The necrotroph Botrytis cinerea promotes disease development in Panax ginseng by manipulating plant defense signals and antifungal metabolites degradation

Botrytis cinerea hypovirulent strain △BcSpd1 induced Panax ginseng defense

Background

Gray mold, caused by Botrytis cinerea, is one of the major fungal diseases in agriculture. Biological methods are preferred over chemical fungicides to control gray mold since they are less toxic to the environment and could induce the resistance to pathogens in plants. In this work, we try to understand if ginseng defense to B. cinerea could be induced by fungal hypovirulent strain △BcSpd1. BcSpd1 encodes Zn(II)2Cys6 transcription factor which regulates fungal pathogenicity and we recently reported △BcSpd1 mutants reduced fungal virulence.

Methods

We performed transcriptomic analysis of the host to investigate the induced defense response of ginseng treated by B. cinerea △BcSpd1. The metabolites in ginseng flavonoids pathway were determined by UPLC-ESI-MS/MS and the antifungal activates were then performed.

Results

We found that △BcSpd1 enhanced the ginseng defense response when applied to healthy ginseng leaves and further changed the metabolism of flavonoids. Compared with untreated plants, the application of △BcSpd1 on ginseng leaves significantly increased the accumulation of p-coumaric acid and myricetin, which could inhibit the fungal growth.

Conclusion

B. cinerea △BcSpd1 could effectively induce the medicinal plant defense and is referred to as the biological control agent in ginseng disease management.

Metabolomics Insight into the Variety-Mediated Responses to Aspergillus carbonarius Infection in Grapevine Berries

Limited knowledge regarding the susceptibility of grape varieties to ochratoxin A (OTA)-producing fungi is available to date. This study aimed to investigate the susceptibility of different grape varieties to Aspergillus carbonarius concerning OTA contamination and modulation at the metabolome level. Six grape varieties were selected, sampled at early veraison and ripening, artificially inoculated with A. carbonarius, and incubated at two temperature regimes. Significant differences were observed across cultivars, with Barbera showing the highest incidence of moldy berries (around 30%), while Malvasia and Ortrugo showed the lowest incidence (about 2%). OTA contamination was the lowest in Ortrugo and Malvasia, and the highest in Croatina, although it was not significantly different from Barbera, Merlot, and Sauvignon Blanc. Fungal development and mycotoxin production changed with grape variety; the sugar content in berries could also have played a role. Unsupervised multivariate statistical analysis from metabolomic fingerprints highlighted cultivar-specific responses, although a more generalized response was observed by supervised OPLS-DA modeling. An accumulation of nitrogen-containing compounds (alkaloids and glucosinolates), phenylpropanoids, and terpenoids, in addition to phytoalexins, was observed in all samples. A broader modulation of the metabolome was observed in white grapes, which were less contaminated by OTA. Jasmonates and oxylipins were identified as critical upstream modulators in metabolomic profiles. A direct correlation between the plant defense machinery and OTA was not observed, but the information was acquired and can contribute to optimizing preventive actions.

Transcriptome and metabolite analyses indicated the underlying molecular responses of Asian ginseng (Panax ginseng) toward Colletotrichum panacicola infection

Panax ginseng Meyer is one of the most valuable plants and is widely used in China, while ginseng anthracnose is one of the most destructive diseases. Colletotrichum panacicola could infect ginseng leaves and stems and causes serious anthracnose disease, but its mechanism is still unknown. Here, transcriptome and metabolism analyses of the host leaves were conducted to investigate the ginseng defense response affected by C. panacicola. Upon C. panacicola infection, ginseng transcripts altered from 14 to 24 h, and the expression of many defense-related genes switched from induction to repression. Consequently, ginseng metabolites in the flavonoid pathway were changed. Particularly, C. panacicola repressed plant biosynthesis of the epicatechin and naringin while inducing plant biosynthesis of glycitin, vitexin/isovitexin, and luteolin-7-O-glucoside. This work indicates C. panacicola successful infection of P. ginseng by intervening in the transcripts of defense-related genes and manipulating the biosynthesis of secondary metabolites, which might have antifungal activities.

Botrytis cinerea tolerates phytoalexins produced by Solanaceae and Fabaceae plants through an efflux transporter BcatrB and metabolizing enzymes

Botrytis cinerea, a plant pathogenic fungus with a wide host range, has reduced sensitivity to fungicides as well as phytoalexins, threatening cultivation of economically important fruits and vegetable crops worldwide. B. cinerea tolerates a wide array of phytoalexins, through efflux and/or enzymatic detoxification. Previously, we provided evidence that a distinctive set of genes were induced in B. cinerea when treated with different phytoalexins such as rishitin (produced by tomato and potato), capsidiol (tobacco and bell pepper) and resveratrol (grape and blueberry). In this study, we focused on the functional analyses of B. cinerea genes implicated in rishitin tolerance. LC/MS profiling revealed that B. cinerea can metabolize/detoxify rishitin into at least 4 oxidized forms. Heterologous expression of Bcin08g04910 and Bcin16g01490, two B. cinerea oxidoreductases upregulated by rishitin, in a plant symbiotic fungus Epichloë festucae revealed that these rishitin-induced enzymes are involved in the oxidation of rishitin. Expression of BcatrB, encoding an exporter of structurally unrelated phytoalexins and fungicides, was significantly upregulated by rishitin but not by capsidiol and was thus expected to be involved in the rishitin tolerance. Conidia of BcatrB KO (ΔbcatrB) showed enhanced sensitivity to rishitin, but not to capsidiol, despite their structural similarity. ΔbcatrB showed reduced virulence on tomato, but maintained full virulence on bell pepper, indicating that B. cinerea activates BcatrB by recognizing appropriate phytoalexins to utilize it in tolerance. Surveying 26 plant species across 13 families revealed that the BcatrB promoter is mainly activated during the infection of B. cinerea in plants belonging to the Solanaceae, Fabaceae and Brassicaceae. The BcatrB promoter was also activated by in vitro treatments of phytoalexins produced by members of these plant families, namely rishitin (Solanaceae), medicarpin and glyceollin (Fabaceae), as well as camalexin and brassinin (Brassicaceae). Consistently, ΔbcatrB showed reduced virulence on red clover, which produces medicarpin. These results suggest that B. cinerea distinguishes phytoalexins and induces differential expression of appropriate genes during the infection. Likewise, BcatrB plays a critical role in the strategy employed by B. cinerea to bypass the plant innate immune responses in a wide variety of important crops belonging to the Solanaceae, Brassicaceae and Fabaceae.

Tea plant (Camellia sinensis) lipid metabolism pathway modulated by tea field microbe (Colletotrichum camelliae) to promote disease

Tea is one of the most popular healthy and non-alcoholic beverages worldwide. Tea anthracnose is a disease in tea mature leaves and ultimately affects yield and quality. Colletotrichum camelliae is a dominant fungal pathogen in the tea field that infects tea plants in China. The pathogenic factors of fungus and the susceptible factors in the tea plant are not known. In this work, we performed molecular and genetic studies to observe a cerato-platanin protein CcCp1 from C. camelliae, which played a key role in fungal pathogenicity. △CcCp1 mutants lost fungal virulence and reduced the ability to produce conidia. Transcriptome and metabolome were then performed and analysed in tea-susceptible and tea-resistant cultivars, Longjing 43 and Zhongcha 108, upon C. camelliae wild-type CCA and △CcCp1 infection, respectively. The differentially expressed genes and the differentially accumulated metabolites in tea plants were clearly overrepresented such as linolenic acid and linoleic acid metabolism, glycerophospholipid metabolism, phenylalanine biosynthesis and metabolism, biosynthesis of flavonoid, flavone and flavonol etc. In particular, the accumulation of jasmonic acid was significantly increased in the susceptible cultivar Longjing 43 upon CCA infection, in the fungal CcCp1 protein dependent manner, suggesting the compound involved in regulating fungal infection. In addition, other metabolites in the glycerophospholipid and phenylalanine pathway were observed in the resistant cultivar Zhongcha 108 upon fungal treatment, suggesting their potential role in defense response. Taken together, this work indicated C. camelliae CcCp1 affected the tea plant lipid metabolism pathway to promote disease while the lost function of CcCp1 mutants altered the fungal virulence and plant response.

Urate oxidase from tea microbe Colletotrichum camelliae is involved in the caffeine metabolism pathway and plays a role in fungal virulence

Tea is one of the most well-known, healthy beverages in the world. Tea plants produce caffeine as a secondary metabolite. Colletotrichum camelliae is one of the most important microbes frequently isolated from tea fields, and it causes anthracnose disease in tea plant. In the present work, we performed molecular microbiology and transcriptomic analyses of the C. camelliae - tea plant interaction to investigate the mechanism of fungal virulence and plant defense. Upon infection of tea plant with C. camelliae, we observed alterations in the expression of fungal transcripts, including those of many genes associated with caffeine metabolism, such as those encoding various transporters, xanthine dehydrogenase, and urate oxidase (UOX). In particular, the deletion of C. camelliae urate oxidase (CcUOX), which is involved in the caffeine metabolism pathway, reduced fungal tolerance to caffeine, and impaired fungal virulence. CcUOX is involved in caffeine metabolism by the degradation of uric acid contents. C. camelliaeΔCcUOX mutants impaired uric acid degradation in vivo. The CcUOX gene was cloned from C. camelliae, overexpressed in Escherichia coli, and the recombinant CcUOX protein displayed maximum activity at 30°C and a pH of 4.0. The recombinant CcUOX efficiently reduced uric acid in vitro suggesting a promising application in caffeine-contaminated environment management and in producing food with low purine contents to prevent uric acid related human diseases, such as hyperuricemia and gout.

The Necrotroph Botrytis cinerea BcSpd1 Plays a Key Role in Modulating Both Fungal Pathogenic Factors and Plant Disease Development

Botrytis cinerea is a necrotrophic microbe that causes gray mold disease in a broad range of hosts. In the present study, we conducted molecular microbiology and transcriptomic analyses of the host-B. cinerea interaction to investigate the plant defense response and fungal pathogenicity. Upon B. cinerea infection, plant defense responses changed from activation to repression; thus, the expression of many defense genes decreased in Arabidopsis thaliana. B. cinerea Zn(II)2Cys6 transcription factor BcSpd1 was involved in the suppression of plant defense as ΔBcSpd1 altered wild-type B05.10 virulence by recovering part of the defense responses at the early infection stage. BcSpd1 affected genes involved in the fungal sclerotium development, infection cushion formation, biosynthesis of melanin, and change in environmental pH values, which were reported to influence fungal virulence. Specifically, BcSpd1 bound to the promoter of the gene encoding quercetin dioxygenase (BcQdo) and positively affected the gene expression, which was involved in catalyzing antifungal flavonoid degradation. This study indicates BcSpd1 plays a key role in the necrotrophic microbe B. cinerea virulence toward plants by regulating pathogenicity-related compounds and thereby suppressing early plant defense.