Teosinte is a wild grass that grows in the Mexican Sierra Madre and
it looks nothing like the corn, or maize that blanket Midwestern
farms. Yet 7,000 years ago, early Mesoamerican crop breeders
were able to transform this bushy grass into stalk-like maize,
the third most planted crop in the world after rice and wheat.
This amazing genetic feat is the subject of a discovery recently
published by a team of UCSD biologists. In the December 2, 2004 issue
of the journal Nature, the scientists reported they had found a gene
that regulates the development of secondary branching in plants.
This gene presumably played a role in the transformation of the highly-branched
teosinte plant into the single-stalked maize.
Numerous variants of this gene are present in teosinte, but only
one variant of the gene is found in all inbred varieties of modern
maize. The researchers concluded this was evidence that Mesoamerican
crop breeders most likely used this trait in combination with a small
number of other traits to selectively transform teosinte to maize.
“What we know is that this gene is critical for branching to take
place in maize, including the branches that give rise to the ears
of corn,” says Robert J. Schmidt, a professor of biology, who
made the discovery with Andrea Gallavotti, a postdoctoral researcher
in his laboratory, and with colleagues at other institutions. “We
presume that there was something unusual in the morphology that these
early farmers selected from the wild teosinte that made it easier
for them to plant, grow or harvest their crops.”
The gene cloned by the scientists is called barren stalk1 because,
when the gene product is absent, a relatively barren stalk results—one
with leaves, but without secondary branches. In maize, these secondary
branches include the female reproductive parts, or ears of corn,
and the male reproductive organ, or tassel, the multiple-branched
crown at the top of the plant.
Teosinte has numerous tassels and
tiny ears in its highly branched architecture, while maize has
only one tassel and much fewer, but
much larger ears. The early plant breeders selected traits that
enhanced the size of the ears in teosinte. According to the UCSD
biologists
the change, on a molecular level, involved some combination of
the barren stalk1
and other genes that limited branching in teosinte. That, in turn,
allowed improved varieties to concentrate the plant’s resources
on producing bigger seeds on
bigger ears of corn. And that turned out
to be a good thing—not only for the first Mesoamerican farmers,
but for our modern backyard barbeques.  — Kim McDonald
|
