Tip‐to‐nucleus migration dynamics of the asexual development regulator FlbB in vegetative cells

Abstract

SummaryIn Aspergillus nidulans, asexual differentiation requires the presence of the transcription factor FlbB at the cell tip and apical nuclei. Understanding the relationship between these two pools is crucial for elucidating the biochemical processes mediating conidia production. Tip-to-nucleus communication was demonstrated by photo-convertible FlbB::Dendra2 visualization. Tip localization of FlbB depends on Cys382 in the C-terminus and the bZIP DNA-binding domain in the N-terminus. FlbE, a critical FlbB interactor, binds the bZIP domain. Furthermore, the absence of FlbE results in loss of tip localization but not nuclear accumulation. flbE deletion also abrogates transcriptional activity indicating that FlbB gains transcriptional competence from interactions with FlbE at the tip. Finally, a bipartite nuclear localization signal is required for nuclear localization of FlbB. Those motifs of FlbB may play various roles in the sequence of events necessary for the distribution and activation of this transcriptionally active developmental factor. The tip accumulation, FlbE-dependent activation, transport and nuclear import sketch out a process of relaying an environmentally triggered signal from the tip to the nuclei. As the first known instance of transcription factor-mediated tip-to-nucleus communication in filamentous fungi, this provides a general framework for analyses focused on elucidating the set of molecular mechanisms coupling apical signals to transcriptional events.

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…Notably, FlbB shows higher concentrations in the most apical nuclei and decreasing concentrations in successive nuclei (186). The actin cytoskeleton and the small protein FlbE are required for FlbB transport and accumulation at the hyphal tip (283).…”

The Golgi apparatus: insights from filamentous fungi

“…The dependence of Golgi organization on its position in the hypha may reflect possible quantitative differences in Golgi activity depending on the proximity to the apex. Golgi activity in turn may depend on biosynthetic activity (Some data indeed indicate that there are differences in gene expression depending on the nuclear position in hyphae [Kohli et al 2008, Herrero-Garcia et al 2015). …”

Rewiring of transcriptional networks as a major event leading to the diversity of asexual multicellularity in fungi

“…Furthermore, deletion of M. oryzae MoflbB exacerbated conidiation instead of inhibiting it (Tang et al 2014), suggesting that MoFlbB performs an opposite role compared to the A. nidulans ortholog. FlbB orthologs conserve different domains and residues compared to related TFs that control the response to oxidative stress (Vivancos et al 2004;Cortese et al 2011;Herrero-Garcia et al 2015). This may indicate that FlbB orthologs retain mechanistic features enabling them to control signal transduction, such as importation into nuclei or transcriptional regulation, but can participate in the alternate cellular process in different species.…”

“…FlbA antagonizes the activity of a trimeric G-protein complex formed by FadA, GpgA and SfaD in order to inhibit cell proliferation and induce asexual development Yu et al 1996). FlbC is a C2H2-type TF that binds the promoter of brlA, FlbB migrates from the tip to nuclei, where jointly with the cMyb TF FlbD binds the promoter of brlA and induces asexual spore production Herrero-Garcia et al 2015).…”