12.30 - 13.30
The molecular basis of floral adaptations to plant breeding systems
Different breeding systems in plants are associated with characteristic floral features, yet their molecular basis remains poorly understood. We are using heterostyly and the selfing syndrome as two model systems to address this issue. Heterostyly is a wide-spread floral adaptation to promote outbreeding. In Primula (primroses), heterostyly is controlled by the S-locus supergene that determines the reciprocal arrangement of reproductive organs and incompatibility between the two morphs. The S-locus supergene comprises at least three individual causal genes controlling the different traits that are held together in tight linkage by suppressed recombination. We have recently identified the Primula CYP734A50 gene, encoding a putative brassinosteroid-degrading enzyme, as the G locus that determines the style-length dimorphism. I will discuss the implications of this finding for our understanding of the evolution and genetic basis of heterostyly.
The transition from outbreeding to selfing is often associated with a dramatic reduction in reproductive structures, such as a reduced flower size in plants. We are using the pair of closely related species Capsella grandiflora and C. rubella to study the molecular basis of evolutionary changes in flower size. The outbreeding ancestor C. grandiflora forms large attractive flowers, while the derived selfing species C. rubella only shows small, inconspicuous flowers. Using a quantitative-genetic approach, we have identified three genes whose variation between the two species contributes to flower-size reduction in C. rubella. One of these indicates that variation in splicing efficiency underlies morphological evolution in this system, and highlights the role of higher-than-optimal hormone levels in generating phenotypic variation.