Whe fireflies can also master some mushrooms: They shine in self-produced light. Independent of various animals and microorganisms, mushrooms from the group of mushrooms developed the ability to produce bioluminescence, about 160 million years ago. Scientists working with Huei-Mien Ke from the Biodiversity Research Center of Academia Sinica in Taipei discovered this in molecular genetic studies.
Luminous mushrooms use 3-hydroxyhispidine as a light-bringing substance: oxidized with an enzyme called luciferase, this substance disintegrates and releases light quanta. As the always identical molecular machinery attests, bioluminescence in fungi has only arisen once. But why are luminous species so rare and so widely scattered in the family tree? To find out, the researchers from Taiwan, together with Chan-Yi Ivy Lin from Yale University in New Haven, Connecticut and László G. Nagy from Eötvös-Loránd University in Budapest, took the gene cluster responsible for bioluminescence among the Magnifying glass. Probably, so write the biologists in the “Proceedings” of the American National Academy of Sciences, the luminosity once developed in a part of the fungal genome that did not contain any indispensable information. There, DNA could be remodeled with little impunity, whereby the genes necessary for glow were often lost again.
This happened particularly often in the genus of the helmlings: of the currently around six hundred species, only about twelve percent have retained the ability to produce bioluminescence. During a comparative study of five species of helmets, Huei-Mien Ke and colleagues once discovered the complete loss of the gene cluster responsible for bioluminescence: during the day the species named is presented Mycena indigotica in brilliant blue, but does not glow in the dark. The other four types of helmet ring produce bright green light on the basis of differently composed bioluminescence clusters. Once one of the genes changed direction, another time a gene doubled, and in a third species it happened twice.
Honey mushrooms are far more conservative because their bioluminescence cluster has moved to a stable region of the genome. Apart from the duplication of a gene in the Northern Hallimasch (Armillaria borealis) the eight species studied did not change the cluster. Their ability to produce bioluminescence, however, is limited to the mycelium called mycelium, which usually grows hidden. The fruiting bodies, which often sprout out of the infected wood in dense clusters, do not glow. The same can be said of the radish helmling (Mycena pura), a fungus that smells strongly of radish and is common in many forests in this country. In other helmets, especially those from Southeast Asia, not only the fungal threads glow, but also the fruiting bodies.
Such differences raise the question of what significance the self-generated light has for the mushrooms. The Brazilian species Neonothopanus gardneri seems to attract insects at night with its brightly glowing fruiting bodies that grow out of the ground on palm trunks. Beetles, flies, bedbugs and wasps also fly on electrically illuminated synthetic resin replicas. This is what scientists working with Anderson G. Oliveira from the Universidade de São Paulo report in the online journal “Current Biology”. Presumably, they concluded, insects then distribute the fungal spores with which they are covered after they land in the area.
It cannot be ruled out that species of helmets, whose fruiting bodies shine mysteriously in Southeast Asian forests, also attract insects to spread the spores. The fruiting bodies of the olive mushroom, which sometimes also shimmer greenish at the base of oaks and chestnuts, do not seem particularly attractive to insects. Why mushroom threads emit light even though they grow underground or hidden in wood also remains a mystery. It is quite possible that bioluminescence in fungi originally arose as a by-product of other biological processes and only developed a function here and there in the course of evolution.