Hydroxyl carlactone derivatives are predominant strigolactones in Arabidopsis

Strigolactones (SLs) regulate important aspects of plant growth and stress responses. Many diverse types of SL occur in plants, but a complete picture of biosynthesis remains unclear. In Arabidopsis thaliana, we have demonstrated that MAX1, a cytochrome P450 monooxygenase, converts carlactone (CL) into carlactonoic acid (CLA) and that LBO, a 2‐oxoglutarate‐dependent dioxygenase, can convert methyl carlactonoate (MeCLA) into a metabolite called [MeCLA + 16 Da]. In the present study, feeding experiments with deuterated MeCLAs revealed that [MeCLA + 16 Da] is hydroxymethyl carlactonoate (1'‐HO‐MeCLA). Importantly, this LBO metabolite was detected in plants. Interestingly, other related compounds, methyl 4‐hydroxycarlactonoate (4‐HO‐MeCLA) and methyl 16‐hydroxycarlactonoate (16‐HO‐MeCLA), were also found to accumulate in lbo mutants. 3‐HO‐, 4‐HO‐, and 16‐HO‐CL were detected in plants, but their expected corresponding metabolites, HO‐CLAs, were absent in max1 mutants. These results suggest that HO‐CL derivatives may be predominant SLs in Arabidopsis, produced through MAX1 and LBO.