strigolactones

Strigolactones are carotenoid-derived plant hormones that function as signaling molecules in the rhizosphere. They regulate shoot branching by inhibiting the outgrowth of axillary buds, thereby influencing plant architecture, and they affect root development and nutrient acquisition. Production and exudation of strigolactones increase under nutrient limitation, particularly phosphate deficiency, facilitating interactions with soil microbes that aid nutrient uptake.

Biosynthesis begins with cleavage of carotenoids by the enzymes CCD7 and CCD8 to produce carlactone, which is oxidized by the cytochrome P450 enzyme MAX1 and related enzymes to yield a variety of strigolactone structures, such as orobanchol and 5-deoxystrigol. This structural diversity leads to species-specific profiles of strigolactones across plants.

Perception involves the D14 receptor and the SCFMAX2 ubiquitin ligase complex. Binding of strigolactone to D14 promotes interaction with MAX2, triggering ubiquitin-mediated degradation of SMXL transcriptional repressors. This signaling cascade alters gene expression and results in reduced shoot branching as well as changes in root architecture and symbiotic responses.

Ecologically, strigolactones are exuded by roots into the rhizosphere, where they stimulate colonization by arbuscular mycorrhizal fungi to enhance phosphate uptake. They also induce germination of seeds of parasitic plants such as Striga and Orobanche, contributing to crop burdens in susceptible systems. Synthetic analogs like GR24 are widely used in research to study strigolactone signaling and functions.