Molecular Cloning, Characterization, and Expression of an ω-3 Fatty Acid Desaturase Gene from Sapium sebiferum

A full-length cDNA (SsFAD3) for an ω-3 fatty acid desaturase (ω-3 FAD) was cloned from Sapium sebiferum (L.) Roxb. using rapid amplification of cDNA ends and reverse transcription polymerase chain reaction methods. SsFAD3 contained a 1119-bp open reading frame encoding a 372-amino acid polypeptide. The genomic sequence region of the SsFAD3 ORF was composed of 8 exons and 7 introns, similar to other ω-3 FADs found in most plants. The amino acid sequence showed a higher identity with microsomal ω-3 FADs than plastidial ω-3 FADs. Southern blot analysis of SsFAD3 suggested the existence of a small gene family composed of several copies or closely linked genes. SsFAD3 transcripts were detected in shoots, roots, leaves, stems, and seeds, but were most abundant in shoots. The function of SsFAD3 was confirmed by the accumulation of α-linolenic acid (α-18:3) in Saccharomyces cerevisiae transformants.