HighlightsHistory of seven fungal species used as models for studying development and pathogenicity.Outline of central stages of their life cycle and their infection processes.Molecular toolkits used to study different aspects of pathogenicity.Insight gained from genome sequencing projects.Current research trends and future challenges.

One of the challenges of establishing an industrially competitive process to ferment lignocellulose to value-added products using Saccharomyces cerevisiae is to get efficient mixed sugar fermentations. Despite successful metabolic engineering strategies, the xylose assimilation rates of recombinant S. cerevisiae remain significantly lower than for the preferred carbon source, glucose. Previously, we established a panel of in vivo biosensor strains (TMB371X) where different promoters (HXT1/2/4p; SUC2p, CAT8p; TPS1p/2p, TEF4p) from the main sugar signaling pathways were coupled with the yEGFP3 gene, and observed that wild-type S. cerevisiae cannot sense extracellular xylose. Here, we expand upon these strains by adding a mutated galactose transporter (GAL2-N376F) with improved xylose affinity (TMB372X), and both the transporter and an oxidoreductase xylose pathway (TMB375X). On xylose, the TMB372X strains displayed population heterogeneities, which disappeared when carbon starvation was relieved by the addition of the xylose assimilation pathway (TMB375X). Furthermore, the signal in the TMB375X strains on high xylose (50 g/L) was very similar to the signal recorded on low glucose (≤5 g/L). This suggests that intracellular xylose triggers a similar signal to carbon limitation in cells that are actively metabolizing xylose, in turn causing the low assimilation rates.

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Regulation of development and entry into sporulation is critical for fungi to ensure survival of unfavorable environmental conditions. Here we present an analysis of gene sets regulating sporulation in the homothallic ascomycete Ashbya gossypii. Deletion of components of the conserved pheromone/starvation MAP kinase cascades, e.g., STE11 and STE7, results in increased sporulation. In kar3 mutants sporulation is severely reduced, while deletion of KAR4 as well as of homologs of central Saccharomyces cerevisiae regulators of sporulation, IME1, IME2, IME4, and NDT80, abolishes sporulation in A. gossypii. Comparison of RNAseq transcript profiles of sporulation-deficient mutants identified a set of 67 down-regulated genes, most of which were up-regulated in the oversporulating ste12 mutant. One of these differentially expressed genes is an endoglucanase encoded by ENG2. We found that Eng2p promotes hyphal fragmentation as part of the developmental program of sporulation, which generates single-celled sporangia. Sporulationdeficient strains are arrested in their development but form sporangia. Supply of new nutrients enabled sporangia to return to hyphal growth, indicating that these cells are not locked in meiosis. Double-strand break (DSB) formation by Spo11 is apparently not required for sporulation; however, the absence of DMC1, which repairs DSBs in S. cerevisiae, results in very poor sporulation in A. gossypii. We present a comprehensive analysis of the gene repertoire governing sporulation in A. gossypii and suggest an altered regulation of IME1 expression compared to S. cerevisiae.A SHBYA gossypii is a riboflavin/vitamin B 2 overproducing filamentous ascomycete grouped within the Saccharomycetaceae (Kurtzman and Robnett 2003). A. gossypii belongs to the pre-whole genome duplication fungi but shares homologs of 95% of its genes with Saccharomyces cerevisiae (Deng et al. 2007). A. gossypii and its relative Eremothecium cymbalariae can complete their life cycle starting from a single spore that forms a sporulating mycelium and are thus homothallic (Wendland and Walther 2011). Sporulation in A. gossypii occurs at the end of its growth phase, when hyphae develop sporangia derived from septate compartments. Sporangia separate from each other by fragmentation of the hyphae at septal sites and spores are set free by lysis of the sporangia. A. gossypii spores are uninucleate and contain a haploid genome (Wendland and Walther 2005).In S. cerevisiae mating pheromones induce signaling via a conserved MAP kinase cascade that leads to the activation of the Ste12 transcription factor. Ste12 binds to the pheromone response element of target genes and induces their expression, which induces events leading to cell fusion and karyogamy (Bardwell 2005). In A. gossypii mating is apparently not required for sporulation as mutant strains deleted for both STE2 and STE3 pheromone receptor genes can still sporulate. On the contrary, deletion of the AgSTE12 homolog resulted in an oversporulation phenotype .Meiosis and sporulati...

Engineering of the yeast Saccharomyces cerevisiae towards efficient d-xylose assimilation has been a major focus over the last decades since d-xylose is the second most abundant sugar in nature, and its conversion into products could significantly improve process economy in biomass-based processes. Up to now, two different metabolic routes have been introduced via genetic engineering, consisting of either the isomerization or the oxido-reduction of d-xylose to d-xylulose that is further connected to the pentose phosphate pathway and glycolysis. In the present study, cytosolic d-xylose oxidation was investigated instead, through the introduction of the Weimberg pathway from Caulobacter crescentus in S. cerevisiae. This pathway consists of five reaction steps that connect d-xylose to the TCA cycle intermediate α-ketoglutarate. The corresponding genes could be expressed in S. cerevisiae, but no growth was observed on d-xylose indicating that not all the enzymes were functionally active. The accumulation of the Weimberg intermediate d-xylonate suggested that the dehydration step(s) might be limiting, blocking further conversion into α-ketoglutarate. Although four alternative dehydratases both of bacterial and archaeon origins were evaluated, d-xylonate accumulation still occurred. A better understanding of the mechanisms associated with the activity of dehydratases, both at a bacterial and yeast level, appears essential to obtain a fully functional Weimberg pathway in S. cerevisiae.Electronic supplementary materialThe online version of this article (10.1186/s13568-018-0564-9) contains supplementary material, which is available to authorized users.