Madelaine Bartlett: What grass flowers can teach us about mechanisms of morphological evolution

Determining how conserved molecular components generate diversity is a key goal of evolutionary biology. We use the grasses as a model family for determining how floral morphological diversity is assembled. Here, I will discuss our work dissecting the function and evolution of two genes with core roles in plant development: GRASSY TILLERS1 (GT1) and RAMOSA3 (RA3). We discovered that GT1 acts with the trehalose-6-phosphate phosphatase gene RA3 to in multiple developmental contexts, including axillary meristem suppression, meristem determinacy, and floral organ suppression. To determine how these pleiotropic functions are regulated and how they emerged, we have been dissecting GT1 and RA3 function in species with divergent morphologies, and across homologous contexts in different species. We show conserved roles for RA3 in maize’s phylogenetically close but morphologically divergent relative, Setaria viridis. In maize, we used a high-throughput method for quantitative phenotyping of grass flowers to show that distinct mechanisms operate upstream of GT1 and RA3 in axillary meristem vs. floral organ suppression. Our results indicate that, rather than wholesale adoption of genetic networks, developmental genes can retain ancient functions and be adopted into other programs in the evolution of form.