How do parasitic fungi sense optimal fruiting conditions from inside the host?
In model fungi, the G protein coupled receptor Gpr1 is known to sense sugars and upregulate a cAMP linked PKA pathway, while in pathogenic strains, it senses Methionine. This probably is the environmental cue that sets off fruiting. There is a recently published extensive review too: Heterotrimeric G protein signaling in filamentous fungi



Reference


Li, Liande, Sara J. Wright, Svetlana Krystofova, Gyungsoon Park, and Katherine A. Borkovich. “Heterotrimeric G Protein Signaling in Filamentous Fungi.” Annual Review of Microbiology 61, no. 1 (October 2007): 423–452.