FIGURE 1.

Overview of lateral root organogenesis in the model plant Arabidopsis thaliana and comparison with callus formation. (A) Schematic of an Arabidopsis plant where primary and lateral organs are shown. (B) Upon hormonal induction during in vitro culture, tissue explants can be reprogrammed. Only xylem-pole-pericycle-like cells are susceptible of developmental reprograming. (C) Pluripotent cells divide to form a callus. (D) Xylem-pole-pericycle cells are normally reprogramed during post-embryonic development to form lateral root founder cells. Note that as not all cells are reprogrammed this creates a branching pattern. (E) Lateral root initiation occurs through the asymmetric cell division regulated by ALF4 and auxin signaling. Subsequent divisions create a primordium with stereotypic morphologies and expression of the root regulators SHORTROOT, SCARECROW, WUSCHEL RELATED HOMEOBOX 5 (WOX5), and GLABRA2 (GL2). Note the similarities with callus formation.