Monkeyflowers as a Model System

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, and plant-pollinator interactions. More recently, it has also attracted considerable interest in studies of meiotic drive, population genomics, and evolution of development (Evo-Devo).

Corolla_tubeFigure 1. Natural variation of Mimulus flower color and shape.

Of particular interest to our research program is Mimulus lewisii, a typical bumblebee-pollinated species that has light pink flowers with a pair of yellow ridges in the ventral (lower) petal acting as nectar guides (highlighted by the red box in Figure 1). Along with its hummingbird-pollinated sister species M. cardinalis, M. lewisii has been the subject of a series of classic studies on pollinator-mediated reproductive isolation and speciation. Although the two species are interfertile with hand pollination, they rarely hybridize in wild sympatric populations due to pollinator preference.

M. lewisii has several features that greatly facilitate genetic analysis, including high fecundity (ca. 1000 seeds per fruit), short generation time (3 months), and a relatively small genome size (ca. 500 Mb). Together with Dr. Toby Bradshaw at the University of Washington, we have developed a wealth of genetic and genomic resources for M. lewisii, in conjunction with community resources developed for M. guttatus, the other model species in the genus. We have established an efficient in planta stable transformation system that allows transgenic experiments to rigorously characterize gene function in M. lewisii, and an agrobacterium-mediated leaf transient assay that allows rapid gene and protein expression analyses. Furthermore, we have an active ethyl methanesulfonate (EMS) mutagenesis program for M. lewisii, which was initiated in Dr. Toby Bradshaw’s laboratory  and has been continued in our lab. To date we have recovered many remarkable floral mutants 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.