PSIX-14 Genome-wide association study for PTC Sensitivity in Rangeland Rams.

Abstract Sheep are known to have diverse tolerance for sagebrush and other bitter-tasting forages. Selecting sheep with higher tolerances for these bitter plants may allow for better utilization of range forages and contribute to rangeland management strategies. Previous studies have used the bitter-tasting compound phenylthiocarbamide (PTC) to distinguish between animals that are highly sensitive (“supertasters”), have some sensitivity (“tasters”), or have no sensitivity (“nontasters”) to bitter taste. While a family of taste receptor genes (TAS2R) have been associated with PTC sensitivity, the current literature lacks precise understanding of other genes that impact taste perception and preference. To address this, a genome-wide association study (GWAS) approach was used to investigate associations between PTC taster status and single nucleotide polymorphism (SNP) markers in rangeland sheep. In total, 116 rams belonging to Targhee, Rambouillet, and Polypay breeds were tested in a two-day trial with 0.20 mM and 2.03 mM concentrations of PTC delivered in water. The proportion of PTC-dosed water ingestion out of total water ingestion was calculated for each test. Using the data from the 2.03 mM dose trial, n = 30 rams were identified as supertasters (PTC ingestion = 0.05 - 0.31) and the remaining n = 86 rams were identified as tasters (PTC ingestion = 0.33 to 0.98) for the purposes of case-control GWAS design. One genome-wide significant SNP was identified (rs399606980, p-value = 2.53e-07) through the efficient mixed-model association expedited (EMMAX) in a dominant inheritance model. This SNP is positioned within the second intron of the gene PBX homeobox 1 (PBX1), a transcription factor belonging to the three amino acid loop extension (TALE) family. Of particular interest, Pbx1 is necessary for the neurogenesis of periglomerular cells of the olfactory bulb and has been found to be expressed in olfactory sensory areas of the adult brain. Many studies have demonstrated the strong relationship between scent and taste and olfaction is known to play a dominant role in the perception of tasting food. It is possible that splice variants or differential expression patterns of PBX1 in the olfactory bulb affect the overall perception of PTC, but further research is needed to elucidate the relationship between PBX1 and TAS2R-family genes within the context of bitter taste perception in sheep. These findings may improve rangeland sustainability efforts and allow sheep producers the ability to preferentially select sheep best suited for rangeland foraging systems.