# Production of Fungal Pigments: Molecular Processes and Their Applications
## 3 Stress Factors and Fungal Pigment Production
demonstrated that ionizing radiation could enhance cell growth by augmenting cell division and cell size [111]. The wild-type (WT) strain and melanin-lacking mutant _wdpks1_ of _W. dermatitisidis_ were investigated under irradiation versus non-irradiation conditions. It was found that long-term exposure to low-dose radiation promoted the survival of both the WT and _wdpks1_ mutant. In addition, in association with lowered reactive oxygen species (ROS) levels, there was increased carotenoid production and induction of translesion DNA synthesis. In terms of carotenogenesis, Raman spectral analysis of single cells revealed that ionizing radiation triggered the production of carotenoids in _W. dermatitisidis_, with elevated expression of carotenoid biosynthesis genes. This result is reminiscent of the finding by [PERSON] and [PERSON] [112] that carotenoid syntheses by _W. dermatitisidis_ in both WT and melanin-deficient (Mel-) strains required photoinduction. The above-described data [111] highlights that participation of an array of cellular components/pathways other than melanin could facilitate _W. dermatitis_ to acclimate to radiation stress for survival and proliferation. In addition to the light that induces the accumulation of carotenoids in diverse _Fusarium_ species, including _F. aquaudeututum_[89], _F. fujikuroi_[86], _F. verticillioides_[95], and _F. oxysporum_[113], another regulatory stressor is nitrogen availability, which can exert a negative effect on carotenogenesis in this fungal genus [60]. Previous work with immobilized mycelia of _F. fujikuroi_ incubated under nitrogen limitations revealed an enhanced carotenoid production in comparison to that under an abundant nitrogen supply. Furthermore, the promoting effect of nitrogen deprivation on _F. fujikuroi_carotenogenesis is additive to that induced by light. The photo-induction of carotenoid accumulation is known to act at the transcriptional level, as previously described, whereas the regulation by nitrogen likely involves control of expression at the level of the chromatin structure, as evidenced by the differences in histone methylation found for the genes of the _car_ cluster in a _F. graminearum_ mutant with impaired methyltransferase KMT6 [114]. Besides light and nitrogen availability, _carS_, encoding a protein of the ring finger family, has been found to be a key regulatory gene affecting _Fusarium_ carotenoid biosynthesis. Loss of function of _carS_ leads to up-regulation of the structural _car_ genes at the transcriptional level [88] and accumulation of high-level carotenoids under different culture conditions [88; 115]. While the biochemical routes of the carotenoid biosynthesis share many similarities amongst different fungal producers, the regulatory mechanisms often differ, which likely reflects the different demands of different fungal species as finely tuned adaptations to their corresponding habitats in nature [91]. _Monascus_ pigments are well-known and described as a mixture of azaphilone compounds, including yellow, orange, and red constituents produced by the Genus _Monascus_. Recent studies with _M. purpuneus_ YY-1, an extensively used industrial strain in China, have demonstrated that carbon starvation, arising from the supply of relatively low-quality sustained-release carbon sources, may result in the high yield of pigments. The mechanism behind the stimulatory effects of carbon starvation on pigment biosynthesis was proposed to be linked to perturbed central carbon metabolism, thus augmenting the acetyl-CoA pool. Transcriptome studies revealed that carbon starvation stress might cause the downregulation of genes associated with the utilization of glucose from glycolysis to the tricarboxylic acid (TCA) cycle. Altered glycolytic flux might influence the availability of acetyl-CoA, thereby affecting production of secondary metabolites including pigments.