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. 2018 Mar;111(3):311-322.
doi: 10.1007/s10482-017-0952-1. Epub 2017 Sep 30.

The FlbA-regulated predicted transcription factor Fum21 of Aspergillus niger is involved in fumonisin production

David Aerts  1 , Esther E Hauer  1 , Robin A Ohm  1 , Mark Arentshorst  2 , Wieke R Teertstra  1 , Christopher Phippen  3 , Arthur F J Ram  2 , Jens C Frisvad  3 , Han A B Wösten  4
Affiliations

The FlbA-regulated predicted transcription factor Fum21 of Aspergillus niger is involved in fumonisin production

David Aerts et al. Antonie Van Leeuwenhoek. 2018 Mar.

Abstract

Aspergillus niger secretes proteins throughout the colony except for the zone that forms asexual spores called conidia. Inactivation of flbA that encodes a regulator of G-protein signaling results in colonies that are unable to reproduce asexually and that secrete proteins throughout the mycelium. In addition, the ΔflbA strain shows cell lysis and has thinner cell walls. Expression analysis showed that 38 predicted transcription factor genes are differentially expressed in strain ΔflbA. Here, the most down-regulated predicted transcription factor gene, called fum21, was inactivated. Growth, conidiation, and protein secretion were not affected in strain Δfum21. Whole genome expression analysis revealed that 63 and 11 genes were down- and up-regulated in Δfum21, respectively, when compared to the wild-type strain. Notably, 24 genes predicted to be involved in secondary metabolism were down-regulated in Δfum21, including 10 out of 12 genes of the fumonisin cluster. This was accompanied by absence of fumonisin production in the deletion strain and a 25% reduction in production of pyranonigrin A. Together, these results link FlbA-mediated sporulation-inhibited secretion with mycotoxin production.

Keywords: Asexual development; Aspergillus; Fumonisin; Fungus; Mycotoxin; Protein secretion; Secondary metabolism.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Spatial distribution of sporulation (a, b), protein secretion (c, d), and the number of spores that were produced (e) in 8-day-old xylose-grown colonies of the wild-type strain MA234.1 (a, c) and Δfum21 (b, d). Secretion was monitored by immobilizing 14C-labeled secreted proteins on a PVDF membrane that had been placed underneath the colony. Localization and quantification of sporulation was monitored 48 h after removal of the upper membrane of sandwiched colonies
Fig. 2
Fig. 2
Amount of fumonisin B2, B4, and B6 (FB2, FB4, and FB6, respectively) (a) and other secondary metabolites (b) in arbitrary units (a.u.), produced by the wild-type strain MA234.1 (open bars) and Δfum21 (gray shaded bars) in CYA medium. Asterisk indicates significant differences (p ≤ 0.05) between the two strains indicated by the horizontal line below the asterisk
See this image and copyright information in PMC

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