As early fungi made the evolutionary journey from water to land and branched off from animals, they shed tail-like flagella that propelled them through their aquatic environment and evolved a variety of new mechanisms (including explosive volleys and fragrances) to disperse their spores and reproduce in a terrestrial setting.
"What's particularly interesting is that species retained their flagella for different lengths of time and developed different mechanisms of spore dispersal," said David McLaughlin, professor of plant biology at the University of Minnesota in the College of Biological Sciences and co-author of a paper published in the Oct. 19 issue of Nature describing how fungi adapted to life on land.
The discovery is the latest installment in an international effort to learn the origins of species. McLaughlin is one of five principal investigators leading a team of 70 researchers at 35 institutions. The group analyzed information from six key genetic regions in almost 200 contemporary species to reconstruct the earliest days of fungi and their various relations.
McLaughlin is directing the assembly of a shared database of fungal structures obtained through electron microscopy, which produces detailed images that provide clues to the diversity of these organisms. The work is funded by a $2.65 million "Assembling the Tree of Life" grant from the National Science Foundation that was awarded to Duke University, the University of Minnesota, Oregon State University and Clark University in January 2003.
The discovery provides a new glimpse into evolution of life on Earth. It will also help scientists better understand this unusual group of organisms and learn how to develop uses for their unique properties in medicine, agriculture, conservation and industry.
McLaughlin believes fungi are a valuable untapped natural resource. They play a variety of roles in nature, such as supplying plants with nutrients through mutualistic relationships and recycling dead organisms. He estimates that there are about 1.5 million species on the Earth, but only about 10 percent of those are known. And civilization has only identified uses for a few of those, such as using yeast to make bread, beer, wine, cheese and a few antibiotics.
"Understanding the relationships among fungi has many potential benefits for humans," McLaughlin said. "It provides tools to identify unknown species that may lead to new products for medicine and industry. It also helps us to manage natural areas, such as Minnesota's oak savannahs, where the fungi play important roles but are often hidden from view."
Fungi are also intriguing because their cells are surprisingly similar to human cells, McLaughlin said. In 1998 scientists discovered that fungi split from animals about 1.538 billion years ago, whereas plants split from animals about 1.547 billion years ago. This means fungi split from animals 9 million years after plants did, in which case fungi are actually more closely related to animals than to plants. The fact that fungi had motile cells propelled by flagella that are more like those in animals than those in plants, supports that.
Not all fungi are beneficial to humans. A small percent have been linked to human diseases, including life-threatening conditions. Treating these can be risky because human and fungal cells are similar. Any medicine that kills the fungus can also harm the patient. Thus knowing more about fungi helps identify new and better ways to treat serious fungal infections in humans. Fungi are also the major cause of disease in agricultural crops, so understanding them also helps track and control these plant diseases.
McLaughlin and his colleagues will continue their efforts to establish genetic relationships among fungi and to understand their roles in nature. Additional structural studies, especially of key species, are needed to determine how the organisms adapted.
McLaughlin is curator of fungi for the University of Minnesota Bell Museum of Natural History, past president of the national mycological society, and adviser to the state society. He has used his knowledge of fungi to identify species that may be useful to treat cancer and to preserve oak savannahs at Cedar Creek Natural History Area in central Minnesota.
Journal
Nature