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Rapid tip-directed movement of Golgi equivalents in growing Aspergillus nidulans hyphae suggests a mechanism for delivery of growth-related materials

Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2, Canada

Correspondence
Susan G. W. Kaminskyj
Susan.Kaminskyj{at}usask.ca

Golgi equivalents (GEs) process materials in the fungal secretory pathway. Despite the importance of localized secretion in fungal tip growth, GE behaviour in living hyphae has not been documented. The distribution was monitored of an Aspergillus nidulans putative GE-associated protein, CopA, tagged with GFP (CopA–GFP). This co-localized with a Golgi body/GE marker established in other systems, -2,6-sialyltransferase, tagged with red fluorescent protein (ST–RFP). CopA–GFP and ST–RFP distributions responded similarly to brefeldin A, which impairs Golgi/GE trafficking. We used a CopA–GFP, hypA1 strain to study GE distribution and behaviour in growing A. nidulans hyphae. This strain has a wild-type phenotype at 28 °C, can be manipulated by changing growth temperature or by use of cytoskeleton inhibitors, and its GE behaviour is consistent with that in a wild-type-morphology strain. A. nidulans GEs were more abundant at hyphal tips than subapically, and showed saltatory motility in all directions. Anterograde GE movements predominated. These were positively correlated with, but at least 10-fold faster than, hyphal growth rate, under all growth and experimental conditions investigated. The actin inhibitor latrunculin B reduced both anterograde GE movement and hyphal growth rate, whereas the microtubule (MT) depolymerizer benomyl increased anterograde GE movement and decreased hyphal growth rate. The MT stabilizer taxol increased A. nidulans GE movement but not hyphal growth rate. A. nidulans GE motility appears to have a complex dependence on both actin and MTs. We present a model for apical delivery of growth materials in which A. nidulans GEs play a role in long-distance transport.

A supplementary figure (video clip) showing Golgi equivalent motility in Aspergillus nidulans strain AAB1 is available with the online version of this paper.