Septins and cytokinesis in the polymorphic fungus Aureobasidium pullulans

During cytokinesis of animals and fungi, a contractile actomyosin ring (CAR) assembles at target locations and constricts to drive cell separation. In animal cells, the position of the CAR is determined by the mitotic spindle, so that the cleavage plane is perpendicular to the mitotic axis. However, in budding yeasts, the location of CAR assembly is specified by a cortical septin cytoskeleton that recruits CAR components to the neck. In the polymorphic fungus Aureobasidium pullulans, we show that septins assemble at mother-bud necks and predict the site of CAR assembly. Cells lacking septins stochastically failed to assemble CARs at a subset of bud necks. However, even cells lacking all four core septins were able to assemble CARs at 75% of bud necks. Our findings suggest the existence of a novel CAR positioning strategy that requires neither septin scaffolds nor nuclear/spindle cues to enable CAR assembly and constriction at bud necks. eTOC SUMMARYBudding yeasts are thought to use septins to mark mother-bud necks as sites for cytokinesis. Here, we find that the multibudding yeast Aureobasidium pullulans can position cytokinetic machinery at most bud necks even in the absence of septins, revealing a novel pathway to mark cytokinesis sites.