We've called them scum, lifesavers, and even hors d'oeuvres, but only since 1995 has anyone called them relatives. That was the year scientists determined that mushrooms, yeast, mildews and other fungi are more closely related to animals than to plants. Now, the National Science Foundation has awarded $2.65 million to the University of Minnesota, along with Duke, Oregon State and Clark universities, to sort out relationships among this diverse group of organisms, to which the world owes several antibiotics, beer, wine, cheese and bread, among other things. The four-year grant is part of NSF's Assembling the Tree of Life program, which seeks to determine exact evolutionary relationships within several of its branches.
The study may help scientists find ways to deal with an aquatic fungus that is now attacking frogs and may be partly responsible for their recent worldwide decline. The study could also point researchers to species of fungi that, by virtue of being related to medically or commercially important species, may produce drugs or other useful products. Fungal-produced drugs discovered to date include penicillin; griseofulvin, used on athlete's foot; and the cephalosporins, which are similar to penicillin.
"Some fungi are crucial for life, but others cause many medical, plant and animal diseases, and it's important to learn which ones are closely related so we can choose the correct model organism to study the troublemakers," said David McLaughlin, professor of plant biology in the College of Biological Sciences and principal investigator for the university's $510,000 share of the grant. "In assembling the family tree of fungi, our team will look at multiple genes and structural characteristics across a broad spectrum of fungi and put them in a database. Here at the University of Minnesota, we're studying the very finest elements of structure."
"Good" fungi do considerably more than supply people with drugs and comestibles. Fungi combine with algae to form lichens, which can grow on bare rock and begin breaking it down, the first step in soil formation. They digest fallen leaves and wood, helping to recycle piles of detritus that would otherwise choke the landscape. Also, fungi often form extensive associations with the roots of trees, a service that allows trees to absorb water and such nutrients as nitrogen and phosphorus more efficiently, McLaughlin said. About 90 percent of all plants depend on fungi to supply these nutrients. In return, the plants produce simple sugars that nourish the fungi. Without these fungi, few plants would grow, and animals would die en masse.
Certain fungi work for ants.
"We're working on fungi that are inoculated into leaf litter by New World tropical ants," said McLaughlin. "These fungi break down leaves, then the ants eat the fungi and gain the nutrients the fungi have extracted from the leaves."
In his lab, McLaughlin keeps cultures of the same fungi in petri dishes. In that environment, the fungi often produce fruiting bodies--spore-forming structures that tend to form when the fungus experiences low nutrient levels or other stress. To scientists, fruiting bodies are desirable because they can be used to identify fungi. Under the ants' care, however, the fungi rarely form fruiting bodies, possibly because the ants keep the fungi well supplied with nutrients, McLaughlin said. This practice may be the ants' way of keeping their crops from "going to seed."
Many fungi look alike, and sorting them out can have economic and culinary ramifications, said Bryn Dentinger and Peter Avis, graduate students in McLaughlin's lab. For instance, the delectable and pricey porcini mushroom has a lookalike and "tastealike" that grows in Minnesota. But neither mushroom can be cultivated. To cultivate such mushrooms, one would have to determine growing conditions for both species and, more difficult, find a way to tell which species is which. This can be done by examining DNA, but it's a time-consuming process. McLaughlin, a specialist in the fungal group that includes mushrooms and toadstools, is helping improve the identification process by searching for structural traits that correspond to specific species as determined by DNA analysis.
The evolutionary line leading to fungi split from lines leading to plants and animals more than 1.5 billion years ago, said McLaughlin. The best guess is that only 5-10 percent of the fungi are known. Still, that's 80,000 to 85,000 species out of what may be 1.5 million species worldwide.
Fungi, like other organisms, are threatened by pollution. In particular, the rain of nitrogen from agricultural and industrial sources may harm fungi that nourish plant roots. Understanding how different species are affected and how they may be protected is another potential outcome of the fungi project, McLaughlin said.
RSS