Apparently, teosinte rejects the newfangled human-bred stuff. From ScienceDaily:
It was known that a cluster of genes called Tcb1-s is one of three that confers incompatibility between these rarely hybridizing maize and teosinte populations. Unlike the other two, it is found almost exclusively in wild teosinte. It contains both male and female genes that encode wild teosinte’s ability to reject maize pollen.
In sexually compatible plants, the pollen, which is basically a sperm delivery vehicle, lands on the pistil and forms a tube that elongates and burrows down into the ovary, where the egg is fertilized. But that’s not what happens when maize pollen lands on the pistil, or silk, of a wild teosinte plant.
Evans and his colleagues — Carnegie’s Yongxian Lu (the first author), Samuel Hokin, and Thomas Hartwig, along with Jerry Kermicle of the University of Wisconsin Madison — demonstrated that the Tcb1-female gene encodes a protein that is capable of modifying cell walls, likely making maize pollen tubes less elastic and thus preventing them from reaching the teosinte eggs. When these tubes can’t stretch all the way to the eggs, fertilization can’t occur, and hybrids won’t be possible.
What’s more, because teosinte pollen can fertilize itself, the researchers think that the Tcb1-male genes encode an ability that allows teosinte pollen to overcome this pollen tube barrier building. Paper. open access – Yongxian Lu, Samuel A. Hokin, Jerry L. Kermicle, Thomas Hartwig, Mathew M. S. Evans. A pistil-expressed pectin methylesterase confers cross-incompatibility between strains of Zea mays. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-10259-0 More.
The researchers don’t hazard a guess as to why the wild plant rejects its descendant. It’s tempting to liken it to a wolf pack chasing away a stray dog (if not outright killing him). Interesting development.
See also: Carefully Preserved Jumping Gene In Corn Shows How Intelligent Design Produces Massive Changes
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