Comparative Transcriptomic Analysis of Key Genes Involved in Citrinin Biosynthesis in Monascus purpureus

Abstract

Monascus pigments (MPs) display many beneficial biological activities and have been widely utilized as natural food-grade colorants in the food processing industry. The presence of the mycotoxin citrinin (CIT) seriously restricts the application of MPs, but the gene regulation mechanisms governing CIT biosynthesis remain unclear. We performed a RNA-Seq-based comparative transcriptomic analysis of representative high MPs-producing Monascus purpureus strains with extremely high vs. low CIT yields. In addition, we performed qRT-PCR to detect the expression of genes related to CIT biosynthesis, confirming the reliability of the RNA-Seq data. The results revealed that there were 2518 differentially expressed genes (DEGs; 1141 downregulated and 1377 upregulated in the low CIT producer strain). Many upregulated DEGs were associated with energy metabolism and carbohydrate metabolism, with these changes potentially making more biosynthetic precursors available for MPs biosynthesis. Several potentially interesting genes that encode transcription factors were also identified amongst the DEGs. The transcriptomic results also showed that citB, citD, citE, citC and perhaps MpigI were key candidate genes to limit CIT biosynthesis. Our studies provide useful information on metabolic adaptations to MPs and CIT biosynthesis in M. purpureus, and provide targets for the fermentation industry towards the engineering of safer MPs production.

Metabolic Regulation of Two pksCT Gene Transcripts in Monascus ruber Impacts Citrinin Biosynthesis

“…Although mrl3, mrl4, mrl5, mrl6, mrl7, mrr1, and mrr5 were downregulated in the ihpRNA-pksCTα and ihpRNA-pksCT (α + β) transformants, the expression levels of mrl3, mrl5, mrr1, and mrr5 were lower in the latter transformant, potentially are closely associated with lower CIT yield. Huang et al [8] found that several genes involved in CIT biosynthesis were substantially downregulated in Monascus strains with low CIT yield (0.02 ± 0.01 mg/L). These genes included CtnG (encoding carbonic anhydrase; mrr5), CtnC (encoding membrane transporter/major facilitator superfamily protein; mrr1), CitB (encoding oxygenase; mrl2), CitD (encoding dehydrogenase; mrl4), CitE (encoding dehydrogenase; mrl6), and CitC (encoding oxidoreductase; mrl7).…”

“…However, DEGs related to the transformation of pyruvate to acetyl-coA were downregulated in both transformants. Regarding amino acid metabolism, most relevant DEGs were downregulated in the ihpRNA-pksCT (α + β) transformant, indicating reduced protein synthesis when CIT biosynthesis capacity was almost abolished [8]. Moreover, genes involved in the degradation of branched-chain amino acids (valine, leucine, and isoleucine) were upregulated.…”

“…The hepatotoxicity and nephrotoxicity of CIT have raised global concerns regarding food contamination [7]. Consequently, several regions and countries, including the European Union, Japan, Korea, and China, have implemented strict limits of food and feed on CIT content [8], substantially limiting the application and development of Monascus-derived products. To effectively combat CIT contamination, understanding the CIT biosynthetic pathway is crucial.…”

Effects of Main Nutrient Sources on Improving Monascus Pigments and Saccharifying Power of Monascus purpureus in Submerged Fermentation

“…For the initial growth, M. purpureus G11 was inoculated onto MEA slant (6% malt extract and 2% agar; pH 6-7; sterilized at 121 • C for 30 min) and incubated at 35 • C for 10 d. The seed and liquid media consisted of 6% glucose, 3% soluble starch, 1% peptone, 0.15% KH 2 PO 4 , 0.2% K 2 HPO 4 , 0.2% MgSO 4 , and 0.1% NaNO 3 without pH adjustment, and were sterilized at 121 • C for 30 min. The seed culture was prepared as described previously, and 6% of the seed was inoculated onto 50 mL of aseptic liquid fermentation medium and incubated at 35 • C and 180 rpm for 96 h [27].…”

Screening Antibacterial Photodynamic Effect of Monascus Red Yeast Rice (Hong-Qu) and Mycelium Extracts

“…MPs, oligoketides synthesized by the concerted action of polyketide synthase, fatty acid synthase and tailoring enzymes [ 6 , 7 ], can be divided into three groups according to their colour: yellow with absorption maxima in the light region at 330–450 nm, orange with absorption maxima in the visible light region at 460–480 nm and red with absorption maxima in the visible light region at 490–530 nm [ 6 ]. Figure 1 shows six major MPs, i.e.…”