What Are We Actually Eating: Corn
The mid and late summer harvest brings one of the most prevalent crops grown around the world...corn! For human consumption, sweet corn is highly valued for the high content of sucrose in the young kernels, while the highly versatile field corn is processed into consumables such as tortilla chips, high fructose corn syrup, various bioplastics, and fodder or animal feed. Since it encompasses 99% of all corn grown, field corn is economically important and processing it for biofuels and bioplastics will hopefully push us away from petroleum-based products, but the amount of field corn grown for animal feed is largely detrimental to the environment since industrial agriculture is a major contributor of green house gasses.
Corn is a member of the grass family, Poaceae (poe-ay-see-aye), which includes other closely related crops such as wheat, oats, rye, sorghum, and rice. But what we know as modern corn is a far cry from the plant that was grown ~9,000 years ago. In fact, the ancestor of corn, a plant called teosinte (tea-oh-sin-tay), looked incredibly different (almost indistinguishable) from modern corn and had traits that made it successful for survival and reproduction in the wild, but terrible for cultivation. In fact, during the process of domesticating teosinte much of the plant’s shape and composition underwent massive changes to give us our modern corn.
Teosinte is native to Mexico and Central America and these are the regions where modern corn was domesticated. In other words, they are the regions where humans altered the plant to make it more adaptive to cultivation rather than surviving the harsh environment. Teosinte has several traits that make it advantageous for reproducing and surviving the wild including the production of branches (like trees), maximizing seed dispersal, and hard casings around the grain for protection. But these traits are less than ideal in an agricultural setting.
Unlike modern corn, teosinte produces many branches and several hundred low-yielding ears (about 10 grains per ear). This is advantageous in the wild for the large production of seeds but gives the plant the look of a large shrub. This doesn’t bode well in an agricultural setting where crops are planted in rows to optimize harvesting and very wide (highly branched) plants can crowd and shade their neighbors making harvesting a huge pain and decreasing the amount of light each plant receives.
One trait that contributes to success in the wild is the ability to survive being eaten (this holds true for not only for plants but ….really every organism). There are many ways plants have evolved to protect themselves and teosinte is no different. Surrounding the grains of teosinte are modified leaves called glumes. At maturity, the glumes are nearly unbreakable and fully encapsulate the grain. This makes the grain indigestible when eaten by an animal, but this makes the grain useless for human consumption. In modern corn, the glumes are reduced and papery, and exposing the grains allows them to be both easily harvested and digested.
Ultimately, the traits of teosinte were recognized as bad for the cultivation of corn, and modifying them would contribute to the rise of modern civilization. While many more traits have been selected to produce modern corn, the few described above have been well studied. In fact, scientists have been able to pinpoint a few key genes that contribute to these traits. For example, a single gene called TB1 has been implicated in the reduction of branching that we see in modern corn. Throughout corn domestication, TB1 was selected to be constantly turned “on” in order to prevent the corn plants from forming branches. Another major event in corn domestication was the selection for a change (mutation, see the GMO vs transgenic article from August) in the DNA sequence of the gene TGA1. This change in the DNA sequence of the gene prevents the hardening of the glumes and frees the grain from a hard indigestible casing.
Modifying the traits of teosinte through selection and breeding was necessary to produce modern corn. As such, this classifies your “non-GMO” corn as a genetically modified organism. So, the next time you take a bite out of your freshly steamed and buttered corn you’ll know that the organism in your hands would not exist without human intervention.
DR. MICHAEL SCHWARTZ
Dr. Michael Schwartz is a postdoctoral research associate at North Carolina State University where he is working on developing a way to 3D bioprint plants and holds a Ph.D. in plant biology from the University of California, Riverside where he utilized molecular biology and genetics to study leaf angle in black-eyed peas. Michael is fascinated by all things weird about plants and their development, from carnivory to attraction, and is interested in communicating the science behind the plants we eat to the general public. In his free time, he enjoys tending to his indoor and outdoor plants, playing computer games, and watching his dog tear apart her toys.
For more (jargon heavy) reading, check out this very detailed review: