Pollen-pistil interactions and reproductive isolation in maize and teosinte

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Reproductive isolation is critical for speciation. This can be achieved by geographic isolation or by having plants that grow together to prevent fertilization by pollen from foreign populations of plants. Some plants prevent fertilization by foreign pollen by using a species-specific pollinator, such as a single insect species, to deliver only the correct pollen to the female parts of the flower, called the pistil. However, in wind-pollinated species in which many types of pollen can land on the pistil, reproductive isolation is achieved in other ways, including the physiological rejection of foreign pollen grains by the pistil. This type of reproductive isolation is poorly understood because of the simple fact that plants of different types cannot be crossed together. An example of this second strategy occurs between some strains of teosinte, the wild progenitor of maize, and cultivated maize. It is postulated that selection for teosintes that can reject maize pollen has occurred during maize cultivation. Because hybrids can be made in controlled conditions by pollinating maize plants with teosinte, this situation provides a model system for the study of physiological, reproductive isolation in a wind-pollinated crop plant. By crossing maize females by teosinte pollen this trait has been conferred to some maize lines, and in many cases the trait is controlled by a single locus, Teosinte crossing barrier1 (Tcb1). The Tcb1 gene has been located to a small region of chromosome 4. In this project, the Tcb1 gene is to be cloned and its DNA sequence determined. With the DNA sequence of the gene known, the manner in which the protein encoded by Tcb1 creates a barrier to maize pollen can be studied, and studies of the role of Tcb1 like genes in reproductive isolation and speciation of wind-pollinated plant families will be possible. The broader impacts of this project include a greater understanding of the molecular basis for speciation, which has implications far beyond this study system. This project also provides training opportunities for high school students, undergraduate students and a postdoctoral researchers.