Myosin Light Chain Plays a Role in Cell Division in the Fungus Aspergillus nidulans

Abstract

Cell division in the filamentous fungi involves inward growth of the plasma membrane at predetermined sites, accompanied by synthesis of new cell wall material to create a partially closed barrier termed a septum. Research in budding and fission yeasts has established a role for the actin/myosin cytoskeleton in this process. The mechanisms of septation in the filamentous fungi are less well understood. We have GFP‐tagged a protein (product of gene AN6732) from the filamentous fungus Aspergillus nidulans, which shows sequence homology to myosin light chains (MLC), demonstrating its localization to sites of septum formation. Strains in which we have replaced AN6732 with the Aspergillus fumigatus gene encoding RiboA are still able to form septa at lower growth temperature (e.g., 30°C). However septation is blocked at 37°C, at which temperature wild type strains septate normally. Thus, MLC's role in septation must be viewed as one of fine‐tuning of the process rather than as a component necessary for its completion. We show that under conditions where septation is blocked in the AN6732‐deletion strain, both myosin II (MyoB) and the Septation Initiation Network Protein MobA successfully localize as rings at potential septation sites, while in strains where either of those proteins is deleted or suppressed MLC does not localize to pre‐septal rings.