title: Carlactone is an endogenous biosynthetic precursor for strigolactones.
abstract: Strigolactones (SLs) are a class of terpenoid plant hormones that regulate shoot branching as well as being known as root-derived signals for symbiosis and parasitism. SL has tricyclic-lactone (ABC-ring) and methyl butenolide (D-ring), and they are connected through an enol ether bridge. Recently, a putative biosynthetic intermediate called carlactone (CL), of which carbon skeleton is in part similar to those of SLs, was identified by biochemical analysis of three biosynthetic enzymes, DWARF27, CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7), and CCD8 in vitro. However, CL has never been identified from plant tissues, and the conversion of CL to SLs has not been proven in vivo. To address these questions, we chemically synthesized (13)C-labeled CL. We show that (13)C-labeled CL is converted to (-)-[(13)C]-2'-epi-5-deoxystrigol ((-)-2'-epi-5DS) and [(13)C]-orobanchol, endogenous SLs in rice, in the dwarf10 mutant, which is defective in CCD8. In addition, we successfully identified endogenous CL by using liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry in rice and Arabidopsis. Furthermore, we determined the absolute stereochemistry of endogenous CL to be (11R)-configuration, which is the same as that of (-)-2'-epi-5DS at the corresponding position. Feeding experiments showed that only the (11R)-isomer of CL, but not the (11S)-isomer, was converted to (-)-2'-epi-5DS in vivo. Taken together, our data provide conclusive evidence that CL is an endogenous SL precursor that is stereospecifically recognized in the biosynthesis pathway.
authors.affiliation: Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Seto
authors.forename: Aika
authors.initials: A
authors.lastname: Sado
authors.forename: Kei
authors.initials: K
authors.lastname: Asami
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hanada
authors.forename: Mikihisa
authors.initials: M
authors.lastname: Umehara
authors.forename: Kohki
authors.initials: K
authors.lastname: Akiyama
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Yamaguchi
mesh_terms: D053898:Biosynthetic Pathways; D002853:Chromatography, Liquid; D007783:Lactones / Q000378:metabolism*; D012275:Oryza / Q000378:metabolism; D053719:Tandem Mass Spectrometry
chemical_list: D007783:Lactones; C571055:carlactone; C483518:strigol
keywords: cytochrome P450; phosphate deficiency