Characterization of a Clematis terniflora DC. coumarin synthase involved in coumarin biosynthesis

<em>Clematis terniflora</em> DC. has been used for anti-inflammatory, antihypertensive and other diseases in some Asian countries, and has high medicinal value. Coumarins are the major secondary metabolites produced by<em> C. terniflora</em> leaves under ultraviolet B (UV-B) radiation followed by dark treatment, but the synthesis of coumarin in <em>C. terniflora</em> has not been fully elucidated. Coumarin synthase is a key enzyme to produce coumarin core structure, which is the first step to form coumarins. Based on previous transcriptome data, we identified a BADH acyltransferase CtCOSY highly expressed in leaves after stresses and characterized it functionally. Experiments have proved that CtCOSY could couple with 4-coumarinyl CoA-ligase in vitro to produce umbelliferone. By analyzing the proteomics and metabolomics of control plants and CtCOSY-silenced plants before and after UV-B followed by dark treatment, we found that double stresses disturbed the energy metabolism pathway and phenylpropanoids synthesis pathway. CtCOSY silencing affected plant’s regulation of primary metabolism to a certain extent, and it also affected the accumulation of compounds in shikimic acid pathway and coumarin synthesis. This study provides evidence that CtCOSY is involved in the synthesis of coumarin in <em>C. terniflora.</em>