Abstract
Although α-1,3-glucan is one of the major cell wall polysaccharides in filamentous fungi, the physiological roles of α-1,3-glucan remain unclear. The model fungus Aspergillus nidulans possesses two α-1,3-glucan synthase (AGS) genes, agsA and agsB. For functional analysis of these genes, we constructed several mutant strains in A. nidulans: agsA disruption, agsB disruption, and double-disruption strains. We also constructed several CagsB strains in which agsB expression was controlled by the inducible alcA promoter, with or without the agsA-disrupting mutation. The agsA disruption strains did not show markedly different phenotypes from those of the wild-type strain. The agsB disruption strains formed dispersed hyphal cells under liquid culture conditions, regardless of the agsA genetic background. Dispersed hyphal cells were also observed in liquid culture of the CagsB strains when agsB expression was repressed, whereas these strains grew normally in plate culture even under the agsB-repressed conditions. Fractionation of the cell wall based on the alkali solubility of its components, quantification of sugars, and 13C-NMR spectroscopic analysis revealed that α-1,3-glucan was the main component of the alkali-soluble fraction in the wild-type and agsA disruption strains, but almost no α-1,3-glucan was found in the alkali-soluble fraction derived from either the agsB disruption strain or the CagsB strain under the agsB-repressed conditions, regardless of the agsA genetic background. Taken together, our data demonstrate that the two AGS genes are dispensable in A. nidulans, but that AgsB is required for normal growth characteristics under liquid culture conditions and is the major AGS in this species.
Highlights
The fungal cell wall is a complex structure that is essential for the maintenance of cellular shape and integrity, prevention of cell lysis, and protection against adverse environmental conditions
The activation of the cell wall integrity signaling (CWIS) pathway leads to activation of the downstream mitogen-activated protein kinase (MAPK) cascade via Pkc1p and the small G protein Rho1p, which acts upon Pkc1p [8]
We constructed the disruption cassettes, which replaced the region between part of the promoter region of agsA and part of the coding region of the A. oryzae pyrG gene as the selectable marker in A. nidulans, by means of PCR fusion and introduced the cassette into the parental strain (Figure S1)
Summary
The fungal cell wall is a complex structure that is essential for the maintenance of cellular shape and integrity, prevention of cell lysis, and protection against adverse environmental conditions. Because of the biological importance and structural specificity of the fungal cell wall, inhibitors that affect the fungal cell wall have been considered ideal drugs against both mammalian- and plant-pathogenic fungi for many years. The group of b-1,3-glucan synthase inhibitors called ‘‘echinocandins’’, which include anidulafungin, caspofungin, and micafungin, have been used commercially to control a variety of fungal pathogens [5]. Cell wall biogenesis and its regulation by cell signaling have been well characterized in the yeast Saccharomyces cerevisiae [6,7]. The MAPK Mpk protein activates the transcription factor Rlm1p, which regulates the transcription of at least 25 genes involved in cell wall biogenesis, including b1,3-glucan synthase genes and chitin synthase genes [9]. In the model filamentous fungus Aspergillus nidulans, Fujioka et al [10] constructed disruptants of mpkA and rlmA (orthologues of S. cerevisiae MPK1 and RLM1, respectively), as well as disruptants of
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
