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 DeltakipA 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.