4/2/2007

The Fresno Bee (Fresno, CA)

By Doug Hoagland

Nematodes are not our friends, and a Fresno State professor wants to make them commit suicide.

The sometimes-microscopic, worm-like organisms suck the life out of tomatoes, grapes, cotton, melons and other crops that are the backbone of the Valley's economy.

Plant developmental geneticist Alejandro Calderon-Urrea is working to genetically engineer plants to make parasitic nematodes kill themselves if they start sucking away.

If he succeeds, Calderon-Urrea could produce a scientific advance to help preserve crops. The environment might benefit, too. Calderon-Urrea's research could provide alternatives to pesticides now used to kill the pests.

The Colombian-born associate professor -- who got his doctorate from Yale University and has taught at California State University, Fresno, since 1997 -- does his research from a basement lab in a three-story building known as Science One.

You might call his lab "nematode central" where it's all nematodes, almost all the time.

"Nematodes inhabit almost every corner of the planet," Calderon-Urrea said. "All the way from the North Pole to the South Pole to the depths of the oceans."

Nematodes that infect roots are the most devastating to crops.

Root-knot nematodes are true to their name, forming knots that resemble beads on a rosary strand, Calderon-Urrea said. Equally damaging are cyst nematodes that leave teardrop-like cysts on roots.

By attacking the root system, parasitic nematodes deprive plants of water and nutrients in the soil.

Nematodes are not worms. "Evolutionarily speaking, they separated from earthworms very long ago," Calderon-Urrea said. They range in size from microscopic to 20 centimeters long, and there are even "good" nematodes that eat bacteria and don't go after crops.

In the lab, Calderon-Urrea pulverizes parasitic nematodes that are no wider than a hair to separate the basic components of the cells.

He is looking for genes that are in all cells conveying heredity and controlling cell function. But he doesn't want just any genes. He's after genes that turn off normal cell development in nematodes, which could lead to death for the pests.

All life forms -- from humans to green algae -- have genes that can kill. Some do a job that's necessary. Fetuses, for example, develop with webs of membrane between their fingers, but if all goes as planned, genes trigger those membranes to die before birth, Calderon-Urrea said.

Finding the right cells in nematodes is a painstaking process -- and it's where his research now is focused.

"The genes we're looking for aren't saying, 'Pick me! Pick me!' " Calderon-Urrea said.

"There are a gazillion possibilities. Imagine going to a Fresno State football game to meet someone you didn't know, and telling them to wear red so you'd recognize them. Everyone would be in red."

If Calderon-Urrea finds the right genes, he hopes to multiply them in the laboratory. Next, he would introduce those genes into crop seeds. When the seeds grow into plants and nematodes latch onto the plants, the pests would be eating material that would cause their cells to die.

Calderon-Urrea said he already has had results that show he is on the right track.

He has used cell suicide genes found in nonparasitic nematodes, attached them to tobacco plant DNA and discovered that the suicide genes kill the nematodes, but not the plants.

Nematode expert Andrea Skantar, a research molecular biologist with the Agricultural Research Service of the U.S. Department of Agriculture in Maryland, said Calderon-Urrea's research is noteworthy.

"I think Alejandro is unique in looking at programmed cell death for this purpose," Skantar said.

But it's not the only work being done on nematodes.

Valerie Williamson, a molecular biologist and nematologist at the University of California at Davis, is doing research involving a gene in tomatoes that provides natural resistance to the pests.

In the meantime, Williamson said, it's important that Calderon-Urrea's research continues because parasitic nematodes are such a big problem. Published reports put U.S. crop losses annually in the billions of dollars.

For years, growers chose methyl bromide as the primary pesticide to kill parasitic nematodes, but the government said it damaged the atmosphere. It's being phased out.

Growers now use other pesticides, but making plants resistant to nematodes would be safer for the environment, said Richard Molinar, a farm adviser for the University of California Cooperative Extension in Fresno.

"Nobody would disagree with that, even a pesticide salesman," Molinar said.

Would the suicide genes that kill the nematodes harm people who ate the genetically-modified crops? Calderon-Urrea said he doesn't think that would happen, though that question is part of his research.

"People have the perception that maybe these genetically-modified plants are harmful," he said. "But there is a large body of evidence to the contrary."

Some people still worry about the ramifications of genetically engineering crops.

Joseph Oldaker, a spokesman for the Institute on Biotechnology & the Human Future, a think tank in Chicago, said he wasn't familiar with Calderon-Urrea's work. But, he said, there are general concerns about genetically-modified plants.

Such plants might displace natural plants, reducing biodiversity and harming the environment, said Oldaker.

In addition, techniques used to create the new plants could threaten public safety, Oldaker said. "We don't know how the genes in the new environment are going to interact with our natural biochemistry in the long term."

Calderon-Urrea knows about the concerns.

"These are very sensitive issues," he said, "and I would be the first one to kiss this work goodbye if it caused any harm to humans, animals or the environment."