Hof1 of Aspergillus nidulans is Essential for Cytokinesis and Septum Formation

Abstract

Cytokinesis is an essential component of cellular development in filamentous fungi. The process parallels that of cell division in animal cells in requiring assembly and constriction of a contractile actomyosin ring (CAR) in the cell periphery. However, the process differs from that in animals by involving the simultaneous construction of a chitin‐rich cross wall termed a septum, which separates semi‐independent compartments of the fungal hypha. Through randomized mutations, we have generated a temperature‐sensitive mutant defective in septum formation, designated strain RCH59. Mendelian crossing confirmed that the temperature sensitive phenotype results from a single locus mutation. Next Generation Whole Genome Sequencing identified a mutation that is located in gene AN4566 encoding the homolog of Saccharomyces cerevisiae's Hof1. The mutation in Aspergillus nidulans’ version of Hof1 (AnHof1) is at base 2436 out of 5536 and is a transition from cytosine to thymine. The mutation is predicted to remove an Arginine and introduce a premature stop codon after residue 738. The missing 342 C‐terminal residues includes the entire SH3 domain of AnHof1. We cloned the wildtype version of AnHof1 into plasmid pRG3 and complemented the phenotype in RCH59, confirming that the mutation occurs in AnHof1. We also deleted AnHof1 to demonstrate that a AnHof1 minus strain has an aseptate phenotype. In the yeasts (S. cerevisiae and S. pombe), Hof1 forms a ring structure that co‐localizes with the CAR and is involved with mediating the cytoskeletal rearrangements necessary for cytokinesis. We GFP tagged AnHof1 to demonstrate that the protein product localizes to sites of septum formation and co‐localizes with actin during at least part of CAR assembly and constriction. In further work, we have generated double‐mutant strains in which a GFP‐tagged septation‐related protein is expressed in the RCH59 strain to demonstrate a network of genetics interactions between AnHof1 and other proteins involved in septation.Support or Funding InformationThis research was supported by NSF grant RUI‐0742907 to TWH and LJH and NSF grant RUI‐1615192 to LJH and TWH.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.