Evolutionary genomics in Achimenes

Using comparative genomics in an evolutionary-developmental context allows us to begin understanding the molecular mechanisms underlying species diversification. Achimenes is a small genus of 26 species native to Mexico and Central America that contains enormous variation in floral form that is closely tied to pollinator preferences. Flowers in Achimenes are visited by bees, butterflies, and hummingbirds, and represent distinct pollination syndromes. We have sequenced, assembled, and annotated the floral transcriptomes in 10 species of Achimenes (Roberts and Roalson 2017, Roberts and Roalson 2018, Roberts and Roalson 2020), representing species that display each pollination syndrome. Each species was sampled using two or three time points during flower development in order to take advantage of inter- and intraspecies comparisons.

I have taken multiple strategies to begin understanding flower diversification. First, comparing gene expression within and between species has revealed complex patterns in several pathways that correspond to the different floral forms (Roberts and Roalson 2017). Second, phylogenomic analyses of gene flow and introgression have found widespread phylogenetic discordance and specific cases of introgression occurring between sympatric species pairs that share pollinator groups (Roberts and Roalson 2018). Third, the examination of co-expression networks has identified numerous modules and hub genes correlated to floral form and found an association between network connectivity and selective constraint (Roberts and Roalson 2020).

Macroevolution of Gesneriaceae

Gesneriaceae (African violet family) represents a large lineage (>3500 species) with an enormous amount of diversity, particularly in floral form and growth form. The family is known for its diverse flowers that are visited by a number of different pollinators, as well as containing a high number of epiphytes, lithophytes, and unifoliate plants. Constructing the largest dated phylogeny for gesneriads (nearly a quarter of species) and inferring divergence times has allowed us to test hypotheses related to the effects of geography, floral traits, epiphytism, and growth form on diversification (Roalson and Roberts 2016). Our analyses provide evidence for distinct patterns of evolution across different lineages in the Gesneriaceae.

Developmental genetics in Achimenes

In order to test the functional role of specific candidate genes in planta, it is useful to have an efficient regeneration and transformation system. We have developed an successful micropropagation and Agrobacterium-mediated transformation for Achimenes erecta (Roberts et al., in prep). The ability to efficiently transform plant species with high success will be useful to develop Achimenes into a model for evolutionary-developmental studies.