科学美国人60秒:Bite Me: The Mutation That Made Corn Kernels Consumable

Nothing says summer like a sweet ear of corn. But that treat would be much harder to eat if it weren’t for a crucial mutation. The change, in just one letter of the DNA code, appears to have cracked the hard casing that covered every kernel in corn’s wild ancestor. That’s according to a study in the journal Genetics. [Huai Wang et al, Evidence That the Origin of Naked Kernels During Maize Domestication Was Caused by a Single Amino Acid Substitution in tga1]

Corn was domesticated from a wild grass called teosinte some 9,000 years ago. But how did our ancestors make maize the agricultural marvel it is today? Seems they selectively propagated plants with a particular mutation—one that made the kernels more accessible to hungry Homo sapiens.

The researchers compared the DNA of 16 varieties of modern corn and 20 types of teosinte. And they found a single, key mutation that is present in modern corn but absent in its wild-grass ancestor. This genetic hiccup disrupts the activity of a protein called tga1.

In teosinte, the tga1 protein directs the formation of a hard shell around every corn kernel. But the modern maize mutation gives tga1 a new set of marching orders. The mutant protein turns the ear inside out, converting the seed cases into a cob that holds all the kernels in place.

When the researchers reversed the effects of the mutant protein, the ancestral seed-case remnants started to reappear.

The results suggest that even minor genetic changes can lead to some pretty tasty developments. You might call it a-maize-ing. But that would be corny.

—Karen Hopkin

(The above text is a transcript of this podcast)