Abstract
McrA is a key transcription factor that functions as a global repressor of fungal secondary metabolism in Aspergillus species. Here, we report that mcrA is one of the VosA-VelB target genes and McrA governs the cellular and metabolic development in Aspergillus nidulans. The deletion of mcrA resulted in a reduced number of conidia and decreased mRNA levels of brlA, the key asexual developmental activator. In addition, the absence of mcrA led to a loss of long-term viability of asexual spores (conidia), which is likely associated with the lack of conidial trehalose and increased β-(1,3)-glucan levels in conidia. In supporting its repressive role, the mcrA deletion mutant conidia contain more amounts of sterigmatocystin and an unknown metabolite than the wild type conidia. While overexpression of mcrA caused the fluffy-autolytic phenotype coupled with accelerated cell death, deletion of mcrA did not fully suppress the developmental defects caused by the lack of the regulator of G-protein signaling protein FlbA. On the contrary to the cellular development, sterigmatocystin production was restored in the ΔflbA ΔmcrA double mutant, and overexpression of mcrA completely blocked the production of sterigmatocystin. Overall, McrA plays a multiple role in governing growth, development, spore viability, and secondary metabolism in A. nidulans.
Highlights
McrA is a key transcription factor that functions as a global repressor of fungal secondary metabolism in Aspergillus species
Previous study described that mRNA levels of mcrA in conidia were drastically low by the lack of VelB or VosA, and a promoter region of mcrA contains a putative VosA response element (VRE), suggesting that McrA is a potential target of the VosA-VelB complex in A. nidulans[30]
The deletion of mcrA resulted in a reduced number of conidia and reduced levels of brlA compared to Wild type (WT) and complemented strains (Figs. 1C,D and S1B)
Summary
McrA is a key transcription factor that functions as a global repressor of fungal secondary metabolism in Aspergillus species. McrA plays a multiple role in governing growth, development, spore viability, and secondary metabolism in A. nidulans. A conidiophore is composed of varying cell types and the process of its production is precisely regulated by multiple positive and negative regulators[10]. Some of these developmental regulators are thought to be conserved in Aspergillus species, and they have been extensively studied in the model fungus A. nidulans[11,12]. Early vegetative growth phase, key negative regulators such as NsdD, VosA, and SfgA cooperatively repress expression of brlA, the essential activator for the initiation of conidiation, until the acquisition of the developmental competence[13,14,15,16]. It is speculated that these negative regulators are displaced from the brlA promoter, and upstream positive regulators induce brlA mRNA expression, thereby the fungus begins conidiation and forms conidiophores[10]
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