Filamentation Profiling Reveals Multiple Transcription Regulators Contributing to the Differences Between Candida albicans and Candida dubliniensis.

Candida dubliniensis is the most closely related species to C. albicans, one of the leading causes of fungal infections in humans. However, despite sharing many characteristics, C. dubliniensis is significantly less pathogenic. To better understand the molecular underpinnings of these dissimilarities, we focused on the regulation of filamentation, a developmental trait fundamental for host colonization. We generated a collection of 44 C. dubliniensis null mutants of transcription regulators whose orthologs in C. albicans had been previously implicated in filamentous growth. These regulators are very similar at the sequence level, but phenotypic screening identified several mutants with contrasting interspecific filamentation phenotypes beyond previously known differences. Bcr1, a well-known regulator of biofilm formation, stands out as its mutant mainly showed a filamentation defect in C. dubliniensis. Phenotypic and transcriptional characterization showed that the bcr1 defect is condition dependent and that this regulator plays a central role in the filamentation of C. dubliniensis, possibly by regulating the hyphal activator Ume6. Overall, our results suggest that several regulatory pathways are involved in the filamentation differences between C. albicans and C. dubliniensis and show that the C. dubliniensis mutant collection is a valuable resource to compare, at a molecular level, these species of medical relevance.