Orchestration of chitin synthesis in Candida albicans

Chitin synthesis and septum formation are highly regulated processes, fundamental for cell viability, taking place during cell division. Understanding fungal septation may lead to the identification of novel drug targets for future antifungal chemotherapeutic strategies. In the pathogenic fungus Candida albicans, a primary septum consisting of chitin is formed between two dividing cells. In C. albicans, chitin is synthesised by four chitin synthases: Chs1, Chs3, Chs2 and Chs8 and all four enzymes localise to sites of septation. Strains expressing pairs of fluorescently tagged chitin synthases were generated and assessed by live-cell fluorescence microscopy to elucidate the temporal and spatial distribution of the chitin synthases in relation to each other. It was observed that the timing and pattern of configuration of the chitin synthases during septation is different in yeasts and hyphae with Chs3 potentially playing a role in secondary septum formation. This information was used to generate a new model for septal chitin synthesis during septation in C. albicans yeasts and hyphae. Proteomic analyses of GFP pull down assays identified further proteins that may be part of the septation complex. Through Chs3-GFP immunoprecipitation, it was shown that Chs3 may interact with different sets of proteins in yeasts versus hyphae. Moreover, the localisation of the chitin synthases in the absence of CaCdc10 and CaBni4 whose homologues are involved in tethering of ScChs3 at the septation site of S. cerevisiae was assessed. This study demonstrates that the septation model regarding the regulation and tethering of the chitin synthases to septation site is different between C. albicans and S. cerevisiae yeast cells, as well as between C. albicans yeasts and hyphae. This study has extended our knowledge of how chitin synthesis is orchestrated during septation and identified proteins that might be involved in septum formation.