Pka, Ras and RGS Protein Interactions Regulate Activity of AflR, a Zn(II)2Cys6 Transcription Factor in Aspergillus nidulans

Abstract

Sterigmatocystin (ST) is a carcinogenic polyketide produced by several filamentous fungi including Aspergillus nidulans. Expression of ST biosynthetic genes (stc genes) requires activity of a Zn(II)2Cys6 transcription factor, AflR. aflR is transcriptionally and post-transcriptionally regulated by a G-protein/cAMP/protein kinase A (PkaA) signaling pathway involving FlbA, an RGS (regulator of G-protein signaling) protein. Prior genetic data showed that FlbA transcriptional regulation of aflR was PkaA dependent. Here we show that mutation of three PkaA phosphorylation sites in AflR allows resumption of stc expression in an overexpression pkaA background but does not remediate stc expression in a ΔflbA background. This demonstrates negative regulation of AflR activity by phosphorylation and shows that FlbA post-transcriptional regulation of aflR is PkaA independent. AflR nucleocytoplasmic location further supports PkaA-independent regulation of AflR by FlbA. GFP-tagged AflR is localized to the cytoplasm when pkaA is overexpressed but nuclearly located in a ΔflbA background. aflR is also transcriptionally and post-transcriptionally regulated by RasA. RasA transcriptional control of aflR is PkaA independent but RasA post-transcriptional control of AflR is partially mediated by PkaA.

Natural products of filamentous fungi: enzymes, genes, and their regulation

“…269 This inhibitory effect was later found to be partially mediated by PKA at both the transcriptional and posttranscriptional level through aflR regulation. 270,271 Further genetic dissection of A. nidulans signaling components indicated that the G-protein b-and c-subunits, SfaD and GpgA respectively, were required for both cleistothecial and sterigmatocystin formation, 272,273 leading to the proposal that b/c and FadAa signaling were directly opposed with regard to sterigmatocystin regulation. 224,267 The role of two other A. nidulans a subunits, GanA and GanB, in sterigmatocystin formation is yet to be elucidated.…”

Presence, Mode of Action, and Application of Pathway Specific Transcription Factors in Aspergillus Biosynthetic Gene Clusters

“…The approach of replacing the promoter of PSTF can work spectacularly well, but not always. This might be due to domain function loss of a PSTF, lack of an unknown natural inducer, requirement for a different or second TF, requirement of a specific precursor, or requirement of post-translational modification of a PSTF, among other possibilities [104]. In some cases, synthetic PSTFs circumvented these problems.…”

Fatty Acids and Oxylipins as Antifungal and Anti-Mycotoxin Agents in Food: A Review

“…G protein signaling has been shown to regulate the synthesis of aflatoxin and its precursor, sterigmatocystin (ST). The Gα subunit FadA and its RGS FlbA are part of an adenylate cyclase/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) (PkaA) pathway, which controls ST production in A. nidulans via transcriptional and posttranscriptional regulation of aflR [67][68][69]. In recent years, studies have shown that oxylipins, as ligands, are sensed by G-protein coupled receptors (GPCRs) to regulate physiological processes in Aspergillus [70][71][72].…”