A seed specific Δ-12 oleate desaturase gene is duplicated, rearranged, and weakly expressed in high oleic acid sunflower lines

The seed oils of wild-type sunflower (Helianthus annuus L.) germplasm typically contain 140 to 350 g kg(-1) oleic acid (18:1). Sunflower germplasm with 800 to 950 g kg(-1) 18:1 (high oleic germplasm) has been developed with a dominant mutation (OI) originating from the cultivar 'Pervenets'. We speculated that this mutation reduced the activity or expression of a Delta-12 oleate desaturase (OLD) gene. This was tested by cloning OLD genes expressed in developing seeds and comparing nucleotide sequences, OLD transcript concentrations, and OLD restriction fragment lengths among wild-type (low oleic) and backcross-derived mutant (high oleic) lines fixed for ol or Ol alleles, respectively. An Arabidopsis thaliana L. OLD (At OLD) cDNA probe was used to isolate a full-length cDNA clone (OLD-7) from a developing seed cDNA library of sunflower. OLD-7 was strongly expressed in developing seeds, but was not expressed in the other tissues sampled. The nucleotide sequences for OLD-7 ORFs from partially isogenic low and high oleic acid lines (HA89 and HA341) a ere 100% identical. High oleic lines had substantially lower OLD-7 transcript concentrations than low oleic:lines. Restriction fragment analyses showed that OLD-7 is duplicated and rearranged in mutant lines and linked to the Ol locus; thus, increased oleic acid content seems to be caused by DNA changes affecting OLD-7 cis regulatory sequences. OLD-7 RFLPs distinguish between Ol locus genotypes and can be used to accelerate the development of high oleic lines in sunflower.