Aspects of the Neurospora crassa sulfur starvation response are revealed by transcriptional profiling and DNA affinity purification sequencing

Accurate nutrient sensing is important for rapid fungal growth and exploitation of available resources. Sulfur is an important nutrient source found in a number of biological macromolecules, including proteins and lipids. The model filamentous fungus Neurospora crassa is capable of utilizing sulfur found in a variety of sources from amino acids to sulfate. During sulfur starvation, the transcription factor CYS-3 is responsible for upregulation of genes involved in sulfur uptake and assimilation. Using a combination of RNA sequencing and DNA affinity purification sequencing, we performed a global survey of the N. crassa sulfur starvation response and the role of CYS-3 in regulating sulfur responsive genes. Along with genes known to be involved in sulfur metabolism, the CYS-3 transcription factor also directly activated the expression of a number of uncharacterized transporter genes, suggesting that regulating sulfur import is an important aspect of regulation by CYS-3. Additionally, CYS-3 directly regulated the expression of genes involved in mitochondrial electron transfer. During sulfur starvation, genes involved in nitrogen metabolism, such as amino acid and nucleic acid metabolic pathways, along with genes encoding proteases and nucleases that are necessary for scavenging nitrogen, were activated. Sulfur starvation also caused changes in the expression of genes involved in carbohydrate metabolism, such as those encoding glycosyl hydrolases. Thus, our data suggest a connection between sulfur metabolism and other aspects of cellular metabolism. mRNA profiles of wild type N. crassa cells and N. crassa cells with a cys-3 partial deletion exposed to media with 24uM sulfate and sulfur starvation for 4 hours. Each of the two strains (mutant and wild type control) was exposed to both sulfur conditions for 4 total experiments, each done in biological triplicate. There are a total of 12 samples.