Hormonal regulation of root hair growth and responses to the environment in Arabidopsis thaliana

The main functions of plant roots are water and nutrient uptake, soil anchorage and interaction with soil-living biota. Root hairs, single cell tubular extensions of root epidermal cells, facilitate or enhance the latter by drastically enlarging the root's absorptive surface. Root hair development is constantly adapted to changes in the root's surrounding, allowing for optimization of root functionality in heterogeneous soil environments. The underlying molecular pathway is the result of a complex interplay between position-dependent signalling and feedback loops. Phytohormone signalling interconnects this root hair signalling cascade with biotic and abiotic changes in the rhizosphere, enabling dynamic hormone-driven changes in root hair growth, density, length and morphology. This review aims to critically discuss the influence of the major plant hormones on the root hair developmental scheme, and how changes in rhizosphere properties impact on the latter.