Figure 8.

Root architectural responses to P limitation and their regulation. Low P availability alters root architecture by at least two mechanisms, one that is independent of auxin transport and BIG function leads to primary root growth inhibition and root hair growth stimulation, and one where low P promotes root branching interacting with auxin. In low P, lateral root development is a two-step process involving LRP initiation from the pericycle and the further maturation of these LRP into fast-growing lateral roots. In our model, LRP initiation requires auxin transport and normal BIG function, whereas LRP maturation is a BIG independent process. High P availability represses low P-induced root developmental responses.