Biology subjects

Bastakis, E.

Publications and source records attributed to Bastakis, E..

5 recordsLinked to original sources

bioRxiv2025

The homeobox transcription factor HbxB coordinates distinct gene regulatory networks for asexual development and secondary metabolism in Aspergillus nidulans

Formation of conidia as asexual spores and sometimes worldwide distribution through the air is a very important feature of the fungal life style. This process is controlled by several regulatory proteins, including homeobox domain transcription factors. HbxB is one such regulator with implications in the control of development, secondary metabolism and various stress responses in the filamentous fungus Aspergillus nidulans. However, the molecular mechanism of the regulatory role of HbxB during asexual development is still elusive. Here we show that HbxB is a nuclear localized protein with great impact on asexual sporogenesis. Employment of high throughput assays like chromatin immunoprecipitation (ChIP-seq) and transcriptomics (RNA-seq), elucidated the in vivo binding landscape of HbxB in a genome-wide scale. A set of 238 genes as direct targets of HbxB were identified. A nine bases DNA motif where HbxB prefers to bind in vivo was discovered as HbxB response element (HRE). HbxB is influencing the expression of genes encoding master regulators of the asexual development such as SclB, PpoC, FlbA and FlbC. Moreover, the direct transcriptional control of the secondary metabolites sterigmatocystin and emericellamides biosynthesis by HbxB was discovered. Lastly also a previously elusive mutual regulatory control circuit between HbxB and two major regulators of the asexual development SclB and MsnA was found. Both of these regulators can directly induce the expression of hbxB. This study provides a detailed molecular mechanism on how HbxB controls A. nidulans asexual sporulation. ImportanceFungal distribution mainly relies on the formation of spores that are subsequently dispersed in different media to ensure colonization of substrates and the survival of the fungus. The asexual developmental program is a widely used strategy in the fungal kingdom for production of spores (conidia). The HbxB transcription factor is a nuclear localized, homeobox domain protein, with a strong impact on asexual sporulation of presumably numerous fungal species. This study enhances our understanding of the mechanism with which HbxB exerts its regulatory actions. HbxB is binding in vivo to specific DNA regulatory elements of genes encoding proteins with key roles in asexual development (like SclB, MsnA and PpoC), secondary metabolism (such as genes from the sterigmatocystin and emericellamide clusters) and stress response/tolerance. Overall, these findings open a window into how Hbx regulators orchestrate and coordinate fungal asexual developmental programs genome-wide at the molecular level.

molecular biology↗

bioRxiv2025

The Aspergillus nidulans transcription factor SclB governs the transition from vegetative to asexual development

Asexual reproduction in filamentous fungi is a common, efficient and fast differentiation process, for producing large numbers of asexual spores (conidia), which can be distributed through the air to colonize new environments. The whole process is tightly controlled by specific regulatory proteins. Among those major regulators is the zinc-finger domain protein of SclB (Sclerotia like B), known to influence various aspects of asexual growth and secondary metabolism in Aspergillus nidulans as well as other filamentous fungi. Two different growth conditions of A. nidulans were compared to obtain a mechanistic overview for the role of SclB, mainly during the transition of the fungus from vegetative to asexual growth. Chromatin immunoprecipitation was coupled with next generation sequencing (ChIP-seq) and combined with transcriptomic analyses (RNA-seq). SclB coordinates this developmental shift mainly by controlling the expression of genes encoding for few, however, prominent regulators of conidiation. They include the transcription factors BrlA, VelB and SclB and the pheromone oxygenase PpoC. Association of SclB to promoter regions requires the newly identified SclB response element (SRE) with a nine base-pair DNA motif. Scl2 is the corresponding protein in the fungal plant pathogen Verticillium dahliae and partially complements the {Delta}sclB A. nidulans asexual deficiency. This supports a conserved function of this regulator among different fungal species. In summary, SclB coordinates transition from vegetative growth to asexual reproduction in A. nidulans through in vivo transcriptional control over genes coding for established players of conidia formation. ImportanceFungi constantly adapt to environmental changes in their various habitats. Asexual spore formation allows to quickly leave an unfriendly habitat through dispersal into the air. The asexual developmental program of fungi ensures large number of spores, in a short period of time and in energetically efficient manner. SclB transcription factor is a key regulator of asexual growth and secondary metabolism in numerous fungal species. The mechanism through which SclB orchestrates the transition of the Aspergillus nidulans filamentous fungus from the vegetative to the asexual growth was revealed. This regulator directly controls in vivo itself as well as expression of master genes for the asexual program such as brlA for transcriptional control or ppoC for pheromone production. This study enhances the molecular understanding, how fungal asexual differentiation is initiated and coordinated, which supports the development of better strategies to control fungal pathogens, improving human health, safety and crop management.

molecular biology↗

bioRxiv2025

The VelB intrinsically disordered domain promotes selective heterodimer formation of velvet domain regulatory proteins for fungal development

Fungi possess several transcription factors with a characteristic velvet domain for DNA-binding and homo- or heterodimerization, which is structurally similar to the mammalian NF-B Rel homology domain. Velvet dimers control fungal development, virulence and mycotoxin formation. VelB is the only regulator, which carries an intrinsically disordered domain (IDD) within the velvet domain. The IDD as well as the positioning within VelB is conserved in the fungal kingdom. Intrinsically disordered regions contribute to transcription activation and DNA binding and frequently appear in eukaryotic transcription factors. The VelB IDD provides selective heterodimerization as well as protein stability control. The IDD is not required for the formation of the VelB-VeA heterodimer of Aspergillus nidulans or Verticillium dahliae, but promotes the formation of the VelB-VosA heterodimer. The IDD destabilizes VelB single molecules and also balances its distribution and ratio between both velvet heterodimers. These balances contribute to control appropriate mycotoxin production and sexual development. Herewith, the VelB IDD represents a novel control mechanism of velvet protein stability and heterodimer formation for precise priming of fungal development.

molecular biology↗

bioRxiv2025

The Aspergillus nidulans velvet domain containing transcription factor VeA is shuttled from cytoplasm into nucleus during vegetative growth and stays there for sexual development, but has to return into cytoplasm for asexual development

Survival of multicellular organisms requires the coordinated interplay between networks regulating gene expression and controlled intracellular transport of respective regulators. Velvet domain proteins are fungal transcription factors, which form various heterodimers and play key roles in controlling early developmental decisions towards more either asexual or sexual differentiation. VeA is the central subunit of the trimeric velvet complex VelB-VeA-LaeA, which links transcriptional to epigenetic control for the coordination of fungal developmental programs to specific secondary metabolite synthesis. Nuclear localization of the VeA bridging factor is carefully controlled in fungi. VeA carries three nuclear localization signals NLS1, NLS2 and NLS3, which all contribute to nuclear import. An additional VeA nuclear export sequence (NES) provides a shuttle function, which allows the cell to relocate VeA to the cytoplasm. VeA is nuclear during vegetative growth, but has to be exported from the nucleus to allow and promote asexual development. In contrast, progression of the sexual pathway requires continuous nuclear VeA localization. Accurate nuclear import and export control of velvet proteins is further connected to specific stability control mechanism as prerequisites for fungal development and secondary metabolism. These results illustrate the various complex mutual dependencies of velvet regulatory proteins for coordinating fungal development and secondary metabolism.

molecular biology↗

bioRxiv2025

Molecular circuit between Aspergillus nidulans transcription factors MsnA and VelB to coordinate fungal stress and developmental responses

Development and secondary metabolism of the filamentous fungus Aspergillus nidulans are tightly controlled by concerted actions of several master regulator transcription factors. The connection between fungal development and cellular stress response programs is often elusive. Here we show that the MsnA zinc finger transcription factor, which controls salt-stress response, is a novel major player in fungal development. A molecular circuit among MsnA and the velvet domain regulator VelB was discovered, which mutually fosters the actions of both regulatory proteins during development. MsnA controls the expression of several genes encoding master transcriptional regulators of asexual as well as sexual development. In addition, MsnA affects directly and indirectly the synthesis of specific secondary metabolites relevant for fungal defense against other organisms and growth, in addition to salt-stress responses. Moreover, the expression of genes encoding the epigenetic regulators VapA and VipC are also directly controlled by MsnA. These subunits of the VapA-VipC-VapB methyltransferase signal transduction complex promote asexual differentiation. MsnA is therefore placed at a novel prominent position of the central regulatory network, which coordinates stress responses with the developmental and metabolic fate of the fungus.

microbiology↗