AoSsk1, a Response Regulator Required for Mycelial Growth and Development, Stress Responses, Trap Formation, and the Secondary Metabolism in Arthrobotrys oligospora.

Ke-Xin Jiang,Jin-Kui Yang,Ke-Qin Zhang,Na Bai,Qian-Qian Liu,Mei-Chen Zhu

doi:10.3390/jof8030260

Abstract

Ssk1, a response regulator of the two-component signaling system, plays an important role in the cellular response to hyperosmotic stress in fungi. Herein, an ortholog of ssk1 (Aossk1) was characterized in the nematode-trapping fungus Arthrobotrys oligospora using gene disruption and multi-phenotypic comparison. The deletion of Aossk1 resulted in defective growth, deformed and swollen hyphal cells, an increased hyphal septum, and a shrunken nucleus. Compared to the wild-type (WT) strain, the number of autophagosomes and lipid droplets in the hyphal cells of the ΔAossk1 mutant decreased, whereas their volumes considerably increased. Aossk1 disruption caused a 95% reduction in conidial yield and remarkable defects in tolerance to osmotic and oxidative stress. Meanwhile, the transcript levels of several sporulation-related genes were significantly decreased in the ΔAossk1 mutant compared to the WT strain, including abaA, brlA, flbC, fluG, and rodA. Moreover, the loss of Aossk1 resulted in a remarkable increase in trap formation and predation efficiency. In addition, many metabolites were markedly downregulated in the ΔAossk1 mutant compared to the WT strain. Our results highlight that AoSsk1 is a crucial regulator of asexual development, stress responses, the secondary metabolism, and pathogenicity, and can be useful in probing the regulatory mechanism underlying the trap formation and lifestyle switching of nematode-trapping fungi.

Highlights

The transmission of extracellular signals to intracellular targets is mediated by a network of interacting proteins that regulate a large number of cellular processes in eukaryotic cells
The fungus A. oligospora (ATCC24927) and the derived mutant strains were routinely inoculated on potato dextrose agar (PDA) medium at 28 ◦ C, and these strains were preserved in the Microbial Library of the Germplasm Bank of Wild Species from Southwest
The absence of an ortholog of ssk1 (Aossk1) resulted in increased trap formation and predation efficiency. These findings suggest that Ssk1 is required for fungal virulence, and its ortholog plays a pivotal role in the trap formation and pathogenicity of NT fungi can produce diverse metabolites during vegetative growth and predator

Summary

Introduction

The transmission of extracellular signals to intracellular targets is mediated by a network of interacting proteins that regulate a large number of cellular processes in eukaryotic cells. Intracellular signal transduction systems regulate growth, development, and reproduction [1]. The mitogen-activated protein kinase (MAPK) signaling cascade is the most conserved signal module in all eukaryotes and consists of three layers of protein kinases: an MAP kinase, an MAP kinase (MAPKK), and an MAPKK kinase (MAPKKK) [2]. Six types of MAPKs have been identified in the model yeasts Saccharomyces cerevisiae and Candida albicans [3,4], and three types of MAPKs (Slt, Hog, and Fus3) have been identified in plant pathogenic and entomopathogenic fungi [5,6]. The high osmotic pressure glycerol (Hog) pathway is essential for the survival of yeast and filamentous fungi in a high osmotic environment [5,7]. In S. cerevisiae, the Hog pathway mainly consists of the

Methods

Results

Discussion

Conclusion