Accumulation of coumarins in Arabidopsis thaliana

The biosynthesis of coumarins in plants is not well understood, although these metabolic pathways are often found in the plant kingdom. We report here the occurrence of coumarins in Arabidopsis thaliana ecotype Columbia. Considerably high levels of scopoletin and its P-D-glucopyranoside, scopolin, were found in the wild-type roots. The scopolin level in the roots was similar to 1200 nmol/gFW, which was similar to 180-fold of that in the aerial parts. Calli accumulated scopolin at a level of 70 nmol/gFW. Scopoletin and scopolin formation were induced in shoots after treatment with either 2,4-dichlorophenoxyacetic acid (at 100 mu M) or a bud-cell suspension of Fusarium oxysporum. In order to gain insight into the biosynthetic pathway of coumarins in A. thaliana, we analyzed coumarins in the Mutants obtained from the SALK Institute collection that carried a T-DNA insertion within the gene encoding the cytochrome P450, CYP98A3, which catalyzes 3'-hydroxylation of p-coumarate units in the phenylpropanoid pathway. The content of scopoletin and scopolin in the mutant roots greatly decreased to similar to 3% of that in the wild-type roots. This observation suggests that scopoletin and scopolin biosynthesis in A. thaliana are strongly dependent on the 3'-hydroxylation of p-cournarate units catalyzed by CYP98A3. We also found that the level of skimmin, a beta-(D)-glucopyranoside of umbelliferone, was slightly increased in the mutant roots. (c) 2005 Elsevier Ltd. All rights reserved.