The Role of the Kinesin Motor KipA in Microtubule Organization and Polarized Growth of Aspergillus nidulans

Polarized growth in filamentous fungi requires the integrity of the microtubule (MT) cytoskeleton. We found that growing MTs in Aspergillus nidulans merge at the center of fast growing tips and discovered that a kinesin motor protein, KipA, related to Tea2p of Schizosaccharomyces pombe, is required for this process. In a ΔkipA strain, MT plus ends reach the tip but show continuous lateral movement. Hyphae lose directionality and grow in curves, apparently due to mislocalization of the vesicle supply center (Spitzenkörper) in the apex. Green fluorescent protein (GFP)-KipA accumulates at MT plus ends, whereas a KipA rigor mutant protein, GFP-KipA(G223E), coated MTs evenly. These findings suggest that KipA requires its intrinsic motor activity to reach the MT plus end. Using KipA as an MT plus-end marker, we found bidirectional organization of MTs and determined the locations of microtubule organizing centers at nuclei, in the cytoplasm, and at septa

Aspergillus nidulans Dis1/XMAP215 Protein AlpA Localizes to Spindle Pole Bodies and Microtubule Plus Ends and Contributes to Growth Directionality

The dynamics of cytoplasmic microtubules (MTs) is largely controlled by a protein complex at the MT plus end. In Schizosaccharomyces pombe and in filamentous fungi, MT plus end-associated proteins also determine growth directionality. We have characterized the Dis1/XMAP215 family protein AlpA from Aspergillus nidulans and show that it determines MT dynamics as well as hyphal morphology. Green fluorescent protein-tagged AlpA localized to MT-organizing centers (centrosomes) and to MT plus ends. The latter accumulation occurred independently of conventional kinesin or the Kip2-familiy kinesin KipA. alpA deletion strains were viable and only slightly temperature sensitive. Mitosis, nuclear migration, and nuclear positioning were not affected, but hyphae grew in curves rather than straight, which appeared to be an effect of reduced MT growth and dynamics