Filamentous development is associated with the ability to cause infections and colonize the host in pathogenic Candida species.Candida tropicalis is one of the major fungal pathogens of humans.The conserved transcriptional repressor Tup1 plays a critical role in the regulation of transcription and filamentation in yeast species.Despite its central role,the full coding sequence of TUP1 has not been found in the reported genome sequence of C.tropicalis to date.In this study,we report the identification of Tup1 and characterize its role in filamentous growth in C.tropicalis.As expected,C.tropicalis Tup1 exhibits general conserved features to the orthologs of other fungi in terms of its structure and function.Deletion of TUP1 in C.tropicalis leads to increased filamentation under several culture conditions.However,Tup1 indeed exhibits species-specific roles in the regulation of filamentous development in C.tropicalis.For example,unlike the tup1/tup1 mutant of Candida albicans,the tup1/tup1 mutant of C.tropicalis is able to exist in the yeast form at low temperatures or in the presence of N-acetylglucosamine (GIcNAc).Acidic pH conditions also favor the yeast form of the tup1/tup1 mutant of C.tropicalis.Quantitative real-time PCR (qRT-PCR) assays indicate that Tup1 may regulate filamentous development through the transcriptional control of key filamentation regulators in C.tropicalis,such as Ume6,Brg1,Wor1,Sfl2,Ahr1,and Zcf3.Taken together,our findings demonstrate both conserved and species-specific roles of Tup1 in the regulation of filamentation and provide novel insights into the biology of C.tropicalis.