Fungal Golgi equivalents process and sort materials in the fungal secretory pathway. Despite the importance of localized secretion in fungal tip growth, Golgi behaviour in living hyphae has not previously been documented. We used an Aspergillus nidulans strain containing the predicted Golgi marker CopA:GFP in a hypA1 ts polarity-defective background (a gift of A. Breakspear and S. Assinder) to study Golgi distribution in growing wildtype and polarity-defective phenotype hyphae. CopA has been shown to have high homology to Saccharomyces cerevisiae alpha-COPI. Predominant Golgi localization of CopA:GFP was confirmed by inserting a tagged copy of the established Golgi marker alpha-2,6-sialyl transferase (ST-RFP) and finding a high degree of co-localization. As expected, the patterns of both markers became more diffuse following treatment with brefeldin A. We used CopA:GFP to study Golgi behaviour in growing A. nidulans hyphae using time-lapse confocal fluorescence microscopy. In wildtype A. nidulans hyphae, Golgi were more abundant near hyphal tips than subapically, as had previously been shown with CopA:GFP in fixed cells. A. nidulans Golgi move independently of each other, in all directions, but predominantly and more rapidly toward the hyphal tip. When hypA1 restrictive phenotype cells re-established polarity at 28 ºC, Golgi moved preferentially into the newly-formed branches. The average rate of tipward Golgi movement was positively correlated with but at least ten-fold faster than the hyphal growth rate in the same cells. This relationship held under all experimental conditions tested. At 5 μg/mL, the actin inhibitor latrunculin B significantly decreased tipward Golgi motility and tip growth rate, whereas at 1 μg/mL the microtubule (MT) inhibitor increased tipward Golgi motility despite decreased growth rate. The MT stabilizing drug taxol, which we had previously shown to increase cytoplasmic MT number without affecting growth rate, increased tipward Golgi movement but again without increased hyphal growth rate. The cytoskeletal basis for Golgi motility appears to be complex. Our data support a model for apical delivery of A. nidulans tip growth materials in which Golgi play a role in long-distance transport.
Full conference title:
9th EUROPEAN CONFERENCE ON FUNGAL GENETICS
- ECFG 9th (2008)