Identification of a cDNA encoding a novel C18‐Δ⁹ polyunsaturated fatty acid‐specific elongating activity from the docosahexaenoic acid (DHA)‐producing microalga, Isochrysis galbana¹

Abstract

Isochrysis galbana, a marine prymnesiophyte micro-

Expression of the Isochrysis C18-Δ9 Polyunsaturated Fatty Acid Specific Elongase Component Alters Arabidopsis Glycerolipid Profiles

“…Expression of IgASE1 in yeast had previously demonstrated its substrate specificity to be restricted to LA and ALA (Qi et al, 2002). Consistent with these findings we have now observed the accumulation of EDA and ETrA in all transgenic plant tissues/organs examined, with the novel C20 fatty acid content reaching 15 mol% of total leaf fatty acid.…”

“…The substrate specificity of IgASE1 is consistent with it catalyzing the condensation reaction of fatty acid elongation (Qi et al, 2003). We have further suggested (Qi et al, 2002(Qi et al, , 2003 that the IgASE1 elongating activity is the first committed step in VLCPUFA synthesis and hence AA, EPA, and DHA formation via the so-called v3 D8 and v6 D8 pathways, respectively ( Fig. 1; Nichols and Appleby, 1969).…”

“…These were identified by comigration and spiking with known standards as EDA and ETrA (Fig. 2) and by comparison with the fatty acid products observed previously in transformed yeast (Qi et al, 2002). They were considered, therefore, to be the elongation products of the IgASE1 elongase component.…”

“…Recently we isolated and characterized a cDNA from I. galbana, which encodes a novel fatty acid elongase component designated IgASE1 (Qi et al, 2002(Qi et al, , 2003. Transgenic yeastexpressing IgASE1 converted linoleic acid (LA; C18:2n-6) and a-linolenic acid (ALA; C18:3n-3) to eicosadienoic acid (EDA; C20:2n-6) and eicosatrienoic acid (ETrA; C20:3n-3), respectively (Qi et al, 2002). The substrate specificity of IgASE1 is consistent with it catalyzing the condensation reaction of fatty acid elongation (Qi et al, 2003).…”

Characterization of membrane-bound fatty acid desaturases

“…In the late 90's the alternative Δ8-pathway has been discover in some protists and algae species e.g. Euglena (Wallis and Browse 1999) or Isochrysis (Qi et al 2002). This pathway involved the Δ9-elongation step of LA or ALA as first one followed by Δ8-desaturation to yield DGLA (in n-6 cascade) or ETA (in n-3 cascade).…”