Functional characterisation of two cytochrome b5-fusion desaturases from Anemone leveillei: the unexpected identification of a fatty acid Δ6-desaturase

The Ranunculaceae are known to accumulate a wide range of unusual fatty acids in their seed lipids, and this variability has been advocated as a taxonomic marker. The Anemone species, Anemone leveillei L. and Anemone rivularis Buch.-Ham., have previously been reported to accumulate Δ5-desaturated fatty acids in their seed tissue [K. Aitzetmüller (1995) Plant Syst Evol 9:229–240]. Two cDNAs, AL1 and AL2, with similarity to plant cytochrome b5-fusion "front-end" desaturases were isolated from developing seeds of A. leveillei and their function identified by expression in Saccharomyces cerevisiae. AL2 was characterised as a sphingolipid long-chain-base Δ8-desaturase, while AL1 acted as a fatty acid desaturase. However, AL1 did not produce Δ5-desaturated fatty acids as expected; instead, when expressed in transgenic S. cerevisiae or Arabidopsis thaliana this enzyme was functionally characterised as a Δ6-desaturase. Northern analysis confirmed the expression of this gene in seed tissue and leaf tissue of A. leveillei, though Δ6-desaturated fatty acids were found to accumulate only in the leaf tissue. The unexpected characterisation of a Δ6-desaturase in A. leveillei has implications for the use of fatty acids in chemotaxonomic studies. This is also the first report of a higher-plant Δ6-desaturase from a family other than the Boraginaceae.