MetR is a global regulator controlling phytochrome-dependent light responses in Aspergillus nidulans

Phytochrome-dependent light signaling has been studied in several fungi. In Aspergillus nidulans light-stimulated phytochrome activates the HOG signaling pathway and thereby controls the expression of a large number of genes, many of which are related to stress responses. In a genome-wide expression analysis in A. nidulans we found that phytochrome, fphA, is under strict expression control of the central regulator of the sulfur-starvation response, MetR. This transcriptional regulator is required for the expression of genes involved in inorganic sulfur assimilation. In the presence of organic sulfur, MetR is probably ubiquitinated and possibly degraded and the transcription of sulfur-assimilation genes, e.g. sulfate permease, is turned off. The expression analysis described here revealed, however, that MetR additionally controls the expression of hundreds of genes, many of which are required for secondary metabolite production. We also show that metR mutation phenocopies fphA deletion, and five other histidine-hybrid kinases are down-regulated in the metR1 mutant. Furthermore, we show that light and phytochrome regulate the expression of at least three carbon-sulfur hydrolases. This work is a further step towards understanding the interplay between light sensing and metabolic pathways. Comparison of transcriptomes of the filamentous fungus Aspergillus nidulans two congenic strains, W1 (yA2; pyroA4; veA1) and RM114 (yA2; metR1; pyroA4; veA1). Two biological replicates of W1 vs metR1 were performed. Each biological replicate had two technical replicates with dye swapping.