Present day crops are the product of the intense selection applied by the first farming communities on the genetic variation of ancestral wild populations. This activity led to the accumulation of genes that control a group of traits known as the "domestication syndrome." These traits comprise visible changes in growth habit, organ size, seed dispersal, and environmental responses. However, with the exception of a few species that were domesticated for their edible roots, root traits have been neglected in domestication studies. Yet, morphological differences between roots of wild and cultivated forms exist and can be considered the product of indirect selection. This observation raises questions about both the number of genes responsible for these differences and their identity.
The main objective of this project is the identification of the genes controlling the root morphological changes associated with the domestication of Phaseolus vulgaris, the common bean, a New World species domesticated 8-10,000 years ago. The target genes and their chromosomal position will be identified through a statistical analysis of root traits (growth rates, branching, etc.) in progeny obtained from a cross between a wild and a domesticated bean. This analysis requires two pieces of information: a measurement of the root trait, and the genetic makeup of each individual in the progeny at previously mapped marker-genes covering all chromosomes. Root traits will be measured via 2D scans using a root scanner, and 3D scans using magnetic resonance imaging (MRI). Tools to evaluate 3D MRI root images quantitatively have been developed and will be expanded to create a computer generative 3D root model. The genetic makeup of the progeny will be obtained with the latest generation of high throughput sequencing and genotyping technologies. The genes controlling the domestication-associated root traits will be identified and located on a chromosome when statistical tests show that progeny with the wild version of the marker-gene exhibit significant differences in root traits from those with the domesticated version.
Identification of genes controlling root traits associated with domestication will have broader scientific and educational impacts. Knowledge about these genes will improve our understanding of the carbon balance of ecosystems in which the carbon storage in root mass is a major concern, and will also facilitate the genetic manipulation of roots for crop improvement. This project will produce a computer generative 3D root model, which will be a powerful teaching tool, and the starting point in the development of a gene-based root model. The training of undergraduate and graduate students from both the University of Florida and Florida A&M University, an institution with minorities who are under-represented in the scientific research community, will be one of the major components of this project.
