Cell fate plasticity of xylem-pole-pericycle in Arabidopsis roots

In Arabidopsis roots, xylem-pole-pericycle (XPP) cells exhibit remarkable cell fate plasticity by contributing to both lateral root (LR) and cambium formation. Despite significant progress in understanding these individual processes, the mechanism orchestrating these two fates and their effects on root architecture and secondary growth remain unclear. Here we combined lineage tracing with molecular genetics to study the fate dynamics of XPP cells. We showed that developmentally arrested lateral root primordia (LRP) that fail to emerge as lateral roots, gradually obtain cambium identity thus contributing to secondary growth. Conversely, preestablished procambium identity within XPP cells can be reverted to LR identity when simulated by auxin, an important player in LR development. This competence for auxin-induced LR formation from XPP cells, termed LR potency, however, decreases as the root matures. We found key cambium regulators play essential roles in shaping LR potency by promoting cambium activation and inhibiting LR development. Consistently, corresponding mutants with impaired cambium activity display broader LR potency. Moreover, cytokinins, essential players in cambium development, facilitate the identity transition of LRPs to cambium and reduce LR potency through key cambium regulators. Overall, our findings highlight the inherent cellular plasticity of XPP cells and elucidate how plant hormones influence root architecture and secondary growth through balancing the two cell fates of XPP cells.