A Sensing Role of the Glutamine Synthetase in the Nitrogen Regulation Network in Fusarium fujikuroi

Abstract

In the plant pathogenic ascomycete Fusarium fujikuroi the synthesis of several economically important secondary metabolites (SM) depends on the nitrogen status of the cells. Of these SMs, gibberellin and bikaverin synthesis is subject to nitrogen catabolite repression (NCR) and is therefore only executed under nitrogen starvation conditions. How the signal of available nitrogen quantity and quality is sensed and transmitted to transcription factors is largely unknown. Earlier work revealed an essential regulatory role of the glutamine synthetase (GS) in the nitrogen regulation network and secondary metabolism as its deletion resulted in total loss of SM gene expression. Here we present extensive gene regulation studies of the wild type, the Δgln1 mutant and complementation strains of the gln1 deletion mutant expressing heterologous GS-encoding genes of prokaryotic and eukaryotic origin or 14 different F. fujikuroi gln1 copies with site-directed mutations. All strains were grown under different nitrogen conditions and characterized regarding growth, expression of NCR-responsive genes and biosynthesis of SM. We provide evidence for distinct roles of the GS in sensing and transducing the signals to NCR-responsive genes. Three site directed mutations partially restored secondary metabolism and GS-dependent gene expression, but not glutamine formation, demonstrating for the first time that the catalytic and regulatory roles of GS can be separated. The distinct mutant phenotypes show that the GS (1) participates in NH4 +-sensing and transducing the signal towards NCR-responsive transcription factors and their subsequent target genes; (2) affects carbon catabolism and (3) activates the expression of a distinct set of non-NCR GS-dependent genes. These novel insights into the regulatory role of the GS provide fascinating perspectives for elucidating regulatory roles of GS proteins of different organism in general.

TrpE feedback mutants reveal roadblocks and conduits toward increasing secondary metabolism in Aspergillus fumigatus

“…Intracellular amino acid pools are stored in vacuoles (Sekito et al, 2008) and their accessibility will differ from supplementation from external sources. Our data allude to different intra- and extracellular amino tryptophan sensing mechanisms in A. fumigatus , supporting a hypothesis of distinct nitrogen sensing mechanisms in other filamentous fungi (Wagner et al, 2013; Wiemann and Tudzynski, 2013). Our expression profiling data suggests that several tryptophan degradation pathways could be important in this regard (Fig.…”

Nitrate Assimilation in Fusarium fujikuroi Is Controlled by Multiple Levels of Regulation

“…The main effector mediating rapid and strong repression of these two SM clusters was shown to be glutamine, while addition of nitrate to cultures led to a significantly delayed down-regulation of these genes compared to glutamine (Wagner et al, 2013). …”

Apicidin F: Characterization and Genetic Manipulation of a New Secondary Metabolite Gene Cluster in the Rice Pathogen Fusarium fujikuroi

“…In addition, the glutamine synthetase (GS) was shown to be involved in regulation of secondary metabolism in F. fujikuroi because the production of the gibberellins, bikaverin and fusarins is abolished in the Δ GLN1 mutant [23], [29], [51].…”