The novel membrane protein SccA affects cell wall integrity in Aspergillus nidulans

Abstract

This research describes a novel gene designated SccA, which affects cell wall integrity in the filamentous fungus Aspergillus nidulans. Plasmid‐borne extra copies of SccA can suppress the calC2 mutation in the A. nidulans orthologue of protein kinase C (PkcA), which results in hypersensitivity to the chitin‐binding agent Calcofluor White (CFW). In filamentous fungi, as in yeasts, hypersensitivity to CFW correlates with defects in cell wall integrity. The hypothetical translated product of SccA is an ST‐rich 271‐aa protein (42% S/T) of 27.4 kDa mass (unprocessed), with a cleavable N‐terminal ER‐targeting domain and a probable internal membrane anchor. No known homologies have been identified in the sequence databases. A SccA‐GFP hybrid localizes to the plasma membrane of vegetative hyphae and is especially enriched in septa. When SccA is placed under the control of the regulatable AlcA promoter, vegetative growth is normal under both high expression and low expression conditions (growth on glycerol or glucose containing medium, respectively), but asexual sporulation is suppressed during growth on glycerol. Taking into consideration the protein's cell surface location and its influence on the function of PkcA, we hypothesize that SccA plays a role in signal transduction as part of a cell wall integrity pathway.