Blakeslea trispora Photoreceptors: Identification and Functional Analysis

The GATA transcription factor BcWCL2 regulates citric acid secretion to maintain redox homeostasis and full virulence in Botrytis cinerea

Botrytis cinerea is a typical necrotrophic plant pathogenic fungus which can deliberately acidify host tissues and trigger oxidative bursts therein to facilitate its virulence. The white collar complex (WCC), consisting of BcWCL1 and BcWCL2, is recognized as the primary light receptor in B. cinerea. Nevertheless, the specific mechanisms through which the WCC components, particularly BcWCL2 as a GATA transcription factor, control virulence are not yet fully understood. This study demonstrates that deletion of BcWCL2 results in the loss of light-sensitive phenotypic characteristics. Additionally, the Δbcwcl2 strain exhibits reduced secretion of citrate, delayed infection cushion development, weaker hyphal penetration, and decreased virulence. The application of exogenous citric acid was found to restore infection cushion formation, hyphal penetration, and virulence of the Δbcwcl2 strain. Transcriptome analysis at 48 h post-inoculation revealed that two citrate synthases, putative citrate transporters, hydrolytic enzymes, and reactive oxygen species scavenging-related genes were down-regulated in Δbcwcl2, whereas exogenous citric acid application restored the expression of the above genes involved in the early infection process of Δbcwcl2. Moreover, the expression of Bcvel1, a known regulator of citrate secretion, tissue acidification, and secondary metabolism, was down-regulated in Δbcwcl2 but not in Δbcwcl1. ChIP-qPCR and electrophoretic mobility shift assays revealed that BcWCL2 can bind to the promoter sequences of Bcvel1. Overexpressing Bcvel1 in Δbcwcl2 was found to rescue the mutant defects. Collectively, our findings indicate that BcWCL2 regulates the expression of the global regulator Bcvel1 to influence citrate secretion, tissue acidification, redox homeostasis, and virulence of B. cinerea.IMPORTANCEThis study illustrated the significance of the fungal blue light receptor component BcWCL2 protein in regulating citrate secretion in Botrytis cinerea. Unlike BcWCL1, BcWCL2 may contribute to redox homeostasis maintenance during infection cushion formation, ultimately proving to be essential for full virulence. It is also demonstrated that BcWCL2 can regulate the expression of Bcvel1 to influence host tissue acidification, citrate secretion, infection cushion development, and virulence. While the role of organic acids secreted by plant pathogenic fungi in fungus-host interactions has been recognized, this paper revealed the importance, regulatory mechanisms, and key transcription factors that control organic acid secretion. These understanding of the pathogenetic mechanism of plant pathogens can provide valuable insights for developing effective prevention and treatment strategies against fungal diseases.

Light irradiation changes the regulation pattern of BtCrgA on carotenogenesis in Blakeslea trispora

CrgA has been shown to be a negative regulator of carotenogenesis in some filamentous fungi, while light irradiation is an inducible environmental factor for carotenoid biosynthesis. To clarify the relationship between CrgA and light-inducible carotenogenesis in Blakeslea trispora, the cis-acting elements of the btcrgA promoter region were investigated, followed by the analyses of correlation between the expression of btcrgA and carotenoid structural genes under different irradiation conditions. A variety of cis-acting elements associated with light response was observed in the promoter region of btcrgA, and transcription of btcrgA and carotenoid structural genes under different irradiation conditions was induced by white light with a clear correlation. Then, RNA interference and overexpression of btcrgA were performed to investigate their effects on carotenogenesis at different levels under irradiation and darkness. The analyses of transcription and enzyme activities of carotenoid structural gene, and accumulation of carotenoids among btcrgA-interfered, btcrgA-overexpressed, and wild-type strains under irradiation and darkness indicate that btcrgA negatively regulates the synthesis of carotenoid in darkness, while promotes the carotenogenesis under irradiation regardless of reduced or overexpression of btcrgA .

Genetic and Environmental Factors Influencing the Production of Select Fungal Colorants: Challenges and Opportunities in Industrial Applications

Natural colorants, mostly of plant and fungal origins, offer advantages over chemically synthetic colorants in terms of alleviating environmental pollution and promoting human health. The market value of natural colorants has been increasing significantly across the globe. Due to the ease of artificially culturing most fungi in the laboratory and in industrial settings, fungi have emerged as the organisms of choice for producing many natural colorants. Indeed, there is a wide variety of colorful fungi and a diversity in the structure and bioactivity of fungal colorants. Such broad diversities have spurred significant research efforts in fungi to search for natural alternatives to synthetic colorants. Here, we review recent research on the genetic and environmental factors influencing the production of three major types of natural fungal colorants: carotenoids, melanins, and polyketide-derived colorants. We highlight how molecular genetic studies and environmental condition manipulations are helping to overcome some of the challenges associated with value-added and large-scale productions of these colorants. We finish by discussing potential future trends, including synthetic biology approaches, in the commercial production of fungal colorants.

Multilevel Regulation of Carotenoid Synthesis by Light and Active Oxygen in Blakeslea trispora

Although Blakeslea trispora has been used for industrial production of β-carotene, the effects of light and oxidative stress on its synthesis have not been fully clarified. The present study focuses on the effects of light and reactive oxygen species (ROS) on carotenoid synthesis and their multilevel regulation in B. trispora. Blue light significantly influenced the intracellular ROS levels, carotenoid contents, and transcription of carotenoid structural genes, while ROS levels were positively correlated with intracellular carotenoid contents and transcriptional levels of carotenoid structural genes. Blue light and ROS were both significant factors affecting carotenoid synthesis with a significant interaction between them. Irradiation by pulsed blue light and (or) addition of generating agents for active oxygen could partially compensate for the inhibition derived from the transcription inhibitor (dactinomycin) and translation inhibitor (cycloheximide) on the multilevel phenotype. Therefore, blue light and ROS act on the transcription and translation of carotenoid structural genes to promote the accumulation of carotenoid in B. trispora.

Structure prediction and function characterization of WC-2 proteins in Blakeslea trispora

Blakeslea trispora is known for its potential to produce an excess of carotenoids in mixed cultures of strains of opposite sex. The biosynthesis of β-carotene in B. trispora is activated not only by sex hormone trisporic acid but also by light, especially blue light. In fungi, the most intensively investigated blue-light reception proteins are WC-1 and WC-2, and the two proteins form a transcription factor complex which is called WCC by their PAS domains. Notably, multiple genes similar to wc-1 and wc-2 have been identified and characterized in Phycomyces, Mucor, and Rhizopus. Here we report that there are four members of wc-2-like gene family in B. trispora genome: Btwc-2a, Btwc-2b, Btwc-2c, and Btwc-2d. When the mycelia were exposed to blue light, their transcription levels are regulated differentially. Except for BtWC-2b, which only has a PAS domain, the other three proteins contain both a PAS domain and a ZnF domain. BtWC-2a interacts with either BtWC-1a or BtWC-1c to form different photoreceptor complexes in yeast two-hybrid assays, which is the unique situation not yet described in other fungi. In addition, the protein-protein docking analysis by the predicted 3D structures showed that the two complexes are structurally different. These results suggested that WC proteins of B. trispora are still involved in light regulation by forming WCC and the regulation mechanism of the photobiology appears to be more complex.

Protoplast fusion between Blakeslea trispora 14,271 (+) and 14,272 (-) enhanced the yield of lycopene and β-carotene

Blakeslea trispora, a heterothallic Zygomycota with two mating types (termed "plus" and "minus"), is an ideal source of lycopene and β-carotene. The lycopene and β-carotene yields when the two type strains are used for fermentation separately are lower than those when they are joint together. To enhance the yield of lycopene and β-carotene in B. trispora, protoplast fusion technology was carried out between ATCC 14,271 (+) and ATCC 14,272 (-). After protoplast preparation, protoplast fusion, fusion sorting, fusion regeneration, and high-throughput screening, two fusions (Fu-1and Fu-2) with high lycopene and β-carotene yields were obtained. The lycopene yields of Fu-1 and Fu-2 were increased to 0.60 mg/gDW and 0.90 mg/gDW, which were respectively 3.62- and 5.44-fold those of 14,271 and 1.76- and 2.64-fold those of 14,272. The β-carotene yields of Fu-1 and Fu-2 were increased to 22.07 mg/gDW and 36.93 mg/gDW, which were respectively 1.72- and 2.89-fold those of 14,271 and 1.23- and 2.06-fold those of 14,272. In this study, the protoplast fusion technique was successfully used in Blakeslea trispora, providing new ideas for improving lycopene and β-carotene production.