Strigolactones - Hormone Synthetic Pathways and Genes in Arabidopsis

Strigolactones were first discovered in root exudates of plants and characterized as seed germination stimulants of root parasitic plants such as Striga and Orobanche species. They were later shown to act as a plant-derived signal that induces hyphal branching of arbuscular mycorrhizal fungi, which facilitate the uptake of mineral nutrients by the host plants in a symbiotic manner. More recently, strigolactones were discovered as endogenous shoot branching inhibitors (or their biosynthetic precursors), which had been genetically defined by a series of increased branching mutants, including ramosus (rms) of pea, decreased apical dominance (dad) of petunia, more axillary growth (max) of Arabidopsis and a particular subclass of dwarf (d) mutants of rice. Although both genetic and biochemical data suggest that strigolactones are biosynthesized from carotenoid(s) through its oxidative cleavage, the exact biosynthesis pathway has still to be elucidated.