In algae, the biosynthesis of docosahexaenoic acid (22:6 3; DHA) proceeds via the elongation of eicosapentaenoic acid (20:5 3; EPA) to 22:5 3, which is required as a substrate for the final ⌬ 4 desaturation. To isolate the elongase specific for this step, we searched expressed sequence tag and genomic databases from the algae Ostreococcus tauri and Thalassiosira pseudonana , from the fish Oncorhynchus mykiss , from the frog Xenopus laevis , and from the sea squirt Ciona intestinalis using as a query the elongase sequence PpPSE1 from the moss Physcomitrella patens . The open reading frames of the identified elongase candidates were expressed in yeast for functional characterization. By this, we identified two types of elongases from O. tauri and T. pseudonana : one specific for the elongation of ( ⌬ 6-)C18-PUFAs and one specific for ( ⌬ 5-)C20-PUFAs, showing highest activity with EPA. The clones isolated from O. mykiss , X. laevis , and C. intestinalis accepted both C18-and C20-PUFAs. By coexpression of the ⌬ 6-and ⌬ 5-elongases from T. pseudonana and O. tauri , respectively, with the ⌬ 5-and ⌬ 4-desaturases from two other algae we successfully implemented DHA synthesis in stearidonic acid-fed yeast. This may be considered an encouraging first step in future efforts to implement this biosynthetic sequence into transgenic oilseed crops. -Meyer, A., H. Kirsch, F. Domergue, A. Abbadi, P. Sperling, J. Bauer, P. Cirpus, T. K. Zank, H. Moreau, T. J. Roscoe, U. Zähringer, and E. Heinz. Novel fatty acid elongases and their use for the reconstitution of docosahexaenoic acid biosynthesis.

The LAFL (i.e. LEC1, ABI3, FUS3, and LEC2) master transcriptional regulators interact to form different complexes that induce embryo development and maturation, and inhibit seed germination and vegetative growth in Arabidopsis. Orthologous genes involved in similar regulatory processes have been described in various angiosperms including important crop species. Consistent with a prominent role of the LAFL regulators in triggering and maintaining embryonic cell fate, their expression appears finely tuned in different tissues during seed development and tightly repressed in vegetative tissues by a surprisingly high number of genetic and epigenetic factors. Partial functional redundancies and intricate feedback regulations of the LAFL have hampered the elucidation of the underpinning molecular mechanisms. Nevertheless, genetic, genomic, cellular, molecular, and biochemical analyses implemented during the last years have greatly improved our knowledge of the LALF network. Here we summarize and discuss recent progress, together with current issues required to gain a comprehensive insight into the network, including the emerging function of LEC1 and possibly LEC2 as pioneer transcription factors.