Abstract
Adaptation to changes in the environment is crucial for the viability of all organisms. Although the importance of calcineurin in the stress response has been highlighted in filamentous fungi, little is known about the involvement of ion-responsive genes and pathways in conferring salt tolerance without calcium signaling. In this study, high-throughput RNA-seq was used to investigate salt stress-induced genes in the parent, ΔcnaB, and ΔcnaBΔcchA strains of Aspergillus nidulans, which differ greatly in salt adaption. In total, 2,884 differentially expressed genes including 1,382 up- and 1,502 downregulated genes were identified. Secondary transporters, which were upregulated to a greater extent in ΔcnaBΔcchA than in the parent or ΔcnaB strains, are likely to play important roles in response to salt stress. Furthermore, 36 genes were exclusively upregulated in the ΔcnaBΔcchA under salt stress. Functional analysis of differentially expressed genes revealed that genes involved in transport, heat shock protein binding, and cell division processes were exclusively activated in ΔcnaBΔcchA. Overall, our findings reveal that secondary transporters and stress-responsive genes may play crucial roles in salt tolerance to bypass the requirement for the CchA-calcineurin pathway, contributing to a deeper understanding of the mechanisms that influence fungal salt stress adaption in Aspergillus.
Highlights
Rapid adaptation to different environmental conditions, including appropriate adaptive responses to various cations, is crucial for the survival and proliferation of microorganisms
By comparing the various strains used in the experiment, 1,964 differentially expressed genes (DEGs) (1,067 upregulated and 897 downregulated) and 1,863 DEGs (1,016 upregulated and 847 downregulated) were induced by salt stress in ΔcnaB and ΔcnaBΔcchA, respectively, in comparison to 2,159 DEGs (1,153 upregulated and 1,006 downregulated) induced by salt stress in the parent strain
Though the DEGs from ΔcnaB were similar to those of ΔcnaBΔcchA, many genes were identified as being differentially expressed between these two strains
Summary
Rapid adaptation to different environmental conditions, including appropriate adaptive responses to various cations, is crucial for the survival and proliferation of microorganisms. The cell possesses intracellular signaling systems that can identify these stimuli in order to implement cellular responses to counteract stress conditions [1]. Calcium signaling is conserved in eukaryotes and plays an important role in sensing environmental stimuli, transmitting extracellular signals to the nucleus to modulate gene expression, regulating morphology, responding to abiotic and biotic stresses, and defending against virulence/pathogenicity [2,3,4]. Small changes in [Ca2+]cyt levels can activate various Ca2+-sensing proteins, such as calmodulin and calcineurin, which lead to the induction of various downstream signal transduction pathways [7]. In Saccharomyces cerevisiae, the response to salt stress is mediated by calcineurin, a conserved Ca2+/calmodulinmodulated protein phosphatase that plays an important role in coupling Ca2+ signals to cellular responses. Calcineurin (CaN) is a heterodimer consisting of two subunits, the catalytic subunit A (CnA) and regulatory subunit B (CnB)
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