The role of strigolactones in root development.

Strigolactones (SLs) and their derivatives were recently defined as novel phytohormones that orchestrate shoot and root growth. Levels of SLs, which are produced mainly by plant roots, increase under low nitrogen and phosphate levels to regulate plant responses. Here, we summarize recent work on SL biology by describing their role in the regulation of root development and hormonal crosstalk during root deve-lopment. SLs promote the elongation of seminal/primary roots and adventitious roots (ARs) and they repress lateral root formation. In addition, auxin signaling acts downstream of SLs. AR formation is positively or negatively regulated by SLs depending largely on the plant species and experimental conditions. The relationship between SLs and auxin during AR formation appears to be complex. Most notably, this hormonal response is a key adaption that radically alters rice root architecture in response to nitrogen- and phosphate-deficient conditions.