The Path from β-Carotene to Carlactone, a Strigolactone-Like Plant Hormone

TLDR

Strigolactones are phytohormones with diverse signaling activities, sharing a core structure of two lactones linked by an enol‑ether bridge, and are synthesized from carotenoids through a pathway involving D27, CCD7, and CCD8. The study aims to elucidate the structure of carlactone to advance understanding of strigolactone biology and inform strategies against parasitic weeds. We demonstrate that D27 converts all‑trans‑β‑carotene to 9‑cis‑β‑carotene, which CCD7 cleaves to a 9‑cis aldehyde; CCD8 then incorporates three oxygens and rearranges the molecule to produce carlactone, a compound with strigolactone‑like activity.

Abstract

Strigolactones, phytohormones with diverse signaling activities, have a common structure consisting of two lactones connected by an enol-ether bridge. Strigolactones derive from carotenoids via a pathway involving the carotenoid cleavage dioxygenases 7 and 8 (CCD7 and CCD8) and the iron-binding protein D27. We show that D27 is a β-carotene isomerase that converts all-trans-β-carotene into 9-cis-β-carotene, which is cleaved by CCD7 into a 9-cis-configured aldehyde. CCD8 incorporates three oxygens into 9-cis-β-apo-10'-carotenal and performs molecular rearrangement, linking carotenoids with strigolactones and producing carlactone, a compound with strigolactone-like biological activities. Knowledge of the structure of carlactone will be crucial for understanding the biology of strigolactones and may have applications in combating parasitic weeds.