Differential analysis of ergosterol function in response to high salt and sugar stress in Zygosaccharomyces rouxii

Zygosaccharomyces rouxii is an osmotolerant and halotolerant yeast that can participate in fermentation. To understand the mechanisms of salt and sugar tolerance, the transcription levels of Z. rouxii M 2013310 under 180 g/L NaCl stress and 600 g/L glucose stress were measured. The transcriptome analysis showed that 2227 differentially expressed genes (DEGs) were identified under 180 g/L NaCl stress, 1530 DEGs were identified under 600 g/L glucose stress, and 1278 DEGs were identified under both stress conditions. Then, KEGG enrichment analyses of these genes indicated that 53.3% of the upregulated genes were involved in the ergosterol synthesis pathway. Subsequently, quantitative PCR was used to verify the results, which showed that the genes of the ergosterol synthesis pathway were significantly upregulated under 180 g/L NaCl stress. Finally, further quantitative testing of ergosterol and spotting assays revealed that Z. rouxii M 2013310 increased the amount of ergosterol in response to high salt stress. These results highlighted the functional differences in ergosterol under sugar stress and salt stress, which contributes to our understanding of the tolerance mechanisms of salt and sugar in Z. rouxii.

Multilocus resistance evolution to azole fungicides in fungal plant pathogen populations

Evolution of fungicide resistance is a major threat to food production in agricultural ecosystems. Fungal pathogens rapidly evolved resistance to all classes of fungicides applied to the field. Resistance to the commonly used azole fungicides is thought to be driven mainly by mutations in a gene (CYP51) encoding a protein of the ergosterol biosynthesis pathway. However, some fungi gained azole resistance independently of CYP51 mutations and the mechanisms leading to CYP51-independent resistance are poorly understood. We used whole-genome sequencing and genome-wide association studies (GWAS) to perform an unbiased screen of azole resistance loci in Rhynchosporium commune, the causal agent of the barley scald disease. We assayed cyproconazole resistance in 120 isolates collected from nine populations worldwide. We found that mutations in highly conserved genes encoding the vacuolar cation channel YVC1, a transcription activator, and a saccharopine dehydrogenase made significant contributions to fungicide resistance. These three genes were not previously known to confer resistance in plant pathogens. However, YVC1 is involved in a conserved stress response pathway known to respond to azoles in human pathogenic fungi. We also performed GWAS to identify genetic polymorphism linked to fungal growth rates. We found that loci conferring increased fungicide resistance were negatively impacting growth rates, suggesting that fungicide resistance evolution imposed costs. Analyses of population structure showed that resistance mutations were likely introduced into local populations through gene flow. Multilocus resistance evolution to fungicides shows how pathogen populations can evolve a complex genetic architecture for an important phenotypic trait within a short time span.