Carbon sources effects on conidiation in Penicillium camemberti: a transcriptomic analysis

The asexual reproduction cycle of the cheese-ripening fungus Penicillium camemberti is typical for a filamentous ascomycete fungus. It involves the production of conidia by successive mitotic divisions from specialized cells called conidiophores. Conidia are used for inoculating the fungus onto French soft cheeses and are produced industrially by submerged fermentation. However, the impact of mycelium macromorphology on conidial production for this type of fermentation has been little investigated. By studying the physiological effect of different sources and concentrations of carbohydrates at the laboratory scale, it was observed that the fungus takes on different morphologies associated with varying ability to produce conidia. Especially, a dispersed morphology was not always associated with production of conidia. Through RNA-seq transcriptomic analyses, we followed the expression profiles of P. camemberti genes during the time course of liquid cultures made in the presence of two concentrations of glucose, one of sucrose and one with a mix of glucose and fructose, which are conditions for which P. camemberti presents varying morphologies and efficiencies to produce conidia. This led to confirm that, like other ascomycetes, P. camemberti likely uses the conidiation pathway first described in the model fungus Aspergillus nidulans. It also enabled the identification of a potential conidiation-inhibiting transcription factor, specific to Eurotiales and only upregulated in conditions without conidia production. Functional studies of its ortholog in A. nidulans, for which the conidiation pathway has been extensively studied, should allow to verify whether this factor indeed plays a role in the asexual cycle.