Transcriptome analysis on fructose as the sole carbon source enhancing perylenequinones production of endophytic fungus Shiraia sp. Slf14

Heat stress-induced NO enhanced perylenequinone biosynthesis of Shiraia sp. via calcium signaling pathway

Perylenequinones (PQs) are natural photosensitizing compounds used as photodynamic therapy, and heat stress (HS) is the main limiting factor of mycelial growth and secondary metabolism of fungi. This study aimed to unravel the impact of HS-induced Ca2+ and the calcium signaling pathway on PQ biosynthesis of Shiraia sp. Slf14(w). Meanwhile, the intricate interplay between HS-induced NO and Ca2+ and the calcium signaling pathway was investigated. The outcomes disclosed that Ca2+ and the calcium signaling pathway activated by HS could effectively enhance the production of PQs in Shiraia sp. Slf14(w). Further investigations elucidated the specific mechanism through which NO signaling molecules induced by HS act upon the Ca2+/CaM (calmodulin) signaling pathway, thus propelling PQ biosynthesis in Shiraia sp. Slf14(w). This was substantiated by decoding the downstream positioning of the CaM/CaN (calcineurin) pathway in relation to NO through comprehensive analyses encompassing transcript levels, enzyme assays, and the introduction of chemical agents. Concurrently, the engagement of Ca2+ and the calcium signaling pathway in heat shock signaling was also evidenced. The implications of our study underscore the pivotal role of HS-induced Ca2+ and the calcium signaling pathway, which not only participate in heat shock signal transduction but also play an instrumental role in promoting PQ biosynthesis. Consequently, our study not only enriches our comprehension of the mechanisms driving HS signaling transduction in fungi but also offers novel insights into the PQ synthesis paradigm within Shiraia sp. Slf14(w). KEY POINTS: • The calcium signaling pathway was proposed to participate in PQ biosynthesis under HS. • HS-induced NO was revealed to act upon the calcium signaling pathway for the first time.

Biotechnological production and potential applications of hypocrellins

Hypocrellins (HYPs), a kind of natural perylenequinones (PQs) with an oxidized pentacyclic core, are important natural compounds initially extracted from the stromata of Hypocrella bambusae and Shiraia bambusicola. They have been widely concerned for their use as anti-microbial, anti-cancers, and anti-viral photodynamic therapy agents in recent years. Considering the restrictions of natural stromal resources, submerged fermentation with Shiraia spp. has been viewed as a promising alternative biotechnology for HYP production, and great efforts have been made to improve HYP production over the past decade. This article reviews recent publications about the mycelium fermentation production of HYPs, and their bioactivities and potential applications, and especially summarizes the progresses toward manipulation of fermentation conditions. Also, their chemical structure and analytic methods are outlined. Herein, it is worth mentioning that the gene arrangement in HYP gene cluster is revised; previous unknown genes in HYP and CTB gene clusters with correct function annotation are deciphered; the homologous sequences of HYP, CTB, and elc are systematically aligned, and especially the biosynthetic pathway of HYPs is full-scale proposed. KEY POINTS: • The mycelial fermentation process and metabolic regulation of hypocrellins are reviewed. • The bioactivities and potential applications of hypocrellins are summarized. • The biosynthesis pathway and regulatory mechanisms of hypocrellins are outlined.

Heat stress enhanced perylenequinones biosynthesis of Shiraia sp. Slf14(w) through nitric oxide formation

Perylenequinones (PQs) are a class of natural polyketides used as photodynamic therapeutics. Heat stress (HS) is an important environmental factor affecting secondary metabolism of fungi. This study investigated the effects of HS treatment on PQs biosynthesis of Shiraia sp. Slf14(w) and the underlying molecular mechanism. After the optimization of HS treatment conditions, the total PQs amount reached 577 ± 34.56 mg/L, which was 20.89-fold improvement over the control. Also, HS treatment stimulated the formation of intracellular nitric oxide (NO). Genome-wide analysis of Shiraia sp. Slf14(w) revealed iNOSL and cNOSL encoding inducible and constitutive NOS-like proteins (iNOSL and cNOSL), respectively. Cloned iNOSL in Escherichia coli BL21 showed higher nitric oxide synthase (NOS) activity than cNOSL, and the expression level of iNOSL under HS treatment was observably higher than that of cNOSL, suggesting that iNOSL is more responsible for NO production in the HS-treated strain Slf14(w) and may play an important role in regulating PQs biosynthesis. Moreover, the putative biosynthetic gene clusters for PQs and genes encoding iNOSL and nitrate reductase (NR) in the HS-treated strain Slf14(w) were obviously upregulated. PQs biosynthesis and efflux stimulated by HS treatment were significantly inhibited upon the addition of NO scavenger, NOS inhibitor, and NR inhibitor, indicating that HS-induced NO, as a signaling molecule, triggered promoted PQs biosynthesis and efflux. Our results provide an effective strategy for PQs production and contribute to the understanding of heat shock signal transduction studies of other fungi.Key points• PQs titer of Shiraia sp. Slf14(w) was significantly enhanced by HS treatment.• HS-induced NO was first reported to participate in PQs biosynthetic regulation.• Novel inducible and constitutive NOS-like proteins (iNOSL and cNOSL) were obtained and their NOS activities were determined.

L-Arginine enhanced perylenequinone production in the endophytic fungus Shiraia sp. Slf14(w) via NO signaling pathway

Perylenequinones (PQ) are natural polyketides used as anti-microbial, -cancers, and -viral photodynamic therapy agents. Herein, the effects of L-arginine (Arg) on PQ biosynthesis of Shiraia sp. Slf14(w) and the underlying molecular mechanism were investigated. The total content of PQ reached 817.64 ± 72.53 mg/L under optimal conditions of Arg addition, indicating a 30.52-fold improvement over controls. Comparative transcriptome analysis demonstrated that Arg supplement promoted PQ precursors biosynthesis of Slf14(w) by upregulating the expression of critical genes associated with the glycolysis pathway, and acetyl-CoA and malonyl-CoA synthesis. By downregulating the expression of genes related to the glyoxylate cycle pathway and succinate dehydrogenase, more acetyl-CoA flow into the formation of PQ. Arg supplement upregulated the putative biosynthetic gene clusters for PQ and activated the transporter proteins (MFS and ABC) for exudation of PQ. Further studies showed that Arg increased the gene transcription levels of nitric oxide synthase (NOS) and nitrate reductase (NR), and activated NOS and NR, thus promoting the formation of nitric oxide (NO). A supplement of NO donor sodium nitroprusside (SNP) also confirmed that NO triggered promoted biosynthesis and efflux of PQ. PQ production stimulated by Arg or/and SNP can be significantly inhibited upon the addition of NO scavenger carboxy-PTIO, NOS inhibitor N_ω-nitro-L-arginine, or soluble guanylate cyclase inhibitor NS-2028. These results showed that Arg-derived NO, as a signaling molecule, is involved in the biosynthesis and regulation of PQ in Slf14(W) through the NO-cGMP-PKG signaling pathway. Our results provide a valuable strategy for large-scale PQ production and contribute to further understanding of NO signaling in the fungal metabolite biosynthesis. KEY POINTS: • PQ production of Shiraia sp. Slf14(w) was significantly improved by L-arginine addition. • Arginine-derived NO was firstly reported to be involved in the biosynthesis and regulation of PQ. • The NO-cGMP-PKG signaling pathway was proposed for the first time to participate in PQ biosynthesis.

Current State and Future Directions of Genetics and Genomics of Endophytic Fungi for Bioprospecting Efforts

The bioprospecting of secondary metabolites from endophytic fungi received great attention in the 1990s and 2000s, when the controversy around taxol production from Taxus spp. endophytes was at its height. Since then, hundreds of reports have described the isolation and characterization of putative secondary metabolites from endophytic fungi. However, only very few studies also report the genetic basis for these phenotypic observations. With low sequencing cost and fast sample turnaround, genetics- and genomics-based approaches have risen to become comprehensive approaches to study natural products from a wide-range of organisms, especially to elucidate underlying biosynthetic pathways. However, in the field of fungal endophyte biology, elucidation of biosynthetic pathways is still a major challenge. As a relatively poorly investigated group of microorganisms, even in the light of recent efforts to sequence more fungal genomes, such as the 1000 Fungal Genomes Project at the Joint Genome Institute (JGI), the basis for bioprospecting of enzymes and pathways from endophytic fungi is still rather slim. In this review we want to discuss the current approaches and tools used to associate phenotype and genotype to elucidate biosynthetic pathways of secondary metabolites in endophytic fungi through the lens of bioprospecting. This review will point out the reported successes and shortcomings, and discuss future directions in sampling, and genetics and genomics of endophytic fungi. Identifying responsible biosynthetic genes for the numerous secondary metabolites isolated from endophytic fungi opens the opportunity to explore the genetic potential of producer strains to discover novel secondary metabolites and enhance secondary metabolite production by metabolic engineering resulting in novel and more affordable medicines and food additives.