Thousands of years ago, sometime in our pre-history, early man dropped a wheat seed in the ground for the first time. Between then and now, wheat has undergone major changes, usually for the better.
But recently Jorge Dubcovsky, a wheat breeder at the University of California-Davis, found that in domesticating wheat, a vital gene controlling protein, zinc and iron was switched off. Now, Dubcovsky wants to turn back the clock — or at least replace a small, but vitally important gear in the mechanism. Doing so, he says, will provide a better, more nutritious crop.
Dubcovsky is originally from Argentina, where he earned a doctorate from the University of Buenos Aires. He went to the Davis, Calif., campus as a visiting scientist in 1992.
In 1994, he returned to Argentina for two years before going back to Davis in 1996. He's been a professor heading up UC-Davis' wheat breeding program ever since.
“I began studying biology and was interested in ecology. I did my doctorate on the evolution of grasses in South America. That's when I really got interested in the genetic side of things — I realized genetics was a powerful tool to answer questions at a very detailed level.”
Dubcovsky went to UC-Davis to familiarize himself with molecular technologies. While doing that, “I got involved in wheat improvements and have kept at it for the last 14 years.”
“Wheat is what's allowed the human population to grow. It was one of the first domesticated crops. Various human groups moved around the world and carried wheat seed with them.”
Today, wheat provides 23 percent of the world population's caloric intake. That shows how important wheat is — “it is every fourth or fifth bite of what we eat.”
As for the recent discovery, Dubcovsky is reluctant to take too much credit.
“With science, it's rare to have something discovered (in a vacuum). Usually, discoveries are the result of contributions from many people.”
The story of this discovery begins exactly 100 years ago when Aaron Aaronshon found wild wheat growing in Israel. More recently, in the 1970s, Moshe Feldman found that some of those wild wheats have more protein than their commercially available cousins.
Another researcher, Leonard Joppa, spent 10 to 15 years working in North Dakota, transferring chromosomes from wild wheat species into cultivated pasta wheat. That allowed him to demonstrate that the gene producing the difference in protein was located in chromosome 6.
That's the point where Dubcovsky began his research.
“I began trying to identify what particular gene was producing that protein difference. We finally unlocked it.”
The procedure used to find the gene has been used before when cloning genes from humans or other organisms. Map-based cloning entails an extremely detailed genetic map. To do that, Dubcovsky and colleagues used 9,000 plants to get close to the gene.
“We then constructed a library where we placed pieces of the DNA covering the entire genome. So, in a freezer, we have 500,000 clones containing large DNA pieces of wheat.
“Once we knew where the gene was located on the map, we used the genetic markers around the gene to screen the library's large DNA pieces and picked the one that contained the markers on both sides of the target gene.
“That way we knew that gene was in the big piece of DNA. We then sequenced that complete piece of DNA and identified the gene. That's how we found it.”
But science is a rigorous discipline and the researcher had to double check that he had the proper gene.
“First, we sequenced the two parents — one with high protein and one without. We discovered the low-protein parent has a non-functioning version of the gene. That was a strong indication to us that this was, indeed, the proper gene.”
They followed that up with an experiment on a transgenic wheat plant.
“We created a plant in which the activity of the genes was reduced. We found exactly what was predicted — there was less protein, less zinc and iron and the transgenic plant matured much later than the control.”
That finding demonstrated that Dubcovsky's hypothesis about the gene was correct. With that result, he and colleagues were able to publish their findings in a well-respected journal, Science.
So now that Dubcovsky has identified the gene that was holding the plant back, he'll turn it into a positive?
“Exactly — and we can do that through normal crosses without using transgenics. You can cross wild wheat easily with cultivated wheat. So we'll make the crosses and transfer the functional version of the gene. We're essentially replacing the broken gene with the one that's normal.
“However, it's important to test the new varieties in the field because in some genetic backgrounds and environments, the early maturity induced by this gene can negatively affect grain size.”
How will this gene discovery be deployed in the real world?
“As I mentioned, we made genetic maps of these genes early on. By 1998, we already had the markers that were close to the gene. We've been using those molecular markers to move that gene into commercial varieties for the last eight years.”
Developing a variety typically takes eight to 10 years.
“You must make a lot of crosses and stabilize the plants. It's a long process.
“But we began this work long ago, so there's already a variety we're releasing in California this year. We'll be producing foundation seed this year for Lassik.
“It's was tested this year with millers and bakers. They liked it very much because it has high protein and qualities that translate to good bread.”
To produce Lassik, “We took an old California wheat variety with very low protein. It was used for feed. We put this (newly discovered) gene into it and increased the protein content from 11.5 percent to 13 percent.”
What might happen five years down the road with this discovery?
“The gene does two things: it increases protein and the zinc and iron content. The gene essentially accelerates the remobilization of the nutrients from the leaf to the grain while the plant is drying.”
How it might be imparted around the world is more a political question than a scientific one, says Dubcovsky. By incorporating this gene, 10 percent more iron and 10 percent more protein are produced.
“Will the wheat with the better profile reach the people who really need it? I don't know. If we use this gene in the wheat we produce for food aid and send it to the people who need it, it would be a positive for them.
“But if you really want to deploy this gene into developing countries, a breeding program is needed — one that puts it into their varieties. And wheat breeding is a long-term investment.”
Wheat breeding is also largely a public enterprise. Most people have no idea that most wheat varieties are developed in U.S. universities.
“Almost 80 percent of the wheat grown in this country is from varieties developed in the public sector, not from private companies.”
What's next for Dubcovsky?
“Our objectives are very clear and focus on nutrition.
“We've been trying to understand the physiological process of how the plant remobilizes zinc.”
There's another obvious target in wheat, though. All cereal crops contain a compound called phytic acid.
“It's actually an anti-nutrient. When you eat cereals, the phytic acid interacts with zinc and iron in a way that makes them unavailable to the consumer.
“So even though the zinc and iron are in the cereal, a large part of them isn't there for the betterment of the consumer. We are working to reduce phytic acid content in the grain.”
Dubcovsky also worries that so few have a clear understanding of where food actually comes from.
“Your readers are obviously more informed about agriculture. But the general public is used to the idea that food comes from the markets. They don't understand the effort it takes to grow a crop, to have good varieties that can be grown in the real world.
“They don't understand the real need to support those activities if we want to have better crops in the future. That needs to change.”