Negative regulation and developmental competence in Aspergillus

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.

The GATA‐type IVb zinc‐finger transcription factor SsNsd1 regulates asexual–sexual development and appressoria formation in Sclerotinia sclerotiorum

“…In addition, nearly all late light response genes are misregulated in the loss‐of‐function sub‐1 mutant in a white collar complex‐dependent manner (Chen et al ., ). This role in N. crassa is also consistent with the reported function of the A. nidulans NsdD orthologue as a positive regulator of sexual development and component of the endogenous regulatory circuit including brlA , rosA , nosA and nsdB functioning to balance asexual and sexual development (Han et al ., ; Lee et al ., ). Given the positive roles of Sub‐1 orthologues in light‐responsive sexual development, we hypothesized that loss‐of‐function Δ Ssnsd1 mutants would exhibit phenotypes associated with light‐dependent apothecium development.…”

Adenylate Cyclase AcyA Regulates Development, Aflatoxin Biosynthesis and Fungal Virulence in Aspergillus flavus

“…Although the negative role of cAMP/PKA pathway acts in asexual development in Aspergillus , defect in sporulation is a common event found in the adenylate cyclase deficient mutants of previously known filamentous fungi. As we know, inactivation of AcyA, leading to a low level of intracellular cAMP, causes a severe defect in fungal growth, which might also affect conidia formation concurrently, which has to gone through a period of vegetative growth that is necessary for cells to acquire the ability to respond to development signals (Lee et al, 2016). Former studies had also shown that conidial and sclerotial production were likely to remain balanced (Amaike and Keller, 2011).…”

A MADS‐box transcription factor regulates a central step in sporulation of the oomycete Phytophthora infestans

“…The transcriptional networks that mediate spore formation can be complex. For example, conidiation in Aspergillus nidulans is controlled by multiple transcription factors including both activators and repressors (Lee et al, 2016). Even in bacterial systems, spore formation involves the sequential action of multiple regulators (Kovacs, 2016).…”