Lateral/Secondary Roots

Abstract The plant root system is made of an elongating primary root of embryonic origin as well as multiple lateral or secondary roots initiated post‐embryonically. Initiation, organisation and emergence/elongation of lateral roots are tightly regulated by local and global, as well as endogenous and environmental factors, resulting in the adaptation of the whole root system to its functions. The plant hormone auxin is a key player in lateral root initiation, development and elongation. Yet, complex interactions with other hormones such as cytokinins, ethylene, brassinosteroids or abscisic acid (ABA) are also involved. Transcription factors and other proteins of unknown function have been identified in the signalling cascades regulating lateral root formation in response to endogenous or environmental cues. Progresses in understanding the multiple regulations of lateral root formation open new possibilities to use these strategies for plant adaptation to abiotic stresses such as drought or nutrient deprivation. Key Concepts: The regulation of lateral root formation influences the overall architecture of the root system and its adaptation to various constraints. The commitment of pericycle cells to become lateral root founder cells is the first step of formation of secondary roots and determines their positioning.