Breakout - lateral root emergence in Arabidopsis thaliana

•Lateral root emergence requires the integration of chemical and mechanical signals.•Auxin promotes LR development via distinct Aux/IAA-ARF signalling modules.•The endodermis plays a key role during LR emergence.•LR emergence occurs in two phases.•Hydrodynamics play an important role during LR emergence.

Lateral roots are determinants of plant root system architecture. Besides providing anchorage, they are a plant's means to explore the soil environment for water and nutrients. Lateral roots form post-embryonically and initiate deep within the root. On its way to the surface, the newly formed organ needs to grow through three overlying cell layers; the endodermis, cortex and epidermis. A picture is emerging that a tight integration of chemical and mechanical signalling between the lateral root and the surrounding tissue is essential for proper organogenesis. Here we review the latest progress made towards our understanding of the fascinating biology underlying lateral root emergence in Arabidopsis.