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Gene "talk" triggers fungus defense.

Plants can't speak, but they do communicate. When a spore from a disease-causing fungus lands on an alfalfa leaf, an intricate chemical conversation takes place that determines whether the plant becomes infected. Interpreting this complex interplay of signals could be a key to unlocking novel ways to develop disease-resistant plants, suggests plant pathologist Marty Dickman, University of Nebraska-Lincoln.

Developing alfalfa plants resistant to anthracnose, a disease caused by a fungus, is one focus of Dickman's research. His broader interest is how fungi cause plant diseases and how plants defend themselves against fungi. "It's amazing how little we know about disease," he points out.

What Dickman does know about alfalfa anthracnose is that when a spore from the disease-causing fungus Colletotricum trifolii lands on an alfalfa leaf, it grows a long tube that develops a cushion-like structure at its tip that penetrates the leaf. Once inside the leaf, the fungus generates branching structures, called hyphae, that spread through the plant cells, causing disease.

In some plants, hyphae never spread after penetrating the leaf, so the plant remains healthy. Dickman believes the host plant and the fungus communicate during this initial meeting. The fungus is looking for a place to eat and reproduce. "When the fungus lands on a plant, it recognizes `This is a place where I can do business,' and the plant immediately responds with a yes or no."

How do the plant and fungus communicate? He thinks genes and the proteins they code for are the signals in plant-fungus communication. Understanding how they work means deciphering the molecular world of genes, proteins, and DNA, a world accessible only through recombinant DNA technology.

Determining which genes to study was the first challenge. Using genes known to control animal cell-signaling tasks as guides, Dickman searched for similar genes in the C. trifolii fungus. He and his team conducted their search with synthetic DNA probes based on the animal genes. Probes are single DNA strands that seek out complementary strands and bind to them, marking the gene of interest.

The team located a previously unknown gene and named it TB3, then cloned it so they could test whether the gene performs signaling functions similar to those in animal cells. Next, they decoded its DNA, revealing the exact order of the thousands of repeating building blocks that make up the gene.

They found that TB3 closely resembled a gene in a Neurospora fungus that is required for hyphal growth. Dickman and his team theorized that TB3 might be needed for the same function in their fungus. If so, it could be a genetic switch that might be used to interrupt the communication between fungus and host plant, turning off the alfalfa anthracnose infection process. Further experiments with TB3 suggest it is important during spore germination or is necessary for the hyphae to grow, but more research lies ahead. Different forms of the gene must be incorporated into C. trifolii to test Dickman's theories about fungal infection.
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Publication:USA Today (Magazine)
Article Type:Brief Article
Date:Jun 1, 1998
Words:493
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