A BRC1-modulated switch in auxin efflux accounts for the competition between Arabidopsis axillary buds
Fig 3
Branching behaviors of 2-node explants can be captured by a model with self-activating and mutually-inhibiting buds.
(A) and (B) Model conceptualization and mathematical formulation. The interaction between two buds in a 2-node explant can be considered as a set of self-activating and mutually-inhibiting feedbacks on auxin efflux. Each bud promotes its own auxin efflux and inhibits efflux from the other bud. The auxin efflux E and F from the top and bottom bud, respectively, is influenced by three components (i) a basal rate of auxin efflux v0, (ii) a Hill function which creates a positive feedback on auxin efflux, where v sets the maximum rate of auxin efflux, S the strength of auxin efflux, K the Hill saturation coefficient, n the degree of non-linearity of the Hill function, D the strength of the mutual inhibition between the auxin efflux of the two buds, and (iii) a linear decrease in auxin efflux, the strength of which is set by ยต. E and F influence bud lengths N and M, respectively. The relationship between auxin efflux and growth rate is a Hill function, where m influences the degree of nonlinearity, and Q is the saturation coefficient. (C) Steady state growth rate as a function of the steady state of auxin efflux, for different values of Q and m. Three grey vertical lines mark three steady states of auxin efflux at 0.25, 0.5, and 0.75. (D) and (E) Three stochastic simulations illustrating the model behaviors. Each set of simulations is represented with a different color. (F) Deterministic simulation showing the change in auxin efflux E over time for 5 different values of v0: 0.01, 0.03, 0.05, 0.07, and 0.09. Scripts of simulations underlying this figure can be found at https://doi.org/10.17863/CAM.120831.
doi: https://doi.org/10.1371/journal.pbio.3003395.g003