A cDNA encoding a novel cytochrome P450-dependent monooxygenase from Arabidopsis thaliana.

Although more than 100 P450s have been isolated from animal and bacterial sources, it has only been in the past 5 years that genes encoding P450s have been cloned from plants. Their isolation has identified severa1 new families of P450s, and these include cinnamate-4-hydroxylase (family CYP73) (Mizutani et al., 1993; Teutsch et al., 1993), flavonoid 3',5'-hydroxylase (CYP75) (Holton et al., 1993), and allene oxide synthase (CYP74) (Song et al., 1993), as well as a number of other P450s of unknown function, such as the avocado-ripening-related P450 (family CYP71) (Bozak et al., 1990), a putative geraniol-10-hyroxylase from Catkaranfhus roseus (CYP72) (Vetter et al., 1992), P450s from Solanum melongena (CYP76 and CYP77) (Toguri et al., 1993; Toguri and Tokugawa, 1994), and a P450 from Tklaspi aruense (Udvardi et al., 1994). Recently, a mutant of Arabidopsis was identified that appeared to be defective in the activity or expression of ferulate-5-hydroxylase (Chapple et al., 1992), an enzyme that had previously been reported to be a P450 (Grand, 1984). This mutant has been named fakl and we have since identified a T-DNA-tagged version of this mutant and have used plasmid rescue to clone the affected gene (C.C.S. Chapple, unpublished data). It was not surprising, considering that many P450s exhibit significant sequence homology, that in the course of these experiments an additional P450 was isolated, presumably by cross-hybridization of conserved sequences in the two genes. The newly identified P450 cDNA encodes a protein of approximately 57.5 kD, consistent with the size of other P450s (Table I). The hydrophobic N terminus of the protein likely serves to anchor the protein to the ER. Amino acid sequence comparison shows that the new P450 is most similar to the avocado-ripening-related P450 (family CYP71) (Bozak et al., 1990) with an overall sequence identity of 32%. By convention, P450s sharing less than 40% sequence identity are designated as members of separate families (Nebert and Nelson, 1991). Thus, this cDNA identifies a new P450 family and has been designated CYP83.