Bioconversion of 5-deoxystrigol stereoisomers to monohydroxylated strigolactones by plants

The bioconversion of 5-deoxystrigol (5DS) and 4-deoxyorobanchol (4DO), the simplest canonical strigolactones (SLs), into monohydroxylated SLs such as strigol, sorgomol and orobanchol was confirmed by administering of stable isotope-labeled substrates to hydroponically grown plants. Liquid chromatography-mass spectrometry analyses established that 5DS was stereoselectively converted into strigol and sorgomol by cotton (Gossypium hirsutum) and Chinese milk vetch (Astragalus sinicus), respectively. 4DO was converted into orobanchol by rice (Oryza sativa). However, the red bell pepper (Capsicum annuum), red clover (Trifolium pratense), and pea (Pisum sativum) negligibly converted 4DO into orobanchol. The red bell pepper converted ent-4DO into 2',8-bisepi-sorgomol. These results suggest that some plants generate orobanchol without passing through 4DO.