Fig.3-17 Expression levels of pigment genes of Monascus C100, ΔMareA and OE-MareA in solid-state fermentation under different nitrogen sources
Morphological development and secondary metabolism in fungi are regulated by a diverse array of genes or gene families(Wang et al., 2015). In numerous fungal species, the regulation of these processes has been attributed to two velvet protein complexes known as VeA andVosA VeA is highly conserved in a variety of fungi and controls sexual/asexual development and secondary metabolism in filamentous fungi(Wang et al., 2019).The VosA gene was initially identified in Aspergillus globulus and plays a crucial role in long-term spore viability along with the regulation of conidial maturation and conidiogenesis (Ni and Yu, 2007). LaeA serves as a global transcription factor that orchestrates fungal growth, development, and metabolism(Pomraning et al., 2022). Fungi perceive external signals to modulate growth, development, and metabolic signaling pathways; within this context, GprD participates in G protein signaling pathway exerting significant influence on this intricate process(Wang et al., 2013).
As shown in Figure 3-18, under the control condition without added nitrogen source, the expression of VeA and GprD genes of the knockout strain ΔMareA did not differ much from that of the original strain C100, while the expression of VosA andLaeA genes was significantly down-regulated. The expression ofVeA and VosA genes of overexpression strain OE-MareA did not change. It indicates that the deletion ofMareA gene affects the growth and conidial production ofMonascus , while the overexpression of the gene has its promoting effect to a certain extent. When Gln was added to the medium, the gene expression of the three strains did not differ much, indicating that even the deletion of the MareA gene would not affect the growth of monascus too much when Gln was present in the environment. The expression of VeA, VosA, LaeA and GprD genes of the knockout strain ΔMareA was severely suppressed by the addition of NaNO3 to the medium, while the expression of the four genes of the overexpression strain OE-MareA was significantly up-regulated. It indicates that when NaNO3 is present in the environment, the MareA gene-deficient strain cannot utilize secondary nitrogen sources for growth and reproduction, whereas overexpression of the genes promotes the growth and spore production of monascus.
In summary, deletion of the MareA gene slowed down the growth ofMonascus and also reduced spore production, while overexpression of the gene promoted the growth and spore production of Monascus . The presence of Gln in the environment did not affect the growth and reproduction of Monascus when the MareA gene was present. However, in an environment with NaNO3, deletion of theMareA gene resulted in an inability to utilize NaNO3, leading to inhibition of Monascus growth. Conversely, overexpression of the gene promoted Monascus growth and development.