Reaction-Diffusion Dynamics of Complex Petal Pigmentation Patterning in hybrid Mimulus

A fundamental question in developmental biology is how self-organized spatial patterns form in natural systems. In 1952, Turing proposed the reaction-diffusion model, a simple but elegant theoretical mechanism in which two molecules interact and generate periodic pattern spontaneously. Ever since then, this model has helped explained a wide range of biological pattern formation like the stripes in zebrafish skin and digit development in vertebrates. However, very few such inquiries have been made in plants.  Flowers of a hybrid F2 population between two Mimulus luteus sister species M. cupreus and M. l. variegatus exhibit stunningly complex pigment patterning and thus serves a perfect model organism to explore the preliminaries of the RD theoretical model. In this study, we developed a two-dimensional reaction diffusion model based on the transcriptional regulation dynamics of R2R3MYB activators and potential R3 repressors with customized spatial boundaries. Since the petal spot patterning arises after the hybridization of two tetraploids species, with this model we are able to infer: 1) to what extend is petal pigmentation pattern  an allelic effect, and to what extend is patterning multigenetically controlled, and generated by the interactions of paralogs from different parental genomes; 2) whether the special expression profiles of the activator and repressor take parts in generating the pattern, and in particular, if expression sub-functionalization have happened in our hybrids; 3) does the transportation path, presumably through plasmodesmata between cells, affect the final pattern shape. Combined with quantitative trait measuring and genetic mapping, this study can shed light on the developmental complexity of petal pigment patterning in mimulus. Moreover, we provide a novel approach that can be generalized to other model systems to address spatial pattern formation in plants.

Zheng, Xingyu 3