Gul-1 mediates cell wall remodeling via the cot-1 pathway in Neurospora crassa

Inbal Herold 1 David Kowbel 2 Yaron Orenstein 3 Oded Yarden 1
1Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
2Department of Plant and Microbial Biology, University of California at Berkeley UC Berkeley, Berkeley, California, USA
3Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel

In Neurospora crassa, impaired function of the NDR kinase COT-1 results in markedly thickened cell walls. This effect is partially suppressed by inactivation of gul-1 (an RNA-binding protein involved in translational regulation of cell wall remodeling proteins). Using electron microscopy, we determined that inactivation of gul-1 also results in improved characteristics of the cot-1 cell wall and septa. These observations coincide with our findings that 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-1 double mutant. The gul-1 mutant was also found to be almost 2-fold more sensitive to a chitin synthase inhibitor (Nikkomycin Z), when compared to the wild type. We suggest that GUL1 contributes to changes in cell wall morphology and composition in a manner that confers the suppressive effect on cot-1. We found that gul-1 is involved in regulation of the expression of several cell wall remodeling genes such as glucan/chitin synthases and chitinase in a manner which is at least partially independent of the classic cell wall integrity pathway. Our RNASeq analysis revealed that GUL-1 affects transcript abundance of at least 25 genes involved in cell-wall remodeling via the COT-1 pathway. Moreover, GUL-1 was also found to regulate additional pathways such as transmembrane transport as well as amino acid metabolism. Based on catRAPID algorithm analysis mRNAs of some of the differentially-expressed cell wall-related genes have been predicted to physically interact with the GUL-1 protein. RNA antisense purification (RAP) analysis coupled with mass spectrometry is currently being employed to determine GUL-1-mRNA interactions, including the possibility that GUL-1 binds its own transcript.