Transcriptomics Reveals the Effect of Thymol on the Growth and Toxin Production of Fusarium graminearum

Colonization by the endophytic fungus Phyllosticta fallopiae combined with the element Si promotes the growth of Dendrobium nobile

Endophytic fungi can promote plant growth and development, particularly of Orchidaceae species. Previously, we found that the endophytic fungus Phyllosticta fallopiae DN14, collected from Dendrobium nobile growing on rocks in a wild habitat, significantly promoted growth of its host plant D. nobile, an important herb in Chinese traditional medicine that contains the bioactive component dendrobine. Phyllosticta was positively correlated with FW and dendrobine content of D. nobile and with Si content of the epiphytic matrix. Si is also highly beneficial for the growth and productivity of many plants. Here, we co-cultured D. nobile with P. fallopiae DN14 in half-strength Murashige and Skoog medium with and without various concentrations of Si to investigate the effects of DN14 and Si on plant fresh weight and dendrobine content. We also explored the effects of DN14 infection and colonization on host plant growth, Si accumulation and transport, and expression of key genes, as well as the interaction between DN14 and Si. The combination of DN14 and Si promoted the lignification of D. nobile roots, stems, and leaves and markedly increased the thickening of xylem cell walls. Co-culture with DN14 increased transport of Si from roots to stems and from stems to leaves. Transcriptome sequencing and qRT-PCR analyses showed that enhancement of D. nobile growth by DN14 and Si may involve upregulation of plant hormone-related genes (AUX/IAA and MYC) and lignin biosynthesis genes (HCT, PAL1, and PAL2). Insoluble Si promoted the growth of DN14, perhaps through downregulation of genes (e.g., FBP, MPI, RPIAD) related to carbohydrate metabolism, and DN14 in turn promoted the transformation of insoluble Si into soluble Si for plant uptake. These findings demonstrate that endophytic fungi and Si can improve the growth of D. nobile and therefore show promise as organic amendments for commercial cultivation.

Inhibition mechanism of fusarium graminearum growth by g-C3N4 homojunction and its application in barley malting

The increase of deoxynivalenol (DON) caused by Fusarium graminearum (F. graminearum) during the malting process is a serious safety problem. In our work, the inhibition mechanism of F. graminearum growth by g-C3N4 homojunction and its application in barley malting were studied. The reason why the growth activity of F. graminearum decreased after photocatalysis by g-C3N4 homojunction was that under visible light irradiation, a large amount of •O2- elicited by g-C3N4 homojunction destroyed the cell structure of F. graminearum, leading to the deficiency of cell membrane selective permeability and serious disorder of intracellular metabolism. The application of photocatalysis technology in malting can effectively inhibit the growth of F. graminearum and the accumulation of ergosterol was reduced by 30.55 %, thus reducing the DON content in finished malt by 31.82 %. Meanwhile, the physicochemical indexes of barley malt after photocatalytic treatment still met the requirements of second class barley malt in Chinese light industry standard QB/T 1686-2008. Our work provides a new idea for the control of fungal contamination in barley malt.

Low Molecular Weight and High Deacetylation Degree Chitosan Batch Alleviates Pathogenesis, Toxin Accumulation, and Fusarium Gene Regulation in Barley Leaf Pathosystem

Fusarium graminearum is a cosmopolitan fungal pathogen that destroys cereal production, in terms of loss of yield and grain contamination with mycotoxins, worldwide. Chitosan is a natural biopolymer abundant in the environment with proven antifungal properties that also acts as a plant immunity elicitor. Despite a number of articles, there is a lack of systematic comparison of antifungal activity of diverse batches of chitosan. The current study aimed to test the inhibitory effects of a collection of diverse chitosan samples on the growth and production of F. graminearum toxins, validated by changes in the Fusarium transcriptome. Experiments included testing antifungal activity of different chitosan samples, the application of the best performing one in vitro to investigate the impact on F. graminearum growth, followed by analyzing its effect on Fusarium toxins accumulation, and Fusarium transcriptomics in the barley leaf pathosystem. Confirmatory antifungal assays revealed that CS_10, a specific batch of chitosan, retarded Fusarium growth with an application concentration of 200 ppm, significantly reducing toxin synthesis and disease symptoms in Fusarium-inoculated barley leaves. RNA-Seq analysis of F. graminearum in barley leaf pathosystem exposed to CS_10 showed a list of differentially expressed genes involved in redox balance, cell respiration, nutrient transport, cell wall degradation enzymes, ergosterol biosynthesis, and trichothecenes production. The genes functioning in these essential pathways are discussed and assigned as critical checkpoints to control Fusarium infections. The results suggest some important molecular targets in F. graminearum that may be suitable in gene-specific targeting or transgene-free methods, such as spray-induced gene silencing during host-pathogen interactions.

Characterization of tea (Camellia sinensis L.) flower extract and insights into its antifungal susceptibilities of Aspergillus flavus

BACKGROUND

Tea (Camellia sinensis L.) flowers will compete with tea leaves in nutrition and are abandoned as an undesirable by-product. In this study, the biological efficacy of tea flowers was investigated. Further exploration of its antifungal activity was explained.

METHODS

Tea flowers harvested from China were characterized in term of component, antioxidant ability, tyrosinase inhibition, and antifungal ability. Chemical compounds of tea flowers were analyzed by LC-MS. Disinfectant compounds were identified in tea flowers, and 2-ketobutyric acid exhibited antifungal activity against Aspergillus flavusCCTCC AF 2023038. The antifungal mechanism of 2-ketobutyric acid was further investigated by RNA-seq.

RESULTS

Water-soluble tea flower extracts (TFEs) exhibited free radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) as well as a high ferric-reducing ability. However, no inhibition of tyrosinase activity was observed. In the antifungal test, 6.4 mg/mL TFE reached 71.5% antifungal rate and the electrical conductivity of the culture broth increased with increasing concentration of TFE, implying that it damaged the fungal cell membrane by the TFE. Several disinfectants were identified in TFE by LC-MS, and 2-ketobutyric acid was also confirmed to be capable of fungal inhibition. Propidium iodide (PI) staining indicated that 2-ketobutyric acid caused damage to the cell membrane. RNA-seq analysis revealed that 3,808 differentially expressed genes (DEGs) were found in A. flavus CCTCC AF 2023038 treated by 2-ketobutyric acid, and more than 1,000 DEGs involved in the integral and intrinsic component of membrane were affected. Moreover, 2-ketobutyric acid downregulated aflatoxin biosynthesis genes and decreased the aflatoxin production.

CONCLUSIONS

Overall, TFE exhibited excellent antioxidant ability and fungal inhibition against A. flavus CCTCC AF 2023038 due to its abundant disinfectant compounds. As a recognized food additive, 2-ketobutyric acid is safe to use in the food industry and can be utilized as the basis for the research and development of strong fungicides.

Novel Strategies for the Biodegradation and Detoxification of Mycotoxins in Post-Harvest Grain

Mycotoxins are toxic secondary metabolites produced by filamentous fungi belonging, in particular, to the Aspergillus, Fusarium, and Penicillium genera [...].

Transcriptomic Profiling of Fusarium pseudograminearum in Response to Carbendazim, Pyraclostrobin, Tebuconazole, and Phenamacril

Fusarium pseudograminearum has been identified as a significant pathogen. It causes Fusarium crown rot (FCR), which occurs in several major wheat-producing areas in China. Chemical control is the primary measure with which to control this disease. In this study, transcriptome sequencing (RNA-Seq) was used to determine the different mechanisms of action of four frequently used fungicides including carbendazim, pyraclostrobin, tebuconazole, and phenamacril on F. pseudograminearum. In brief, 381, 1896, 842, and 814 differentially expressed genes (DEGs) were identified under the carbendazim, pyraclostrobin, tebuconazole, and phenamacril treatments, respectively. After the joint analysis, 67 common DEGs were obtained, and further functional analysis showed that the ABC transported pathway was significantly enriched. Moreover, FPSE_04130 (FER6) and FPSE_11895 (MDR1), two important ABC multidrug transporter genes whose expression levels simultaneously increased, were mined under the different treatments, which unambiguously demonstrated the common effects. In addition, Mfuzz clustering analysis and WGCNA analysis revealed that the core DEGs are involved in several critical pathways in each of the four treatment groups. Taken together, these genes may play a crucial function in the mechanisms of F. pseudograminearum's response to the fungicides stress.

Carotenoids Occurring in Maize Affect the Redox Homeostasis of Fusarium graminearum and Its Production of Type B Trichothecene Mycotoxins: New Insights Supporting Their Role in Maize Resistance to Giberella Ear Rot

Fusarium graminearum is the causal agent of Gibberella ear rot (GER) in maize, a devastating fungal disease resulting in yield reduction and contamination of grains with type B trichothecene (TCTB) mycotoxins. Reducing GER damage requires the implementation of an integrated management strategy in which the use of resistant maize genotypes is a key factor. The present study aimed at providing new phenotyping tools to improve breeding pipelines by investigating the yet understudied contribution of carotenoids to GER resistance. Here, we demonstrated for the first time the efficiency of carotenoid extracts from various maize genotypes to inhibit the production of TCTB by F. graminearum. We further suggested that zeaxanthin could be a key actor of this inhibition efficiency, notably via a negative transcriptional control of several biosynthetic genes of the TCTB pathway. Besides, we demonstrated that zeaxanthin treatments led to profound perturbations in the fungal redox homeostasis by affecting the expression of key genes encoding ROS detoxifying enzymes, several of them being involved in F. graminearum virulence during plant infection. Altogether, our data support the contribution of carotenoids to the mechanisms employed by maize to counteract F. graminearum infection and its production of TCTB.

Biological potential of Bacillus subtilis BS45 to inhibit the growth of Fusarium graminearum through oxidative damage and perturbing related protein synthesis

Fusarium root rot (FRR) caused by Fusarium graminearum poses a threat to global food security. Biological control is a promising control strategy for FRR. In this study, antagonistic bacteria were obtained using an in-vitro dual culture bioassay with F. graminearum. Molecular identification of the bacteria based on the 16S rDNA gene and whole genome revealed that the species belonged to the genus Bacillus. We evaluated the strain BS45 for its mechanism against phytopathogenic fungi and its biocontrol potential against FRR caused by F. graminearum. A methanol extract of BS45 caused swelling of the hyphal cells and the inhibition of conidial germination. The cell membrane was damaged and the macromolecular material leaked out of cells. In addition, the mycelial reactive oxygen species level increased, mitochondrial membrane potential decreased, oxidative stress-related gene expression level increased and oxygen-scavenging enzyme activity changed. In conclusion, the methanol extract of BS45 induced hyphal cell death through oxidative damage. A transcriptome analysis showed that differentially expressed genes were significantly enriched in ribosome function and various amino acid transport pathways, and the protein contents in cells were affected by the methanol extract of BS45, indicating that it interfered with mycelial protein synthesis. In terms of biocontrol capacity, the biomass of wheat seedlings treated with the bacteria increased, and the BS45 strain significantly inhibited the incidence of FRR disease in greenhouse tests. Therefore, strain BS45 and its metabolites are promising candidates for the biological control of F. graminearum and its related root rot diseases.