Figure 5.

An iFFL regulates the bistable states of NRT1.1. (A) Decoupling and coupling of the NRT1.1 dimer generates specific calcium waves that active the kinase CIPK23, having positive and negative effects on NRT1.1P, the phosphorylation state. (B) An incoherent feedforward circuit that integrates calcium-dependent negative (X) and positive (Y) effects on NRT1.1P. (C) The model predicts bistability. At low nitrate concentration, it establishes the high-affinity state, and at the high nitrate concentration, it establishes the low-affinity state. (D) At low nitrate concentration, the NRT1.1P attains its saturation level exponentially, whereas at the high nitrate concentration, the NRT1.1P displays a unimodal response with the peak and then continuously slides down to a lower stable state. (E) The model predicts the continuous sliding from the high-concentration phosphorylated state to the lowest level along the increasing gradient of nitrate concentrations. (F) The calculated Lyapunov exponent at the steady states along the increasing nitrate gradient from 0.1 to 25 mM: it is indicating the biphasic changes of NRT1.1P with increasing soil nitrate concentrations. This allows us to predict the low, the high, and the transient ranges of soil nitrate concentrations that were categorized with respect to the chosen parameter values. To see this figure in color, go online.