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.