A BRCT Domain-Containing Protein Induced in Early Phagocytosis Plays a Crucial Role in Mucorales Pathogenesis
Mucormycosis, caused by Mucoralean fungi, is among the most lethal fungal diseases, and a deeper understanding of its pathogenesis is urgently needed. In this study, we examined the early stages of fungal interaction with host macrophages using Mucor lusitanicus and Rhizopus microsporus as model organisms. Transcriptomic profiling of virulent (WT) and an RNAi-deficient strain (r3b2?) of M. lusitanicus strains during phagocytosis uncovered thousands of differentially expressed genes (DEGs), highlighting early metabolic activation as a key survival strategy inside the phagosome. Enriched pathways included amino acid transport, nucleotide metabolism, and translation, reflecting an adaptive fungal response to nutrient deprivation and host immune stress. Integrative analyses of mRNA and sRNA profiles also revealed a critical role of the RNAi pathways in modulating gene expression during infection. Building on these observations, we identified four chromatin- and transcription-related candidate virulence genes—brca1, box, hist1, and hda10—which were strongly upregulated during phagocytosis and regulated by RNAi. Functional validation through gene deletion in M. lusitanicus and disruption in R. microsporus revealed that while loss of these genes in M. lusitanicus did not significantly affect virulence, R. microsporus mutants for brca1, hist1, and hda10 showed attenuated virulence in a murine model. Our findings suggest that although M. lusitanicus remains a valuable tool for genetic manipulation, species-specific differences must be considered when studying virulence. The study also underscores the importance of using multiple Mucorales models to uncover conserved and divergent strategies employed by pathogenic fungi. These insights contribute to a broader understanding of fungal adaptation, immune evasion, and the identification of novel targets for antifungal intervention. Overall design: Transcriptomic analysis using RNA-seq to study the impact of R3B2 gene deletion on gene expression at both messenger RNA (mRNA) and small RNA (sRNA) levels in Mucor lusitanicus. Wild-type strain MU636 and r3b2? mutant MU412 were used. Total RNA was extracted from samples collected after 1 hour of interaction with macrophages and after 1 hour of saprophytic growth as a control condition. Three biological replicates were performed for each condition.