Aspergillus nidulans FlbE is an upstream developmental activator of conidiation functionally associated with the putative transcription factor FlbB

Abstract

SummaryAspergillus nidulans switches from vegetative growth to conidiation when aerial hyphae make contact with the atmosphere, or are subjected to specific environmental stress. The activation of the central conidiation pathway led by the transcription factor brlA is a critical milestone in this morphogenetic transition. A number of upstream developmental activators (UDAs), expressed in vegetative cells, are required for this process to occur in conjunction with cessation of vegetative growth. Mutants affected in these factors remain aconidial (fluffy) with low brlA expression levels (flb). In this report, we describe FlbE as a UDA containing two conserved but hitherto uncharacterized domains, which functions in close association with putative transcription factor FlbB. Both UDAs are functionally interdependent, and colocalize at the hypha tip in an actin cytoskeleton-dependent manner. Moreover, bimolecular fluorescence studies show that they physically interact in vivo. These findings add evidence in favour of the existence of a signalling complex at or near the Spitzenkörper as an important part of the machinery controlling the morphogenetic transition between vegetative growth and conidiation.

KapI, a non-essential member of the Pse1p/Imp5 karyopherin family, controls colonial and asexual development in Aspergillus nidulans

“…For other stresses KCl (0.6 M), NaH 2 PO 4 (0.5 M), sorbitol (1.2 M) or sucrose (1.0 M) was added to MMA. Experiments in liquid media were performed essentially as described by Garzia et al (2009). Briefly, strains were cultivated in supplemented MMA for 18 h at 37 uC, and then the mycelium was transferred to different stress conditions (see text) in MMA and cultured for an additional 20 h.…”

“…DNA and RNA samples for Southern and Northern blot experiments were isolated and manipulated as described previously (Etxebeste et al, 2008;Garzia et al, 2009). …”

“…4, first row). Under glucose starvation, both DkapI and wild-type strains generated simplified conidiophores (Etxebeste et al, 2008;Garzia et al, 2009;Fig. 4, second row), consisting of phialide-like structures with a single conidium at their end; however, the DflbB mutant produced narrow hyphae, approximately 1.5 mm in diameter, from which single conidium-like structures rarely emerged (Fig.…”

“…Since the conidiation pattern of DkapI was similar to that shown by mutants from the upstream developmental pathway of conidiation (Etxebeste et al, 2008Garzia et al, 2009), we analysed the aconidial phenotypes of single and double null kapI and flbB strains on solid media under different stress conditions which are known to promote conidiation (Etxebeste et al, 2008Garzia et al, 2009). In synthetic complete minimal medium, both DflbB and DkapI strains showed an aconidial phenotype, although the former was more prominently fluffy (Fig.…”

“…Many UDAs are putative TFs (Adams et al, 1998;Etxebeste et al, 2008;Seo et al, 2006;Wieser & Adams, 1995). The best-known member of this family is the bZIPtype TF FlbB, which is localized in the most apical nucleus of vegetative hyphae, and remarkably, in the Spitzenkörper (Etxebeste et al, 2008Garzia et al, 2009). However, the mechanisms which regulate FlbB function, and that of other UDAs, remain to be clarified.…”