Graduate Studies


Date of this Version

Fall 8-21-2012


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Steven D. Harris. Lincoln, Nebraska: August, 2012

Copyright (c) 2012 Bradley M. Downs


In filamentous fungi, such as Aspergillus nidulans, growth is directed by polarized regions in hyphal cells. This polarized growth occurs through cell wall deposition and cell surface expansion at specific sites such as hyphal tips. In mature hyphae, additional growth sites are generated by the formation of lateral branches from sub-apical cells. Conversely, during conidiation, branch formation appears to be suppressed in developing conidiophores. Prior studies of Cdc42 and RacA GTPases in A. nidulans found that Cdc42 is required for hyphal branching while RacA has little function during branching. To further understand GTPases regulation, characterization of the effector PakB (homologue of yeast Cla4) was preformed. This study shows evidence that PakB localizes to the site of polarized growth in A. nidulans. This localization correlates with suppression of spurious branches. Similar to other fungi, there is evidence that both Cdc42 and RacA function in the same pathway as PakB. Results suggest that PakB may function in a parallel pathway to Cdc42 during endocytosis. Interestingly, it seems that the RacA-PakB interaction helps suppress branching formations in developing conidiophores. These results give a new understanding of the function of the effector PakB and the role of Cdc42/Rac GTPases in A. nidulans.