The roles of microtubules in fungal cell growth and morphogenesis

Hyphae are the characteristic tubular cellular element of filamentous fungi. These cellular elements are fundamentally important to fungi in order to assimilate nutrients, explore and colonize new environments, and establish either beneficial or pathogenic associations with other organisms. Determining the cellular and molecular mechanisms of apical extension of hyphae has been on going research. So far, it is acknowledged that the coordinated actions of an underlying secretory network composed of microtubules, microfilaments, their associated proteins, and secretory vesicles are involved in this process. In addition, it has been proposed that a component of the secretory machinery, the Spitzenkorper, (= apical body), orchestrates the reception and delivery of secretory vesicles to the apical plasma membrane.;This study reports the details of how microtubules and the components of secretory machinery are involved in polarized hyphal extension of Aspergillus nidulans, Neurospora crassa, and Phytophthora infestans using the integration of standard and advanced bioimaging methods. The study of a novel thiazole carboxamide fungicide, ethaboxam showed that microtubules in P. infestans are indeed a primary target site for ethaboxam. The negative impacts on the elements of microtubule dynamic instability and the growth rates in leading hyphae of N. crassa suggest a role for microtubule motors in promoting these microtubule events and hyphal growth. The study of hyphal growth behavior of N. crassa wild type and kinesin mutants provides the first evidence that duration required to grow in the direction of the Spitzenkorper shifts greatly affects hyphal morphology. In addition, it was found that kinesin motor contributes to apical transport of mitochondria and microtubule distribution in N. crassa. Lastly, the utility of electron tomography provided the 3-D organizations of secretory vesicles and their cytoskeletal and plasma membrane associations within and around the Spitzenkorper in A. nidulans hypha at high spatial resolution. These findings provide further insights into the mechanisms involved in polarized hyphal growth.