Root branching plasticity: collective decision-making results from local and global signalling.

Cells within tissues can be regarded as autonomous entities that respond to their local environment and to signals from neighbours. Coordination between cells is particularly important in plants, as the architecture of the plant adapts to environmental cues. To explain the architectural plasticity of the root, we propose to view it as a swarm of coupled multi-cellular structures, rhizomers, rather than a large set of autonomous cells. Each rhizomer contains a primed site with the potential to develop a single lateral root. Rhizomers are spaced through oscillatory genetic events that occur at the basal root tip. The decision whether or not to develop a lateral root primordium results from the interplay between local interactions of the rhizomer with its immediate environment, such as local nutrient availability, long-range interactions between the rhizomers and global cues, such as overall nutrient uptake. It can halt lateral root progression through its developmental stages, resulting in the observed complex root architecture.