Cell-end marker proteins are required for hyphal ring formation and size determination of traps in <i>Arthrobotrys flagrans</i>

Filamentous fungi grow by apical extension where secretory vesicles are transported long distances by microtubules and by actin prior to fusion with the cell membrane. Apical, membrane-bound cell-end marker proteins (CEMPs) organise the cytoskeletons and thereby the growth machinery. CEMPs have been characterised mainly in Schizosaccharomyces pombe and Aspergillus nidulans. Here, we studied the role of CEMPs in the nematode-trapping fungus Arthrobotrys flagrans. This predatory fungus forms ring-shaped adhesive traps to capture nematodes, such as Caenorhabditis elegans. Traps are morphologically and physiologically different from vegetative hyphae and are generated by hyphal turning and fusion of the trap tip cell with the basal hypha. The absence of the membrane-anchored CEMP receptor protein, TeaR, caused a reduction in ring size, whereas deletion of teaA or teaC largely prevented the formation of ring-shaped hyphae, and most traps appeared as adhesive sticks. Hence, compared to Schizosaccharomyces pombe and Aspergillus nidulans, loss of function of the CEMPs results in a severe morphological phenotype. The mutant strains also show changes in cell-to-cell communication and hyphal fusion, suggesting novel functions and interconnections with other signalling processes in the cell.