BACKGROUND Taste is fundamental to diet selection in vertebrates. Genetic basis of sweet taste receptor in the shaping of food habits has been extensively studied in mammals and birds, but scarcely studied in fishes. Grass carp is an excellent model for studying vegetarian adaptation, as it exhibits food habit transition from carnivory to herbivory. RESULTS We identified six sweet taste receptors (gcT1R2A-F) in grass carp. The four gcT1R2s (gcT1R2C-F) have been suggested to be evolved from and paralogous to the two original gcT1R2s (gcT1R2A and gcT1R2B). All gcT1R2s were expressed in taste organs and mediated glucose-, fructose- or arginine-induced intracellular calcium signaling, revealing they were functional. In addition, grass carp was performed to prefer fructose to glucose under a behavioral experiment. Parallelly, compared with gcT1R2A-F/gcT1R3 co-transfected cells, gcT1R2C-F/gcT1R3 co-transfected cells showed a higher response to plant-specific fructose. Moreover, food habit transition from carnivory to herbivory in grass carp was accompanied by increased gene expression of certain gcT1R2s. CONCLUSIONS We suggested that the gene expansion of T1R2s in grass carp was an adaptive strategy to accommodate the change in food environment. Moreover, the selected gene expression of gcT1R2s might drive the food habit transition from carnivory to herbivory in grass carp. This study provided some evolutional and physiological clues for the formation of herbivory in grass carp.

中文翻译：

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草鱼（Ctenopharyngodon idellus）甜味受体基因的扩增与素食主义者的适应相吻合。

背景技术味道对于脊椎动物的饮食选择至关重要。甜味受体在饮食习惯形成中的遗传基础已在哺乳动物和鸟类中得到了广泛研究，但在鱼类中却鲜有研究。草鱼是研究素食适应性的极佳模型，因为它表现出从食肉到食草的饮食习惯转变。结果我们在草鱼中鉴定出六个甜味受体（gcT1R2A-F）。已建议将四个gcT1R2（gcT1R2C-F）从两个原始gcT1R2（gcT1R2A和gcT1R2B）进化而来。所有gcT1R2在味觉器官中表达，并介导葡萄糖，果糖或精氨酸诱导的细胞内钙信号传导，表明它们具有功能。另外，在行为实验中，对草鱼进行了偏爱果糖而不是葡萄糖的研究。平行地 与gcT1R2A-F / gcT1R3共转染的细胞相比，gcT1R2C-F / gcT1R3共转染的细胞对植物特异果糖的反应更高。此外，草鱼的饮食习惯从食肉动物向草食动物的转变伴随着某些gcT1R2s基因表达的增加。结论我们认为草鱼中T1R2s的基因扩增是适应食物环境变化的一种自适应策略。此外，gcT1R2s的选定基因表达可能会推动草鱼的饮食习惯从食肉动物向食草动物转变。该研究为草鱼草食性的形成提供了一些进化和生理学线索。食物习性从草鱼的食肉动物向食草动物的转变伴随着某些gcT1R2s基因表达的增加。结论我们认为草鱼中T1R2s的基因扩增是适应食物环境变化的一种自适应策略。此外，gcT1R2s的选定基因表达可能会推动草鱼的饮食习惯从食肉动物向食草动物转变。该研究为草鱼草食性的形成提供了一些进化和生理学线索。食物习性从草鱼的食肉动物向食草动物的转变伴随着某些gcT1R2s基因表达的增加。结论我们认为草鱼中T1R2s的基因扩增是适应食物环境变化的一种自适应策略。此外，gcT1R2s的选定基因表达可能会推动草鱼的饮食习惯从食肉动物向食草动物转变。该研究为草鱼草食性的形成提供了一些进化和生理学线索。