Abstract: Rapeseed oil is primarily composed of palmitic, stearic, oleic, linoleic and linolenic fatty acids. Delta-12 desaturase (FAD2) in plants converts oleic acid (18:1) to linoleic acid (18:2) by inserting a double bond at the delta-12 position. Fatty acid desaturase-2 gene (fad2) encodes delta-12 desaturase that functions in the endoplasmic reticulum. Fifty-six fad2 DNA clones and nine fad2 seed cDNA clones of B. napus cv. Xiangyou 15 were randomly selected and sequenced in this study. These 56 DNA sequences share 91.0-99.9% identity in nucleotides. Through combination of identical sequences, 11 different sequences were found, of which each represented various copy of fad2 gene. Deduced amino acid sequences revealed that many stop codons occurred in the coding region of six copies, the other five copies shared 90.60-99.74% amino-acid identity. Two differential cDNA were found from nine fad2 seed cDNA sequence, no stop codons in the coding region, revealing that more than one fad2 gene express in developing seeds, and oleic acid content is controlled by multigene. The eleven copies in genome could be divided into two groups based on their homology, and designated as fad2I and fad2II, respectively. RT-PCR analysis in seeds at twenty-seven days after pollination showed that fad2I expressed strongly in seeds, and no expression of fad2II was found, but both of them expressed in leaves.

Key words: Brassica napus, Oleate desaturase, Gene copy number, Sequence-specific primer