Deep homology or convergence? Comparative genomics elucidates the origins of the heterostyly supergene
ID: 613 / 420
Proposed Symposium Title: Deep homology or convergence? Comparative genomics elucidates the origins of the heterostyly supergene
Elena Conti, Barbara Keller, Narjes Yousefi, Emiliano Mora Carrera, Irina Gavrilina, Giacomo Potente
Affiliations: Department of Systematic and Evolutionary Botany, University of Zurich, Switzerland
The rapid accumulation of high-quality reference genomes now enables us to re-examine long-standing questions on evolutionary convergence: Does convergence at the phenotypic level correspond to shallow convergence or deep homology at the genotypic level? Do the same genes and genetic architectures underlie convergent traits or can different genes be recruited to achieve the same phenotypic outcome? Heterostyly in Primulaceae represents an ideal system to investigate these questions. Found in 28 families of flowering plants, heterostyly refers to the co-occurrence in a population of different plants characterized by self-incompatible floral morphs with reciprocally placed male and female sexual organs, a combination promoting outcrossing while restricting selfing. Originally investigated by Darwin in Primula, heterostyly in this genus is now known to be controlled by the S-locus, a hemizygous supergene comprising a minimum of four genes with paralogues elsewhere in the genome. Published phylogenetic analyses of trait evolution showed that heterostyly evolved independently three times in Primulaceae, namely in the ancestor of Primula, in Hottonia palustris, and in Androsace vitaliana. However, it remains unknown whether the genes determining heterostyly also evolved multiple times concomitantly with heterostyly or were already present in the common ancestor of the three heterostylous lineages but were subsequently lost in non-heterostylous relatives. To test the alternative predictions stemming from these two hypotheses, we generated highly contiguous, chromosome-scale, haplotype-phased assemblies of heterostylous and non-heterostylous genomes of Primulaceae and performed comparative genomic analyses across Ericales, the order that includes Primulaceae. Preliminary results suggest that the three independent origins of heterostyly inferred via phylogenetic analyses of trait evolution might stem from both deep homology of duplicated S-locus genes and genetic reinvention. Primulaceae thus represent an ideal system to clarify the connections and disconnections of evolutionary convergence from the genotypic to the phenotypic level and back.