The genus Mimulus (monkeyflowers) contains 160-200 species that exhibit tremendous phenotypic variation (Figure 1), and has served as a classic model system in studying ecological adaptation, speciation, plant-pollinator interactions, and species range limits. More recently, it has also emerged as a powerful model system in studying plant developmental genetics and evo-devo.
Figure 1. Natural variation of Mimulus flower color and shape. Photo credits: Dena Grossenbacher, Naomi Fraga, Arielle Cooley, and Yao-Wu Yuan.
Of particular interest to our research program is a group of closely related species that diverged ~3 million years ago, including the bumblebee-pollinated M. lewisii, the hummingbird-pollinated M. cardinalis and M. verbenaceus, and the self-pollinated M. parishii (highlighted by the red box in Figure 1). Despite their dramatic phenotypic differences, these species are genetically very similar (>97% identical in coding regions) and can be readily crossed with hand-pollination in the greenhouse to produce fertile offspring.
These species have several features that greatly facilitate genetic analysis and developmental interrogation, including high fecundity (up to 1,000 seeds per flower), short generation time (2.5-3 months), small genome size (~450 Mb), and amenability to chemical mutagenesis and transgenic experiments. In the past several years we have developed a wealth of genetic and genomic resources and functional tools for these species. Specifically, we have generated high-quality, chromosome-level genome assemblies for all focal species (http://mimubase.org/), which enabled both conventional recombination-based genetic mapping and bulked segregant analysis based on high throughput sequencing to identify causal genes responsible for natural phenotypic variation. We have established an efficient Agrobacterium-mediated, in planta stable transformation protocol for these species to rigorously characterize gene function and developmental mechanisms through transgenic experiments. We have generated large-scale ethyl methanesulfonate (EMS) mutant libraries that furnish the raw materials to study the developmental genetics of many ecologically important floral traits (e.g., carotenoid pigmentation, corolla tube formation and elaboration, nectar volume, pistil length) that are difficult to study using other model systems.