Ohio, suggested that fungi from different families, by horizontal transfer from other fungi that grew nearby, received clusters of genes that encode enzymes for the synthesis of psilocybin. Unlike vertical transfer, during which DNA is transmitted from ancestors to offspring, organisms that are not relatives are transmitted to each other during horizontal transfer. For example, parasitic bacteria can transmit their DNA to the host organism, and eventually it is embedded in its genome.
To test their hypothesis, the scientists sequenced genomes of three kinds of hallucinogenic fungi: Psilocybe cyanescens from the family of stropharia, a firefly (Gymnopilus dilepis) from the family of cobwebs, and Panaeolus cyanescens from the family of the bigbirds. To control, the authors of the work sequenced the genomes of three species of fungi that do not produce psilocybin. To confirm the functions of the cluster, the researchers tested the expression of the fungal genes in the bacterial system. And the presence of the substances obtained by enzymatic synthesis was analyzed by mass spectrometry. As suggested by the authors, all hallucinogenic fungi showed the desired gene cluster, and in control species - no. According to researchers, the same gene cluster in three "distant relatives" indicates that the fungi exchanged genes through horizontal transfer.
Researchers in their work suggested that fungi began to develop psilocybin for protection against insects. Most hallucinogenic fungi grow either in manure, or in rotting or living trees; where there are many insects that can either compete with mushrooms for food, or use them for their own food. Presumably, psilocybin can change the behavior of insects, in particular termites, which also feed on wood. Although the authors do not give any proof of their hypothesis, they illustrate it with the example of flies-drosophila, in which the antagonist serotonin 5-HT2A antagonist, analogous to psilocybin, blocks eating behavior.
Earlier, botanists discovered an earlier unknown strategy by which desert plants are protected from eating. They produce a sticky substance, which during the gusts of the sand adheres sand and creates the effect of sandpaper for herbivores.