Cloning and sequence analysis of maize FAD2 gene.

Delta-12 desaturases are involved in the conversion of oleic acid to linoleic acid in plant. Based on the conserved oligo amino acid residues of the published delta-12 desaturase genes from other higher plant species, a cDNA fragment was amplified by RT-PCR (reverse transcriptase-polymerase chain reaction) from the total RNA of immature maize embryos. According to bioinformation analysis of the cDNA sequence, a specific fragment of FAD2 gene was isolated by RT-PCR from immature maize embryos, and DNA of the same length was amplified from maize genome. Results of sequence analysis indicate that they are all 1 164 bp long, and have just an open reading frame (ORF) coding for 387 amino acids, and there is no intron in the FAD2 ORF (GenBank accession DQ496227). The deduced amino acid sequence of the cloned FAD2 showed high identity to those of other plant delta-12 fatty acid desaturases. It contains three histidine motifs and two long stretches of hydrophobic residues, indicative of an integral membrane protein spanning membrane four times. Analysis by semi-quantitive RT-PCR showed that FAD2 was strongly expressed in maize immature embryos than in leaves, stems and roots.