Genome-wide functional analysis of AreA and AreB

"Background: The ascomycete Fusarium fujikuroi causes “bakanae” disease of rice due to its ability to produce gibberellins (GA), but is also known for producing a broad spectrum of other secondary metabolites, (SM) such as pigments and harmful mycotoxins. Biosynthesis of multiple SM is regulated by nitrogen availability. The global GATA transcription factors (TF) AreA and AreB were shown to play key roles in this nitrogen-dependent regulation. Recently, we have shown that AreA activates the transcription of AREB, but not vice versa. Both regulators interact in the nucleus, indicating a complex regulatory interplay between both regulators. Results: We performed transcriptome and proteome analyses of the wild type and ΔAREA and ΔAREB mutants under nitrogen limiting and sufficient conditions. Microarray analysis revealed that each transcription factor regulates a total set of about 4,200 genes under nitrogen limiting conditions. Gene enrichment analysis revealed that significantly up- and down-regulated genes belong to functional classes of primary/secondary metabolism, transporters, cell defense/virulence and transcription. Under nitrogen excess, AreA is not active as a transcriptional regulator, while AreB affects expression of about 4,400 genes. Both transcription factors regulate a common set of about 2,100 genes, often coordinately either as positive or as negative regulators. Our proteomics analysis identified 446 AreA-regulated and 386 AreB-regulated proteins under nitrogen limitation and 138 AreA-regulated and 447 AreB-regulated proteins under nitrogen sufficiency, respectively. Comparison of the proteome and transcriptome data indicates that both GATA-factors not only regulate expression of target genes but also affect protein abundance by post-transcriptional regulations, for example on enzymes involved in glutamate cycling, as well as histone acetylation at some of the target SM gene clusters. Conclusion: This study provides novel insights into the AreA- and AreB-mediated regulation network on a cellular scale. Microarray analysis clearly demonstrated that both GATA-factors are major regulators of alternate nitrogen assimilatory pathways and secondary metabolism. Moreover, proteome analysis of the AREA and AREB deletion mutants showed that both TF are global players interconnecting carbon and nitrogen regulation. They mainly act as mutualistic, but also antagonistic regulators and operate by transcriptional and post-transcriptional regulations and epigenetic modifications." (Abstract taken from manuscript)