Stacy Smith
Identifying the genetic changes underlying phenotypic differences between species remains a fundamental challenge in evolutionary biology. While mapping approaches have been useful for detecting regions of the genome affecting trait variation, pinpointing the specific changes responsible at the DNA sequence level remains difficult, unless candidate genes within the region are known. This project uses a candidate gene approach to identify the genetic changes involved in adaptive transitions in flower color in Iochroma, a genus in the tomato family, Solanaceae. Flower color is an ideal trait for studying the genetic basis of adaptation because it has clear adaptive significance and because the pigment biosynthetic pathways are well-characterized at the genetic level and highly conserved across flowering plants. Color differences among Iochroma species are largely due to differences in anthocyanin pigments, a class of flavonoids. This research investigates the genetic changes in the anthocyanin pathway responsible for the evolutionary transition from purple to white flowers in I. loxense and from purple to red flowers in I. gesnerioides. Combining the detailed understanding of the pathway and knowledge of which pigments are present in the study species, strong predictions can be made about which anthocyanin genes were involved in the color transitions. The association of candidate anthocyanin genes and color differences will be assessed by (1) examining the cosegregation of candidate genes with flower color phenotypes in interspecific crosses between red and purple and white and purple species, (2) cloning candidate genes showing cosegregation to test their functionality in vitro, and (3) using expression studies to examine possible differences in regulation. The results will help to address basic questions regarding the number, location and types of genetic changes involved in phenotypic evolution.