title: Theoretical and experimental evidence indicates that there is no detectable auxin gradient in the angiosperm female gametophyte.
abstract: The plant life cycle alternates between a diploid sporophytic and a haploid gametophytic generation. The female gametophyte (FG) of flowering plants is typically formed through three syncytial mitoses, followed by cellularisation that forms seven cells belonging to four cell types. The specification of cell fates in the FG has been suggested to depend on positional information provided by an intrinsic auxin concentration gradient. The goal of this study was 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 FGs: polar influx at early stages and localised auxin synthesis at later stages. However, no gradient could be generated using classical, one-dimensional theoretical models under these assumptions. Thus, we tested other hypotheses, including spatial confinement by the large central vacuole, background efflux and localised 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 re-examine the response to an auxin gradient in developing FGs using various auxin reporters, including a novel degron-based reporter system. In agreement with the predictions of our models, auxin responses were not detectable within the FG of Arabidopsis or maize, suggesting that the effects of manipulating auxin production and response on cell fate determination might be indirect.
authors.affiliation: Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland.
authors.forename: Dmytro S
authors.initials: DS
authors.lastname: Lituiev
authors.forename: Nádia G
authors.initials: NG
authors.lastname: Krohn
authors.forename: Bruno
authors.initials: B
authors.lastname: Müller
authors.forename: David
authors.initials: D
authors.lastname: Jackson
authors.forename: Barbara
authors.initials: B
authors.lastname: Hellriegel
authors.forename: Thomas
authors.initials: T
authors.lastname: Dresselhaus
authors.forename: Ueli
authors.initials: U
authors.lastname: Grossniklaus
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism; D019521:Body Patterning / Q000187:drug effects; D019070:Cell Lineage / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D003198:Computer Simulation; D004058:Diffusion; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D019684:Magnoliopsida / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D056771:Ovule / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism; D003313:Zea mays / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; C100794:AUX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C519873:PGP19 protein, Arabidopsis
keywords: Arabidopsis; Auxin; Female gametophyte; Gradient; Maize; Modelling