An Antifungal Role of Hydrogen Sulfide on Botryosphaeria Dothidea and Amino Acid Metabolism Involved in Disease Resistance Induced in Postharvest Kiwifruit

Fermentation of waste water from agar processing with Bacillus subtilis by metabolomic analysis

Fungal infection has become a major threat to crop loss and affects food safety. The waste water from agar processing industries extraction has a number of active substances, which could be further transformed by microorganisms to synthesize antifungal active substances. In this study, Bacillus subtilis was used to ferment the waste water from agar processing industries extraction to analyze the antifungal activity of the fermentation broth on Alternaria alternata and Alternaria spp. Results showed that 25% of the fermentation broth was the most effective in inhibited A. alternata and Alternaria spp., with fungal inhibition rates of 99.9% and 96.1%, respectively, and a minimum inhibitory concentration (MIC) was 0.156 μg/mL. Metabolomic analysis showed that flavonoid polyphenols such as coniferyl aldehyde, glycycoumarin, glycitin, and procyanidin A1 may enhance the inhibitory activity against the two pathogenic fungal strains. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that polyphenols involved in the biosynthesis pathways of isoflavonoid and phenylpropanoid were upregulated after fermentation. The laser confocal microscopy analyses and cell conductivity showed that the cytoplasm of fungi treated with fermentation broth was destroyed. This study provides a research basis for the development of new natural antifungal agents and rational use of seaweed agar waste. KEY POINTS: • Bacillus subtilis fermented waste water has antifungal activity • Bacillus subtilis could transform active substances in waste water • Waste water is a potential raw material for producing antifungal agents.

Hydrogen sulfide enhances kiwifruit resistance to soft rot by regulating jasmonic acid signaling pathway

As the third active gas signal molecule in plants, hydrogen sulfide (H2S) plays important roles in physiological metabolisms and biological process of fruits and vegetables during postharvest storage. In the present study, the effects of H2S on enhancing resistance against soft rot caused by Botryosphaeria dothidea and the involvement of jasmonic acid (JA) signaling pathway in kiwifruit during the storage were investigated. The results showed that 20 μL L-1 H2S fumigation restrained the disease incidence of B. dothidea-inoculated kiwifruit during storage, and delayed the decrease of firmness and the increase of soluble solids (SSC) content. H2S treatment increased the transcription levels of genes related to JA biosynthesis (AcLOX3, AcAOS, AcAOC2, and AcOPR) and signaling pathway (AcCOI1, AcJAZ5, AcMYC2, and AcERF1), as well as the JA accumulation. Meanwhile, H2S promoted the expression of defense-related genes (AcPPO, AcSOD, AcGLU, AcCHI, AcAPX, and AcCAT). Correlation analysis revealed that JA content was positively correlated with the expression levels of JA biosynthesis and defense-related genes. Overall, the results indicated that H2S could promote the increase of endogenous JA content and expression of defense-related genes by regulating the transcription levels of JA pathway-related genes, which contributed to the inhibition on the soft rot occurrence of kiwifruit.

Bacillus sp. alone or combined with salicylic acid inhibited Trichoderma spp. infection on harvested white Hypsizygus marmoreus

Introduction

White Hypsizygus marmoreus is a popular edible mushroom. It is rich in nutrition and flavor but vulnerable to fungal disease, resulting in nutrient loss and aging.

Methods

In this study, the pathogenic fungus Trichoderma spp. BBP-6 and its antagonist Bacillus sp. 1-23 were isolated and identified. The negative effects caused by this pathogen were judged by detecting a series of changes in the infected white H. marmoreus. The effects of Bacillus sp. 1-23 on Trichoderma spp. BBP-6 and the infected white H. marmoreus were detected. The effect of Bacillus sp. 1-23 treatment combined with salicylic acid (SA) was also considered.

Results

The results showed that Trichoderma spp. BBP-6 could affect the activities of antioxidant enzymes PAL, POD, CAT, SOD, GR, PPO, and APX to interfere with the stability of the white H. marmoreus antioxidant enzyme system and cause the mushroom severe browning and nutrition loss, as well as general quality deterioration. Bacillus sp. 1-23 could produce chitinase and chitosanase enzymes to inhibit Trichoderma spp. BBP-6 directly. SA reinforced this inhibitory. Bacillus sp. 1-23 alone or combined with SA could help white H. marmoreus from the Trichoderma spp. BBP-6 infection to effectively maintain nutrients, restore and stabilize the antioxidant system, and reduce the production of malondialdehyde, superoxide anion and hydrogen peroxide.

Discussion

Thus, such treatments could be considered potential methods to alleviate damage from disease and extend the shelf life of white H. marmoreus.

Octanal enhances disease resistance in postharvest citrus fruit by the biosynthesis and metabolism of aromatic amino acids

Octanal was found to be able to reduce green mold incidence in citrus fruit by a defense response mechanism. However, the underlying mechanism remains largely unclear. Herein, the metabolomics, RNA-seq and biochemical analyses were integrated to explore the effect of octanal on disease resistance in harvested citrus fruit. Results showed that octanal fumigation at 40 μL L-1 was effective in controlling citrus green mold. Metabolomics analysis showed that octanal mainly led to the accumulation of some plant hormones including methyl jasmonate, abscisic acid, indole-3-butyric acid, indoleacetic acid (IAA), salicylic acid, and gibberellic acid and many phenylpropanoid metabolites including cinnamyl alcohol, hesperidin, dihydrokaempferol, vanillin, quercetin-3-O-malonylglucoside, curcumin, naringin, chrysin, coniferin, calycosin-7-O-β-D-glucoside, trans-cinnamaldehyde, and 4',5,7-trihydroxy-3,6-dimethoxyflavone. Particularly, IAA and hesperidin were dramatically accumulated in the peel, which might be the contributors to the resistance response. Additionally, transcriptome analysis showed that octanal greatly activated the biosynthesis and metabolism of aromatic amino acids. This was further verified by the accumulation of some metabolites (shikimic acid, tryptophan, tyrosine, phenylalanine, IAA, total phenolics, flavonoids and lignin), increase in some enzyme activities (phenylalanine ammonia-lyase, tyrosine ammonia-lyase, 4-coumarate CoA ligase, cinnamic acid 4-hydroxylase, polyphenol oxidase, and peroxidase), up-regulation of some genes (tryptophan pyruvate aminotransferase, aldehyde dehydrogenase, shikimate kinase and shikimate dehydrogenase) expressions and molecular docking results. Thus, these results indicate that octanal is an efficient strategy for the control of postharvest green mold by triggering the defense response in citrus fruit.

Antifungal Activity and Action Mechanisms of 2,4-Di-tert-butylphenol against Ustilaginoidea virens

Ustilaginoidea virens is a destructive phytopathogenic fungus that causes false smut disease in rice. In this study, the natural product 2,4-di-tert-butylphenol (2,4-DTBP) was found to be an environmentally friendly and effective agent for the first time, which exhibited strong antifungal activity against U. virens, with an EC50 value of 0.087 mmol/L. The scanning electron microscopy, fluorescence staining, and biochemical assays indicated that 2,4-DTBP could destroy the cell wall, cell membrane, and cellular redox homeostasis of U. virens, ultimately resulting in fungal cell death. Through the transcriptomic analysis, a total of 353 genes were significantly upregulated and 367 genes were significantly downregulated, focusing on the spindle microtubule assembly, cell wall and membrane, redox homeostasis, mycotoxin biosynthesis, and intracellular metabolism. These results enhanced the understanding of the antifungal activity and action mechanisms of 2,4-DTBP against U. virens, supporting it to be a potential antifungal agent for the control of false smut disease.