Strigolactones (SLs) are a class of phytohormones and rhizosphere signaling compounds with high structural diversity. Three enzymes, carotenoid isomerase DWARF27 and carotenoid cleavage dioxygenases CCD7 and CCD8, were previously shown to convert all-trans-β-carotene to carlactone (CL), the SL precursor. However, how CL is metabolized to SLs has remained elusive. Here, by reconstituting the SL biosynthetic pathway in Nicotiana benthamiana, we show that a rice homolog of Arabidopsis MORE AXILLARY GROWTH 1 (MAX1), encodes a cytochrome P450 CYP711 subfamily member that acts as a CL oxidase to stereoselectively convert CL into ent-2′-epi-5-deoxystrigol (B-C lactone ring formation), the presumed precursor of rice SLs. A protein encoded by a second rice MAX1 homolog then catalyzes the conversion of ent-2′-epi-5-deoxystrigol to orobanchol. We therefore report that two members of CYP711 enzymes can catalyze two distinct steps in SL biosynthesis, identifying the first enzymes involved in B-C ring closure and a subsequent structural diversification step of SLs.
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We thank Y. Wang from the Institute of Genetics and Developmental Biology at the Chinese Academy of Science for the p35s:OsD27:PJTK13 plasmid and K. Yoneyama (Weed Science Center, Utsunomiya University, Utsunomiya, Japan) and T. Asami (Department of Applied Biological Chemistry, The University of Tokyo, Japan) for supplying SL standards. We thank J. Beekwilder and K. Cankar (Plant Research International, Wageningen, the Netherlands) for technical advice on the yeast assays and B. Ramakers (Nijmegen University) for technical support with the CD spectra measurement of CL. We thank A. Reeder from the Centre for Microscopy, Characterisation and Analysis (University of Western Australia (UWA)) and M. Clarke from the Centre for Metabolomics (UWA) for technical assistance and instrument access. We acknowledge funding by the Netherlands Organization for Scientific Research (VICI grant 865.06.002 and equipment grant 834.08.001 to H.J.B.), the Australian Research Council (LP0882775 for A.S. and FT110100304 for G.R.F.) and the UK Biotechnology and Biological Sciences Research Council (for J.H. and O.L.). Research reported in this publication was supported by the King Abdullah University of Science and Technology and was cofinanced by the Centre for BioSystems Genomics, which is part of the Netherlands Genomics Initiative/Netherlands Organization for Scientific Research.
The authors declare no competing financial interests.
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Zhang, Y., van Dijk, A., Scaffidi, A. et al. Rice cytochrome P450 MAX1 homologs catalyze distinct steps in strigolactone biosynthesis. Nat Chem Biol 10, 1028–1033 (2014). https://doi.org/10.1038/nchembio.1660
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