Format: ORAL

Lachezar Nikolov

Department of Biology, Indiana University, Bloomington IN, 47405 USA

Brassicaceae are a model plant clade which epitomizes the value of rigorous taxonomic foundation, firm phylogenetic framework, extensive genomic resources, and a cohesive and collaborative research community in creating a rich medium to explore novel biology. As one of the most densely sampled angiosperm groups at the genomic scale, Brassicaceae are the textbook example about how genomes are shaped by evolutionary forces, and complementary efforts aim to uncover how gene expression evolves in this model clade. Recent advances in single-cell transcriptomics, which allows the detection of thousands of expressed genes in thousands of individual cells, has revealed extensive transcriptional heterogeneity reflecting different cell types and cell states. Building upon Tabula Floris, our single-cell floral atlas of Arabidopsis thaliana, we have generated comparable developmental floral atlases for eight mustard species, which belong to diverse mustard lineages and span 25 million years of evolution. We have characterized the expression profiles of diverse floral cell populations across these species. Using multispecies embedding based on orthologous genes, we have identified homologous floral cell types and inferred gene co-expression networks underlying their specialized physiology and developmental programs. We have compared these networks to uncover shared nodes and modules, as well as to identify unique network motifs, which may underlie phenotypic divergences. We further focus on the nectary secretory cell to study the contributions of phylogenetic distance and drift to homologous cell types with conserved function among species. These results highlight the enduring utility of model clades in general and of Brassicaceae in particular to address a wide range of comparative questions.