Proteins Expressed during Hyphal Aggregation for Fruiting Body Formation in Basidiomycetes

The first visible step in fruiting body development in basidiomycetes is the formation of small hyphal knots by localized intense branching of hyphae of restricted length accompanied by hyphal aggregation. In Coprinopsis cinerea, the first not yet fruiting-specific step of hyphal branching occurs in the dark, the second step requires a light signal. Hyphal aggregation implies cell-cell contacts and protein interactions on the outer cell walls are anticipated. Few protein candidates were identified and discussed in the past for such function. Amongst were the galectins of C. cinerea and the Aa-Pri1 protein (aegerolysin) of Agrocybe aegerita that are specifically expressed during the step of hyphal aggregation as well as during subsequent primordia development. In this study, we follow up the distribution of genes for proteins with lectin and/or hemolysin function in the steadily growing number of available genomes of basidiomycetes. Neither galectin genes nor genes for other lectins nor Aa-pri1-like genes nor other hemolysin genes are present in all mushroom species, making an essential role for such functions in hyphal aggregation unlikely.