(ORDO NEWS) — The three mushrooms known as the destroying angel, the deadly toadstool, and the death bell have one thing in common: the fabulously deadly toxin alpha-amanitin.
If you eat one of these mushrooms, symptoms may not appear for several hours. But soon the toxin begins to destroy your body’s ability to transcribe genes.
Around the fourth day after eating mushrooms, the liver and kidneys begin to fail. You may die in about a week.
This amazing lethality has a mystery at its core: These mushrooms belong to three separate genera, or groups of mushroom species, that are not closely related. How could they produce the same toxin?
In a paper published Monday in the Proceedings of the National Academy of Sciences, scientists who have sequenced the genomes of 15 fungal species from these three groups make an intriguing claim: the genes for producing alpha-amanitin, rather than being inherited from a common ancestor of these groups, were transmitted to them directly from an unknown, probably extinct fungus.
Such gene transfer, called horizontal gene transfer, is common among bacteria, says Hong Luo, a researcher at the Kunming Institute of Botany in China and author of the new paper.
Small pieces of DNA are passed from one microbe to another and then passed on to their offspring. However, there is growing evidence that somehow genes can move between complex multicellular creatures, perhaps with the help of pathogens.
In April, another group of scientists reported that genes moved between snakes and frogs living in the same forest habitat using common parasites. This sounds unusual, but it may help explain some of the other puzzling observations on the tree of life.
The team behind the mushroom article already suspected that horizontal gene transfer had resulted in identical toxins in these mushrooms.
However, at the end of the study, some surprises awaited them. They expected that their look at fungal genetics would confirm that one of the groups had passed on genes to the others. Instead, the gene toxin clusters appeared to be equidistant from their origin.
“That puzzled us,” Dr. Luo said.
After discussing this, the authors of the article decided that the simplest explanation is horizontal gene transfer – but not necessarily between these three groups.
“Then we started to think that there must be another, possibly extinct species,” says Francis Martin, a scientist at the French National Research Institute for Agriculture, Food and the Environment and author of the paper.
This long-extinct fungus may have possessed the genetic makeup to produce the toxin and pass it on in an as yet unknown way to still-living species.” poisonous power.
Scientists may never know much about this putative gene donor for the toxin, if one existed. But researchers are wondering why exactly these three groups of mushrooms received and used his legacy.
Do toxins play a special role in the ecology of these particular fungi? Or are fungi just particularly good at the mysterious ways in which genes from the environment get into their own genomes?
As scientists learn more about how horizontal gene transfer works outside of bacteria, perhaps some of these answers will become clearer.
“We know it happens,” Dr. Martin said, “but we don’t know how.”
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