Abstract
Asexual development (conidiation) in the filamentous fungus Aspergillus nidulans is governed by orchestrated gene expression. The three key negative regulators of conidiation SfgA, VosA, and NsdD act at different control point in the developmental genetic cascade. Here, we have revealed that NsdD is a key repressor affecting the quantity of asexual spores in Aspergillus. Moreover, nullifying both nsdD and vosA results in abundant formation of the development specific structure conidiophores even at 12 h of liquid culture, and near constitutive activation of conidiation, indicating that acquisition of developmental competence involves the removal of negative regulation exerted by both NsdD and VosA. NsdD’s role in repressing conidiation is conserved in other aspergilli, as deleting nsdD causes enhanced and precocious activation of conidiation in Aspergillus fumigatus or Aspergillus flavus. In vivo NsdD-DNA interaction analyses identify three NsdD binding regions in the promoter of the essential activator of conidiation brlA, indicating a direct repressive role of NsdD in conidiation. Importantly, loss of flbC or flbD encoding upstream activators of brlA in the absence of nsdD results in delayed activation of brlA, suggesting distinct positive roles of FlbC and FlbD in conidiation. A genetic model depicting regulation of conidiation in A. nidulans is presented.
Highlights
A key event responding to the developmental inductive signal is activation of brlA, which encodes a C2H2 zinc finger transcription factor (TF) (Fig. 1B)[5]
We have found that VosA and NsdD are the major factors repressing brlA expression, and thereby influencing the acquisition of developmental competence in A. nidulans
We quantified the conidiation levels of FGSC4, ∆sfgA, ∆nsdD, ∆vosA, ∆nsdD ∆vosA, ∆sfgA ∆nsdD and ∆sfgA ∆vosA strains by spreading conidia onto solid medium with 1% glucose (MMG) and incubating for 2 days
Summary
A key event responding to the developmental inductive signal is activation of brlA, which encodes a C2H2 zinc finger transcription factor (TF) (Fig. 1B)[5]. The wetA gene, activated by AbaA, functions in late phase of conidiation for the synthesis of crucial cell wall components and conidial metabolic remodeling[8,9] These three genes have been proposed to define a central regulatory pathway that acts in concert with other genes to control conidiation-specific gene expression and determine the sequence of gene activation during conidiophore development and spore maturation[10,11,12] Subsequent studies have identified various upstream developmental activators (UDAs), fluG, flbA, flbB, flbC, flbD, and flbE that influence brlA expression (Fig. 1B)[13,14,15]. We have found that VosA and NsdD are the major factors repressing brlA expression, and thereby influencing the acquisition of developmental competence in A. nidulans. A working genetic model depicting the positive and negative regulations of brlA expression and conidiation in A. nidulans is presented
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