Functional expression of cinnamate 4-hydroxylase from Ammi majus L

Total RNA was isolated from dark-grown cell suspension cultures of Ammi majus L. that had been induced with fungal elicitor or treated with water for control and used as template with cytochrome P450-specific primers for DD-RT-PCR amplifications. A cDNA clone was generated from the elicited transcripts and assigned to cinnamate 4-monooxygenase based on sequence alignments and functional expression in yeast cells. Comparison of the translated polypeptide with database accessions of heterologous cytochrome P450 monooxygenases revealed a high degree of similarity (99.6%) with 98.6% identity to cinnamic acid 4-hydroxylase from parsley, documenting the close evolutionary relationship within the Apiaceae family. Maximal activity of the Ammi hydroxylase in yeast microsomes was determined at 25 degrees C and in the pH range of 6.5-7.0 reaching 2.5 pkat/mg on average. An apparent K(m) of 8.9 microM was determined for cinnamate. Preincubations with psoralen or 8-methoxypsoralen added up to 100 microM in the presence or absence of NADPH hardly affected the turnover rate. A. majus cell cultures accumulate sets of O-prenylated umbelliferones and linear furanocoumarins besides lignin-like compounds upon treatment with elicitor, and cinnamic acid 4-hydroxylase catalyzes the initial reaction leading from the general into the various phenylpropanoid branch pathways. Correspondingly, the hydroxylase transcript abundance was induced in the elicited cells.