S AMORIM-VAZ¹, V TRAN², S PRADERVAND², M PAGNI², AT COSTE¹, D SANGLARD<sup>1

1</sup>Institute of Microbiology, University Hospital Lausanne and University Hospital Center, Lausanne, Switzerland, ²Vital-IT Group, SIB Swiss Institute of Bioinformatics, Lausanne, Switzerland

Candida albicans systemic infections in immunocompromised patients result in over 40% fatalities, despite the available treatments. Novel therapeutic agents are needed, and specific mediators of pathogenesis could be used as targets. To better understand C. albicans pathogenesis mechanisms, a genetic screen was recently carried out to identify factors necessary to establish an infection in animal models (mice and larvae of Galleria mellonella). Among the genes identified as playing a role in virulence, we identified MBF1, a putative transcriptional regulator in C. albicans, and which identified was required for a successful systemic infection in both infection models. To identify potential MBF1 targets, we compared the gene expression profiles of a null mutant (mbf1Δ/Δ) and wild type strain SC5314, both in in vitro conditions and during systemic infection of mice and G. mellonella larvae. In vivo genome-wide transcriptional profiling was made possible by an RNA enrichment approach that allowed deep sequencing of C. albicans transcripts directly from infected animals. Our results suggested, among other observations, a connection between MBF1 and GCN4, since some known GCN4 targets were significantly regulated in the mbf1Δ/Δ mutant, such as GLN3, TTR1 or RHR2. It is known that GCN4 and MBF1 interact in Saccharomyces cerevisiae and this association is involved in regulation of nitrogen metabolism. Consistent with this hypothesis, the mbf1Δ/Δ mutant was sensitive to 3-amino-1,2,4-triazole (3-AT, a competitive inhibitor of the HIS3 product) as did a gcn4Δ/Δ mutant. Undergoing work includes co-immunoprecipitation (Co-IP) of Mbf1 and Gcn4, in order to verify whether a direct interaction exists between the two proteins. In addition, since Mbf1 is a putative transcriptional coactivatior of other regulators, we are currently determining other client proteins of Mbf1 by tandem affinity purification. In conclusion, we achieved the in vivo transcriptome of a mutant with reduced virulence, thus highlighting the utility of the fungal RNA enrichment from infected host tissues. MBF1 is being further characterized in order to clarify its involvement in C. albicans pathogenesis.