Advances on Fungal Phytotoxins and Their Role in Grapevine Trunk Diseases

Grapevines are produced worldwide with important impact on local economies. Several biotic stresses induce serious diseases of grapevine, which severely affect the quantity and quality of production. One of the most important problems of vineyards worldwide is the high incidence of grapevine trunk diseases (GTD) induced by fungi belonging to several genera. Environmentally friendly methods for GTD control are being studied. This perspective offers an advanced overview on the fungal phytotoxins involved in GTD and their eventual role in the development of disease symptoms.

Phytotoxic Lipophilic Metabolites Produced by Grapevine Strains of Lasiodiplodia Species in Brazil

Phytotoxic metabolites produced in liquid culture by six species of Lasiodiplodia isolated in Brazil and causing Botryosphaeria dieback of grapevine were chemically identified. As ascertained by LC/MS, L. brasiliense, L. crassispora, L. jatrophicola, and L. pseudotheobromae produced jasmonic acid, and L. brasiliense synthesized, besides jasmonic acid, also (3R,4S)-4-hydroxymellein. L. euphorbicola and L. hormozganensis produced some low molecular weight lipophilic toxins. Specifically, L. euphorbicola produced (-)-mellein, (3R,4R)-(-)- and (3R,4S)-(-)-4-hydroxymellein, and tyrosol, and L. hormozganensis synthesized tyrosol and p-hydroxybenzoic acid. This is the first report on the production of the above cited metabolites from L. euphorbicola and L. hormozganensis. The phytotoxic activity of the metabolites produced is also discussed and related to the symptoms these pathogens cause in the grapevine host plants.

Melleins-Intriguing Natural Compounds

Melleins are 3,4-dihydroisocoumarins mainly produced by fungi, but also by plants, insects and bacteria. These specialized metabolites play important roles in the life cycles of the producers and they are involved in many biochemical and ecological processes. This review outlines the isolation and chemical and biological characterizations of natural-occurring melleins from the first report of (R)-mellein in 1933 to the most recent advances in their characterization in 2019. In addition, the pathways that could be involved in mellein biosynthesis are discussed, along with the enzymes and genes involved.

Phytotoxic metabolites by nine species of Botryosphaeriaceae involved in grapevine dieback in Australia and identification of those produced by Diplodia mutila, Diplodia seriata, Neofusicoccum australe and Neofusicoccum luteum

Botryosphaeria dieback is one of the main trunk diseases of grapevine caused by several species of Botryosphaeriaceae. Twenty-four fungal isolates representing the eight most widespread and most virulent Botryosphaeriaceae were tested for their ability to produce phytotoxic metabolites. The chromatographic profiles of their culture filtrates organic extracts showed the ability of all isolates to produce several and different metabolites. When tested on grapevine leaves and tomato cuttings the organic extracts phytotoxicity varied among isolates and species. To our knowledge, this is the first study on phytotoxic compounds produced by Botryosphaeriaceae species found in Australian vineyards. The phytotoxic metabolites produced by Diplodia seriata, Diplodia mutila, Neofusicoccum australe and, for the first time, by Neofusicoccum luteum were isolated and chemically identified essentially by spectroscopic methods.

The fungal phytotoxin lasiojasmonate A activates the plant jasmonic acid pathway

Jasmonates are signaling compounds that regulate plant responses to stress. Jasmonic acid (JA) is the direct precursor of the bioactive plant hormone JA-isoleucine (JA-Ile), the ligand of the CORONATINE INSENSITIVE 1-jasmonate ZIM-domain (COI1-JAZ) co-receptor complex. JA, its methyl ester, and three furanonyl esters were recently isolated from the grapevine pathogen Lasiodiplodia mediterranea. The JA ester lasiojasmonate A (LasA) is the first reported naturally occurring JA-furanone, and its mode of action has not yet been elucidated. Here, we show that LasA activates many JA-regulated responses in planta, including protein degradation, gene expression, and physiological processes. These in vivo effects require LasA conversion into JA, formation of JA-Ile, and its recognition by the plant JA-Ile perception complex. These findings suggest a mode of action of the natural fungal LasA as an inactive JA pool that can be transformed into the bioactive JA-Ile form. We propose that fungal production of JA derivates such as LasA occurs at late infection stages to induce plant JA responses such as cell death, and can facilitate fungal infection.

Challenges in LC-MS-based metabolomics for Alzheimer's disease early detection: targeted approaches versus untargeted approaches

BACKGROUND

Alzheimer's disease (AD) is one of the most common causes of dementia in old people. Neuronal deficits such as loss of memory, language and problem-solving are severely compromised in affected patients. The molecular features of AD are Aβ deposits in plaques or in oligomeric structures and neurofibrillary tau tangles in brain. However, the challenge is that Aβ is only one piece of the puzzle, and recent findings continue to support the hypothesis that their presence is not sufficient to predict decline along the AD outcome. In this regard, metabolomic-based techniques are acquiring a growing interest for either the early diagnosis of diseases or the therapy monitoring. Mass spectrometry is one the most common analytical platforms used for detection, quantification, and characterization of metabolic biomarkers. In the past years, both targeted and untargeted strategies have been applied to identify possible interesting compounds.

AIM OF REVIEW

The overall goal of this review is to guide the reader through the most recent studies in which LC-MS-based metabolomics has been proposed as a powerful tool for the identification of new diagnostic biomarkers in AD. To this aim, herein studies spanning the period 2009-2020 have been reported. Advantages and disadvantages of targeted vs untargeted metabolomic approaches have been outlined and critically discussed.

Phytotoxic Metabolites from Three Neofusicoccum Species Causal Agents of Botryosphaeria Dieback in Australia, Luteopyroxin, Neoanthraquinone, and Luteoxepinone, a Disubstituted Furo-α-pyrone, a Hexasubstituted Anthraquinone, and a Trisubstituted Oxepi-2-one from Neofusicoccum luteum

Different phytotoxic metabolites were isolated from the organic extract of Neofusicoccum luteum, Neofusicoccum australe, and Neofusicoccum parvum, causal agents of Botryosphaeria dieback in Australia. N. luteum produced a new disubstituted furo-α-pyrone, a hexasubstituted anthraquinone, and a trisubstituted oxepi-2(7H)-one, luteopyroxin (4), neoanthraquinone (5), and luteoxepinone (7), respectively, together with the known (±)-nigrosporione (6), tyrosol (8), (R)-(-)-mellein (1), and (3R,4S)-(-)- and (3R,4R)-(-)-4-hydroxymellein (2 and 3). The three melleins and tyrosol were also produced by N. parvum, while N. australe produced (R)-(-)-mellein (1), neoanthraquinone (5), tyrosol (8), and p-cresol (9). Luteopryoxin (4), neoanthraquinone (5), and luteoxepinone (7) were characterized by analyses of physical data, essentially one- and two-dimensional nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry. The relative and absolute configurations of luteopyroxin (4) were determined by nuclear Overhauser effect spectroscopy and experimental and calculated electronic circular dichroism data. When assayed on grapevine leaves, neoanthraquinone (5) showed the highest toxic effect, causing severe shriveling and withering. Luteopyroxin (4), nigrosporione (6), and luteoxepinone (7) also showed different degrees of toxicity, while p-cresol (9) displayed low phytotoxicity.

SARS-COV-2 Serological Profile in Healthcare Professionals of a Southern Italy Hospital

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the first coronavirus that has caused a pandemic. Assessing the prevalence of anti-SARS-CoV-2 in healthcare worker groups offers a unique opportunity to study the correlation between seroconversion and immunization because of their occupational exposure and a higher risk of contagion. The study enrolled 3242 asymptomatic employees of "Policlinico Riuniti", Foggia. After the first screening, we collected sequential serum samples for up to 23 weeks from the same subjects. In order to perform a longitudinal follow-up study and get information about the titration of IgG levels, we analyzed data from subjects (33) with at least two consecutive serological IgG-positive tests; 62 (1.9%; 95% CI: 1.4-2.3) tested positive for at least one anti-SARS-CoV-2 antibody. The seroprevalence was lower in the high-risk group 1.4% (6/428; 95% CI: 0.5-2.6) vs. the intermediate-risk group 2.0% (55/2736; 95% CI: 1.5-2.5). Overall, within eight weeks, we detected a mean reduction of -17% in IgG levels. Our data suggest a reduction of about 9.27 AU/mL every week (R2 = 0.35, p = 0.0003). This study revealed the prevalence of SARS-CoV-2 antibodies among Foggia's hospital healthcare staff (1.9%). Moreover, the IgG level reduction suggests that the serological response fades fast in asymptomatic infections.

Isolation of Phytotoxic Phenols and Characterization of a New 5-Hydroxymethyl-2-isopropoxyphenol from Dothiorella vidmadera, a Causal Agent of Grapevine Trunk Disease

Polyphenols were characterized from Dothiorella vidmadera (DAR78993), which was isolated from a grapevine in Australia. In total, six polyphenols were isolated including a new polyphenol characterized by a spectroscopic method (essentially NMR and HR ESIMS) as 5-hydroxymethyl-2-isopropoxyphenol. Tyrosol, benzene-1,2,4-triol, resorcinol, 3-(hydroxymethyl)phenol, and protocatechuic alcohol, the latter being the main metabolite, were also isolated. Although these are already known as naturally occurring compounds in microorganisms and plants, this is the first time they have been isolated from fungal organisms involved in grapevine trunk disease. When assayed on tomato seedlings, all the compounds show similar phytotoxic effects. However, when assayed on grapevine leaves (Vitis vinifera cv Shiraz), resorcinol was the most toxic compound, followed by protocatechuic alcohol and 5-hydroxymethyl-2-isopropoxyphenol.

The main phytotoxic metabolite produced by a strain of Fusarium oxysporum inducing grapevine plant declining in Italy

A strain of Fusarium oxysporum was isolated from grapevine showing heavy decline disease in a vineyard of Veneto region in Italy. The fungus showed to produce phytotoxic metabolites when grown in liquid culture. The main metabolite was identified as fusaric acid produced for the first time as a phytotoxin by a strain of F. oxysporom isolated from diseased grapevine plants. Its quantification in the fungus cultures filtrates was accomplished by HPLC. When tested on tobacco by leaf-puncture assay fusaric acid at 0.5 mg/mL induced the formation of extensive necrosis.

On the metabolites produced by Colletotrichum gloeosporioides a fungus proposed for the Ambrosia artemisiifolia biocontrol; spectroscopic data and absolute configuration assignment of colletochlorin A

Ambrosia artemisiifolia L. is responsible for serious allergies induced on humans. Different approaches for its control were proposed during the COST Action FA1203 "Sustainable management of Ambrosia artemisiifolia in Europe" (SMARTER). Fungal secondary metabolites often show potential herbicidal activity. Three phytotoxins were purified from the fungal culture filtrates of Colletotrichum gloeosporioides, isolated from infected leaves of A. artemisiifolia. They were identified by spectroscopic and chemical methods as colletochlorin A, orcinol and tyrosol (1, 2 and 3). The absolute configuration 6'R to colletochlorin A was assigned for the first time applying the advanced Mosher's method. When assayed by leaf-puncture on A. artemisiifolia only 1 caused the appearance of large necrosis. The same symptoms were also induced by 1 on ambrosia plantlets associated with plant wilting. On Lemna minor, colletochlorin A caused a clear fronds browning, with a total reduction in chlorophyll content.

Influence of light on the biosynthesis of ophiobolin A by Bipolaris maydis

Ophiobolin A (O-A) is a sesterpenoid with numerous biological activities, including potential anticancer effects. Its production at an industrial level is hampered due to inability of fungus Bipolaris maydis to biosynthesise it in vitro in large amount. Among the environmental factors regulating fungal metabolism, light plays a crucial role. In this study, the use of different light wavelength (light emitting diodes (LEDs)) was evaluated to increase the O-A production. The white light allowed the highest production of the metabolite. The blue and green lights showed an inhibitory effect, reducing the production to 50%, as well as red and yellow but at a lower level. No correlation between fungal growth and metabolite production was found in relation to the light type. A novel application of LED technologies, which can be optimised to foster specific pathways and promote the production of metabolites having scientific and industrial interest was proposed.

Production of Phytotoxic Metabolites by Botryosphaeriaceae in Naturally Infected and Artificially Inoculated Grapevines

Grapevine trunk diseases (GTDs) are considered a serious problem to viticulture worldwide. Several GTD fungal pathogens produce phytotoxic metabolites (PMs) that were hypothesized to migrate to the foliage where they cause distinct symptoms. The role of PMs in the expression of Botryosphaeria dieback (BD) symptoms in naturally infected and artificially inoculated wood using molecular and analytical chemistry techniques was investigated. Wood samples from field vines naturally infected with BD and one-year-old vines inoculated with Diplodia seriata, Spencermartinsia viticola and Dothiorella vidmadera were analysed by cultural isolations, quantitative PCR (qPCR) and targeted LC-MS/MS to detect three PMs: (R)-mellein, protocatechuic acid and spencertoxin. (R)-mellein was detected in symptomatic naturally infected wood and vines artificially inoculated with D. seriata but was absent in all non-symptomatic wood. The amount of (R)-mellein detected was correlated with the amount of pathogen DNA detected by qPCR. Protocatechuic acid and spencertoxin were absent in all inoculated wood samples. (R)-mellein may be produced by the pathogen during infection to break down the wood, however it was not translocated into other parts of the vine. The foliar symptoms previously reported in vineyards may be due to a combination of PMs produced and climatic and physiological factors that require further investigation.

A Targeted Mass Spectrometry Approach to Identify Peripheral Changes in Metabolic Pathways of Patients with Alzheimer's Disease

Alzheimer's disease (AD), a neurodegenerative disorder, is the most common cause of dementia in the elderly population. Since its original description, there has been intense debate regarding the factors that trigger its pathology. It is becoming apparent that AD is more than a brain disease and harms the whole-body metabolism. We analyzed 630 polar and apolar metabolites in the blood of 20 patients with AD and 20 healthy individuals, to determine whether the composition of plasma metabolites could offer additional indicators to evaluate any alterations in the metabolic pathways related to the illness. Multivariate statistical analysis showed that there were at least 25 significantly dysregulated metabolites in patients with AD compared with the controls. Two membrane lipid components, glycerophospholipids and ceramide, were upregulated, whereas glutamic acid, other phospholipids, and sphingolipids were downregulated. The data were analyzed using metabolite set enrichment analysis and pathway analysis using the KEGG library. The results showed that at least five pathways involved in the metabolism of polar compounds were dysregulated in patients with AD. Conversely, the lipid pathways did not show significant alterations. These results support the possibility of using metabolome analysis to understand alterations in the metabolic pathways related to AD pathophysiology.

Luteoethanones A and B, two phytotoxic 1-substituted ethanones produced by Neofusicoccum luteum, a causal agent of Botryosphaeria dieback on grapevine

Two new phytotoxic 1-substituted ethanones, named luteoethanones A and B, were isolated from Neofusicoccum luteum, the causal agents of Botryosphaeria dieback in Australia. Luteoethanones A and B were characterized, by spectroscopic methods (essentially 1 D and 2 D NMR and HR ESIMS), as 1-(8-Methoxy-2,4-methyl-1-oxa-4-aza-spiro[2.5]octa-5,7-dien-6-yl)-ethanone and its 2-demethyl analogue. When assayed on detached grapevine leaves (Vitis vinifera cv. Shiraz) both the compounds showed phytotoxic activity.

Diploquinones A and B, Two New Phytotoxic Tetrasubstituted 1,4-Naphthoquinones from Diplodia mutila, a Causal Agent of Grapevine Trunk Disease

Two new phytotoxic tetrasubstituted 1,4-naphthoquinones, named diploquinones A and B, were isolated together with vanillic acid from Diplodia mutila (DAR78993), a grapevine pathogen involved in Botryosphaeria dieback in Australia. Diploquinones A and B were characterized as 6,7-dihydroxy-2-methoxy-5-methylnaphthalene-1,4-dione and 3,5,7-trihydroxy-2-methoxynaphthalene-1,4-dione using spectroscopic methods (essentially 1D and 2D ¹H and ¹³C NMR and HR ESIMS). The already known vanillic acid was isolated for the first time as fungal phytotoxin and as metabolite of D. mutila. The three compounds were assayed on detached grapevine leaves ( Vitis vinifera cv. Shiraz) at concentrations of 10^-3 M and 2.5 × 10^-3 M. Vanillic acid showed the highest phytotoxic effect on grapevine leaves irrespective of the tested concentration, while diploquinones A and B showed varying degrees of toxicity.

Synthesis and mode of action studies of N-[(-)-jasmonyl]-S-tyrosin and ester seiridin jasmonate

Recent analyses on fungal jasmonic acid (JA)-containing metabolites suggest a mode-of-action of these naturally occurring compounds as inactive storage pools of JA. Plants and/or fungi can catabolize JA into the bioactive jasmonyl-isoleucine (JA-Ile) that in turn activates the JA-Ile-pathway in planta. To extend our knowledge on JA-derivates related to natural occurring JA conjugates, N-[(-)-jasmonyl]-S-tyrosin (JA-Tyr) and the ester JA-Sei between JA and seiridin, a fungal disubstituted furanone, were synthesized. The classical procedures for ester synthesis were applied for compound JA-Sei, while N-[(-)-jasmonyl]-S-tyrosin was synthesized with an optimized procedure. JA-Tyr and JA-Sei were characterized by spectroscopic method (essentially 1D and 2D NMR spectroscopy and ESI-MS) and their stereochemical composition was determined by means of HPLC and circular dichroism analysis. Finally, the activity of these JA-derivates was analyzed in planta. JA-Tyr and JA-Sei trigger JA-regulated plant responses, such as protein degradation and growth inhibition. These effects require the conversion of JA into JA-Ile and its recognition by the plant JA-Ile perception complex COI1-JAZ. Overall, these data suggest a mode-of-action of JA-Tyr and JA-Sei as inactive pool of JA that can be transformed into the bioactive JA-Ile to induce the canonical JA-Ile-pathway.

SARS-CoV-2 Gamma and Delta Variants of Concern Might Undermine Neutralizing Activity Generated in Response to BNT162b2 mRNA Vaccination

The Delta variant raised concern regarding its ability to evade SARS-CoV-2 vaccines. We evaluated a serum neutralizing response of 172 Italian healthcare workers, three months after complete Comirnaty (BNT162b2 mRNA, BioNTech-Pfizer) vaccination, testing their sera against viral isolates of Alpha, Gamma and Delta variants, including 36 subjects with a previous SARS-CoV-2 infection. We assessed whether IgG anti-spike TRIM levels and serum neutralizing activity by seroneutralization assay were associated. Concerning Gamma variant, a two-fold reduction in neutralizing titres compared to the Alpha variant was observed, while a four-fold reduction of Delta virus compared to Alpha was found. A gender difference was observed in neutralizing titres only for the Gamma variant. The serum samples of 36 previously infected SARS-CoV-2 individuals neutralized Alpha, Gamma and Delta variants, demonstrating respectively a nearly three-fold and a five-fold reduction in neutralizing titres compared to Alpha variant. IgG anti-spike TRIM levels were positively correlated with serum neutralizing titres against the three variants. The Comirnaty vaccine provides sustained neutralizing antibody activity towards the Alpha variant, but it is less effective against Gamma and even less against Delta variants.

Arabidopsis Defense against the Pathogenic Fungus Drechslera gigantea Is Dependent on the Integrity of the Unfolded Protein Response

Drechslera gigantea Heald & Wolf is a worldwide-spread necrotrophic fungus closely related to the Bipolaris genus, well-known because many member species provoke severe diseases in cereal crops and studied because they produce sesterpenoid phytoxins named ophiobolins which possess interesting biological properties. The unfolded protein response (UPR) is a conserved mechanism protecting eukaryotic cells from the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER). In plants, consolidated evidence supports the role of UPR in the tolerance to abiotic stress, whereas much less information is available concerning the induction of ER stress by pathogen infection and consequent UPR elicitation as part of the defense response. In this study, the infection process of D. gigantea in Arabidopsis thaliana wild type and UPR-defective bzip28 bzip60 double mutant plants was comparatively investigated, with the aim to address the role of UPR in the expression of resistance to the fungal pathogen. The results of confocal microscopy, as well as of qRT-PCR transcript level analysis of UPR genes, proteomics, microRNAs expression profile and HPLC-based hormone analyses demonstrated that ophiobolin produced by the fungus during infection compromised ER integrity and that impairment of the IRE1/bZIP60 pathway of UPR hampered the full expression of resistance, thereby enhancing plant susceptibility to the pathogen.

Phytotoxic Metabolites Produced by Fungi Involved in Grapevine Trunk Diseases: Progress, Challenges, and Opportunities

Grapevine trunk diseases (GTDs), caused by fungal pathogens, are a serious threat to vineyards worldwide, causing significant yield and economic loss. To date, curative methods are not available for GTDs, and the relationship between the pathogen and symptom expression is poorly understood. Several plant pathologists, molecular biologists, and chemists have been investigating different aspects of the pathogenicity, biochemistry, and chemical ecology of the fungal species involved in GTDs. Many studies have been conducted to investigate virulence factors, including the chemical characterization of phytotoxic metabolites (PMs) that assist fungi in invading and colonizing crops such as grapevines. Moreover, multidisciplinary studies on their role in pathogenicity, symptom development, and plant-pathogen interactions have also been carried out. The aim of the present review is to provide an illustrative overview of the biological and chemical characterization of PMs produced by fungi involved in Eutypa dieback, Esca complex, and Botryosphaeria dieback. Moreover, multidisciplinary investigations on host-pathogen interactions, including those using cutting-edge Omics techniques, will also be reviewed and discussed. Finally, challenges and opportunities in the role of PMs for reliable field diagnosis and control of GTDs in vineyards will also be explored.

Status of Phytotoxins Isolated from Necrotrophic Fungi Causing Diseases on Grain Legumes

Fungal phytotoxins can be defined as secondary metabolites toxic to host plants and are believed to be involved in the symptoms developed of a number of plant diseases by targeting host cellular machineries or interfering with host immune responses. As any crop, legumes can be affected by a number of fungal diseases, causing severe yield losses worldwide. In this review, we report and discuss the isolation, chemical, and biological characterization of fungal phytotoxins produced by the most important necrotrophic fungi involved in legume diseases. Their possible role in plant-pathogen interaction and structure-toxicity relationship studies have also been reported and discussed. Moreover, multidisciplinary studies on other prominent biological activity conducted on reviewed phytotoxins are described. Finally, we explore the challenges in the identification of new fungal metabolites and their possible applications in future experiments.

Tandem Mass Spectrometry as Strategy for the Selective Identification and Quantification of the Amyloid Precursor Protein Tyr682 Residue Phosphorylation Status in Human Blood Mononuclear Cells

Background: Alzheimer's disease (AD) is a devastating neurodegenerative disease without guidelines for early diagnosis or personalized treatment. Previous studies have highlighted a crucial role of increasing phosphorylation levels of the amyloid precursor protein (APP) Tyr682 residue in predicting neuronal deficits in AD patients. However, the lack of a method for the identification and quantification of Tyr682 phosphorylation levels prevents its potential clinical applications. Methods: Here we report a method to identify and quantify APP Tyr682 phosphorylation levels in blood mononuclear cells of AD patients by tandem mass spectrometry (tMS). Results: This method showed excellent sensitivity with detection and quantification limits set respectively at 0.035 and 0.082 ng injected for the phosphorylated peptide and at 0.02 and 0.215 ng injected for the non-phosphorylated peptide. The average levels of both peptides were quantified in transfected HELA cells (2.48 and 3.53 ng/μg of protein, respectively). Preliminary data on 3 AD patients showed quantifiable levels of phosphorylated peptide (0.10-0.15 ng/μg of protein) and below the LOQ level of non-phosphorylated peptide (0.13 ng/μg of protein). Conclusion: This method could allow the identification of patients with increased APP Tyr682 phosphorylation and allow early characterization of molecular changes prior to the appearance of clinical signs.