Nov. 27, 2001

BTI scientist hunts for medical benefits from fungus that killed American chestnut by turning pathogen to friend from foe

Once again Longfellow's village smithy could have a spreading chestnut tree under which to stand. And the bountiful tree's fungal foe could provide the village doctor with medicine for the sexton and the parson.

The American chestnut tree, once proud queen of Eastern and Midwestern forests, was decimated out by an Asian fungus accidentally imported a century ago. However, the tree could mount a comeback within the next decade due to the efforts of the American Chestnut Foundation and multiple research groups across the country.

Plant pathologists at the Boyce Thompson Institute for Plant Research (BTI), located on the campus of Cornell University, are studying the genetic and chemical arsenal that Cryphonectria parasitica , the chestnut blight fungus, uses to cause disease in the tree, which today survives only a few years after being attacked. When the fungal contribution to the disease is understood, new tools could be made available to render chestnut trees immune to the pathogen.

Alice Churchill, a scientist in molecular mycology at BTI, is examining the role that fungal chemical pigments play in the battle between the fungus and its tree host. When the fungus grows, it produces pigments that are orange in color. When the fungus attacks a chestnut tree, orange cankers develop on the trunk and girdle and kill the tree.

Churchill, believing that the fungal pigments are important for the success of the pathogen, has been searching for genes that control pigment production. Once those genes are located, says Churchill, it will be possible to eliminate them and determine what role the pigments play in the tree disease. The American chestnut is an indigenous tree that once grew from Maine to Mississippi and across the Midwest. With its distinctive and wide-spreading branches and deep, broad-rounded crown, the tree could easily grow to 5 feet in diameter and 100 feet high. The American Chestnut Foundation says that the tallest chestnuts grew in the southern Appalachian Mountains.

After the fungus entered the United States, the symptoms of the blight were first spotted at the New York Zoological Gardens (now the New York Zoological Park, or Bronx Zoo) in 1904. Within two decades, the fungal pathogen had spread 1,000 miles.

Yet, ironically, the chestnut tree fungus could provide the basis for the development of future pharmaceuticals.

In the process of bringing back the chestnut, Churchill is examining how chemical compounds produced by both the C. parasitica fungus and native American and Asian medicinal herbs, such as aloe vera, buckthorn and rhubarb, are made. Isolating the biosynthetic genes for the therapeutic compounds from the fungus should be relatively straightforward compared to isolating comparable genes from plants, she says.

Churchill says the fungus makes biologically active chemicals that reportedly have antiviral, antimicrobial, immunosuppression and anticancer activities. Furthermore, some of the chemicals inhibit plant-seed and fungal-spore germination.

Using molecular genetics and analytical chemistry analyses, Churchill's laboratory is examining pigment production in many strains of the C. parasitica fungus. The BTI researchers are making progress towards isolating pigment genes, ultimately leading to a better understanding of the genetic "machinery" needed to synthesize such pigments. Understanding how nature makes these types of chemicals is a first step in learning how to create new compounds with novel biological uses, she says.

Says Churchill: "Although the fungus is a devastating plant pathogen, it should prove to be of significant value in understanding how medicinal pigments from fungi and plants are synthesized."