An issue of broad concern in biology is the impact of hybridization ("crossing") between different species, which encompasses phenomena as diverse as the escape of transgenes from cultivated crops, to the dynamics and outcomes of hybridization between native species. The proposed research aims to study from a genetic perspective the spread by hybridization of the ability in plants to produce seeds without fertilization, a phenomenon termed apomixis. In this research, hybrids between sexual and apomictic plants in a common herb (fleabane, Erigeron, sunflower plant family) will be studied. Genetic mapping using molecular markers will be used to test different hypotheses relating to the tempo of trait spread and also to evaluate the number, location, and interactions among genome regions affecting apomictic reproduction.
This research is important because it provides a novel perspective on the genetics and evolution of asexual reproduction. Results will inform (1) efforts to transfer apomictic reproduction from wild to agronomic species; (2) models for the maintenance of sexual reproduction in natural populations; and (3) our understanding of how gene interactions influence the dynamics of the hybridization process. In addition, money from this project will be used to train several undergraduate and graduate students in molecular biology.
The goal of this project was to better understand reproductive biology of plants through the study of a native weedy species (daisy fleabane, Erigeron strigosus) in the sunflower plant family. This plant has the ability to make seeds that are identical clones of itself (a process known as apomixis) and so bypasses the normal reproductive process involving two parents. Understanding this process in Erigeron could help the development of new techniques in agriculture to multiply one-of –a-kind hybrids with desirable traits. The initial efforts funded by this reward involved 1) survey of wild populations to assess natural expression levels of apomixis in natural populations of Erigeron, 2) a crossing strategy and study of hybrid populations to understand how the genes that control apomixis move within the species by pollen and to understand trait expression across generations, and, 3) development of genetic resources to better be able to track gene regions associated with apomixis. These efforts were used to recruit about 15 undergraduates and 3 graduate students into the lab. Changes in technology, namely the development and increased accessibility of Next Generation Sequencing methods led us to scale-back on older laborious, low-yield methods and to embrace a new strategy. This coincided with a discovery in our lab of a process through crosses to produce apomictic Erigeron with low chromosome numbers. Lower chromosome number means simplified genetics, streamlined analysis, and more efficient use of resources. Simplified target plants and new genetic tools allowed us to establish collaborative relationships with researchers at R1 Universities and Institutes to forward our project goals. Thus genome and transcriptome sequencing for Erigeron using Next Generation tools was accomplished at the University of Texas, Health Science Center, San Antonio. That data is currently being assembled into reference genomes by researchers at the University of British Columbia, Vancouver in the lab of Dr. Loren Rieseberg, one of the leads on an International effort to study genomes in the sunflower family. DNAs for a simple experimental Erigeron population segregating for apomixis was subject to a novel Next Generation Sequencing approach ("Genotyping-by-Sequencing") at the Institute for Genomic Diversity, Cornell University, to generate markers that targets one of the specific genes controlling reproduction. Data has just been downloaded and will be analyzed in conjunction with the genome assembly at the University of British Columbia. The combination of these two approaches is anticipated to produce a notable and high profile example of the power of the combination of new techniques for gene discovery in non-model plant species. For further genetic resource development, we perfected in my lab techniques to isolate DNA from cellular organelles (chloroplasts and mitochondria). These DNAs were sequenced at the University of Texas, Health Science Center, San Antonio and analysis underway using undergraduate researchers at the University of Central Arkansas and collaborator Dr. Jennifer Mandel at the University of Memphis is yielding new insights into organelle DNA structure and evolution in Erigeron and relatives. While there remains some pending analysis and results, all signs point to exciting findings within the next year.
