Genome-wide mRNA and miRNA analysis in the early stages of germ tube outgrowth in Coprinopsis cinerea.

Coprinopsis cinerea is a model mushroom-forming basidiomycete which produces basidiospores during sexual reproduction. This fungus is widely used to study fruiting body formation and development. Molecular mechanisms controlling its growth from vegetative mycelium to multicellular mature fruiting body have been studied extensively. However, little is known about the underlying biological processes during germ tube outgrowth or the transition from basidiospores to multinucleate hyphae. To better understand sexual spore germination in fungi, here we examined the time-dependent cellular events at resting, germinating and fully germinated basidiospores of C. cinerea by genome-wide transcriptional and post-transcriptional analyses and by carbohydrate composition analysis. Our results revealed a high demand of protein degradation, and biosynthesis of various compounds at the early stage of basidiospore gemination and dynamic changes of carbohydrate metabolism throughout the germination process. Seven microRNA-like RNAs (milRNAs) were identified in the resting basidiospores of C. cinerea, six of which were basidiospore-specific. Glycogen and trehalose were shown to be the carbon sources supporting the initiation of germ tube outgrowth. One basidiospore-specific milRNA, cci-milR-37, was found to be a potential regulator of glycogen metabolic pathways related to vegetative hyphal growth. Our results demonstrated the mRNA and miRNA-mediated regulation on energy production, protein and carbohydrate metabolisms at the early developmental stages of germ tube to form totipotent hyphae. To our knowledge, this is the first study to show the roles of miRNAs in mushroom basidiospore germination and out-growth.