Figure 1.

Peptide-receptor signaling throughout LR development. Overview of the different steps of LR development and the peptide-receptor pairs currently known to be involved in each of these steps. During a DR5:LUC maximum in the elongation zone, XPP cells are primed for LR formation. In the maturation zone, LR initiation takes place, a process that is influenced by the stimulatory and inhibitory effects of multiple peptide signaling pathways. Additionally, several signaling peptides repress LR development in the vicinity of pre-existing primordia in a process called “lateral inhibition.” During later developmental stages, several peptide-receptor pathways affect LR primordium growth and its spatial accommodation in the surrounding tissues, allowing for emergence from the primary root. Finally, signaling peptides also control the elongation of LRs in response to environmental stimuli.