PLANT GENETICS • ORIGINAL PAPER Fatty acid composition and desaturase gene expression in flax

Abstract Little is known about the relationship between ex-pression levels of fatty acid desaturase genes during seed development and fatty acid (FA) composition in flax. In the present study, we looked at promoter structural variations of six FA desaturase genes and their relative expression through-out seed development. Computational analysis of the nucleo-tide sequences of the sad1, sad2, fad2a, fad2b, fad3a and fad3b promoters showed several basic transcriptional ele-ments including CAAT and TATA boxes, and several putative target-binding sites for transcription factors, which have been reported to be involved in the regulation of lipid metabolism. Using semi-quantitative reverse transcriptase PCR, the ex-pression patterns throughout seed development of the six FA desaturase genes were measured in six flax genotypes that differed for FA composition but that carried the same desaturase isoforms. FA composition data were determined by phenotyping the field grown genotypes over four years in two environments. All six genes displayed a bell-shaped pattern of expression peaking at 20 or 24 days after anthesis. Sad2was the most highly expressed. The expression of all six desaturase genes did not differ significantly between genotypes (P=0.1400), hence there were no correlations be-tween FA desaturase gene expression and variations in FA composition in relatively low, intermediate and high linolenic acid genotypes expressing identical isoforms for all six desaturases. These results provide further clues towards un-derstanding the genetic factors responsible for FA composi-tion in flax