Strigolactones in root growth & development.

Strigolactones (SLs) are carotenoid-derived phytohormones discovered 50 years ago as germination stimulants for the parasitic plants of the Orobanchaceae family. Later, they were also classified as stimulants for the arbuscular mycorrhizal fungi hyphal branching, and finally as a new class of phytohormones acting as suppressor of the shoot branching. Among their many roles in controlling plant development, they were recognized as regulators of root development. This chapter discusses the SL critical role in the regulation of root architecture system, being involved in primary root, lateral roots, adventitious roots and root hair development. In particular, the mode of action of SLs seems to strictly depend on the growth conditions, the nutritional status, and the plant species. Therefore, a focus on the SL regulation of root development under nutrient starvation conditions is also provided.