Aspergillus nidulans septin AspD appears to regulate new growth emergence in the vegetative phase

Septins are novel cytoskeletal proteins found in animals, fungi and microsporidia. They are essential for orderly cell division and are major determinants of morphology. The model filamentous fungus Aspergillus nidulans has five septins: AspA, AspB, AspC, AspD and AspE. In vivo localization of the AspD-GFP fusion protein shows that aspD localizes to dormant conidia, isotropically growing conidia, germ tubes, hyphal tips, septa, along the hyphae, at the base of branches, at the periphery of branches, and at metulae and phialides in conidiophores. Deletion of the aspD gene resulted in early germination of conidia, multiple germ tubes emergence, hyperbranching, early septation, swollen conidia, hyphal splits and abnormal conidiophores. From this we suggest that aspD in A. nidulans influences germination timing, germ tube emergence, conidial and basal compartment morphology, hyphal tip integrity, septum formation timing and branch emergence. Overall, AspD is thought to be involved in new growth emergence in the vegetative phase of A. nidulans.