The concerted action of bZip and cMyb transcription factors FlbB and FlbD induces brlA expression and asexual development in Aspergillus nidulans

Abstract

SummaryFungi are capable of generating diverse cell types through developmental processes that stem from hyphae, acting as pluripotent cells. The formation of mitospores on emergence of hyphae to the air involves the participation of transcription factors, which co-ordinate the genesis of new cell types, eventually leading to spore formation.In this investigation, we show that bZip transcription factor FlbB, which has been attributed to participate in transducing the aerial stimulus signal, activates the expression of c-Myb transcription factor FlbD. Both factors then jointly activate brlA, a C 2H2 zinc finger transcription factor, which plays a central role in spore formation. This sequence of regulatory events resembles developmental control mechanisms involving c-Myb and bZip counterparts in metazoans and plants.

Transcriptional Changes in the Transition from Vegetative Cells to Asexual Development in the Model Fungus Aspergillus nidulans

“…These TFs are expressed both at VG and at early AD (17,27,28,68), and some of them show remarkable differences in expression according to results of Northern blot experiments (27,28,68). Our RNA-seq results do not correlate with those previously described, but their transcript levels support the proposed role of UDA factors at both time points of development studied in this work.…”

“…With the aim of identifying the genes and determining the cellular processes significantly altered during this transition, we used in this work a RNA-seq approach to compare the transcriptomes of submerged 19 h-old vegetative hyphae (nonspecialized cells) and 5 h-old airexposed samples (in which asexual structures started to develop). The first time point was chosen based, on one hand, on the acquisition of the developmental competence, which is required to develop conidiophores (16) and, on the other hand, because this was the reference time point for the vegetative stage in our previous works (27,28). The second time point was chosen based on the expression peak of UDA coding genes, which coincide with a remarkable induction of brlA and the CDP pathway (17).…”

NsdD Is a Key Repressor of Asexual Development inAspergillus nidulans

“…Such derepression triggers the transition from vegetative growth to development, involving the sequential activation of FlbE-B/D and FlbC. Activated FlbB-FlbD (Garzia et al 2010) and FlbC then displace NsdD from the brlA promoter and further activates brlA. VosA is likely removed from the brlA promoter by VelB , not indicated in the model).…”

“…FlbE physically interacts with FlbB, and they activate FlbD interdependently (Garzia et al 2009;Kwon et al 2010b). FlbD (a cMyb-type TF) and FlbB then cooperatively function in activating expression of brlA (Garzia et al 2010). Both of these two independent conidiation activation cascades ( Figure 1A) are necessary for full activation of brlA expression and proper conidiation (Wieser and Adams 1995;Garzia et al 2010;Kwon et al 2010a).…”

“…FlbD (a cMyb-type TF) and FlbB then cooperatively function in activating expression of brlA (Garzia et al 2010). Both of these two independent conidiation activation cascades ( Figure 1A) are necessary for full activation of brlA expression and proper conidiation (Wieser and Adams 1995;Garzia et al 2010;Kwon et al 2010a). Importantly, loss of fluG or flbA function results in the blockage in both conidiation and production of the carcinogenic mycotoxin sterigmatocystin (ST), the penultimate precursor of the betterknown potent carcinogen aflatoxins (Lee and Adams 1994a;Hicks et al 1997).…”