The fungus Magnaporthe oryzae uses a specialized pressure-generating infection cell called an appressorium to break into rice leaves and initiate disease. Appressorium functionality is dependent on the formation of a cortical septin ring during its morphogenesis, but precisely how this structure assembles is unclear. Here we show that F-actin rings are recruited to the circumference of incipient septin disc-like structures in a pressure-dependent manner, and that this is necessary for their contraction and remodeling into rings. We demonstrate that the structural integrity of these incipient septin discs requires both an intact F-actin and microtubule cytoskeleton and provide fundamental new insight into their functional organization within the appressorium. Lastly, using proximity-dependent, labelling we identify the actin modulator coronin as a septin proximal protein and show that F-actin-mediated septin disc-to-ring remodeling is perturbed in the genetic absence of coronin. Taken together, our findings provide new insight into the dynamic remodeling of infection-specific higher-order septin structures in a globally significant fungal plant pathogen.

Rice blast disease, caused by the fungus Magnaporthe oryzae, destroys enough rice each year to feed 60 million people, and is a major threat to global food security. To establish disease, M. oryzae forms a specialized infection structure called an appressorium, which it uses to physically break into rice leaves. Essential for this process is the timely assembly of a septin ring structure at the base of the appressorium. Septins are a conserved family of GTP‐binding proteins, forming hetero‐oligomeric rods and filaments that are organized into higher‐order structures at the cell cortex. The M. oryzae septin ring scaffolds the formation of a donut‐shaped filamentous actin network, needed for the emergence of a polarized penetration structure from the base of the appressorium. Importantly, relatively little is understood about how higher‐order septin structures form in the right place and at the right time in appressoria to drive infection. We are using a proximity‐dependent proteomics to identify novel proteins involved in septin organization, and are functionally characterizing these using reverse genetics, and cell biological approach. We genetically tagged the septin protein Cdc11/Sep5 with TurboID, and identified a host of putatively proximal and interacting proteins. Here, we validate a number of these, and investigate their broader role in fungal biology. The outcomes of this research will provide fundamental new insight into the cellular control of septin organization in a global cereal killer.

To celebrate the 50th anniversary of the American Society for Cell Biology's Women in Cell Biology Committee (WICB), members of WICB and the MBoC Editorial Board invited a diverse group of scientists to highlight MBoC papers by women that have had a scientific or personal impact on the authors of the highlight.This study established Ashbya gossypii as a model to study septin complex assembly into higher-order structures independently from the cell cycle. DeMay et al.