PHB regulates root meristem activity downstream of SHR-SCR.

(A) Seedlings of shr phb (7 DAG) mutants display significant recovery in root length. (B) Growth restoration in shr phb roots compared with other shr HD-ZIP III mutants and shr phb phv-5 mutants. (C) Meristem size over time in the shr, shr phb, and wild-type roots. (D) Root length measured over a time course. The shr phb roots grow in a more determinate manner than do the wild-type roots. (E) Expression of pCycB1.2:GUS in the shr, shr phb, and wild-type roots (5 DAG). (F) phb-mediated recovery in root meristem/growth is specific to the SHR-SCR pathway. The error bars represent the standard error (n = 20–40 plants). Scale bars: A, 1 cm; E, 20 μm.