Several years ago, we proposed that reactive oxygen species (ROS) play essential roles in cell differentiation. Enzymes of the NADPH oxidase (NOX) family produce ROS in a regulated manner. In Aspergillus nidulans, Neurospora crassa and other fungi, NOX are needed for sexual cell differentiation and/or polarized growth. Fungal NOX require and interact with other proteins such as Rac, NoxR and possibly BEM-1. However, little is known about how NOX activity is regulated or about how ROS are connected to development and polarized growth. A candidate to mediate part of ROS functions in A. nidulans is the transcription factor FlbD, which is a member of the redox-regulated MYB family. Elimination of the flbD gene results in decreased asexual sporulation (conidiation), increased polar growth and derepressed sexual development. This proposal is focused on four major points. First, we will determine the cellular localization of ROS and NOX and will look for NOX-interacting proteins. Second, we will determine if all NOX functions are dependent on ROS production, considering that NOX interacting proteins like Rac might have additional functions. Third, we will determine if FlbD is regulated by redox mechanisms in vivo through ROS produced by NOX or by other sources and, fourth, the transcription factors AtfA and AapA and the peroxiredoxins will be evaluated as mediators of ROS signaling.
The expression of a dominant-active form of RacA (DARacA) in liquid culture results in a switch from polar to non-polar growth (arrowheads). 14 h glucose-grown mycelia from wild-type and two independent alcA::DARacA strains were transferred to medium containing threonine (alcA inducing) for the indicated times.