GUL-1 AFFECTS RNA ABUNDANCE OF GENES EXPRESSING CELL WALL REMODELING PROTEINS IN NEUROSPORA CRASSA

Structure and maintenance of the cell wall are determined, in part, by balanced function of cell wall biosynthesis and degradation. We hypothesized that the abnormally-thick cell walls and septa of the N.crassa NDR kinase cot-1 mutant may be a result of altered expression of the cell wall remodeling machinery. Inactivation of gul-1 (a homologue of the yeast Ssd1 RNA-binding protein involved in translational regulation of cell wall remodeling proteins) partially suppresses the cot-1 phenotype, accompanied by improved characteristics of the cell wall and septa. A 40% increase in chitin content in the cell wall of cot-1 (when compared to the wild type) was almost completely abolished in the gul-1;cot-1strain. Furthermore, the gul-1 mutant was also found to be almost 2-fold more sensitive to chitin synthase inhibition, when compared to the wild type. We have determined that gul-1 is involved in regulation of the expression of cell wall remodeling genes such as glucan synthase, chitin synthases and a chitinasein a manner which is at least partially independent of the classic cell wall integrity pathway. Overall, expression of at least 25 genes involved in cell-wall remodeling was GUL-1-dependent. Moreover, based on GO analysis, GUL-1 was also found to regulate additional pathways such as transmembrane transport (34 genes) andamino acid metabolism (8 genes).We conclude that GUL1 is a regulator of cell wall remodeling and that the suppressive effect on cot-1 is conferred via this capacity.