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Mighty Mold Is Sequenced
By Kate Dalke

Scientists have sequenced the genome of biology’s most beloved mold, an orangey-pink fungus called Neurospora crassa.

Neurospora has played a leading role in biological research for over sixty years. The mold came to fame in 1941, when scientists used the organism to discover that genes make proteins—a feat that earned George W. Beadle and Edward L. Tatum Nobel Prizes. Since then, the mighty mold has been used to study everything from biological clocks to gene silencing.

A rosette of Neurospora asci—which are sacs that contain fungal spores. Four of the eight spores in each ascus are tagged with green-fluorescent protein.

Now, the genome sequence represents a new milestone in the mold’s scientific legacy. Scientists have mapped Neurospora’s 10,000 genes, including genes never before seen in this well-studied creature. The project was led by researchers at the Whitehead Institute in Cambridge, Massachusetts, and included over seventy scientists from all over the world.

The mold’s genome challenges some assumptions about how genes evolve. In Neurospora, a process called RIP destroys duplications in the genome, and thus seems to be slowing the creation of new genes.

Neurospora is not evolving in the way that scientists assumed all organisms evolve,” says James E. Galagan of the Whitehead Institute, who led the genome project. “It can still evolve, but the process of RIP seems to be slowing it down quite a lot.”

RIP, which stands for repeat-induced point mutation, was discovered by Eric Selker of the University of Oregon and a study by Selker and his colleagues accompanies the genome paper published in the journal Nature.

The genome sequence has revealed some surprises. Neurospora does not cause plant diseases, but it shares some genes with fungi that harm plants, such as the fungus that causes rice blast disease. Comparing versions of these genes in pathogenic and non-pathogenic fungi could help scientists better understand virulence genes.

The scientists were also surprised to find genes that may allow the mold to sense red light. Neurospora has been studied extensively for its ability to tell time—the mold feeds and releases spores on a 24-hour cycle. Now, scientists have found genes similar to genes in bacteria and other fungi that detect red light.

Neurospora has come a long way since Paris bakers first noticed the mold in the mid-19th century. After observing the organism in the laboratory for decades, some scientists are turning their attention to how this fungus lives in nature.

The mold likes it hot and sweet. Neurospora uses heat from forest fires to release its spores and reproduce, and then in the aftermath thrives on materials in plants, such as sugars. Neurospora will form bright orange blankets on burnt sugar cane fields.

In recent years, biologists discovered the fungus growing under the bark of trees damaged during fires near Los Alamos, New Mexico. And they have found it throughout the western United States and High Sierras. This surprised researchers who thought Neurospora was a purely tropical fungus.

N. discreta grows on a cottonwood tree in New Mexico six weeks after the fire (left). N. crassa on sugarcane in Louisiana 14 days after a fire (right).

With the genome in hand, researchers are now working on a microchip that could carry all of Neurospora’s genes. Over the past sixty years, scientists have already used classical genetics to determine the function of 1,000 genes. The chip could help elucidate the function of the other 9,000 genes.

There was “certainly a great deal of excitement” about Neurospora following Beadle and Tatum’s discovery in the 1940s, notes David D. Perkins of Stanford University in California, who led much of the research on Neurospora since the 1950s. He adds, however, that subsequent research on bacteria, viruses and yeast drew some interest away from the mold.

“Now, with the genome project and recent advances in technology, I think Neurospora will flourish again,” he says.

See related entry in GNN's Genetics and Genomics Timeline
»1941-Beadle and Tatum

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Galagan, J.E. et al. The genome sequence of the filamentous fungus Neurospora crassa. Nature 422, 859-868 (April 24, 2003).
Selker, E.U. et al. The methylated component of the Neurospora crassa genome. Nature 422, 893-897 (April 24, 2003).

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