Figure 6: Simulation of ARF7 and FLP-regulated PIN3 dynamics.

(a) The coherent feed-forward motif (FFM) scheme and (b) the no-FFM scheme used to model auxin-induced PIN3 transcription. (c–h) Simulations of a PIN3-dependent auxin transport model subject to extracellular auxin pulses. Simulations were performed on model systems with (blue) and without (green) a transcriptional FFM involving FLP (see Methods), using the parameter settings given in Supplementary Table 1. Two-hour long 1 μM auxin pulses were given to the system at t=4 h, t=12 h and t=26 h. The subplots depict the resulting dynamics of PIN3 mRNA (c), total PIN3 protein, that is, the sum of intracellular and membrane-bound PIN3 (d), FLP mRNA (e), FLP protein (f), intracellular auxin (g) and active ARF7 (h) concentrations over time. The model simulations indicate that the FLP feed-forward circuit causes prolonged transcriptional activation of PIN3, resulting in an enhanced memory effect by which auxin stimulation reduces the impact of subsequent extracellular auxin stimuli on ARF7 activity and downstream signalling for a prolonged period of time. The system dynamics are qualitatively independent of the exact parameter settings used (see Supplementary Figs 6-10).