Reverberi M, Punelli M, LA STARZA S., Scala V, Scarpari M, Uva P, Mentzen W, Dolezal A, Woloshuk C, Pinzari F, Fabbri A, Payne G, Fanelli C (2013). GENOTYPIC AND PHENOTYPIC VERSATILITY OF ASPERGILLUS FLAVUS DURING MAIZE EXPLOITATION

Aspergillus flavus is a cosmopolitan fungus able to respond to external stimuli and to shift both its trophic behaviour and the production of secondary metabolites, including that of the carcinogen aflatoxin (AF). To better investigate the versatility of this fungus, we examined genetic and phenotypic responses within the fungus when grown under four conditions that mimic different ecological niches ranging from saprophytic to parasitic growth. Global transcription changes were observed in both primary and secondary metabolism in response to these conditions, particularly in secondary metabolism where transcription of nearly half of the predicted secondary metabolite clusters changed in response to the trophic states of the fungus. The greatest transcriptional change was found between saprophytic and parasitic growth, particularly related to the secondary metabolite cluster 32. This cluster contains two fungal effectors: the necrosis and ethylene-inducing peptide and a salicylate hydroxylase. This cluster is apparently controlled by two ethylene responding transcription factors. We inactivated one of these for checking change in A. flavus virulence phenotype on maize. We also examined tolerance of A. flavus to oxidative stress and found that growth and secondary metabolism were altered in a superoxide dismutase (sod) mutant and an alkyl-hydroperoxide reductase (ahp) mutant of A. flavus. Data presented in this study show a multifaceted response of A. flavus to its environment and suggest that oxidative stress and secondary metabolism are important in the ecology of this fungus, notably in its interaction with host plant and in relation to changes in its lifestyle (i.e. saprobic to pathogenic)