Osmotic Stress Responses, Cell Wall Integrity, and Conidiation Are Regulated by a Histidine Kinase Sensor in .

responds to various environmental stressors through the mitogen-activated protein kinase (MAPK) Tmk3 and MAPK-kinase Pbs2 signaling pathways. In fungi, orthologues to Tmk3 are regulated by a histidine kinase (HK) sensor. However, the role of HKs remains unknown. In this regard, the function of the HK Nik1 was analyzed in response to stressors regulated by Tmk3. The growth of the Δ mutant strains was compromised under hyperosmotic stress; mycelia were less resistant to lysing enzymes than the WT strain, while conidia of Δ were more sensitive to Congo red; however, ∆ and ∆ strains showed a more drastic defect in cell wall stability. Light-regulated and gene expression was induced upon an osmotic shock through Pbs2-Tmk3 but was independent of Nik1. The encoding chitin synthases and genes were downregulated after an osmotic shock in the WT, but and expression were enhanced in ∆, ∆, and ∆. The vegetative growth and conidiation by light decreased in ∆, although Nik1 was unrequired to activate the light-responsive genes by Tmk3. Altogether, Nik1 regulates responses related to the Pbs2-Tmk3 pathway and suggests the participation of additional HKs to respond to stress.