Comparative Genomics elucidates the convergent origins of floral heteromorphism
Convergent evolution is one of the most fundamental yet contentious issues in evolutionary biology. The rapid accumulation of high-quality reference genomes and transcriptomes now enables us to re-examine evolutionary convergence and parallelism in a new framework: Does convergence at the phenotypic level correspond to 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? I will discuss these questions focusing on heterostyly in Primulaceae but within the broader framework of flowering plants.
Heterostyly evolved three times independently in Primulaceae, namely in Primula, Hottonia, and Androsace. Heterostylous taxa of Primulaceae typically comprise two different types of plants with distinct floral morphs characterized by reciprocally placed sexual organs and a heteromorphic incompatibility system that blocks self- or intra-morph fertilization. Heterostyly thus promotes cross-fertilization while preventing the harmful effects of self-fertilization, and it evolved at least 14 times in angiosperms. A supergene known as the S locus operates the genetic control of heterostyly. Despite the numerous genetic, morphological, and reproductive studies on heterostyly over the past 150 years, the molecular nature and evolutionary origins of the S locus remained unknown until recently. What are the genes and genetic architectures of the S locus? Are they the same in independent origins of heterostyly?
Did the S locus evolve through a single, large duplication followed by loss of intervening genes or through multiple, asynchronous gene duplications followed by translocations? We addressed these questions by generating highly contiguous, chromosome-scale, haplotype-phased assemblies of heterostylous and homostylous genomes of Primulaceae and performing comparative genomic analyses across Ericales, the order that includes Primulaceae. Primulaceae thus represent an ideal system to study evolution on repeat in the genomics era, clarifying the connections and disconnections of evolutionary convergence from the genotypic to the phenotypic level and back.
Chair: Yamama Naciri