CAPSEVO · Evolution of flower morphology: the selfing syndrome in Capsella

The change from reproduction by outbreeding to selfing is one of the most frequent evolutionary transitions in plants. This transition is generally accompanied by changes in flower morphology and function, termed the selfing syndrome, including a reduction in flower size and a more closed flower structure. While the loss of self-incompatibility is relatively well understood, little is known about the molecular basis of the associated morphological changes and their evolutionary history. We will address these problems using the species pair Capsella grandiflora (the ancestral outbreeder) and C. rubella (the derived selfing species) as a genetically tractable model. We have established recombinant inbred lines from a cross of C. grandiflora x C. rubella and mapped quantitative trait loci affecting flower size and flower opening. Using this resource, the proposal will address four objectives. (1) We will isolate causal genes underlying the variation in flower size and opening, by combining genetic mapping with next-generation sequencing. (2) We will characterize the developmental and molecular functions of the isolated genes in Capsella and Arabidopsis. (3) We will dissect the molecular basis of the different allelic effects of the causal genes to determine which kinds of mutations have led to the morphological changes. (4) Based on population-genetic analyses of the isolated genes, the evolutionary history of the morphological changes will be retraced. Together, these strands of investigation will provide a detailed understanding of general processes underlying morphological evolution in plants.