Developing and Testing a Mathematical Model for Cell Specification in the Embryo Sac of Arabidopsis thaliana
The plant life cycle alternates between a diploid sporophytic and a haploid gametophytic generation. The female gametophyte of flowering plants (embryo sac) is typically formed through three syncytial mitoses, followed by cellularization that forms seven cells belonging to four cell types. The specification of cell fates in the female gametophyte has recently been suggested to depend on positional information provided by an intrinsic auxin concentration gradient. The goal of this study is to develop mathematical models that explain the formation of this gradient in a syncytium. Two factors were proposed to contribute to the maintenance of the auxin gradient in Arabidopsis embryo sacs: polar influx at early and localized auxin synthesis at later stages, respectively. However, no gradient could be generated using classical one-dimensional models under these assumptions. Thus, we tested other hypotheses, including spatial confinement by the large central vacuole, background efflux and localized degradation, and investigated the robustness of cell specification under different parameters and assumptions. None of the models led to the generation of an auxin gradient that was steep enough to allow sufficiently robust patterning. This led us to reexamine the auxin response in developing female gametophytes using various auxin reporters. In agreement with the predictions of our models, auxin responses were not detectable within the female gametophyte of either Arabidopsis, suggesting the effects of manipulating auxin production and response on cell fate determination may be indirect.
Keywords: Morphogen, Plant, Auxin, Reaction-diffusion Modelback