Polyploidy, or whole genome duplication, is a major force in flowering plant evolution, with many flowering plant species having originated through the combined processes of hybridization and polyploidy. Chromosomal changes may generate genetic diversity via loss and duplication of genes in polyploids and may promote speciation, but the extent of chromosomal evolution in young, naturally occurring polyploid plants is unknown. Molecular cytogenetic methods will be used to investigate chromosomal and genomic changes in Tragopogon mirus and T. miscellus of the sunflower family. These species formed recently (in the past 80 years) and repeatedly through hybridization of different populations of the parental species. Furthermore, synthetic lines of both polyploids have been produced in the lab. Tragopogon therefore provides a unique opportunity to compare chromosomal variation in young natural and synthetic polyploid plants. This project will address the extent of chromosomal variation in new polyploids, whether or not certain "rules" govern the types of changes that occur, and the effect of this variation in natural populations.
Polyploidy is common in flowering plants (a group of 300,000 or more species). Furthermore, all of the world's major crops and most serious weeds are polyploid. Therefore, characterizing the processes that take place shortly after polyploid formation is crucial for understanding the genomes of most plant species, and thus for our ability to conserve plant biodiversity and sustainably benefit from it. In conjunction with DNA sequence analyses, this project will provide new insight into the process of polyploidization at the chromosomal, genomic, and genetic levels.
Polyploidy, or whole-genome duplication, characterizes most of our major crop plants, including wheat, corn, potatoes, oats, cotton, sugarcane, and tobacco, among others, and occurs frequently in flowering plants. Most polyploids combine the parental genomes of two or more parental species. Despite the prevalence of polyploidy, relatively little is known about the evolution of polyploid genomes. In this study, scientists discovered that recently formed polyploids in the genus Tragopogon, a member of the sunflower family, have undergone extensive chromosomal change involving movement of chromosome segments. In addition, they determined that chromosomes of one parental set could substitute for those of the other such that instead of the predicted case of two chromosomes from each parent (a 2 + 2 pattern), individuals also exhibited either 0 + 4 or 1+ 3 patterns. Variation among individuals in terms of chromosomal make-up results in genetic variation as well. Chromosomal variation was detected among seedlings from a single maternal parent, among plants of a single population, and among populations of both Tragopogon mirus and T. miscellus. These results have important implications for the genetics of polyploid species and contribute to our understanding of the role of polyploidy in generating genetic and evolutionary novelty, which may contribute to the success of polyploid species. In fact, many of the traits that make polyploid plants attractive as crops (larger size, larger fruits, greater yield) may derive from these fundamental chromosomal and genetic attributes of polyploidy. Further understanding of polyploidy should contribute to improved crop breeding. In the course of this project, a post-doc received training and mentoring in molecular cytogenetics and in teaching research skills to undergraduates. The post-doc and an REU student organized and did the majority of the training in a 2-day workshop on chromosome painting for 30 participants at the annual Botany meetings in Columbus, OH, in July, 2012. In all, four undergraduates received research experience on this project with REU support.
