Mitochondrial damage produced by phytotoxic chromenone and chromanone derivatives from endophytic fungus Daldinia eschscholtzii strain GsE13

Induced production of defensive secondary metabolites from Aspergillus fumigatiaffinis by co-culture with Aspergillus alabamensis

Seven previously undescribed compounds, including four diketomorpholine alkaloids (1‒4), one indole diketopiperazine alkaloid (9), one chromone (10), and one benzoic acid derivative (13), and nine known compounds (5-8, 11, 12, and 14-16) were isolated from two different fungal sources. Nine of these metabolites (1-9) were obtained from a seagrass-derived Aspergillus alabamensis SYSU-6778, while the others were obtained from a mixed culture of A. alabamensis SYSU-6778 and a co-isolated fungus A. fumigatiaffinis SYSU-6786. The chemical structures of the compounds were deduced via spectroscopic techniques (including HRESIMS, 1D and 2D NMR), chemical reactions, and ECD calculations. It is worth noting that compound 10 was identified as a defensive secondary metabolite of strain SYSU-6786, produced through the induction of compound 8 under co-culture conditions. Compounds 3 and 4 possessed a naturally rare isotryptophan core. Moreover, compounds 1 and 2 exhibited potent inhibitory activities against fish pathogenic bacterium Edwardsiella ictalurid, with minimum inhibitory concentration values of 10.0 μg/mL for both compounds.

Differential Volatile Organic Compound Expression in the Interaction of Daldinia eschscholtzii and Mycena citricolor

Fungi exhibit a wide range of ecological guilds, but those that live within the inner tissues of plants (also known as endophytes) are particularly relevant due to the benefits they sometimes provide to their hosts, such as herbivory deterrence, disease protection, and growth promotion. Recently, endophytes have gained interest as potential biocontrol agents against crop pathogens, for example, coffee plants (Coffea arabica). Published results from research performed in our laboratory showed that endophytic fungi isolated from wild Rubiaceae plants were effective in reducing the effects of the American leaf spot of coffee (Mycena citricolor). One of these isolates (GU11N) from the plant Randia grandifolia was identified as Daldinia eschscholtzii (Xylariales). Its antagonism mechanisms, effects, and chemistry against M. citricolor were investigated by analyzing its volatile profile alone and in the presence of the pathogen in contactless and dual culture assays. The experimental design involved direct sampling of agar plugs in vials for headspace (HS) and headspace solid-phase microextraction (HS-SPME) gas chromatography-mass spectrometry (GC-MS) analysis. Additionally, we used ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS/MS) to identify nonvolatile compounds from organic extracts of the mycelia involved in the interaction. Results showed that more volatile compounds were identified using HS-SPME (39 components) than those by the HS technique (13 components), sharing only 12 compounds. Statistical tests suggest that D. eschscholtzii inhibited the growth of M. citricolor through the release of VOCs containing a combination of 1,8-dimethoxynapththalene and terpene compounds affecting M. citricolor pseudopilei. The damaging effects of 1,8-dimethoxynaphthalene were corroborated in an in vitro test against M. citricolor pseudopilei; scanning electron microscopy (SEM) photographs confirmed structural damage. After analyzing the UHPLC-HRMS/MS data, a predominance of fatty acid derivatives was found among the putatively identified compounds. However, a considerable proportion of features (37.3%) remained unannotated. In conclusion, our study suggests that D. eschscholtzii has potential as a biocontrol agent against M. citricolor and that 1,8-dimethoxynaphthalene contributes to the observed damage to the pathogen's reproductive structures.

Diversified Polyketides With Anti-inflammatory Activities From Mangrove Endophytic Fungus Daldinia eschscholtzii KBJYZ-1

In total, five new polyketide derivatives: eschscholin B (2), dalditone A and B (3 and 4), (1R, 4R)-5-methoxy-1,2,3,4-tetrahydronaphthalene-1,4-dio (5), and daldilene A (6), together with 10 known as analogs (1, 7-15) were isolated from the mangrove endophytic fungus Daldinia eschscholtzii KBJYZ-1. Their structures and absolute configurations were established by extensive analysis of NMR and HRESIMS spectra data combined with ECD calculations and the reported literature. Compounds 2 and 6 showed significant cell-based anti-inflammatory activities with IC₅₀ values of 19.3 and 12.9 μM, respectively. In addition, western blot results suggested that compound 2 effectively inhibits the expression of iNOS and COX-2 in LPS-induced RAW264.7 cells. Further molecular biology work revealed the potential mechanism of 2 exerts anti-inflammatory function by inactivating the MAPK and NF-κB signaling pathways.

Phytotoxic compounds from endophytic fungi

Weeds represent one of the most challenging biotic factors for the agricultural sector, responsible for causing significant losses in important agricultural crops. Traditional herbicides have managed to keep weeds at bay, but overuse has resulted in negative environmental and toxicological impacts, including the increase of herbicide-resistant species. Within this context, the use of biologically derived (bio-)herbicides represents a promising solution because they are able to provide the desired phytotoxic effects while causing less toxic environmental damage. In recent years, bioactive secondary metabolites, in particular those bio-synthesized by endophytic fungi, have been shown to be promising sources of novel compounds that can be exploited in agriculture, including their use in weed control. Endophytic fungi have the ability to produce volatile and nonvolatile compounds with broad phytotoxic activity. In addition, as a result of the beneficial relationships they establish with their host plants, they are part of the colonization mechanism and can provide protection for their hosts. As such, endophytic fungi can be exploited as bioherbicides and as research tools. In this review, we cover 100 nonvolatile secondary metabolites with phytotoxic activity and more than 20 volatile organic compounds in a mixture, produced by 28 isolates of endophytic fungi from 21 host plant families, collected in 8 countries. This information can form the basis for the application of endophytic fungal compounds in weed control. KEY POINTS: • Endophytic fungi produce a wide variety of secondary metabolites with unique and complex structures. • Fungal endophytes produce volatile and nonvolatile compounds with promising phytotoxic activity. • Endophytic fungi are a promising source of useful bioherbicides.