Super-tasters are extremely sensitive to thiourea and have a polymorphism in the TAS2R38 coding for the specific receptor. However, super-tasters are more sensitive to other stimuli, and have more taste fungiform papillae (FP) than non-tasters. In addition, PROP sensitivity is associated with the rs2274333 (A/G) polymorphism of the taste bud trophic factor, gustin gene. We studied the relationship between the gustin gene polymorphism, PROP sensitivity, FP density and morphology. Sixty-four subjects were genotyped for TAS2R38 and gustin gene by PCR techniques. PROP sensitivity was assessed by scaling and threshold methods, and FP density, diameter and morphology were determined. ANOVA showed a main effect of the gustin gene for perceiving low concentrations, and of TAS2R38 for tasting high concentrations. ANOVA also revealed that the FP density depends on the gustin gene, and that subjects with genotype AA had the highest density, the shortest diameter and a regular FP morphology, while GG subjects had the lowest density, the largest diameter and an abnormal morphology. FP density of heterozygous subjects was intermediate between AA and GG values, while the diameter and morphology were similar to those of AA subjects. These novel insights indicate that the rs2274333 polymorphism affects FP development and maintenance, and provides the first mechanistic explanation of why super-tasters are more responsive to a broad range of oral stimuli.