The polyubiquitin gene MrUBI4 is required for conidiation, conidial germination, and stress tolerance in the filamentous fungus Metarhizium robertsii.

Zhangxun Wang,Bo Huang,Yuanyuan Jiang,Yuandong Li,Hong Zhu,Yuran Cheng

doi:10.3390/genes10060412

Abstract

The polyubiquitin gene is a highly conserved open reading frame that encodes different numbers of tandem ubiquitin repeats from different species, which play important roles in different biological processes. Metarhizium robertsii is a fungal entomopathogen that is widely applied in the biological control of pest insects. However, it is unclear whether the polyubiquitin gene is required for fungal development, stress tolerance, and virulence in the entomopathogenic fungus. In the present study, the polyubiquitin gene (MrUBI4, MAA_02160) was functionally characterized via gene deletion in M. robertsii. Compared to the control strains, the MrUBI4 deletion mutant showed delayed conidial germination and significantly decreased conidial yields (39% of the wild-type 14 days post-incubation). Correspondingly, the transcript levels of several genes from the central regulatory pathways associated with conidiation, including brlA, abaA, and wetA, were significantly downregulated, which indicated that MrUBI4 played an important role in asexual sporulation. Deletion of MrUBI4 especially resulted in increased sensitivity to ultraviolet (UV) and heat-shock stress based on conidial germination analysis between mutant and control strains. The significant increase in sensitivity to heat-shock was accompanied with reduced transcript levels of genes related to heat-shock protein (hsp), trehalose, and mannitol accumulation (tps, tpp, nth, and mpd) in the MrUBI4 deletion mutant. Deletion of MrUBI4 has no effect on fungal virulence. Altogether, MrUBI4 is involved in the regulation of conidiation, conidial germination, UV stress, and heat-shock response in M. robertsii.

Highlights

Protein ubiquitination is a well-known process responsible for protein degradation and quality control, which regulates different biological pathways via the ubiquitin-proteasome system (UPS) [1,2].The UPS is the primary cytosolic proteolytic machinery that selectively degrades various forms of misfolded or damaged proteins [3,4]
The results identified a single copy of the polyubiquitin gene (MAA_02160) in M. robertsii that encoded a
The results showed that the brlA, abaA, wetA, and flbD transcript levels were significantly lower in the ∆MrUBI4 strain than in the WT strain (p < 0.01; Figure 3C), which indicated that MrUBI4 was involved in the regulation of conidiation-related gene expression

Summary

Introduction

Protein ubiquitination is a well-known process responsible for protein degradation and quality control, which regulates different biological pathways via the ubiquitin-proteasome system (UPS) [1,2].The UPS is the primary cytosolic proteolytic machinery that selectively degrades various forms of misfolded or damaged proteins [3,4]. Ubiquitin-coding genes in yeast are divided into 2 major classes: polyubiquitin genes and monomeric ubiquitin fusion genes [6,7]. Polyubiquitin genes are arranged in tandem with head-to-tail repeats of 228 bp, and the number of tandem ubiquitin repeats varies between and within different species [8]. These polyubiquitin genes encode a polyubiquitin precursor protein, which is rapidly cleaved to produce mature ubiquitin monomers via deubiquitinating enzymes (DUBs) [9,10]. The monomeric ubiquitin fusion gene only encodes a single ubiquitin repeat that is fused to unrelated peptide sequences [8]

Methods

Results

Conclusion