Signaling through the Aspergillus nidulans orthologue of PKC mediates septum formation

Abstract

We have shown that the Aspergillus nidulans orthologue of protein kinase C (PkcA) participates in regulating cell wall integrity (CWI) and localizes at sites of cell wall synthesis, including growing hyphal tips and septa. To better understand the mechanisms by which PkcA localizes to tips and septa, we have observed the formation of cortical rings at sites of septation by fluorescently tagged PkcA in hyphae defective in expression of other proteins necessary for septum formation. In addition, we have co‐imaged PkcA and other septation proteins bearing complementary fluorescent tags. Here we report that localization of PkcA to septa lies “downstream” of the functions performed by MobA (Mob1p orthologue), TpmA (tropomyosin), SepA (formin), SepD, SepG, and proteins encoded by two other not‐yet‐cloned Sep loci. In the absence of function of these proteins, PkcA cortical rings were not observed. PkcA localization lies “upstream” of MyoB (myosin II orthologue), the A. nidulans orthologue of Bud4p (in yeast, a bud site selection marker), and a protein encoded by a third not‐yet‐cloned Sep locus. PkcA cortical rings still form in the absence of function of these proteins, though septa do not develop. SepA, TpmA, MyoB, and MobA all appear to colocalize with PkcA during normal septum formation. Studies with other septation‐related proteins are ongoing.