September, 2003

by Gillian Klucas 
Research Nebraska September 2003

In the agricultural plant world, male sterility often is a good thing.

Male sterile plants don’t produce pollen. That makes it easier to breed improved hybrids that yield and perform better, and to produce hybrid seed more economically. Sterility also helps ease concerns that genetically modified crops will spread their enhanced genetic characteristics, such as herbicide resistance, to wild plants.

Scientists long have tried to develop male sterile plants through a variety of techniques, from tapping natural mutations to inducing sterility through radiation and chemical methods. But sources of male sterility are nonexistent in some crops, such as soybeans, or limited in others, such as corn. And this characteristic can be unstable — some types of sterile plants can revert to fertility, which causes problems for growers.

Sally Mackenzie, a plant geneticist in the University of Nebraska’s Institute of Agriculture and Natural Resources, thinks she’s found a genetic key to sterility. It promises to work for a wide range of crops and horticultural products.

Scientists long have known that in nature, changes in the cells’ mitochondrial DNA cause the sterility mutation. Mackenzie and her team followed that genetic trail to re-create the mutation in the lab.

They found a gene in the cell’s nucleus that controls genetic changes in the mitochondria, which are the cell’s energy producers and also contain DNA. By inserting foreign DNA into this gene, they turned it off, observed changes in the mitochondria and pinpointed which change actually triggers male sterility.

Mackenzie’s team tracked down the gene in Arabidopsis, a plant whose genetic code is known, but their findings have broad potential. Because all plants carry this gene that affects the mitochondria, IANR researchers can use their technique to trigger male sterility in others.

Mackenzie now is growing transgenic soybeans and tomatoes to search for additional male steriles. “The really cool thing about this is that once I induce a male sterile, it’s stable,” Mackenzie said. After removing the foreign DNA that caused the original genetic change, the plant remains sterile. But by eliminating the foreign DNA, the plant is no longer considered transgenic.

“That’s the beauty of it,” she says. “Nobody has to have any qualms about using GMO technology.”

Agriculture would benefit if this method of inducing male sterility proves successful. Mackenzie wants consumers to benefit, too.

She’s applying her findings to develop a sterile, seedless green bean that vegetable buyers should appreciate. Without seeds, the pod is tenderer and more easily digestible. Sterility also tricks the plant into producing three times the number of pods, increasing yields.

While genetically modified crops have helped reduce the need for agricultural pesticides, consumers have yet to benefit directly, she said.

“If we hit the market with our male steriles and, at the same time, come up with our new seedless bean,” said Mackenzie, “I think the consumer is going to say, ‘This is nice engineering.’”

Researchers hope to work with an agribusiness to make sterile males commercially available in a variety of crops.

NU has filed for a provisional patent on their technique.

Mackenzie also is looking toward human diseases. “The recombination that we’re looking at in plant mitochondria may actually occur in us as well,” she said. Diseases such as diabetes, Parkinson’s and heart conditions may stem from mitochondrial defects that affect one in 8,000 people. As she did in Arabidopsis, Mackenzie is looking for a similar gene in humans that causes mitochondrial changes. If she finds it, researchers could use the same transgenic technique to re-create the genetic defects in mice, a discovery that could launch new explorations in medicine.

The National Science Foundation and U.S. Department of Energy helped fund this research.