Scientists Trace Corn Ancestry from Ancient Grass to Modern Crop

National Science Foundation ^ | 27 May 2005 | Staff

[PatrickHenry]

Researchers have identified corn genes that were preferentially selected by Native Americans during the course of the plant's domestication from its grassy relative, teosinte, (pronounced "tA-O-'sin-tE") to the single-stalked, large-eared plant we know today. The study revealed that of the 59,000 total genes in the corn genome, approximately 1,200 were preferentially targeted for selection during its domestication.

The study, by University of California, Irvine's Brandon Gaut and his colleagues, appears in the May 27 issue of the journal, Science.

Understandably, a primary goal of teosinte domestication was to improve the ear and its kernels. A teosinte ear is only 2 to 3 inches long with five to 12 kernels--compare that to corn's 12-inch ear that boasts 500 or more kernels! Teosinte kernels are also encased in a hard coating, allowing them to survive the digestive tracts of birds and grazing mammals for better dispersal in the wild. But, for humans, the tooth-cracking coating was undesirable so it was selectively reduced…and reduced…and reduced…until all that remains is the annoying bit of paper-thin, translucent tissue that sometimes sticks between the teeth when one munches corn on the cob.

Cultivated corn was domesticated from teosinte more than 6,000 years ago. During the process, corn lost the ability to survive in the wild, but gained valuable agricultural traits. The suppression of branching from the stalk resulted in a lower number of ears per plant but allows each ear to grow larger. The hard case around the kernel disappeared over time. Today, we see just a few ears of corn growing on one unbranched stalk and enjoy larger ears covered with many, many rows of soft corn kernels.

To analyze the genes of modern corn and its ancestral teosinte, Gaut and his coworkers used relatively new genomic techniques to determine the DNA sequence of 700 gene bits in the two plants and used "population genetics," the study of genetic variation, to compare them.

"These results will provide important insights to modern corn breeders in their quest to establish hardier, higher-yielding corn plants," said Gaut. "The scientific approach will also be useful in the study of other domesticated organisms, plants and animals alike."

This work generally confirms the idea that corn went through a "population bottleneck," or a period when a significant portion of corn’s genetic diversity was lost, which typically marks a domestication event. Calculations using these data reveal that fewer than 3,500 teosinte plants may have contributed to the genetic diversity in modern corn.

Between 6,000 and 10,000 years ago, Native Americans living in what is now Mexico began domesticating teosinte, or the "grain of the gods," as the name has been interpreted to mean. Scientists cannot yet say how long this domestication process took, but they do know that around 4,500 years ago, a plant recognizable as today's corn was present across the Americas.

So, thousands of years before Gregor Mendel postulated his theories on genetics and heredity, indigenous Americans were breeding corn to select for desirable traits. By selectively breeding each generation, ancient farmers drastically changed teosinte's appearance, yield, grain quality and survivability—culminating in today's "corn." In fact, teosinte is so unlike modern corn, 19th century botanists did not even consider the two to be related.

"This is a very exciting finding," said Jane Silverthorne of the National Science Foundation's (NSF) biology directorate, which funded the project. "We are beginning to have a much clearer picture of what happened to the genes responsible for the structure of today’s corn plant."

A broad understanding of the genes present in modern-day corn will provide a foundation for improving it as well as its cousin cereal crops. Target goals include yield increases, improved insect and pathogen resistance, enhanced environmental adaptability, and improved nutritional value. To that end, sequencing the entire genome of corn is also critical to improving the crop and its value in human subsistence.

According to the U.S. Department of Agriculture (USDA), nearly 12 billion bushels of corn were harvested in the United States in 2004, which will be used for a diverse array of products including livestock feed, ethanol and plastic consumer items, as well as food. The National Corn Growers Association reported that 2003 corn exports were valued at $4.5 billion.

Supported by NSF's Plant Genome Research Program, this collaborative project included Gaut and co-workers at the University of California, Irvine, together with scientists from the USDA-Agricultural Research Service, the University of Missouri and the University of Wisconsin. NSF is part of an interagency program along with the U.S. Department of Energy and the USDA that plans to support the sequencing of the corn genome over the next three years.

[PatrickHenry]

Plant evolution doesn't usually get much exposure around here, but this seems a good example of human-induced speciation. Everyone be nice.

[PatrickHenry]

EvolutionPing

A pro-evolution science list with over 280 names. See the list's description at my freeper homepage. Then FReepmail to be added or dropped.

[snarks_when_bored]

Interesting study.

[kharaku]

There is a difference between evolution and natural selection, natural selection being a blatently NON active process, also given that humans helped in this case even NATURAL selection is a mysnomer. You say plant evolution, I say good farming.

[metesky]

Wait until the watermelons find out that they're already eating genetically altered corn, eh?

[wideawake]

Can teosinte and maize not be crossed? The article doesn't say.

[b_sharp]

But they're still plants.

They are an artifact of intelligent design.

Cheech and Chong were the intelligent designers.

[AntiGuv]

Reality doesn't care how you describe it. ;^)

[Doctor Stochastic]

It's still a plant!!!!!!!

[orionblamblam]

> There is a difference between evolution and natural selection

Well, DUH. Evolution is the end result. Natural selection is the mechanism.

> given that humans helped in this case even NATURAL selection is a mysnomer.

What, are humans supernatural? Did they even use direct genetic modification?

No to both. The humans involved here were simply another facet of their environment. The plants evolved accordingly to best propogate their DNA down the line.

[RightWhale]

We focus on the plant. Often we forget about the environment. The environment where these plants are encouraged is modified considerably from raw nature. If the environment is allowed to sit and do its thing for a while, it will revert and most all our engineered plants will be choked out by natural vegetation.

[narby]

By selectively breeding each generation, ancient farmers drastically changed teosinte's appearance, yield, grain quality and survivability—culminating in today's "corn."

Somehow I doubt this was any kind of deliberate action on the Indians part. Ancient farming techniques were haphazard, at best, compared with modern techniques. And tribal bands might leave the area for hunting during the growing season, perhaps returning for harvest, perhaps not.

I'd bet that the domestication process merely was indians harvesting the corn they liked, and leaving in the field what they didn't. And then re-planting their harvest.

This is merely "natural selection" by natives that have no clue that they're changing the crop they're eating. The implication that they understood some kind of Mendelian process is silly.

What's interesting is that such a huge change can be evolved into the plant in such a short period of time.

[PatrickHenry]

I'm surprised no one has picked up on this little tidbit from the article:

Between 6,000 and 10,000 years ago, Native Americans living in what is now Mexico began domesticating teosinte ...

[CaptRon]

But, for humans, the tooth-cracking coating was undesirable so it was selectively reduced…and reduced…and reduced…until all that remains is the annoying bit of paper-thin, translucent tissue that sometimes sticks between the teeth when one munches corn on the cob.

So, this report is telling us that the native Americans intuitively made the leap of thought that they could make a fomerly useless plant to one that was useful to them by selective breeding?

[Eric in the Ozarks]

I have fun with the fear-stressed Greenies when I ask if they have any Canola cooking oil in their kitchen...Canola was engineered from Rapeseed, which is poisonous.

[Alamo-Girl]

Thanks for the ping!

[RightWhale]

I'd bet that the domestication process merely was indians harvesting the corn they liked, and leaving in the field what they didn't.

The opposite is what you want. Weeding is the main process. What you don't want to see in the garden is pulled out by the roots. What is left is what you want, and some of what you want goes to seed if you let it.

[narby]

Between 6,000 and 10,000 years ago, Native Americans living in what is now Mexico began domesticating teosinte ...

What's even more interesting is that these corn plants didn't make it on to Noah's ark to be replanted in the old world. How'd they survive the flood?

[Fun Bob]

Stop GM food!

Boycott Corn!

[djf]

I thought he early corn type plants were from something that started with a 'Z'. Can't remember now...