Two Low-temperature-inducible Chlorella Genes for Δ12 and ω-3 Fatty Acid Desaturase (FAD): Isolation of Δ12 and ω-3 fad cDNA Clones,…

Abstract

  In an attempt to clarify the involvement of fatty acid desaturases (FADs) in the freezing tolerance of Chlorella vulgaris IAM C-27, developed by hardening, we have isolated cDNA clones for two types of FADs from the Chlorella strain, based on the sequence information of genes for Δ12 and ω-3 FADs, respectively desaturating oleic acid (18:1) to linoleic acid (18:2) and linoleic acid (18:2) to linolenic acid (18:3). The deduced amino acid sequence of the first clone, designated CvFad2, showed about 66% similarity to the microsomal Δ12 FADs from several higher plants and this gene had Δ12 FAD activity when expressed in Saccharomyces cerevisiae. The predicted protein encoded by a second gene, designated CvFad3, showed about 60% similarity to the microsomal and plastidial ω-3 FADs from several higher plants. The features of the amino acid sequences of the C- and N-terminal regions of CvFAD3 and fatty acid analysis of polar lipids in transgenic tobacco plant expressing the CvFad3 gene suggested that this gene encodes the microsomal ω-3 FAD. Southern blot analysis showed that both genes were single-copy genes in the genome of the Chlorella strain. Different transcriptional patterns were observed with the two genes during hardening in Northern blot analysis.