Dynamic Reprogramming of Fungal Cell Walls Underlies Germination and Immune Exposure in Zygomycetous Fungal Pathogens.

Fungal germination is a critical developmental transition that underlies environmental adaptation and pathogenicity, yet how the cell wall is molecularly reprogrammed during this process remains poorly understood. Here we show that germination of Rhizopus delemar involves a developmentally programmed transition from a β-1,3-glucan-rich dormant scaffold to a chitin-chitosan-dominated polarized wall. Using solid-state nuclear magnetic resonance spectroscopy and cytochemistry approaches, we show that resting conidia contains a rigid β-1,3-glucan- and chitosan-rich core beneath a persistent melanin layer. During swelling, this architecture is largely maintained, but germ tube emergence triggers complete shutdown of β-1,3-glucan synthesis and extensive chitin-chitosan enrichment. Distinct chitosan polymorphs are selectively enriched, while mobile polysaccharides are progressively incorporated into the rigid scaffold. This remodeling enhances neutrophil recognition of swollen and germinating conidia. Our study reveals a molecular mechanism linking fungal morphogenesis, cell wall remodeling, and morphotype-specific immune exposure during mucormycosis.