The High Osmolarity Glycerol Mitogen-Activated Protein Kinase regulates glucose catabolite repression in filamentous fungi

Abstract

The utilization of different carbon sources in filamentous fungi underlies a complex regulatory network governed by signaling events of different protein kinase pathways, including the high osmolarity glycerol (HOG) and protein kinase A (PKA) pathways. This work unraveled cross-talk events between these pathways in governing the utilization of preferred (glucose) and non-preferred (xylan, xylose) carbon sources in the reference fungus Aspergillus nidulans. An initial screening of a library of 103 non-essential protein kinase (NPK) deletion strains identified several mitogen-activated protein kinases (MAPKs) to be important for carbon catabolite repression (CCR). We selected the MAPKs Ste7, MpkB, and PbsA for further characterization and show that they are pivotal for HOG pathway activation, PKA activity, CCR via regulation of CreA cellular localization and protein accumulation, as well as for hydrolytic enzyme secretion. Protein-protein interaction studies show that Ste7, MpkB, and PbsA are part of the same protein complex that regulates CreA cellular localization in the presence of xylan and that this complex dissociates upon the addition of glucose, thus allowing CCR to proceed. Glycogen synthase kinase (GSK) A was also identified as part of this protein complex and shown to potentially phosphorylate two serine residues of the HOG MAPKK PbsA. This work shows that carbon source utilization is subject to cross-talk regulation by protein kinases of different signaling pathways. Furthermore, this study provides a model where the correct integration of PKA, HOG, and GSK signaling events are required for the utilization of different carbon sources.

Genome-Wide Insight into Profound Effect of Carbon Catabolite Repressor (Cre1) on the Insect-Pathogenic Lifecycle of Beauveriabassiana

“…The direct phosphorylation of CreA S262 by casein kinase A (CkiA) [17] and the indirect phosphorylation of CreA S319 by cyclic AMP (cAMP)-dependent protein kinase (PkaA) in the presence of glucose suggest a requirement of CreA phosphorylation for the fungal CCR [18].Three other phosphosites (S262, S268, and T308) have also proved important for CreA protein accumulation, subcellular localization, DNA binding, and repressed enzyme activities in A. nidulans [19]. In protein-protein interaction studies, the mitogen-activated protein kinase (MAPK) MpkB (Fus3) and the MAPK kinases Ste7 and PbsA (Pbs2) were shown to serve as part of a protein complex that regulates subcellular localization of CreA in the presence of xylan and is dissociated for the performance of CCR upon the addition of glucose [20].…”

Carbon Catabolite Repression in Filamentous Fungi Is Regulated by Phosphorylation of the Transcription Factor CreA

“…4a and b ). Pharmaceutical inhibition of GskA by GSK3β-VII strongly suggests involvement of this protein kinase in CCR via regulation of the mitogen-activated protein kinase kinase (MAPKK) PbsA ( 50 ). These results highlight the regulatory complexity at both transcriptional and posttranslational levels that govern CreA, suggesting additional mechanisms which probably occur posttranslationally.…”

“…7b ). Another protein kinase involved in this process is PkaA (catalytic subunit of PKA), previously shown to be required for CreA stability ( 50 ). ChIP-seq under CCR found CreA-GFP binding to the xlnR and xlnD promoters and additional genes involved in xylan/xylose metabolism ( Fig.…”

“…Under these conditions, CreA is also present in the nucleus with the corepressors, although DNA binding is not occurring. PkaA is also involved indirectly in the process, regulating CreA stability and localization ( 1 , 28 , 50 ). (b) Glucose is taken up into the cells, where it undergoes glycolysis and phosphorylation, a step that has been shown as a crucial signal for CreA translocation to the nucleus.…”

Evidence of a New MoYpd1p Phosphotransferase Isoform in the Multistep Phosphorelay System of Magnaporthe oryzae

“…However, the specific roles of HKs in the regulation of physiological processes are not entirely elucidated [ 7 ]. In addition to Alternaria brassicicola , Aspergillus nidulans , Botrytis cinerea , Fusarium oxysporum, and Neurospora crassa , the rice blast fungus Magnaporthe oryzae (anamorph Pyricularia oryzae ) is an important model organism for researching the HOG pathway [ 8 , 9 , 10 , 11 ].…”