Lateral Root Formation

Abstract The underground development of the plant root system is a complex and plastic process. It enables the plants to mine hydromineral resources while dealing with changes in their environment. Root branching via lateral root formation is considered as an important trait because it greatly influences root system architecture and impacts plant growth and crop performance. In the past few years, major progresses in understanding the mechanisms of root branching have been made. Technical advances lift the veil on multiple molecular and cellular processes that contribute to the robust formation of new lateral roots in plant models and to its response to endogenous and environmental cues. Developing translational approaches should increase in the coming decades to allow a global and integrative vision of root system development and the mechanisms of root branching in various plant species. Moreover, exploring the genetic diversity that modulates this fundamental process opens the way to breeding crops with more efficient root system architectures. Key Concepts Lateral root formation significantly influences root system architecture, a key trait for plant interaction with the soil and especially, plant nutrition. Lateral root primordium initiation, development and emergence from the primary root have been well described in several plant model species. Lateral root formation is highly regulated. Many molecular mechanisms involved in this organogenesis process are known in detail, especially in the plant model Arabidopsis thaliana . Among these, the phytohormone auxin is a key regulatory signal influencing each step of lateral root formation. A complex regulatory network, integrating intercellular signals and mechanical constraints, triggers regularly spaced initiation of lateral root formation, allows robust organ patterning, and controls the lateral root primordium growth through the overlaying primary root tissues. Endogenous and environmental signals modulate lateral root formation kinetics and emergence, yielding plasticity in root system development. Comparison of lateral root development in different plant species reveals specific and conserved pathways. Genetic diversity can be explored and used to breed crops with optimised root branching properties.