BioEd Online

The people of Mesoamerica are largely responsible for the golden corn we grow today, having domesticated tough teosinte grass thousands of years ago and bred it into modern maize.

Researchers have now located the gene responsible for some of the traits that the Mesoamericans were selecting. The discovery should help scientists understand how plants develop, and reveals just how strict the ancient breeding regime for maize (Zea mays) must have been.

Robert Schmidt, a maize researcher at the University of California, San Diego, and his colleagues were intrigued by a mutant maize that was found in South America in the 1920s. The mutant is unable to grow branches or flowers, and happens to resemble a particular rice mutant in this respect. Because the sequence of the gene that causes the effect is known for rice, Schmidt and his team were able to pin down the sequence in maize.

They called the mutated gene barren stalk1 and were able to show that the normal version of barren stalk1 regulates how the maize plants branch. They report their results in this week's Nature¹.

But not only does barren stalk1 regulate branching, it is also located within one of five regions that maize researchers have identified as targets of domestication. So, was it one of the genes that the Mesoamericans unknowingly selected for as they tamed teosinte (Zea mexicana)?

Fruitful work

To investigate further, the researchers compared the number of variants of the barrenstalk1 gene in teosinte, which still grows wild in Mexico's Sierra Madre, with the number in modern maize.

In teosinte, there are about a dozen common variants of the gene, all of which probably produced subtly different branching patterns in the plants. It is common for this number of variants to be present in a particular species of plant. But in modern maize, only one variant exists, suggesting that the others must have been eliminated by rigorous selective breeding.

"It's a really impressive paper," says Phillip SanMiguel, geneticist at Purdue University in West Lafayette, Indiana, who works with maize.

Why did the Mesoamericans plump so strongly for one branching pattern rather than another? Schmidt's team has not nailed this down yet. But presumably there was something about the branching of maize with that particular variant that was useful.

"In combination with other genes it probably had some impact on the architecture that was important to the Mesoamericans," suggests Schmidt. "Perhaps by having fewer branches you get bigger seeds. We don't know."

The next step will be to paste all the variants of the barren stalk1 that exist in teosinte into modern maize, Schimdt's team says. Once you see what the differences are in maize, it will be easier to guess why a particular variant was chosen.