http://www.chron.com/cs/CDA/ssistory.mpl/nation/3204347QUOTE
May 30, 2005, 10:33PM
Peeling back corn's genetic profile
The plant's wild ancestor, teosinte, could hold the key to a better crop
By ERIC HAND
St. Louis Post-dispatch
ST. LOUIS - In one hand, plant geneticist Michael McMullen holds black teosinte kernels, the seeds of what scientists say is the grassy ancestor of corn. In the other, he holds needle-nose pliers — definitely needed to crack the tough hulls into a few starchy bits.
"If you have squirrel teeth, you might be able to eat this," said McMullen, a U.S. Department of Agriculture researcher at the University of Missouri at Columbia.
The weedy teosinte plant, with its miserly portfolio of kernels, barely resembles its bountiful descendent. McMullen and his colleagues have pegged the genes responsible for the dramatic transformation. They think wild teosinte, with its high genetic diversity, still has a lot to offer corn while inbreeding eventually could confound the search for higher-yielding hybrids.
"If you want to make corn even better, these are genes you want to work on," said McMullen, tanned from days in the field with his experimental crops.
Corn researcher Brad Barbazuk said McMullen's work will have a big impact on the plant science industry.
"By understanding where we've lost genetic diversity over time, we can look at reintroducing diversity," said Barbazuk, who works at the Donald Danforth Plant Science Center in Creve Coeur, Mo., a nonprofit research institute.
The work, a joint project among the University of Missouri, the University of California at Irvine and the University of Wisconsin at Madison, was published Friday in the journal Science.
Teosinte is a hardy grass of Mexico and Central America with ears of just eight kernels protected in a stony casing. The seeds can be dispersed after passing intact through animals' digestive systems.
Corn has about 500 soft kernels per ear. It needs human cultivation, human protection, to survive. Its seeds would otherwise be eaten by animals — or else corn seedlings, undispersed and growing in place, would wither in the shadow of existing plants.
Scientists say that between 6,000 and 9,000 years ago, ancient breeders tried to tame teosinte. Year after year, they took the best teosinte plants — plants, perhaps, with bigger or softer or more kernels — and crossed them with each other. Thousands of years later, Native Americans had corn.
The problem is the inbreeding. Most corn genes have retained 57 percent of the diversity of teosinte genes, the researchers found. But for at least 1,200 of corn's 50,000 genes — the genes Native Americans were winnowing year after year — there's almost no diversity at all. That makes it increasingly difficult for modern-day breeders to stumble on outstanding traits that would make for better strains of corn.
"The yields are becoming less easy to improve," Barbazuk said. "You're pretty much tapped out."
Eric Sachs, a geneticist at agricultural products developer Monsanto, concurred. "The improvements through conventional breeding are beginning to plateau," he said.
In the paper, the researchers offered a list of 30 genes with a high probability of controlling some important corn characteristic. They aren't sure what all the genes do. Some control the nutrition content, others might control kernel size. But instead of cooking with a 50,000-ingredient recipe, plant scientists can begin experimenting with 30.
"Things like this will make it simpler," Barbazuk said. "There will be less shooting in the dark."
Just thought that was interesting.