Strigolactones: A New Class of Plant Hormones with Multifaceted Roles

Strigolactones (SLs) are terpenoid lactones produced mainly in plant roots and initially identified as seed germination stimulants for parasitic weeds. In 2005, they were described also as boosters of hyphal branching in arbuscular mycorrhizal fungi, and thereby as promoters of arbuscular mycorrhizal symbiosis. In 2008, they emerged as a new class of plant hormones controlling plant architecture through repression of shoot branching. Since then, several new roles were discovered for SLs: in the adaptive responses to a number of environmental stimuli (including light, osmotic stress, interaction with pathogens and nodulating bacteria), and in several aspects of plant development (including seed germination for nonparasitic plants, hypocotyl elongation, reproduction, leaf senescence and nodulation). The biosynthetic and perception/transduction systems of SLs are being elucidated, and the first mechanistic models presented.