Plant Domestication

The domestication of plants represented a critical development in human history. Consequently, unraveling the origin of crops, as well as the molecular and genetic changes that accompany domestication and crop diversification, represents an important undertaking. Until recently, such studies were confined to a handful of crops of major economic importance. However, advances in next generation sequencing technology have allowed the extension of genomic knowledge beyond these species to a wider array of crops and their wild relatives. This information will not only be an important agronomic resource, but it will also improve the understanding of the genomic basis of domestication and adaptation.

The Compositae (Asteraceae) is one of the largest and most successful flowering plant families. Despite the large number of species in this family, only two – sunflower and lettuce – have become major food crops. However, there are many other species in the Compositae that have been cultivated by humans and attained various degrees of domestication. We have developed many genomic resources that will be valuable resource for future population and comparative genomic analyses of crop and weed evolution. In addition, we used the resulting assemblies as well as others previously generated by theCompositae Genome Project, to examine divergence between crops and their putative progenitors, and to consider evidence for introgression between crops and their wild relatives. We are also currently using these data to examine evidence for adaptive evolution during domestication.

Genomic resources will be valuable for detecting gene flow between various crops and their wild and weedy relatives. Such gene flow can have implications for the spread of genetically engineered genes from crops into wild species, or contamination of seed lots by foreign germplasm. More generally, the study of gene flow between domesticated species and their progenitors could give insight into the strength of reproductive barriers and the process of speciation, as well as the evolutionary consequences of hybridization and introgression. Although there have been an increasing number of studies using genetic markers to estimate gene flow between cultivated and weedy populations, there have been few genome-wide studies especially across multiple crop/wild species pairs.

It has been hypothesized that reproductive isolation should facilitate evolution under domestication. To address this question, we conducted a systematic survey of reproductive barriers between 32 economically important crop species and their progenitors to better understand the role of reproductive isolation during the domestication process. We showed that the majority of crops surveyed are isolated from their progenitors by one or more reproductive barriers, despite the fact that the most important reproductive barrier in natural systems, geographical isolation, was absent, at least in the initial stages of domestication for most species. Thus, barriers to reproduction between crops and wild relatives are closely associated with domestication and may facilitate it, thereby raising the question whether reproductive isolation could be viewed as a long-overlooked domestication trait.