Abstract
The multifunctional regulator VelB physically interacts with other velvet regulators and the resulting complexes govern development and secondary metabolism in the filamentous fungus Aspergillus nidulans. Here, we further characterize VelB’s role in governing asexual development and conidiogenesis in A. nidulans. In asexual spore formation, velB deletion strains show reduced number of conidia, and decreased and delayed mRNA accumulation of the key asexual regulatory genes brlA, abaA, and vosA. Overexpression of velB induces a two-fold increase of asexual spore production compared to wild type. Furthermore, the velB deletion mutant exhibits increased conidial germination rates in the presence of glucose, and rapid germination of conidia in the absence of external carbon sources. In vivo immuno-pull-down analyses reveal that VelB primarily interacts with VosA in both asexual and sexual spores, and VelB and VosA play an inter-dependent role in spore viability, focal trehalose biogenesis and control of conidial germination. Genetic and in vitro studies reveal that AbaA positively regulates velB and vosA mRNA expression during sporogenesis, and directly binds to the promoters of velB and vosA. In summary, VelB acts as a positive regulator of asexual development and regulates spore maturation, focal trehalose biogenesis and germination by interacting with VosA in A. nidulans.
Highlights
Fungal spores are widespread in the environment and have a significant impact on daily human life
In A. nidulans, VelB plays an essential role in sexual development, the mycotoxin sterigmatocystin production and trehalose biosynthesis [15,16]
VelB homologues have been characterized in many fungi and are reported to regulate: sporulation and secondary metabolite production in Fusarium fujikuroi [41]; production of the trichothecene and zearalenone mycotoxins, pathogenicity, and sexual reproduction in Fusarium graminearum [42]; cell morphology and spore formation in Histoplasma capsulatum [43]; trehalose biosynthesis and conidiation in Aspergillus fumigatus (Park and Yu, unpublished); and production of the carcinogenic mycotoxin aflatoxin and formation of sclerotia in Aspergillus flavus (Park, Lovendahl and Yu, unpublished)
Summary
Fungal spores are widespread in the environment and have a significant impact on daily human life. Asexual development (conidiation) in A. nidulans involves the formation of specialized multicellular structures called conidiophores. The process of conidiation is genetically regulated and the three genes brlA, abaA and wetA have been proposed to define a central regulatory pathway activating conidiophores formation [4,7,8,9,10]. Recent studies have identified the novel regulator VosA, which functions in trehalose biosynthesis and conidia maturation in A. nidulans. VosA is mainly localized in the nucleus of mature conidia and it contains a potential transcriptional activation domain at the C-terminus. These findings led to the hypothesis that VosA is a transcription factor regulating conidia maturation and the completion of conidiogenesis [13]
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