Collaborative Research: RUI: Mathematical and empirical investigation of a reaction-diffusion system for spot formation in hybrid Mimulus

Life on earth exhibits a dazzling array of patterns. These range from internal patterns, like the repetition of vertebrae in the spinal cord, to external patterns like the stripes of black pigment on a zebra. There are two ideas about how these patterns might form.

The “positional specification” model is that the patterns are created by a set of genes being turned on in specific locations in a controlled fashion. The “reaction-diffusion” model is that patterns can arise from a self-organizing system of interacting genes. According to this second model, the location of each pattern component is determined by random fluctuations in one gene’s activity level.

Other genes in the network respond to the first gene to create the elements needed for making a unit of the pattern. Some traits, such as petal spots in the monkeyflower genus Mimulus, appear to depend on both types of pattern formation. This petal-spot system is being used to study both positional specification and reaction-diffusion, and how they interact to create new, complex patterns in nature.

The collaborative project creates research opportunities for one Ph.D. student and eighteen undergraduates. Three high school students will be recruited from a public school in rural Walla Walla, WA that specifically serves youth not routinely exposed to scientific experiences.

Previous work in Mimulus has established that nectar guide spots of red anthocyanin pigment are formed in a manner consistent with a reaction-diffusion system. The discovery of elaborate spot patterns in the petal lobes of Mimulus cupreus x M. luteus var. variegatus hybrids creates a unique opportunity to examine (a) whether this reaction-diffusion system explains floral patterning in Mimulus more generally, (b) whether positional cues originating from petal vasculature shape these patterns, and (c) how the inter-genomic interactions associated with hybridization can generate novel phenotypes not seen in either parent species.

The researchers will first develop a reaction-diffusion model that recreates the distribution of anthocyanin spotting phenotypes observed in a hybrid F2 genetic mapping population. They will test this model by examining the diverse sets of homozygous genotypes present in a Recombinant Inbred Line population, and by using transgenic manipulation to alter the expression of key genes in the anthocyanin regulatory network.

Finally, they will investigate the hypothesis that petal vasculature influences the location of spot formation. This will be achieved by using digital image analysis and spatial statistics to test for correlations between spot and vein locations, and experimentally manipulating vein development through chemical and transgenic perturbations to test for effects on spot formation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.