A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced a-glucan or galactomannan

Chitin is an important fungal cell wall component that is cross-linked to ß-glucan for structural integrity. Acquisition of chitin to glucan cross-links has previously been shown to be performed by transglycosylation enzymes in S. cerevisiae, called Congo Red hypersensitive (Crh) enzymes. Here, we characterized the impact of deleting all seven gene members of the crh gene family (crhA-G) in Aspergillus niger on cell wall integrity, cell wall composition and genome-wide gene expression. In this study, we show that the seven-fold knockout strain shows slightly compact plate growth, but no increased sensitivity to cell wall perturbing compounds. Additionally, we found that the cell wall composition of this knockout strain was virtually identical to that of the wild type. In congruence with these data, genome-wide expression analysis revealed very limited changes in gene expression and no signs of activation of the cell wall integrity response pathway. However, deleting the entire crh gene family in cell wall mutants that are deficient in either galactofuranose (?ugmA) or a-glucan (?agsE and ?agsA, ?agsE), resulted in a synthetic growth defect and an increased sensitivity towards Congo Red compared the parental strains. Altogether, these results indicate that loss of the crh gene family in A. niger does not trigger the cell wall integrity response in itself, but does play an important role in ensuring cell wall integrity in mutant strains with reduced galactofuranose or a-glucan. Overall design: Expression profiles A. niger strains; wild type versus seven-fold crh deletion strain from bioreactor cultures, using RNA-sequencing, duplicate biological samples, two biomass points (70% and 90% of maximum attained biomass) per biological samples. 8 samples total