Sporulation in Ashbya gossypii

Abstract

Ashbya gossypii is a filamentous ascomycete belonging to the yeast family of Saccharomycetaceae. At the end of its growth phase Ashbya generates abundant amounts of riboflavin and spores that form within sporangia derived from fragmented cellular compartments of hyphae. The length of spores differs within species of the genus. Needle-shaped Ashbya spores aggregate via terminal filaments. A. gossypii is a homothallic fungus which may possess a and α mating types. However, the solo-MATa type strain is self-fertile and sporulates abundantly apparently without the need of prior mating. The central components required for the regulation of sporulation, encoded by IME1, IME2, IME4, KAR4, are conserved with Saccharomyces cerevisiae. Nutrient depletion generates a strong positive signal for sporulation via the cAMP-PKA pathway and SOK2, which is also essential for sporulation. Strong inhibitors of sporulation besides mutations in the central regulatory genes are the addition of exogenous cAMP or the overexpression of the mating type gene MATα2. Sporulation has been dissected using gene-function analyses and global RNA-seq transcriptomics. This revealed a role of Msn2/4, another potential PKA-target, for spore wall formation and a key dual role of the protein A kinase Tpk2 at the onset of sporulation as well as for breaking the dormancy of spores to initiate germination. Recent work has provided an overview of ascus development, regulation of sporulation and spore maturation. This will be summarized in the current review with a focus on the central regulatory genes. Current research and open questions will also be discussed.

New Promoters for Metabolic Engineering of Ashbya gossypii

“…Next, we wanted to confirm the results obtained from the luciferase assay in modifying the expression of an A. gossypii endogenous gene. The MSN2 gene was selected because the alteration on its expression level triggers major changes in the sporulation ability of A. gossypii [28]. We previously observed that the overexpression of MSN2 nearly abolished the sporulation ability of A. gossypii, whereas the msn2∆ strain showed a significant increase in the sporulation capacity with respect to the wild-type strain (unpublished results).…”

“…Moreover, it is also possible to further characterize the regulatory properties of each promoter by a genetic dissection of the promoter CIS-acting elements. A. gossypii, which is mainly considered a microbial factory, also represents an adequate model organism in cell biology studies regarding polarized growth and ploidy [28,29]; therefore, the availability of new molecular tools will strongly benefit A. gossypii research.…”

Natural trait variation across Saccharomycotina species

“…Also salient from the literature is the long, thin ascus form in Metschnikowia and Eremothecium/Ashbya (Fig. 1 ; Lachance 2016 , Wendland 2020 ), which accommodates barbed, needle-like ascospores that may play a role in infection for some pathogens and dispersal in other species. As for the rest of Saccharomycotina , though the ascus structure is roughly globose, ascospore shape and ornamentation vary widely.…”

Role of RIM101 for Sporulation at Alkaline pH in Ashbya gossypii

“…The filamentous ascomycete Ashbya gossypii is a pre-whole genome duplication fungus that belongs to the family of the yeasts Saccharomycetaceae and shares homologs of 95% of its genes with S. cerevisiae [ 15 ]. Previous studies have shown that the main regulators of sporulation in S. cerevisiae are also essential for sporulation in A. gossypii , including IME1 , IME2 , IME4 , KAR4 , NDT80 , and also the cAMP/Protein Kinase A pathway [ 16 , 17 , 18 ]. In S. cerevisiae , IME1 expression requires ScRim101, and sporulation is therefore dependent on alkaline pH [ 19 ].…”