Chemical structures of natural strigolactones : new insights into structural diversity

Abstract

Strigolactones （SLs） are carotenoid-derived plant metabolites that can be classified into two groups based on their chemical structures. Strigol and related compounds that contain a tricyclic ring system （ABC ring） connected to a methylbutenolide group （D ring） via an enol-ether bridge are called canonical SLs.　These SLs are synthesized from carotenoids via an intermediate, carlactone （CL）.　CL serves as a basis for the production of novel germination stimulants, such as avenaol （from black oat）, heliolactone （from sunflower）, and methyl zealactonoate （zealactone, from maize） which are structurally distinct from canonical SLs.　CL itself shows a weak but distinct Striga and Orobanche germination activity.　Therefore, it is reasonable to include these germination stimulants in the SL family.　Here, we introduce current definition of “strigolactone” and new members of the SL family.