Abstract
BackgroundSoil fungi face a variety of environmental stresses such as UV light, high temperature, and heavy metals. Adaptation of gene expression through transcriptional regulation is a key mechanism in fungal response to environmental stress. In Saccharomyces cerevisiae, the transcription factors Msn2/4 induce stress-mediated gene expression by binding to the stress response element. Previous studies have demonstrated that the expression of extracellular proteases is up-regulated in response to heat shock in fungi. However, the physiological significance of regulation of these extracellular proteases by heat shock remains unclear. The nematophagous fungus Clonostachys rosea can secret an extracellular serine protease PrC during the infection of nematodes. Since the promoter of prC has three copies of the stress response element, we investigated the effect of environmental stress on the expression of prC.Methodology/Principal FindingsOur results demonstrated that the expression of prC was up-regulated by oxidants (H2O2 or menadione) and heat shock, most likely through the stress response element. After oxidant treatment or heat shock, the germination of conidia in the wild type strain was significantly higher than that in the prC mutant strain in the presence of nematode cuticle. Interestingly, the addition of nematode cuticle significantly attenuated the production of reactive oxygen species (ROS) induced by oxidants and heat shock in the wild type strain, but not in prC mutant strain. Moreover, low molecule weight (<3 kD) degradation products of nematode cuticle suppressed the inhibitory effect of conidial germination induced by oxidants and heat shock.Conclusions/SignificanceThese results indicate that PrC plays a protective role in oxidative stress in C. rosea. PrC degrades the nematode cuticle to produce degradation products, which in turn offer a protective effect against oxidative stress by scavenging ROS. Our study reveals a novel strategy for fungi to adapt to environmental stress.
Highlights
In the soil environment, fungi likely face many potential adverse environmental conditions such as osmotic shock, high temperature, heavy metals, and UV irradiations
In Saccharomyces cerevisiae, the stress response element (STRE) genes are activated by two transcription factors Msn2 and Msn4 in response to stress such as oxidative stress, heat shock, osmotic shock, and glucose starvation
Results prC expression is induced by oxidants and heat shock To investigate the effect of environmental stress on the expression of prC, conidia of C. rosea were treated by oxidants (H2O2 or menadione), heat shock, hyperosmotic shock and heavy metal ions
Summary
Fungi likely face many potential adverse environmental conditions such as osmotic shock, high temperature, heavy metals, and UV irradiations. In Saccharomyces cerevisiae, the STRE genes are activated by two transcription factors Msn and Msn in response to stress such as oxidative stress, heat shock, osmotic shock, and glucose starvation. Under normal non-stressful conditions, Msn and Msn typically reside in the cytoplasm. During stress, these two proteins are translocated into the nucleus, and bind to the promoters of STRE genes. In Saccharomyces cerevisiae, the transcription factors Msn2/4 induce stress-mediated gene expression by binding to the stress response element. Previous studies have demonstrated that the expression of extracellular proteases is upregulated in response to heat shock in fungi. Since the promoter of prC has three copies of the stress response element, we investigated the effect of environmental stress on the expression of prC
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