Generation of mitochondrial reactive oxygen species through a histidine kinase, HysA in Aspergillus nidulans.

The His-Asp phosphorelay signal transduction from histidine kinase (HK) to the response regulator (RR) is an important mechanism for adaptation to environmental changes. Aspergillus nidulans expresses 15 different HKs, which may be involved in different types of adaptations. As reactive oxygen species (ROS) are a key signal of environmental changes, some HKs might be involved in ROS generation through transcriptional regulation. Previously, we identified 3 HK (NikA, FphA, and HysA) deletion strains that showed increased ROS production during growth. We also showed that the phosphorylation function of HysA is involved in ROS generation. Here, we investigated the role of HysA in ROS production in A. nidulans cells. HysA protein was detected in both the cytosol and mitochondria by biological fractionation of the vegetative cell lysate of A. nidulans. The subcellular localization analysis by expressing the the HysA-GFP fusion protein along with MitoTracker Red staining did not clearly reveal mitochondrial localization of HysA at the conidiophore during asexual development. However, mitochondrial ROS in hysA mutant strains were detected by MitoSOX Red staining, and their excess levels possibly caused morphological changes during asexual development.