The Polyubiquitin Gene MrUBI4 Is Required for Conidiation, Conidial Germination, and Stress Tolerance in the Filamentous Fungus Metarhizium robertsii

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.

Mr-AbaA Regulates Conidiation by Interacting with the Promoter Regions of Both Mr-veA and Mr-wetA in Metarhizium robertsii

“…Therefore, the Δ Mr-abaA mutant showed significantly increased sensitivity to heat stress. Furthermore, some key heat-stress-responsive genes were assessed for their transcript levels in the Δ Mr-abaA mutant, relative to the WT strain ( 32 , 33 ). qRT-PCR results indicated that the heat stress significantly downregulated 2 of 4 genes involved in the glycolytic pathway, 5 of 11 genes encoding heat shock proteins, and 2 of 5 catalase genes but remarkably upregulated 3 of 6 genes involved in the pyruvate-consuming pathway in the Δ Mr-abaA mutant ( Fig.…”

Polyubiquitin protein of Aedes aegypti as an interacting partner of dengue virus envelope protein

“…In case of Metarhizium robertsii (fungal entomopathogen), a study was conducted on polyubiquitin gene ( MrUBI4 and MAA_02160). The gene deletion in the experimental strains showed significant reduction in conidial yields and delay in conidial germination as compared with control strains (Wang et al, 2019).…”

More Than Just Cleaning: Ubiquitin-Mediated Proteolysis in Fungal Pathogenesis

“…Likewise, the polyubiquitin gene CpUBI4 is required for fungal development, stress adaptation, and virulence in Cryphonectria parasitica , a phytopathogenic filamentous fungus that causes chestnut blight disease ( Chen et al., 2018 ). The role of polyubiquitin genes in insect fungal pathogens were also explored recently ( Wang et al., 2019b ; Wang et al., 2020 ). Polyubiquitin genes were functionally characterized via gene deletion in Metarhizium robertsii and Beauveria bassiana .…”

“…Polyubiquitin genes were functionally characterized via gene deletion in Metarhizium robertsii and Beauveria bassiana . MrUBI4 is involved in UV stress and the heat-shock response in M. robertsii ( Wang et al., 2019b ). Deletion of UBI4 leads to a defect in stress tolerance and attenuated virulence in B. bassiana ( Wang et al., 2020 ).…”