Fungal adhesion protein guides community behaviors and autoinduction in a paracrine manner

Abstract

Microbes live mostly in a social community rather than in a planktonic state. Such communities have complex spatiotemporal patterns that require intercellular communication to coordinate gene expression. Here, we demonstrate that Cryptococcus neoformans, a model eukaryotic pathogen, responds to an extracellular signal in constructing its colony morphology. The signal that directs this community behavior is not a molecule of low molecular weight like pheromones or quorum-sensing molecules but a secreted protein. Znf2, a master regulator of morphogenesis in Cryptococcus, is necessary and sufficient for the production of this signal protein. Cfl1, a prominent Znf2-downstream adhesion protein (adhesin), was identified to be responsible for the paracrine communication. Consistent with its role in communication, Cfl1 is highly induced during mating colony differentiation, and some of the Cfl1 proteins undergo shedding and are released from the cell wall. The released Cfl1 is enriched in the extracellular matrix and acts as an autoinduction signal to stimulate neighboring cells to phenocopy Cfl1-expressing cells via the filamentationsignaling pathway. We further demonstrate the importance of an unannotated and yet conserved domain in Cfl1's signaling activity. Although adhesion proteins have long been considered to be mediators of microbial pathogenicity and the structural components of biofilms, our work presented here provides the direct evidence supporting the signaling activation by microbial adhesion/matrix proteins.fungal community behavior | extracellular matrix signaling | fungal dimorphism | flocculin

A Family of Secretory Proteins Is Associated with Different Morphotypes in Cryptococcus neoformans

“…Cell flocculin 1 (Cfl1), a hypha-specific protein of Cryptococcus, was the first adhesin identified in the phylum Basidiomycota (16)(17)(18). CFL1 is one of the most induced genes during Cryptococcus sexual development (17,18).…”

“…CFL1 is one of the most induced genes during Cryptococcus sexual development (17,18). The Cryptococcus adhesin Cfl1 is unique in that it does not contain a common domain structure present in the known ascomycete fungal adhesins, such as a C-terminal glycosylphosphatidylinositol (GPI) anchor, an N-terminal carbohydrate or peptide binding domain, or the middle domain containing serine/threonine-rich repeats (6,19).…”

“…Cfl1 is both cell wall associated and released. Released Cfl1 acts as a signal to regulate colony morphology in autocrine and paracrine manners (18). Therefore, cells expressing Cfl1 can induce the expression of endogenous Cfl1 in neighboring cells, which leads to the formation of biofilm and the production of hyphae (18).…”

“…The domain organization of Cfl1 shows that it contains an N-terminal EGF motif and an amylogenic region that has a predicted function in cell-cell adhesion (18). The C-terminal region containing 80 amino acid residues is highly conserved among Cfl1 homologs across different basidiomycetous species and is named the SIGC domain (signal C-terminal domain) (18).…”

“…The C-terminal region containing 80 amino acid residues is highly conserved among Cfl1 homologs across different basidiomycetous species and is named the SIGC domain (signal C-terminal domain) (18). Interestingly, the genome of Cryptococcus neoformans var.…”