One of the genes whose expression was down regulated was
One of the genes whose expression was down regulated was bgt-2 (NCU09175), encoding a β-1,3-endoglucanase. Deletion of this gene was shown to result in changes in Adenosine 5-monophosphate architecture suggesting that it is involved in remodeling of the cell wall (Martínez-Núñez and Riquelme, 2015). Among the other genes whose expression was altered, some have been analyzed in other fungi. These include NCU05974, whose S. cerevisiae homologue crh1 is hyper sensitive to Congo Red and Calcofluor White (Cabib et al., 2007), while the NCU06781 homologue in Aspergillus fumigatus homologue, gel2, showed altered cell wall composition (Mouyna et al., 2005). In A. fumigatus, AfuEcm33, a homologue of the N. crassa acw-1 (NCU08936) was found to be involved in maintaining cell wall integrity (Romano, 2006). A major down regulated gene, NCU05404, was annotated as a glycosyl hydrolase unclassified family-2. This gene and corresponding protein was described as a secreted endoglucanase by Maddi et al. (2010). The protein also contains an “Auxiliary Activity Family 11″ domain which implies it has monooxygenase activity (http://www.cazypedia.org/index.php). In addition to those mentioned above, we also identified a representative of the “SUN” family, NCU02668, which is homologous to the S. cerevisiae Sun4, a cell wall degrading protein that was shown to be regulated by the yeast Ssd1 (Jansen et al., 2009). Taken together, our data show a considerable change in cell wall remodeling-related transcripts as a result of inactivation of gul-1. It is thus surprising that this does not appear to have a morphological effect on the fungus. One possible explanation is that there are additional proteins and other pathways involved in the stability of the cell wall which can compensate for the transcriptional changes observed. Nonetheless, Δgul-1 was shown to be hypersensitive to the chitin synthase inhibitor Nikkomycin Z (Herold and Yarden, 2017). The significance of GUL-1 in cell wall remodeling was further supported by analysis of changes in transcript abundance occurring in the presence of the drug (Fig. 4). This study demonstrates that GUL-1 affects multiple pathways/processes. As GUL-1 is likely to function as an RNA-binding protein, it is conceivable that the mRNAs involved are bound to GUL-1 as part of the regulatory function of the protein. In fact, in S. cerevisiae Ssd1 was shown to bind multiple transcripts (Hogan et al., 2008, Jansen et al., 2009). To what extent this is the case in N. crassa (and maybe other filamentous fungi) has yet to be determined. However, if that is the case, it is likely that GUL-1 would be found in multiple cellular locations. In S. cerevisiae, the GUL-1 homologue Ssd1 is localized predominantly to cytoplasmic puncta and is associated with P-bodies and stress granules under conditions of cellular stress (Jansen et al., 2009, Kurischko et al., 2011a). These complexes lead to the translational repression of Ssd1-associated mRNAs (Kurischko et al., 2011a).