The bZIP‐type transcription factor FlbB regulates distinct morphogenetic stages of colony formation in Aspergillus nidulans

Abstract

SummaryConidiophore formation in Aspergillus nidulans involves a developmental programme in which vegetative hyphae give rise to an ordered succession of differentiated cells: foot cell, stalk, vesicle, metulae, phialides and conidia. The developmental transition requires factors that are expressed in vegetative hyphae that activate the expression of the main regulator of conidiation, BrlA. One such element is the bZIP-type transcription factor FlbB. We found that flbB -mutants show defective branching patterns and are susceptible to autolysis under high sorbitol or sucrose concentrations, revealing a role in vegetative growth. In addition, FlbB plays a role in conidiophore initiation, as its upregulation reduces conidiophore vesicle swelling and generates a reduced number of metulae. FlbB was located at the tip of growing metulae, following a similar pattern as described in vegetative hyphae. In wild-type strains, the transition from metulae to phialides could be reversed to generate vegetative hyphae, indicating the existence of a specific control point at this stage of conidiophore formation. The combined evidence points to FlbB as a key factor in the transition to asexual development, playing a role at various control points in which the process could be reversed.

AbaA and WetA govern distinct stages of Aspergillus fumigatus development

“…Moreover, after 14 h incubation, the DAfuwetA mutant clearly showed reduced branch density compared to the WT and complemented strains. The branching rates of these strains were defined by peripheral growth unit (PGU) values (Etxebeste et al, 2009;see Fig. 6b).…”

Characterization of the developmental regulator FlbE in Aspergillus fumigatus and Aspergillus nidulans

“…Among these, mutational inactivation of flbB, flbC, flbD or flbE gives rise to mutants that exhibit fluffy delayed conidiation phenotypes (Wieser et al, 1994). The FlbB, FlbC and FlbD proteins contain a b-zip, two C 2 H 2 zinc fingers and a cMyb-DNA binding domain, respectively, and are thought to be potential TFs that act on the activation of brlA expression (reviewed in Adams et al, 1998;Etxebeste et al, 2008Etxebeste et al, , 2009Garzia et al, 2010;Wieser and Adams, 1995). Recent studies demonstrated that FlbB is necessary for the expression of flbD, and FlbB and FlbD activate brlA in a cooperative manner .…”

FlbD, a Myb Transcription Factor of Aspergillus nidulans, Is Uniquely Involved in both Asexual and Sexual Differentiation

“…In contrast, FluG is responsible for the production of an extracellular signaling factor required for activation of the flbD-E genes in vegetative cells and to induce conidiation, along with other unidentified compounds (38,39,44,56,64). FlbB is a TF of the bZIP type that unexpectedly also localizes at the hyphal tips of vegetative hyphae, forming a complex with FlbE (17,18,21). flbE encodes a small protein with two conserved but uncharacterized domains, and FlbE and FlbB are functionally interdependent and proposed to regulate the transition from vegetative growth to conidiation (20,34).…”