Pericycle

Abstract

Abstract Pericycle is a primary tissue of plant roots with meristematic properties and is the site for the initiation of lateral roots and two secondary meristems, the vascular cambium and phellogen (cork cambium). Pericycle pluripotent cell properties are also revealed during cultivation of root explants in shoot regeneration media. In this article, the characteristics of the pericycle related to each of its functions are reviewed. During lateral root development, five important and coordinated events take place in the pericycle: founder cell identity acquisition, cell division competence, asymmetric cell division, new organ growth axis establishment and lateral inhibition. Cellular and molecular bases of these processes as well as transcriptomic insights in pericycle cell identity are discussed. Cell cycle and related genetic control in pericycle development are also addressed. Cellular and molecular bases of participation of pericycle in the formation of lateral meristems, vascular cambium and phellogen (cork cambium), differences among eudicots and monocots in pericycle development, as well as participation of pericycle in loading of mineral nutrients and unloading of organic compounds are also reviewed. Key Concepts The pericycle is a primary tissue with pluripotent properties that participates in lateral root (LR) formation. In eudicots, it also gives rise to two lateral meristems: vascular cambium and cork cambium (phellogen). Pericycle is typical of plant roots and is the most external cell layer (or layers) of the vascular cylinder. In other plant organs, pericycle or pericycle‐like cell layers can also be present depending on taxon. Outside the root apical meristem, in the root differentiation zone of eudicots, the xylem pole pericycle (XPP) maintains its proliferation activity. Due to its proliferation activity, pericycle possesses high regenerative properties involved in regeneration of shoots from roots. The XPP and phloem pole pericycle (PPP) are characterised by distinct transcriptomic profiles related to their adjacent vascular tissues. Pericycle cells committed for LR development in monocots and eudicots retain the common features related to cell cycle, active auxin synthesis, transport and signalling, and responsiveness to nitrates. LR formation starts from pericycle founder cell specification which is auxin dependent and implies drastic developmental changes in genetic programs involved in asymmetric cell division, new organ growth axis establishment and lateral inhibition. The first founder cell specification is followed by the recruitment of neighbouring pericycle cells that leads to the formation of a morphogenetic field of founder cells giving rise to a LR. The transition from primary to secondary growth starts in the pericycle and procambium and leads to the formation of vascular cambium and phellogen which are coordinated processes dependent on auxin and cytokinin. Pericycle maintains high metabolic activity and participates in loading phloem and xylem and in unloading phloem and thus is involved in shoot‐to‐root and root‐to‐shoot long‐distance transport.