UC Berkeley Press Release
Sex or no sex? Only the fungi know for sure
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 Four large mature spores, each encased in a thick orange cell wall, and one tiny immature spore among the fungal threads, called hyphae, of the fungus Glomus etunicatum. These fungi were grown in culture in association with carrot roots (not shown). (Teresa Pawlowska/UC Berkeley) |
BERKELEY – New findings about ancient fungi provide a key to resolving a basic mystery of evolution and may lead to improved agricultural production, according to University of California, Berkeley, scientists.
Biologists believe that sexual reproduction is essential to long-term survival of species, and only a very few species are thought to have survived for long periods without sex. Arbuscular mycorrhizal (AM) fungi, which colonize roots of most land plants and improve both their ability to obtain nutrients and to tolerate disease, may be the group of organisms that has done so. No one has found any sex organs in these fungi, and their 460-million-year-old fossils, from the Ordovician period, look just like modern species.
If these fungi truly are asexual, the age of the oldest known asexual organism would be pushed back by a factor to 10. A group of rotifers currently is the oldest known asexual organism.
Until now, however, tests for asexuality could not be applied to AM fungi because it was thought that they contained many different nuclei in each cell.
In this week's issue of the journal Nature, new evidence by UC Berkeley biologists Teresa Pawlowska and John Taylor shows that the nuclei in AM fungi are identical - information that will allow the tests of asexuality to proceed.
The team used genetics to study inheritance in spores and molecular biology to study genetic variation in individual nuclei to show that each nucleus was just like the others.
"The two challenges that we faced were that AM fungi must be grown with a plant and that there is very little DNA in a single nucleus," said postdoctoral researcher Pawlowska, lead author on the paper. Both she and Taylor are in the Department of Plant and Microbial Biology in the campus's College of Natural Resources.
In addition to the inherent biological interest in the fungi, understanding the life cycle of AM fungi could have agricultural applications. By benefiting plant nutrition and disease resistance, AM fungi provide an alternative to chemical fertilizers, particularly in land reclamation, habitat restoration and sustainable agriculture. Popular interest in organically grown foods has precipitated an explosion of companies that produce and market soil amendments containing AM fungi, currently a $10 million industry worldwide. Yet, scientific development of these products and their evaluation had been hampered by a lack of understanding of the genetics of AM fungi.
"To evaluate the effectiveness of these products, and to develop improved soil amendments, we need to know how AM fungi reproduce," said Pawlowska. "These findings allow us to move forward."
This project was made possible by funding from Syngenta (formerly Novartis) through a grant to UC Berkeley's plant and microbial biology department. Initial results obtained during the Syngenta-funded project then led to grant support from the U.S. Department of Agriculture's competitive grants program.