Putative cell wall integrity sensor proteins in Aspergillus nidulans

The cell wall integrity (CWI) signal transduction pathway, which has been well-studied in the yeast Saccharomyces cerevisiae, plays an important role in the regulation of cell wall biogenesis. Recently, we characterized the CWI stress sensor orthologs WscA and WscB in the filamentous fungus Aspergillus nidulans. Disruption of the wscA and wscB genes causes a change in the transcriptional levels of agsA and agsB, which encode α-1,3-glucan synthase, resulting in an increase in alkaline soluble cell wall glucan. However, the contribution of these putative sensors to downstream CWI pathway signaling remains unclear because MpkA-RlmA signaling remains active in wscA-wscB double disruptants exposed to cell wall stress associated with exposure to micafungin, a potent inhibitor of β-1,3-glucan synthase. In this addendum, we report the results of further studies involving hypo-osmotic shock as a stressor that suggest WscA and WscB are not essential for MpkA-RlmA signaling. Finally, we describe for the first time other Aspergillus CWI stress sensor candidate Mid2-like protein.