Auxin transport is sufficient to generate a maximum and gradient guiding root growth

Abstract

The plant growth regulator auxin controls cell identity, cell division and cell expansion. Auxin efflux facilitators (PINs) are associated with auxin maxima in distal regions of both shoots and roots. Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured root layout. In our model, the stable accumulation of auxin in a distal maximum emerges from the auxin flux pattern. We have experimentally tested model predictions of robustness and self-organization. Our model explains pattern formation and morphogenesis at timescales from seconds to weeks, and can be understood by conceptualizing the root as an 'auxin capacitor'. A robust auxin gradient associated with the maximum, in combination with separable roles of auxin in cell division and cell expansion, is able to explain the formation, maintenance and growth of sharply bounded meristematic and elongation zones. Directional permeability and diffusion can fully account for stable auxin maxima and gradients that can instruct morphogenesis.

Multiscale modelling of auxin transport in the plant-root elongation zone

“…Many computational cell-scale models are being developed to investigate auxin transport (de Reuille et al 2006;Feugier and Iwasa 2006;Feugier et al 2005;Grieneisen et al 2007;Heisler and Jönsson 2006;Jönsson et al 2006;Kramer 2004Kramer , 2009Laskowski et al 2008;Merks et al 2007;Mironova et al 2010;Perrine-Walker et al 2010;Rolland-Lagan and Prusinkiewicz 2005;Smith et al 2006;Stoma et al 2008;Swarup et al 2005); however, little has been done to determine the corresponding tissue-scale descriptions. In this paper, we demonstrate the potential of using (analytical) multiscale methods to simplify an auxin-transport model and to identify the combinations of cell-scale processes that govern the tissue-scale auxin flux.…”

“…In addition, our analytical Table 5 As described in Sect. 4, the dominant tissue-scale behaviour in the wild-type plants and knockout mutants can be described by one of these dimensional governing equations approach could be applied to more comprehensive root models, for example, to gain further insight into the cell-based model in Grieneisen et al (2007), where all the tissue layers in the root elongation zone and meristem were considered and auxin-dependent cell division and cell growth were incorporated.…”

“…Various cell-based models of auxin transport have been developed and have provided insight into auxin's role in the gravitropic response (Grieneisen et al 2007; 2 We consider a two-dimensional model which consists of three rows of cells representing the epidermal, cortical and endodermal layers. Each epidermal cell expresses AUX1 influx carriers on all sides of its membrane and PIN1 and PIN2 efflux carriers on the shootward side.…”

“…Early studies (Goldsmith et al 1981;Martin et al 1990;Mitchison 1980b) considered only a single line of cells, with auxin diffusion within the cytoplasms and with passive and carrier-mediated transport across the cell membranes; these showed how the efflux carriers increase the tissue-scale auxin flux. More recent studies have considered more complex tissue geometries and have incorporated apoplastic diffusion Jönsson et al 2006;Kramer 2004;Laskowski et al 2008;Swarup et al 2005), saturable carrier-mediated transport (de Reuille et al 2006;Feugier et al 2005;Jönsson et al 2006;Merks et al 2007;Smith et al 2006), cytoplasmic structure (Kramer 2004;Perrine-Walker et al 2010), cell growth (Chavarrıa-Krauser et al 2005;Grieneisen et al 2007;Jönsson et al 2006;Mironova et al 2010;Stoma et al 2008), auxin production and degradation (Feugier and Iwasa 2006;Feugier et al 2005;Perrine-Walker et al 2010;Heisler and Jönsson 2006;Jönsson et al 2006;Smith et al 2006;Stoma et al 2008) and dynamics of the efflux carriers Jönsson et al 2006;Kramer 2009;Merks et al 2007;Mironova et al 2010;Stoma et al 2008).…”

Some fundamental aspects of modeling auxin patterning in the context of auxin-ethylene-cytokinin crosstalk

“…However, auxin transport between the cytosol and the cell wall is facilitated by AUX1/LAX influx carriers, 21 and PIN and ABCB auxin efflux carriers located at the plasma membrane. 22,23 While the kinetics of auxin diffusion transport is well established, the kinetics for PINor AUX1-facilitated auxin transport can also be derived, as shown previously. 20 Figure 1.…”