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Cold Spring Harbor Laboratory (CSHL) has started to solve a millennia-old riddle. This story began 9,000 years ago. Maize was domesticated for the first time in the Mexican lowlands. Some 5,000 years later, the crop crossed with teosinte mexicana, a Mexican highland plant.
This led to cold adaptation. From here, corn spread over the continent, giving way to the vegetable that is today an essential in our diets. But how did it adjust so rapidly? What biological factors enabled the highland crop’s qualities to take hold? Today, an appropriate answer arises.
Rob Martienssen, a CSHL Professor and HHMI Investigator, has been researching RNA interference, the process by which short RNAs silence genes, for almost 20 years when University of Wisconsin scientist Jerry Kermicle approached him with an intriguing observation.
His tests with semi-sterile teosinte hybrids and regular maize resulted in highly strange behavior in their offspring. With natural inheritance, the offspring should have become either entirely infertile or fertile. However, no matter how many times Kermicle bred the hybrids with maize, all of the offspring were semi-sterile. What was going on?
In an attempt to figure it out, Martienssen and doctoral student Ben Berube gene sequenced hundreds of pollen grains from the semi-sterile offspring. They observed that each contained the same parts of the teosinte genome. The results are published in the journal Nature.
Two portions of the genome, one on chromosome 5 and one on chromosome 6, were constantly inherited. That showed us the genes responsible had to be in those locations.
On chromosome 5, they discovered that a gene called Dicer-like 2 produces a set of small RNAs that are always present in semi-sterile hybrids but not in regular maize. With this discovery, the Martienssen lab was able to identify what they term Teosinte Pollen Drive (TPD).
This “selfish” genetic system eradicates competing pollen grains without the gene drive. It promotes maize-teosinte hybrids to convey specific features to males more frequently than females. The revelation could have serious implications for the farming industry. But in Martienssen’s opinion, the discovery is much more significant than its prospective weed management applications.
Researchers are more interested in the evolutionary implications, what it may indicate for the process of domestication, and how it could have happened considerably faster than thought.
If Teosinte mexicana is “the Neanderthal of maize,” the researchers may have discovered the “missing link” in corn in TPD. The discovery could explain not just how corn spread across America, but also why particular small RNAs are found in so many plant and animal sperm cells, including our own.
Sources:
Berube, B., Ernst, E., Cahn, J. et al. Teosinte Pollen Drive guides maize diversification and domestication by RNAi. Nature (2024). https://doi.org/10.1038/s41586-024-07788-0
https://phys.org/news/2024-08-teosinte-pollen-scientists-corn-link.html
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