How
Corn Became King
From: Kelly
April Tyrrell, University of Wisconsin-Madison
Ten thousand years ago, a golden grain got naked, brought people together and grew to become one of the top agricultural commodities on the planet.
Now, University of Wisconsin-Madison researchers have found that
just a single letter change in the genetic script of corn's ancestor, teosinte,
helped make it all possible.
Publishing in the journal Genetics this
month, UW-Madison genetics Professor John Doebley and a
team of researchers describe how, during the domestication of corn, a single
nucleotide change in the teosinte glume architectural gene (tga1) stripped away
the hard, inedible casing of this wild grass, ultimately exposing the edible
golden kernel.
"A huge proportion of the world is economically dependent on
the crop and understanding how it was constructed 10,000 years ago is more than
just intellectually satisfying," Doebley says. He has spent his long
career studying the evolution of maize, the plant from which corn grows.
"It tells us something about how important this genetic change was."
Seen side by side, maize and teosinte do not look as if they belong on the same family tree. Teosinte is branched and bushy; its miniscule "ears" bear a stronger resemblance to wheat and contain just 10 to 12 kernels.
Maize, meanwhile, is tall and stalked and grows massive ears
containing hundreds of kernels. Yet research by Doebley years ago traced
maize's roots to a weedy form of teosinte in a valley in southwestern Mexico.
"The big question is, when we look out the window and see a
diversity of forms in the plants and animals around us, what were the genetic
changes that took place to make all of that happen?"
Doebley says.
"Two closely related plants, why do they have a different shape of leaf;
or two people, why is one a little taller?"
The answer often lies in mutations, the currency of evolution.
Sometimes single letters are changed in the genome of a species, while other
times, whole paragraphs are lifted or moved around.
Sometimes, these changes
don't alter the meaning of the story, while other times they do. When those
changes are beneficial, that altered copy survives the test of time. Sometimes
that means the creation of a whole new species.
In the case of maize, in the process of domesticating it for food,
humans decided which mutations were good and which to eliminate by growing more
of the plants they preferred. Previous studies from Doebley's lab had
identified the tga1 gene as responsible for the transition from encased to
exposed kernels, but until now, no one knew just how.
Continue reading at the University of
Wisconsin-Madison.