Identification of a Prunus MAX1 Homolog as a Unique Strigol Synthase from Carlactone Bypassing 5-Deoxystrigol

Abstract

Strigol was the first strigolactone (SL) to be discovered, but the biosynthetic pathway remains elusive. Here, through rapid gene screening using a microbial SL-producing platform, we functionally identified a strigol synthase (PpMAX1c, a cytochrome P450 711A enzyme) in Prunus that synthesizes strigol directly from the SL precursor carlactone through catalyzing multi-step oxidations and C-ring cyclization, bypassing the synthesis of 5-deoxystrigol. The function of PpMAX1c was validated through reconstructing the biosynthesis of strigol in Nicotiana benthamiana. Additional genomic analysis and functional verification confirm that peach also encodes an orobanchol synthase (PpCYP722C, a cytochrome P450 722C enzyme), which hints at the presence of both strigol-type and orobanchol-type SLs in peach and was confirmed through metabolic analysis of peach seedlings. This work highlights the catalytic diversity of the largely unexplored family of CYP711A homologs and sets the foundation to characterize the roles of different types of SLs in the economically important Prunus.