O-methyltransferases catalyze the last step of geniposide biosynthesis in Gardenia jasminoides

Iridoid glycosides, including geniposide, geniposidic acid, and gardenoside, are the main active components of Gardenia jasminoides Ellis. Their biosynthetic pathways have widely attracted researchers' attention, but yet remain unclear. Elucidating geniposide biosynthesis would help to better define the quality of G. jasminoides plants. In this study, we performed multidimensional transcriptional and metabolic analyses of the leaves and flower buds of G. jasminoides at different developmental stages based on the chromosome-level genome. Ten putative genes involved in geniposide biosynthesis were screened based on phylogenetic analysis and the correlation of gene expression with geniposide accumulation. Two non-tandem geniposidic acid methyltransferase (GAMT) genes were cloned, and in vitro enzymatic reactions with the corresponding recombinant proteins revealed that both could catalyze the conversion of geniposidic acid into geniposide. Synteny analysis showed that these two GAMT genes were unique to G. jasminoides, suggesting the existence of a Gardenia-specific geniposide biosynthetic pathway. In summary, two novel species-specific O-methyltransferases that catalyze the last step of geniposide biosynthesis were identified. These findings will help clarify the biosynthetic pathway of iridoid glycosides and support G. jasminoides breeding.