Horizontal genome transfer as an asexual path to the formation of new species.

This description of how a new species can be created by simple grafting offers novel perspectives on mechanisms that support genomic integrity. Plants have a diverse range of strategies to prevent gene flow from even closely related species, including highly regulated meiotic, pollination and fertilization mechanisms, but occasional failures in these can lead to the formation of interspecific hybrids. Like their animal counterparts (e.g. a mule), these hybrids are often sterile because of imperfect patterns of meiotic pairing between diverged chromosomes. However, in plants, these pairing issues can be overcome by infrequent meiotic or mitotic failures, in which duplicated chromosomes fail to partition. In the resulting allopolyploids, chromosomes from each parental genome now have perfect pairing partners. With restored fertility, but ploidy-imposed barriers on gene flow back to parental species, allotetraploids are thought to represent a common route to speciation in plants.