A BRCT domain-containing protein induced in early phagocytosis plays a crucial role in the pathogenesis of the mucoralean Rhizopus microsporus

Mucormycosis, caused by mucoralean fungi, is among the most lethal fungal diseases, and a deeper understanding of its pathogenesis is urgently needed. Transcriptomic profiling of virulent strain (WT) and an RNAi-deficient strain (r3b2Δ) of M. lusitanicus 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 disruption of their orthologs in the clinically relevant pathogen R. microsporus significantly reduced virulence in healthy mice, particularly in the brca1, hda1, and hist1 mutants. The brca1 knockout mutant also exhibited lower fungal burden in the brain and lungs and reduced survival rates after exposure to peritoneal immune cells. In contrast, their deletion in M. lusitanicus had no detectable impact on virulence in healthy animal models, highlighting species-dependent differences in pathogenic potential. These results demonstrate that M. lusitanicus is a valuable genetic model. However, combining studies across multiple Mucorales species is essential to uncover both conserved and species-specific mechanisms of host adaptation and virulence. These insights contribute to a broader understanding of fungal adaptation, immune evasion, and the identification of novel targets for antifungal intervention.