Ndr kinases, such as Neurospora crassa COT-1, are important for cell differentiation and polar morphogenesis in various organisms. N. crassa strains disrupted in cot-1 almost completely cease cell elongation, hyperbranch and have an abnormally thick cell wall and septa, suggesting deregulation of the cell wall modeling machinery. Analysis of expression of the 7 chitin synthases in the fungus indicated the presence of highly- and lowly-expressed chs family members (chs-1,3,4,5,7 and chs-2,6, respectively). The expression of highly-expressed chs genes was further elevated (up to 50%) in a cot-1 (ts) background. No changes in rlm-1 (a transcription factor shown to regulate chs expression in yeast) expression were detected in a cot-1 background, nor were changes in chs expression found in an rlm-1 mutant. However, the increase in chs transcript levels found in cot-1 was alleviated in a gul-1 (encoding a homologue of a yeast RNA-binding translational regulator of cell wall remodeling) background and accompanied by partial suppression of the cot-1 phenotype in a gul-1;cot-1 strain. Preliminary data show that changes in glucan synthase and chitinase expression also occur in cot-1, indicative of multiple changes in cell wall remodeling associated with COT-1 inactivation. Taken together, our data show that changes in cell wall remodeling may contribute to the phenotype of cot-1 and that GUL-1 is a functional link between cot-1 and cell wall biosynthesis.
