## 1 Introduction  
_Yarrozia lipolytica_ is an obligate aerobic heterothallic ascomycetous yeast, originally classified as _Candida lipolytica_, detected in oil-polluted soil, marine and hypersaline environments, and as surface microflora of lipid-rich fermented dairy and meat products [1; 2; 3; 4]. In nature is commonly encountered in one of the two haploid mating types (MatA or MatB) that grows as budding cells, pseudohyphae, and true septated hyphae [5], although diploid strains are occasionally isolated [3]. In the lab, morphology alters by manipulating growth conditions, such as carbon source, pH, and medium supplementation [6]. _Y. lipolytica_, unlike _C. albicans_ and _C. tropicalis_, is considered non-pathogenic (classified as GRAS) and most strains do not grow above 32 \({}^{\circ}\)C [4]. The most attractive trait of this yeast is its ability to robustly grow on diverse carbon sources (from glucose, fructose, xylose, and glycerol to low-cost hydrophobic substrates) and in a wide range of pH and salinity conditions. Owing to these features, _Y. lipolytica_ has been a workhorse for more than 70 years for the biotechnological synthesis of various high value-added bio-products such as lipids, organic acids and sugar alcohols, with eco-friendliness, safety, and high purity [7; 8; 9; 10; 11; 12; 13; 14; 15]. Besides its excellent secretory capability, the availability of various genetic tools makes _Y. lipolytica_ suitable also for the production of industrially relevant enzymes such as lipases, acid and alkaline proteases, and phosphatases [1; 3; 8; 9; 16; 17]. _Y. lipolytica_ possesses an unusually large genome of 20 Mb compared to other yeasts, which range from 10 to 12 Mb. However, this almost two-fold difference does not correspond to higher gene density, which is significantly lower in _Y. lipolytica_ (one gene per 3 kb) than in other yeasts(e.g., one gene per 2 kb in _Saccharomyces cerevisiae_). As expected from its known secretory functions, the secreted proteins that are involved in the metabolism of lipids and fatty acids are over-represented [2; 18]. The average identity level of amino acids between _Y. lipolytica_ and other yeasts is approximately 50%, and when proteins are arranged based on common presence or absence, only around 40% are found in other ascomycetes. Compared to _S. cerevisiae_, a number of protein families expand in the _Yarrowia_ genome, encoding acyl glycerol lipases, sphingomyelliness-like proteins, \(\alpha\)-1,4-glucan glucosidases, alkaline extracellular proteases, choline or allanoate transporters, C-22 sterol desaturase, other cytochrome P450 enzymes or NADPH dehydrogenases [19]. An additional important feature that makes _Y. lipolytica_ highly interesting is the remarkable native ability to accumulate large amounts of storage lipids, which on average correspond to 36% \(w/w\) of the biomass [8; 9; 11; 20; 21]. With efficient utilization of hydrophobic substrates as carbon source, this lipid accumulation can exceed 50% of the cell dry weight (CDW) [13]. The lipid profile consists of free fatty acids (FFA), 80-90% triacylglycerlycerols (TAG) with different chain lengths (11% C16:0; 6% C16:1; 28% C18:1; 51% C18:2) and a small quantity of sterol esters (SE), located in a specialized cellular compartment known as the lipid body (LB) [15; 21; 22]. It was reported that when stearin (an industrial product mainly containing palmitic and stearic acid) was exogenously fed, stearic acid (C18:0) could also accumulate intracellularly to significant levels [20]. The lipocentric metabolism of _Yarrowia_ has been thoroughly studied, mainly for the production of advanced biofuels and oleochemicals from carbohydrate feedstocks [23; 24], but also for the production of lipids with composition similar to various exotic fats (e.g., cocoa butter) [20]. Some crucial metabolic traits that give rise to this oleaginous phenotype include a high acetyl-CoA flux, high tricarboxylic acid (TCA) cycle flux, and absence of undesired fermentative capacity [7; 25].