Distinct actomyosin–septin coordination governs conidiation and septation in Verticillium dahliae

Abstract

Conidiation is the primary mode of reproduction in filamentous fungi and is essential for the dispersal of pathogenic species. However, the fundamental cellular mechanisms regulating conidiation in plant pathogenic fungi remain largely unexplored. Here, using Verticillium dahliae as a model, we investigated the dynamic assembly and function of the contractile actomyosin ring (CAR) and septins during conidiation through live-cell imaging. We show that septins, visualized via VdCdc11-GFP, first accumulate at the tip of budding hyphae during the transition from hyphal elongation to apical budding, and undergo an hourglass-to-double-ring transition at the bud neck. Following mitosis, myosin II and actin assemble simultaneously into a contractile ring to drive cytokinesis. Disruption of core septin function results in defective nuclear segregation and aberrant nuclear migration during mitosis, as well as delayed recruitment of myosin II to the bud neck, indicating that septins scaffold cytokinetic machinery and coordinate nuclear division during conidiation. In contrast, during hyphal septation, myosin II, actin, and septins appear simultaneously as a diffuse cortical band, with septin organization dependent on actin. Collectively, these findings reveal distinct spatial and temporal coordination between actomyosin and septins in two cytokinetic contexts—conidiation and hyphal septation—and define apical budding as a specialized cytokinesis mode in V. dahliae. Our study broadens the understanding of fungal cytokinesis beyond yeast models to multicellular filamentous fungi.

Keywords

conidiation / contractile actomyosin ring / cytokinesis / filamentous fungi / septins

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