Abstract

Candida albicans is a major fungal pathogen capable of undergoing phenotypic transitions in response to environmental cues. These morphological changes are regulated by transcription factors that coordinate key developmental pathways. In this study, we investigate the role of Opaque and Filamentation Inducer 1 (Ofi1) in modulating white-opaque switching and filamentous growth. Overexpression of OFI1 under the ACT1 promoter induced white-to-opaque switching up to 28% in normally non-switching MTL a/α cells, while in MTL homozygous strains, it significantly enhanced white-to-opaque switching, reaching 100%. Our study demonstrates that Ofi1 is a dosage-dependent transcription factor regulating the white-to-opaque and yeast-tofilament transition in C. albicans. Conversely, the deletion of ofi1 greatly reduced the switching frequency, highlighting its essential role in both initiating and maintaining the opaque state. We propose that Ofi1 interacts with the transcription factors Wor2, Wor4, and Czf1, serving as a central regulator of white-opaque switching. Our results suggest that while Ofi1 and Wor2 independently regulate white-to-opaque switching, Wor2 does not contribute to filamentation. Also, the functional arrangement of Czf1 and Ofi1 is completely different in white-to-opaque switching and yeast-to-hyphae transition processes. The phenotype caused by the absence of czf1 is suppressed by overexpression of OFI1 in white-to-opaque switching but completely blocks the function of excess Ofi1 in filamentation. Moreover, deleting wor4 completely blocks white-toopaque switching, but OFI1 overexpression can partially bypass this defect. In filamentation, the ability of Ofi1 to compensate for wor4 deletion depends on the medium, fully restoring filamentation in BSA-supplemented YPD but not in GlcNAc-induced conditions, suggesting Wor4 and Ofi1 regulate filamentation through distinct pathways. Furthermore, our findings highlight a potential role for WOR4 in the Lee’s GlcNAc solid media to induction of hyphal growth.