Cloning, characterization, and expression of two cDNA clones for a rice ferulate-5-hydroxylase gene, a cytochrome P450-dependent monooxygenase

Ferulate-5-hydroxylase (F5H) is a cytochrome P450-dependent monooxygenase that catalyses the hydroxylation of ferulic acid, coniferaldehyde, and coniferyl alcohol in the pathways leading to sinapic acid and the syringyl unit of lignin. We have isolated two F5H genes, OsF5HL and OsF5HL2, from a japonica-type rice (Oryza sativa L. cv. Ilpoombyeo). They are the first F5H genes experimentally identified in monocotyledonous plants. Phylogenetic analysis indicated that both genes are closely related to dicot F5H genes from Arabidopsis thaliana and Brassica napus. Southern blot analysis showed that these genes exist as single copies in the rice genome. Alignments of the OsF5HL and OsF5HL2 cDNAs to their genomic DNAs revealed that OsF5HL has an open reading frame (ORF) of 1590 b from four exons, while OsF5HL2 has an ORF of 1560 b from two exons. Expression of OsF5HL is highest in young leaves, whereas that of OsF5HL2 is greatest in mature leaves. In the roots and stems, transcription levels for both genes are markedly low. These data suggest that the OsF5HL and OsF5HL2 genes belong to the CYP84 subfamily and that their expressions are tissue-specific.