Regulation of Neurospora crassa cell wall remodeling via the cot-1 pathway is mediated by gul-1

Abstract

Impairment of the Neurospora crassa Nuclear DBF2-related kinase-encoding gene cot-1 results in pleiotropic effects, including abnormally thick hyphal cell walls and septa. An increase in the transcript abundance of genes encoding chitin and glucan synthases and the chitinase gh18-5, but not the cell wall integrity pathway transcription factor rlm-1, accompany the phenotypic changes observed. Deletion of chs-5 or chs-7 in a cot-1 background results in a reduction of hyperbranching frequency characteristic of the cot-1 parent. gul-1 (a homologue of the yeast SSD1 gene) encodes a translational regulator and has been shown to partially suppress cot-1. We demonstrate that the high expression levels of the cell wall remodeling genes analyzed is curbed, and reaches near wild type levels, when gul-1 is inactivated. This is accompanied by morphological changes that include reduced cell wall thickness and restoration of normal chitin levels. We conclude that gul-1 is a mediator of cell wall remodeling within the cot-1 pathway.

Altering Neurospora crassa MOB2A exposes its functions in development and affects its interaction with the NDR kinase COT1

“…To determine whether the observed genetic interaction between the mob‐2a(Y117E,Y119E);Δmob‐2b (ts) mutant and gul‐1 is also articulated in GUL1 function, we measured the mRNA levels of genes whose expression was found to be increased in cot‐1 (ts) and suppressed by gul‐1 (Herold and Yarden, ; Herold and Yarden, unpublished). Our results show that chs‐1 (NCU03611) RNA levels are elevated in both cot‐1 (ts) as well as in the mob‐2a(Y117E,Y119E);Δmob‐2b strain, suggesting that the Tyr117 and Tyr119 substitutions may affect COT1 activity.…”

“…In addition to the ultrastructural analysis, we also used calcofluour white and congo red to determine if marked changes in the perithecial cell wall could be observed. This was based on previous evidence concerning significant changes in cell wall morphology and composition in mutants of the major MOB2A target – COT1 (Gorovits et al ., ; Herold and Yarden, ). Clear differences in the staining patterns of perithecia subjected to the two dyes were observed (Fig.…”

“…To do so, we employed a proposed COT1 substrate‐encoding gene, gul‐1 , as a reporter of genetic interactions with its upstream regulator, cot‐1 . Many genes are co‐affected by cot‐1 and gul‐1 (Herold and Yarden, ; Herold and Yarden, unpublished). After gul‐1 had been deleted in the mob‐2a(Y117F,Y119F);Δmob‐2b MOB2A phosphomimetic mutant, we found that colony morphology and hyphal branching were similar to those observed in the Δgul‐1 parent (Figs.…”

“…Deletion of gul‐1 partially suppresses the abnormal cot‐1 (ts) phenotype. The cot‐1;gul‐1 double mutant exhibits improved growth rate and branching accompanied by a thinner cell wall which resembles that of the wild type (Terenzi and Reissig, ; Herold and Yarden, ). The observed phenotypic suppression in the gul‐1;cot‐1 mutant is accompanied by the alteration of gene expression in cot‐1 (ts) mutant.…”

“…The observed phenotypic suppression in the gul‐1;cot‐1 mutant is accompanied by the alteration of gene expression in cot‐1 (ts) mutant. Examples include the chitin synthase family members as well as glucan synthase (Herold and Yarden, ). The fact that the yeast GUL1 homologue (Ssd1) is a direct substrate of the COT1 homolog (Cbk1) and that at least some of the phenotypic consequences of impairing COT1 can be suppressed by deletion of gul‐1 suggests that gul‐1 can serve as a proxy for at least part of the NDR kinase's functions.…”