Apomixis evolution in St. John's wort (Hypericum perforatum)

• Applicant: Professor Dr. Timothy Sharbel
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: from 2007 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 40137698

In plants, the expression of gametophytic apomixis (asexual reproduction through seed) requires the coordination of three independent mechanisms: (1) production of an unreduced embryo sac (apomeiosis); (2) the parthenogenetic development of the embryo in the absence of fertilization; and (3) the fertilization (pseudogamy) and production of a functional endosperm. A number of hypotheses have been proposed to explain the evolution of apomixis from sexual ancestors, including: (1) mutations in one or a few genes which lead to modifications of the sexual pathway; (2) epigenetic changes associated with hybridization and/or polyploidy; (3) heterochronic changes in developmental timing in hybrid genomes; and (4) changes in gene expression associated with supernumerary chromatin. The purpose of this proposal is to examine hypothesis 2. It is known that Pleistocene (Wurm) glaciations have forced many plants/animals into glacial refugia where they underwent geographic isolation and genetic differentiation (Petit, Aguinagalde et al. 2003). Upon glacial retreat, these isolated populations recolonized North America, Europe and Asia and met in secondary contact zones. We will test whether reproduction between genetically-divergent individuals in such contact zones (e.g. post-glacial recolonization into similar geographic areas) could lead to quantitative variation with respect to sexual and apomictic seed production. This study will provide fundamental information about 1) biogeographic genetic variation and gene flow in H. perforatum, 2) biogeographic variation is seed development in sexual and apomictic accessions, and 3) the influence of genetic differentiation on apomictic seed development in controlled laboratory crosses.

• DFG Programme: Research Grants