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Originally published as Genetics Published Articles Ahead of Print on August 9, 2008.
Genetics, Vol. 179, 1919-1932, August 2008, Copyright © 2008
doi:10.1534/genetics.108.089318
Regulation of Apical Dominance in Aspergillus nidulans Hyphae by Reactive Oxygen Species
Camile P. Semighini1 and Steven D. Harris2
Plant Science Initiative and Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68588-0660
2 Corresponding author: Plant Science Initiative, N234 Beadle Center, University of Nebraska, Lincoln, NE 68588-0660.
E-mail: sharri1{at}unlnotes.unl.edu
In fungal hyphae, apical dominance refers to the suppression of secondary polarity axes in the general vicinity of a growing hyphal tip. The mechanisms underlying apical dominance remain largely undefined, although calcium signaling may play a role. Here, we describe the localized accumulation of reactive oxygen species (ROS) in the apical region of Aspergillus nidulans hyphae. Our analysis of atmA (ATM) and prpA (PARP) mutants reveals a correlation between localized production of ROS and enforcement of apical dominance. We also provide evidence that NADPH oxidase (Nox) or related flavoproteins are responsible for the generation of ROS at hyphal tips and characterize the roles of the potential Nox regulators NoxR, Rac1, and Cdc42 in this process. Notably, our genetic analyses suggest that Rac1 activates Nox, whereas NoxR and Cdc42 may function together in a parallel pathway that regulates Nox localization. Moreover, the latter pathway may also include Bem1, which we propose represents a p40phox analog in fungi. Collectively, our results support a model whereby localized Nox activity generates a pool of ROS that defines a dominant polarity axis at hyphal tips.
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