Basic-Zipper-Type Transcription Factor FlbB Controls Asexual Development in Aspergillus nidulans

Abstract

The fungal colony is a complex multicellular unit consisting of various cell types and functions. Asexual spore formation (conidiation) is integrated through sensory and regulatory elements into the general morphogenetic plan, in which the activation of the transcription factor BrlA is the first determining step. A number of early regulatory elements acting upstream of BrlA (fluG and flbA-E) have been identified, but their functional relations remain to be further investigated. In this report we describe FlbB as a putative basiczipper-type transcription factor restricted to filamentous fungi. FlbB accumulates at the hyphal apex during early vegetative growth but is later found in apical nuclei, suggesting that an activating modification triggers nuclear import. Moreover, proper temporal and quantitative expression of FlbB is a prerequisite for brlA transcription, and misscheduled overexpression inhibits conidiation. We also present evidence that FlbB activation results in the production of a second diffusible signal, acting downstream from the FluG factor, to induce conidiation.

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

“…The strains of A. nidulans employed in this study (Table 1) were obtained by crossing or transformation following standard protocols (Etxebeste et al, 2008). Strain BD212 was obtained by meiotic recombination between strains TN02A25 and MAD2159.…”

“…Strain MAD2446 expresses protein H1 : : mCh (hhoA locus; Ramon et al, 2000). Strains MAD2334 and MAD2654 were obtained by the transformation of BD167 (Etxebeste et al, 2008) and MAD2446, respectively, with the fusion PCR products to generate C-terminal mCherry or gfp-tagging of the KapI protein by gene replacement (Etxebeste et al, 2008;Yang et al, 2004).…”

“…Phenotypic analyses under stress growth conditions were done using Aspergillus minimal medium (MMA) as in Etxebeste et al (2008). Strains were point inoculated and cultivated at 37 uC for 72 h in appropriately supplemented MMA.…”

“…Mutations in most UDA genes generate a phenotype commonly known as 'fluffy', which shows delayed or impaired conidiation (Etxebeste et al, 2009, and references therein). 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).…”

“…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.…”