Isolation and Characterization of a Temperature-Regulated Microsomal Oleate Desaturase Gene (CtFAD2-1) from Safflower (Carthamus tinctorius L.)

A cDNA sequence, designated CtFAD2-1 and putatively encoding a delta-12 fatty acid desaturase, was isolated from total RNA of immature normal-type safflower (Carthamus tinctorius L.) seeds using a PCR approach. The deduced amino acid sequence showed three histidine boxes characteristic of all membrane-bound desaturase and a C-terminal endoplasmic reticulum retention signal. Phylogenetic analysis indicated that CtFAD2-1 is grouped with other plant FAD2 sequences which are specifically or highly expressed in developing seeds. Functional expression of the corresponding CtFAD2-1 cDNA in yeast confirmed that it encodes a microsomal oleate desaturase, partially converting oleic fatty acid to linoleic fatty acid. Our transcriptional analysis suggested that CtFAD2-1 is constitutively expressed, with maximum transcript accumulation, in developing seeds. The sequence of this microsomal oleate desaturase gene was also obtained from high oleic safflower genotypes, CtFAD2-1'. The comparison between the coding regions of CtFAD2-1 and CtFAD2-1' revealed that a deletion of cytosine (C) exists at the position +603 bp of CtFAD2-1'. Analysis of transcript level showed that the expression of CtFAD2-1' in high oleic acid genotype is significantly lower than that in normal genotypes during seed development. These results suggested that the change of CtFAD2-1' gene sequence results in the deactivation and lower transcription of delta-12 fatty acid desaturase in high oleic safflower genotypes.