ARABIDOPSIS THALIANA DEFENSE-RELATED PROTEIN ELI3 IS AN AROMATIC ALCOHOL:NADP+ OXIDOREDUCTASE

We expressed a cDNA encoding the Arabidopsis thaliana defense-related protein ELI3-2 in Escherichia coli to determine its biochemical function. Based on a protein database search, this protein was recently predicted to be a mannitol dehydrogenase [Williamson, J. D., Stoop, J. M. H., Massel, M. O., Conkling, M. A. & Pharr, D. M. (1995) Proc. Natl. Acad. Sci. USA 92, 7148–7152]. Studies on the substrate specificity now revealed that ELI3-2 is an aromatic alcohol: NADP+ oxidoreductase (benzyl alcohol dehydrogenase). The enzyme showed a strong preference for various aromatic aldehydes as opposed to the corresponding alcohols. Highest substrate affinities were observed for 2-methoxybenzaldehyde, 3-methoxybenzaldehyde, salicylaldehyde, and benzaldehyde, in this order, whereas mannitol dehydrogenase activity could not be detected. These and previous results support the notion that ELI3-2 has an important role in resistance-related aromatic acid-derived metabolism.