ISOLATION AND SEQUENCE OF A CDNA-ENCODING THE JERUSALEM-ARTICHOKE CINNAMATE 4-HYDROXYLASE, A MAJOR PLANT CYTOCHROME-P450 INVOLVED IN THE GENERAL PHENYLPROPANOID PATHWAY

Cinnamate 4-hydroxylase [CA4H; trans-cinnamate, NADPH:oxygen oxidoreductase (4-hydroxylating), EC 1.14.13.11] is a cytochrome P450 that catalyzes the first oxygenation step of the general phenylpropanoid metabolism in higher plants. The compounds formed are essential for lignification and defense against predators and pathogens. We recently reported the purification of this enzyme from Mn2+-induced Jerusalem artichoke (Helianthus tuberosus L.) tuber tissues. Highly selective polyclonal antibodies raised against the purified protein were used to screen a lambdagt11 cDNA expression library from wound-induced Jerusalem artichoke, allowing isolation of a 1130 -base-pair insert. Typical P450 domains were identified in this incomplete sequence, which was used as a probe for the isolation of a 1.7-kilobase clone in a lambdagt10 library. A full-length open reading frame of 1515 base pairs, encoding a P450 protein of 505 residues (M(r) = 57,927), was sequenced. The N terminus, essentially composed of hydrophobic residues, matches perfectly the microsequenced N terminus of the purified protein. The calculated pI is 9.78, in agreement with the chromatographic behavior and two-dimensional electrophoretic analysis of CA4H. Synthesis of the corresponding mRNA is induced in wounded plant tissues, in correlation with CA4H enzymatic activity. This P450 protein exhibits the most similarity (28% amino acid identity) with avocado CYP71, but also good similarity with CYP17 and CYP21, or with CYP1 and CYP2 families. According to current criteria, it qualifies as a member of a new P450 family.