b'33Teosinte Modern CornAbout 9,000 years ago, maize (right) was domesticated from teosinte (left) in the Balsas River Valley of Mexico. The artwork compares the features of the two species. The photograph at right shows a teosinte plant on the Stanford University campus.Images courtesy Nicolle Rager Fuller, National Science Foundation and Yongxian Lu, Carnegie Institution for Sciencewild teosinte. It contains both female and male genestubes less elastic, preventing them from reaching the that program wild teosinte to reject maize pollen butteosinte eggs. When these tubes cant stretch to the fertilize itself, respectively. eggs, fertilization cant occur and hybrids wont arise.In sexually compatible plants, the pollena spermAdditionally, because teosinte pollen can fertilize delivery vehiclelands on the pistil and forms a tubeitself, the researchers think that the Tcb1-male genes that elongates and burrows into the ovary, whereencode an ability that allows teosinte pollen to the egg is fertilized. This does not happen whenovercome this pollen tube barrier.maize pollen lands on the pistil, or silk, of these wild teosinte plants. Knowing the Tcb1-female gene now allows tests on the cellular mechanisms of pollen rejection and Evans and colleagues demonstrated that thedetermining if the Tcb1-female gene family plays a role Tcb1-female gene encodes a protein that is capablein reproductive isolation and speciation more broadly of modifying cell walls, likely making maize pollenin grasses. '