|Chang, Perng Kuang
|DIANA DI MAVUNGU, JOSE - Ghent University
Submitted to: Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2016
Publication Date: 7/30/2016
Citation: Chang, P.-K., Scharfenstein, L.L., Ehrlich, K., Diana Di Mavungu, J. 2016. The Aspergillus flavus fluP-associated metabolite promotes sclerotial production. Fungal Biology. 120:1258-1268.
Interpretive Summary: Fungi produce a number of secondary metabolites that are of therapeutic values or are harmful to humans and animals. Some fungal metabolites have a protective role to the producing fungi. In an effort to better understand how metabolites produced by Aspergillus flavus affect its own development, we characterized a gene that is required for the synthesis of a polyketide metabolite. We showed that the gene product is involved in the production of a diffusible compound that promotes production of sclerotia. Sclerotia are survival structures of hardened mycelial aggregates that are capable of remaining dormant in harsh environmental conditions. This knowledge will aid in unraveling the mechanisms responsible for sclerotial production and also in understanding the fungus’ ability to survive, propagate and disseminate in agricultural fields.
Technical Abstract: Aspergillus flavus is able to synthesize a variety of polyketide-derived secondary metabolites including the hepatocarcinogen, aflatoxin B1. The fungus reproduces and disseminates predominantly by production of conidia. It also produces hardened mycelial aggregates called sclerotia that are used to cope with unfavorable growth environments. In the present study, we examined the role of A. flavus fluP, the backbone polyketide synthase gene of secondary metabolite gene cluster 41, on fungal development. The A. flavus CA14 fluP deletion mutant (Af'fluP) grew and accumulated aflatoxin normally but produced a lower amount of sclerotia than the wild type. This was also true for the A. parasiticus BN9 fluP deletion mutant (Ap'fluP). The A. flavus fluP gene was positively regulated by developmental regulators of VeA and VelB but not by the global regulator of secondary metabolism, LaeA. Overexpression of fluP in Af'fluP (OEfluP) elevated its ability to produce sclerotia compared to that of the wild-type. Co-culture of OEfluP with wild-type CA14, Af'fluP, Ap'fluP, or an A. flavus pptA deletion mutant (Af'pptA) incapable of producing functional polyketide synthases also allowed increased sclerotial production of the respective strains at edges where colonies made contact. Acetone extracts of OEfluP but not of Af'fluP exhibited the same effect in promoting sclerotial production of Af'fluP. These results suggest that FluP polyketide synthase is involved in the synthesis of a diffusible metabolite that could serve as a signal molecule to regulate sclerotiogenesis.