Beware! These three mushrooms are extremely toxic

Whenever a netizen asks the question "Is this mushroom edible?", there will always be kindhearted people in the comment area who "carefully dissuade" people by saying "Red umbrellas, white poles, eat them and you'll be lying on the floor together." But do you know? The most deadly mushroom is not the "red umbrella", but the inconspicuous "white umbrella", "gray umbrella" and "yellow umbrella" that cause the most deaths . These mushrooms have one thing in common: they contain amatoxins.

Mushrooms containing amatoxin. Image source: Kunming Institute of Botany, Chinese Academy of Sciences

How dangerous is Amatoxin?

Amanita cyclopentane is resistant to high temperatures, acid, alkali and salt . Ordinary cooking methods such as high-temperature steaming or stir-frying will not destroy its toxicity. The popular sayings of high-temperature disinfection and garlic disinfection are extremely unreliable . The most deadly of the amanita cyclopentane toxins is α-amanitin, which is a highly effective inhibitor of eukaryotic RNA polymerase II and can block the transcription of mRNA and thus inhibit protein synthesis.

After accidentally eating mushrooms containing this type of toxin, the toxin enters the liver through the gastrointestinal tract and is quickly absorbed by liver cells. Although most of the amatoxin peptides are excreted in the urine, some of the toxins absorbed by the liver enter the intestines through bile, thus forming an enterohepatic cycle, prolonging the time in the liver and aggravating liver damage. The damage caused by this toxin is irreversible . After the onset of the disease, the patient can only be treated with a liver transplant, and the mortality rate is extremely high .

In the order Amanita, only the genera Amanita , Galerina , and Lepiota contain amanitin. These three types of mushrooms are distantly related and have different nutritional types. Amanita is an ectomycorrhizal fungus; Galerina grows on rotten wood and can decompose wood, playing an important role in the ecosystem cycle; Lepiota grows in the soil.

Why can these three completely different mushrooms produce the same toxin? How did these mushrooms acquire the ability to produce toxins? After years of research, scientists have finally answered these questions.

Horizontal gene transfer leads to toxins

Different synthetic pathways

How is amatoxin produced in the body? The synthesis of this toxin requires the joint efforts of more than a dozen genes, but the four key genes currently known are MSDIN, POPB, P450-29 and FMO1. The MSDIN gene is the raw material for synthesizing the toxin, and POPB, P450-29 and FMO1 can process MSDIN, of which P450-29 and FMO1 increase the activity of the toxin by thousands of times.

The study found that the toxin synthesis pathways of Amanita phalloides, Amanita argyi and Amanita cyclophaga have a common origin, but their toxin production capabilities are very different . Amanita phalloides has the most toxin synthesis precursor genes MSDIN, and nearly 100 genes can synthesize a variety of amanita cyclopeptides.

In stark contrast, the Amanita argyi contains only one MSDIN, encoding one toxin (α-amanitin). The Anopheles cyclosporus is between Amanita phalloides and Amanita gracilis, containing about 4 to 6 MSDINs. This also makes Amanita phalloides the most toxic of the three . Although the toxin synthesis ability varies, all three types of mushrooms contain the most deadly α-amanitin.

MSDIN core peptide sequences and known cyclic peptides in Amanita muscaria, Amanita argyi, and Amanita cyclospora. The core peptides of known MSDIN in the three genera are shown in gray shading. The α-amanitin precursor peptide is marked in red font. Points of the same color represent core peptides shared across species. Image credit: Kunming Institute of Botany, Chinese Academy of Sciences

By analyzing the evolution of these four toxin synthesis genes, the results showed that the distribution of the biosynthesis pathway of amanitin in the three types of mushrooms was caused by horizontal gene transfer. Different from vertical inheritance, toxin synthesis genes are not inherited between parents, but transmitted through a donor species. So how is it transmitted between the three? Who had this toxin-producing ability first? The results of phylogenetic and genetic analysis denied the possibility of transmission among the three.

Three mushrooms, one ancestor

First, the structure of amanita cyclotides is different in the three types of mushrooms. The toxin genes in Amanita and Agaricus cyclosporus are relatively dispersed, and the possibility of transmission from these two types of mushrooms is relatively small. Another possibility is that it was transmitted from the helmet agaric. Although the toxin genes in the helmet agaric are distributed more compactly, forming a gene cluster structure, it is easier to transmit the toxin production pathway, but genetic distance analysis and phylogeny do not support this speculation. The genetic distance between the toxin synthesis genes in the three types of mushrooms is relatively close.

The overall architecture of amanitin biosynthesis. Contigs or scaffolds are represented on the right as blocks of combined size (the percentage of the contig or scaffold containing the toxin gene in the genome is in brackets). a: Distribution of amanitin biosynthesis genes in the genome of the highly toxic Amanita phalloides. b: Distribution of amanitin biosynthesis genes in the genome of the highly toxic Agaricus cyclosporus. c: Distribution of amanitin biosynthesis genes in the genome of the highly toxic Amanita phalloides. MSDIN, POPB, P450-29, and FMO1 are marked in red, green, blue, and black, respectively. Image credit: Kunming Institute of Botany, Chinese Academy of Sciences

To sum up, there is only one truth, that is, these three mushrooms have a common mushroom ancestor , which passed the entire metabolic pathway to these three mushrooms through horizontal gene transfer, and differences arose in the evolutionary process of the three mushrooms, and the highly toxic Amanita phalloides became the king of poisonous mushrooms .

Schematic diagram of the distribution of cyclopeptide toxin synthesis genes and metabolic pathway evolution in Amanita phalloides, Amanita argyi, and Agrocybe cyclosporus. Image source: Kunming Institute of Botany, Chinese Academy of Sciences

In summary, these mushrooms are very toxic. Although they appear harmless to humans and animals, when the toxicity attacks, it may cause death if rescue is not timely, which is a huge harm. Therefore, it is recommended that you do not eat wild mushrooms at will . After all, there are still many delicious mushroom varieties on the market, which should be able to satisfy your cravings!

Produced by: Science Popularization China

Author: Lv Li Yunjiao (Kunming Institute of Botany, Chinese Academy of Sciences)

Producer: China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences

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