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The yeast Yarrowia lipolytica is distantly related to Saccharomyces cerevisiae, can be genetically modified, and can grow in both haploid and diploid states in either yeast, pseudomycelial, or mycelial forms, depending on environmental conditions. Previous results have indicated that the STE and RIM pathways, which mediate cellular switching in other dimorphic yeasts, are not required for Y. lipolytica morphogenesis. To identify the pathways involved in morphogenesis, we mutagenized a wild-type strain of Y. lipolytica with a Tn3 derivative. We isolated eight tagged mutants, entirely defective in hyphal formation, from a total of 40,000 mutants and identified seven genes homologous to S. cerevisiae CDC25, RAS2, BUD6, KEX2, GPI7, SNF5, and PPH21. We analyzed their abilities to invade agar and to form pseudomycelium or hyphae under inducing conditions and their sensitivity to temperature and to Calcofluor white. Chitin staining was used to detect defects in their cell walls. Our results indicate that a functional Ras-cyclic AMP pathway is required for the formation of hyphae in Y. lipolytica and that perturbations in the processing of extracellular, possibly parietal, proteins result in morphogenetic defects.

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The biotechnological potential of Yarrowia lipolytica, as a single cell oil-producing microorganism, is presented in this review. Although initially this yeast species was considered as a lipid-degrading, recently, it was reclassified as a lipid-producing microorganism, since it has been reported to be capable of accumulating diverse desirable fatty acids after metabolic pathway engineering. In the first part of the present document, a general revision of the oil metabolic pathways and the capacity of oil production in Y. lipolytica is presented. The single cell oil produced by these metabolic engineering strategies has been designed by optimization, introduction, or suppression of new pathways to increase yield on lipid production. Later on, the genetic regulation systems and the lipid composition generated by this yeast for industrial purposes are discussed. These lipids could be safely used in the chemical food and biofuel industries, due to their high proportion of oleic acid. This document emphasizes in the overviewing at Y. lipolytica as an ideal oil cell factory, and as an excellent model to produce single cell oil.