Smallestbittertastereceptor(T2Rs)generepertoireincarnivores

Bittertastereceptionispresumablyassociatedwithdietaryselection,preventinganimalsfromingestingpotentiallyharmfulcompounds.Accordingly,carnivores,whoencounterthesetoxicsubstanceslessoften,shouldhavefewergenesassociatedwithbittertastereceptioncomparedwithherbivoresandomnivores.Toinvestigatethegeneticbasisofbittertastereception,weconfirmedbittertastereceptor(T2R)genespreviouslyfoundinthegenomesequencesoftwoherbivores(cowandhorse),twoomnivores(mouseandrat)andonecarnivore(dog).Wealsoidentified,forthefirsttime,theT2Rrepertoirefromthegenomeofotherfourcarnivorespecies(ferret,giantpanda,polarbearandcat)anddetected17-20bitterreceptorgenesfromthefivecarnivoregenomes,including12-16intactgenes,0-1partialbutputativelyfunctionalgenes,and3-8pseudogenes.BoththeintactT2RgenesandthetotalT2Rgenenumberamongcarnivoreswerethesmallestamongthetestedspecies,supportingearlierspeculationsthatcarnivoreshavefewerT2Rgenes,herbivoresanintermediatenumber,andomnivoresthelargestT2Rgenerepertoire.Tofurtherexplainthegeneticbasisforthisdisparity,weconstructedaphylogenetictree,whichshowedmostoftheT2Rgenesfromthefivecarnivoreswereone-to-oneorthologsacrossthetree,suggestingthatcarnivoreT2Rswereconservedamongmammals.Similarly,thesmallcarnivoreT2Rfamilysizewaslikelyduetorareduplicationevents.Collectively,theseresultsstrengthenargumentsfortheconnectionbetweenT2Rgenefamilysize,dietandhabit.