# Production of Fungal Pigments: Molecular Processes and Their Applications
## 3 Stress Factors and Fungal Pigment Production
Studies with _Monascus pilosus_ IFO4520 found that compared to non-illuminated controls, the production of red pigments increased by 1.3-fold after exposure to red light for 7-10 d and displayed a 1.5-fold increase post illumination of 14 d. The above-described findings suggested that red light could stimulate the production of red pigments, especially if applied before stationary growth [106]. Meanwhile, the inhibitory effect of blue light on red pigment production in _M. pilosus_ IFO4520 was also observed. Similarly, compared to controls, production of monacolin K (a cholesterol-lowering agent) increased by red light exposure at an early stationary phase. A further investigation with _Monascus_ revealed that the reduced pigment accumulation under blue light was due to the increased instability under blue light exposure, even though blue light also stimulated pigment biosynthesis [107]. Interestingly, blue light can exert either inhibitory or stimulatory effects on pigment biosynthesis in Monascus, depending on light intensity and illumination time. Specifically, a study with _Monascus purpureus_ strain M9 found that blue light at a low intensity and short exposure time (100 lux, 15 and 30 min/day; 200 lux, 15 min/day) enhanced the production of _Monascus_ yellow pigments monascin and ankaflavin, whereas blue light with a high intensity (300 and 450 lux) and long exposure time (45 and 60 min) attenuated pigment production [108]. More recent studies investigated the molecular mechanism underlying blue light-induced pigmentation in _M. purpureus_ M9 [109]. During their experimentation, short-term exposure to blue light, namely B15 treatment (blue light exposure for 15 min/d over 8d herein) might lead to oxidative stress in this fungus, manifested by the upregulation in genes encoding cytochrome C peroxidase, peroxidase, etc. In contrast, in response to B15 treatment, there was a reduction in primary metabolic activity, including carbon and nitrogen metabolism. Moreover, metabolic pathways were found to be upregulated involving aromatic amino acids, which yields acetyl-CoA and malonyl-CoA, the precursors for _Monascus_ azaphilone pigment biosynthesis. Upon short-term exposure to blue light, _M. purpureus_ M9 exhibited a lowered primary metabolism as well as slowed development and reproduction, concomitant with an elevation of secondary metabolism, as evidenced by the enhanced synthesis of photoprotective pigments that absorb blue light. The above-described work represents the initial investigation regarding the genome-wide response of _Monascus_ to blue light based on transcriptome sequencing, unveiling that the light induction of _M. purpureus_ pigmentogenesis differs remarkably from the well-studied model system observed in _N. crassa_[109]. A previous study with human pathogenic yeast _Malassezia furfur_ identified a chemical UV filter called pitriacitrin, a yellow pigment possessing broad absorptive activity in the UV-A, -B and -C regions [110]. _Malassezia_-associated pitriasis versicolor (PV) in humans is known to be characteristic of unexplained color variation and fluorescence of skin lesions. Synthesis of this pigment is related to UV sensitivity in _M. furfur_. The outer part of the human epidermis is the natural habitat of _M. furfur_, and UV exposure is an environmental risk for the fungus (as well as humans; the production of indole alkaloid pigment pitriacitrin in _M. furfur_ under the UV radiation may confer this pathogenic yeast certain sun-screening advantages [110]. Enhanced growth of melanogaster fungi has been observed under low dose ionizing radiation, both in the laboratory and in the surroundings of the Chernobyl nuclear plant, suggesting their adaptation to survive or even benefit from ionizing radiation exposure. However, the cellular/molecular mechanism of fungal adaptability in responses to such radiation remains largely unknown. In the model of black yeast _Wangiella dermatitisidis_, [PERSON] et al.