Phylogenetic Study Of The Bitter Taste Receptor Gene (T2Rs) Family Of Canine

Taste, together with other sensory information, such as the vision and olfaction, can help animals to evaluate and choose food. Most mammals can perceive five basic taste qualities: sweet, umami, bitter, salty, and sour. Diet shapes the evolution of the species taste receptor genes, in the process of getting energy for maximizing and potentially toxic substances for minimizing, the evolution of taste genes was likely to reflect the evolution of mammals‘ specific diets and their ecological environment. Therefore, understanding the relationship of the taste to the species and their living environment can help us know the fact that how the ecological factors affect the genomes of species and the mechanism of species adapting to the environment. Most poisonous substances tend to be bitter, and bitter taste receptor genes can allow animals to detect and avoid toxins in food which play a function of defense mechanism.There are many researches on vertebrates about the bitter taste receptor genes in domestic and abroad, it focuses on the expansions and contractions of the gene family throughout vertebrates, especially among tetrapods; the divergence of bitter taste receptor genes among different diets; the functional study of bitter taste receptor genes in human and mice. The differentiation and phylogenetic studies for bitter taste receptor gene in population mainly focus on people. The research on canine mainly concentrated in the dog. Canine as on e of the carnivores species, including 12 genera 34 species, are distributed widely across the globe. Canine has a wide difference in sharp, size, habitat, diet, habit among different genera, so it can be used as a model organism for the phylogenetic studies in bitter taste receptor genes.In this study, we use the bitter taste receptor genes as molecular genetic markers; use some biology software, such as PAML4.0, Datamonkey, Mega6.0, Primer5.0, Clustal X1.83, TMHMM sever 2.0, DNAMAN, based on molecular systematic and bioinformatics methods to analyze and discuss the molecular evolution of the canine. The analysis including the sequence of amino acid composition, the sequence of base composition, the phylogeny, the hydrophobicity of simulate protein, the transmembrane, selection pressure, using neighbor-joining(NJ), the maximum likelihood(ML) reconstruction of the mammal part of the phylogenetic relationships among species, we gain the following results:1) In this study, we first obtained the coding sequence of bitter taste receptor from eight canines; they are wolf, jackal, red fox, corsac fox, Tibetan fox, fennec fox, maned wolf, raccoon dog. Wolf and maned wolf has 21 bitter taste receptor genes, the four foxes and jackal have 20 genes, and the raccoon dog has 16 genes.2) Based on the genome data of the dog, with other species reported in GeneBank of bitter taste receptor gene sequence, we found T2R42 gene in maned wolf become pseudogene; T2R4 gene could not be PCR in foxes, and it became pseudogene in other canine; the ratio of the pseudogene was also different in canine, the highest for maned wolf(33.3%), the lowest for four foxes and raccoon dog(25%).3) The phylogenetic analysis show that many gene duplication events occurred prior to the separation of these mammals; different bitter taste receptor gene has already formed before the differentiation of the species; in canine, the bitter taste receptor gene are all together in the phylogenetic tree, some of them have specificity between genera; the difference of bitter taste receptor gene between dog and wolf is little, the diet change have no directly relationship with the bitter taste receptor gene.4) Selective pressure analysis show that bitter taste receptor gene is under strong purifying selection in the process of canine evolution; by Datamonkey, suggesting that most bitter taste receptor genes are equal purifying selection; by PAML, we found T2R7 and T2R10 experienced a positive selection.