Genetic Tweak Caused Corn to Evolve Juicy Kernels
It turns out that corn was first created due to a single genetic mutation. Scientists have discovered that a genetic mutation is responsible for the juicy kernels on a corn cob and caused them to be out in the open rather than trapped inside an inedible casing as tough as a walnut shell.
"Humans completely reshaped the ancestor of corn, effectively turning the cob inside out," said John Doebley, one of the researchers, in a news release. "Our results show that a small genetic change has had a big effect on this remarkable transformation."
Corn was first domesticated in Mexico about 9,000 years ago from the wild grass teosinte. Teosinte seeds are actually protected by a hard casing that makes them impractical to eat. Ancient plant breeders, though, developed varieties with "naked kernels" that allowed them to be more easily harvested. In these plants, the structures that formed the seed case turned into the cob in the center of the ear and left the seed exposed.
Corn kernels today also have a few other traits. They remain firmly attached to the cob rather than easily scattering like in teosinte. The cobs are also much larger, and the corn plant has fewer leaf branches. Although these are big changes, corn evolved relatively rapidly-within a few thousand years at most.
In this latest study, the scientists found that at one particular position in the tga1 sequence, the corn version carried a "C" DNA based instead of the "G" found in teosinte. This single nucleotide difference caused one amino acid in the TGA1 protein to be switched from a lysine in teosinte to an asparagine in corn.
When the researchers tested the effect of this amino acid substitution on TGA1, they found that the corn version of the protein had a greater tendency to bind to itself in pairs of molecules called dimers. The genetic difference also turned TGA1 into a "repressor" of the genes it controls, decreasing their expression.
The findings reveal a bit more about how we got the corn of today. This is important to know when breeding new varieties of corn today.
The findings are published in the journal Genetics.
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