Gβ-Like CpcB Plays a Crucial Role for Growth and Development of Aspergillus nidulans and Aspergillus fumigatus

Abstract

Growth, development, virulence and secondary metabolism in fungi are governed by heterotrimeric G proteins (G proteins). A Gβ-like protein called Gib2 has been shown to function as an atypical Gβ in Gpa1-cAMP signaling in Cryptococcus neoformans. We found that the previously reported CpcB (cross pathway control B) protein is the ortholog of Gib2 in Aspergillus nidulans and Aspergillus fumigatus. In this report, we further characterize the roles of CpcB in governing growth, development and toxigenesis in the two aspergilli. The deletion of cpcB results in severely impaired cellular growth, delayed spore germination, and defective asexual sporulation (conidiation) in both aspergilli. Moreover, CpcB is necessary for proper expression of the key developmental activator brlA during initiation and progression of conidiation in A. nidulans and A. fumigatus. Somewhat in accordance with the previous study, the absence of cpcB results in the formation of fewer, but not micro-, cleistothecia in A. nidulans in the presence of wild type veA, an essential activator of sexual development. However, the cpcB deletion mutant cleistothecia contain no ascospores, validating that CpcB is required for progression and completion of sexual fruiting including ascosporogenesis. Furthermore, unlike the canonical GβSfaD, CpcB is not needed for the biosynthesis of the mycotoxin sterigmatocystin (ST) as the cpcB null mutant produced reduced amount of ST with unaltered STC gene expression. However, in A. fumigatus, the deletion of cpcB results in the blockage of gliotoxin (GT) production. Further genetic analyses in A. nidulans indicate that CpcB may play a central role in vegetative growth, which might be independent of FadA- and GanB-mediated signaling. A speculative model summarizing the roles of CpcB in conjunction with SfaD in A. nidulans is presented.

Survival factor SvfA plays multiple roles in differentiation and is essential for completion of sexual development in Aspergillus nidulans

“…SvfA is involved in ST biosynthesis and development, both of which are known to be functionally interconnected 4 . CpcB, a Gβ-like protein, governs diverse cellular events such as germination, growth, development, and ST synthesis 32 . Similar to the ΔsvfA strain, the cpcB deletion strain produced small and fragile cleistothecia with no ascospores and showed upregulation of veA and nsdD expression during sexual development 32 , suggesting a possible interaction between SvfA and CpcB.…”

“…CpcB, a Gβ-like protein, governs diverse cellular events such as germination, growth, development, and ST synthesis 32 . Similar to the ΔsvfA strain, the cpcB deletion strain produced small and fragile cleistothecia with no ascospores and showed upregulation of veA and nsdD expression during sexual development 32 , suggesting a possible interaction between SvfA and CpcB. When levels of cpcB gene expression in the ΔsvfA strain and svfA gene expression in the ΔcpcB strain were studied during sexual development, cpcB expression was not affected by the lack of SvfA and in turn svfA expression was not affected in ΔcpcB mutants (data not shown).…”

“…(2020) 10:5586 | https://doi.org/10.1038/s41598-020-62455-4 www.nature.com/scientificreports www.nature.com/scientificreports/ Media and culture conditions. Strains were maintained in Aspergillus minimal medium with glucose (GMM) 32 . The minimal medium supplemented with 0.15% yeast extract and 0.15% casamino acid (YCMM) was used as a complete medium for vegetative mycelial ball production.…”

Roles of Rack1 Proteins in Fungal Pathogenesis

“…In addition, the cAMP/PKA pathway regulates the synthesis of several virulence factors [ 71 ]. In both A. nidulans and A. fumigatus , Rack1 proteins, CpcB, play important roles in fungal growth, conidiation, conidial germination, and mycotoxin production ( Table 1 ) [ 49 , 50 ]. In A. nidulans , CpcB represses the cross-pathway control in the presence of amino acids and regulates sexual development [ 50 , 52 ].…”

Molecular Characterization of Gβ-Like Protein CpcB Involved in Antifungal Drug Susceptibility and Virulence in A. fumigatus

“…Based on bioinformatics analyses, CpcB is highly conserved in eukaryotes with Gβ-like homologs exhibiting identities ranging from 60.4 to 95.6% ( Cai et al, 2015 ). Previous studies have demonstrated that CpcB plays important roles in hyphal growth and conidiation in A. fumigatus ( Kong et al, 2013 ; Cai et al, 2015 ). Despite its important functions, the molecular characterization of CpcB has not been performed.…”