When compared to modern lean-type breeds, Portuguese local Alentejano (AL) and Bísaro (BI) pig breeds present a high potential for subcutaneous and intramuscular fat (IMF) deposition which contributes for better meat quality. The aim of this work was to explore the genome function to better understand the underlying physiological mechanisms associated with body fat accretion. Dorsal subcutaneous fat samples were collected at slaughter from adult animals (n = 4 for each breed) with~150 kg body weight. Total RNA was obtained and sequenced for transcriptome analysis using DESeq2. A total of 458 differentially expressed (DE) genes (q-value < 0.05) were identified, with 263 overexpressed in AL and 195 in BI. Key genes involved in de novo fatty acid biosynthesis, elongation and desaturation were upregulated in AL such as ACLY, FASN, ME1, ELOVL6 and SCD. A functional enrichment analysis of the DE genes was performed using Ingenuity Pathway Analysis. Cholesterol synthesis is suggested to be higher in AL via SREBF2, SCAP and PPARG, while lipolytic activity may be more active in BI through GH and AMPK signalling. Increased signalling of CD40 together with the predicted activation of INSIG1 and INSIG2 in BI suggests that this breed is more sensitive to insulin whereas the AL is less sensitive like the Iberian breed.Genes 2020, 11, 422 2 of 20 inherent genetic value for biodiversity, local breeds are used to produce high quality dry-cured meat products, representing an important role in local economies, culture and landscape as the basics of sustainable local pork chains [2,4].Alentejano (AL) and Bísaro (BI) are the two main Portuguese pig breeds. AL evolved from the primitive Sus scrofa mediterraneus, belongs to the Mediterranean group of breeds [5] and is genetically similar to the Iberian (IB) pig [6]. This breed is commonly raised in the south of Portugal and generally characterized by its light bone structure, black color, short and slim extremities and energetic nature [7]. A medium-sized pig, the AL grows at a low rate (except under the finishing phase "montanheira") and presents a low prolificacy [8]. On the other hand, its high and early adipogenic activity provides a meat and fat composition that is attractive for both fresh meat market and for processing high-grade sausage and dry cured products [9,10]. Traditionally, the AL pig is raised under extensive conditions in an integrated pastoral system ("montado") and during the fattening season is fed with acorns from the existing Quercus forests from October to February [5,7]. BI breed belongs to the Celtic group [5], sharing ancestors with highly productive breeds such as Large-White and Landrace. Production of BI is distributed throughout the north of Portugal, from the Tagus River to the northern border with Spain. It is characterized by its docile temperament, presenting a large body with large legs, head and shoulders. BI pig presents a higher prolificacy and productivity than AL, though lower than other genotypes with similar origins but raised under intensive ...