Using Genotyping-By-Sequencing to Identify Adaptive Genomic Regions in Wild Sunflower

Determining the genetic basis of local adaptation is now possible due to the tremendous breakthroughs in genetic marker technology. Population genomic scans were once restricted to well-funded crop species, but now techniques like Genotyping-By-Sequencing (GBS) allow investigations in non-model species that are related to domesticated crops. Understanding the genetic basis of adaptation in crop progenitor species may help adapt crops to predicted changes in climate. Helianthus annuus is the wild progenitor of cultivated sunflower and can be found through much of central North America. To elucidate the genomic regions conferring adaptation across the range we made GBS libraries for 55 individuals originating from three natural populations found in Saskatchewan, Nebraska and Texas. These populations are differentiated for putatively adaptive traits such as flowering time and saturated fatty acid content within seeds. After mapping loci to genome and chromosomal assemblies we were able to calculate F_ST, a measure of population genetic differentiation, for thousands of loci. Exceptionally high F_ST values are characteristic of local adaptation. By combining population genomic scans with existing quantitative trait locus maps it is possible to gain new insights into the genetic architecture of adaptation. Furthermore, an in progress RNA-seq experiment of developing seeds seeks to connect population genetic variation from our GBS genome scan with tests of molecular evolution and differential gene expression to address the relative importance of coding sequence versus regulatory mutations in conferring adaptation.