Fusaric Acid Research Articles

Molecularly Imprinted Photonic Crystals Based on Fusaric Acid for the Detection of Banana Fusarium Wilt

Banana Fusarium wilt is a soil-borne disease caused by Fusarium oxysporum f. sp. cubense (Foc) in which F. oxysporum f. sp. cubense race 4 (Foc4) could infect all kinds of banana and has caused great damage to the banana planting industry. The most important means to prevent and control banana Fusarium wilt in agricultural production is to control the spread and invasion of pathogens. Among them, the detection and determination of banana Fusarium wilt in the field is essential and thus is the basis of protection. Since fusaric acid (FA) is one of the specific products present during the metabolic processing of Fusarium wilt pathogens, by combining FA with molecularly imprinted photonic crystal (MIPC) technologies, a series of MIPCs based on monodispersed silica, FA, and cross-linked polymers, i.e., MIPC-FA, which could be recycled, were designed and prepared. It was found that the responses of MIPC-FA were affected by the cross-linking degree of the polymer matrix and the pH values. The results showed that MIPC-FA could effectively detect FA in a solution of FA in a minute scale, Foc4-containing medium, and banana plants infected by Foc4, and the response was related to the FA concentration, which makes it an effective and fast method to detect and determine banana Fusarium wilt caused by Foc4 in the field.

Mycotoxins produced by Fusarium spp. isolated from Striga hermonthica (Del.) Benth. in Sudan

isolates of F. solani and one isolate of each of F. oxysporum, F. nygamai, F. equiseti, and F. compactum were fully toxicologically characterized. These Fusaria were isolated from naturally infected Striga hermonthica plants collected from sorghum cultivations in central (Gezira), eastern (Gadarif), and southeastern Sudan (Damazin). HPLC/MS or HPLC/DAD system was used for the toxicological characterization of Fusarium spp. using nivalenol, deoxynivalenol, 3-acetyl deoxynivalenol, 15-Acetyl deoxynivalenol, fusarenon X, T2-toxin, HT-2 toxin, diacetoxyscirpenol, zearalenone, fumonisin B (B1 and B2), enniatin B, B1 and A and fusaric acid as toxin standards. The three isolates of F. solani produced none of the above toxins. Fusarium oxysporum and F. nygamai produced fusaric acid. Fusarium nygamai also produced fumonisns B1, B2, and B3. Fusarium equiseti produced nivalenol, fusarenon X, and diacetoxyscirpenol. Fusarium compactum produced nivalenol. This is the first report of nivalenol production by a strain of F. compactum. Non toxin-production by the three isolates of F. solani and production of only fusaric acid by F. oxysporum make them toxicologically safe for further evaluations as biocontrol agents for the witchweed.

Malformation Disease in Tabebuia rosea (Rosy Trumpet) Caused by Fusarium pseudocircinatum in Mexico.

Tabebuia rosea (rosy trumpet) is an economically important neotropical tree in Mexico that is highly valued for the quality of its wood, which is used for furniture, crafts, and packing, and for its use as an ornamental and shade tree in parks and gardens. During surveys conducted in the lower Balsas River Basin region in the states of Guerrero and Michoacán, symptoms of floral malformation were detected in T. rosea trees. The main objectives of this study were to describe this new disease, to determine its causal agent, and to identify it using DNA sequence data. A second set of objectives was to analyze the phylogenetic relationship of the causal agent to Fusarium spp. associated with Swietenia macrophylla trees with malformation surveyed in the same region and to compare mycotoxin production and the mating type idiomorphs of fusaria recovered from T. rosea and S. macrophylla. Tabebuia rosea showed malformed inflorescences with multiple tightly curled shoots and shortened internodes. A total of 31 Fusarium isolates recovered from symptomatic T. rosea (n = 20) and S. macrophylla (n = 11) trees were identified by molecular analysis as Fusarium pseudocircinatum. Pathogenicity tests showed that isolates of F. pseudocircinatum recovered from T. rosea induced malformation in inoculated T. rosea seedlings. Eighteen F. pseudocircinatum isolates were tested for their ability to produce mycotoxins and other secondary metabolites. Moniliformin, fusaric acid, bikaverin, beauvericin, aurofusarin. and 8-O-methylbostrycoidin were produced by at least one strain of the 18 isolates tested. A multiplex PCR assay for mating type idiomorph revealed that 22 F. pseudocircinatum isolates were MAT1-1 and that 9 were MAT1-2. Here, we report a new disease of T. rosea in Mexico caused by F. pseudocircinatum.

Current Perspectives of Biocontrol Agents for Management of Fusarium verticillioides and Its Fumonisin in Cereals-A Review.

Fusarium verticillioides is the most predominant fungal phytopathogen of cereals and it is posing great concern from a global perspective. The fungus is mainly associated with maize, rice, sorghum, wheat, sugarcane, banana, and asparagus and causes cob, stalk, ear, root, crown, top, and foot rot. F. verticillioides produces fumonisins as the major secondary metabolite along with trace levels of beauvericin, fusaric acid, fusarin C, gibberiliformin, and moniliformin. Being a potential carcinogen, fumonisins continue to receive major attention as they are common contaminants in cereals and its processed food products. The importance of elimination of F. verticillioides growth and its associated fumonisin from cereals cannot be overemphasized considering the significant health hazards associated with its consumption. Physical and chemical approaches have been shown to reduce fumonisin B1 concentrations among feeds and food products but have proved to be ineffective during the production process. Hence, biological control methods using microorganisms, plant extracts, antioxidants, essential oils, phenolic compounds, and other advanced technologies such as growing disease-resistant crops by applying genetic engineering, have become an effective alternative for managing F. verticillioides and its toxin. The different methods, challenges, and concerns regarding the biocontrol of F. verticillioides and production of fumonisin B1 have been addressed in the present review.

The Influence of Fusarium Mycotoxins on the Liver of Gilts and Their Suckling Piglets.

Simple SummaryMycotoxins are toxic secondary metabolites of fungi that frequently contaminate animal feed and human food in different combinations; therefore, it is of great importance to determine the effects of mycotoxin co-contamination. Pigs are one of the most sensitive animal species to Fusarium mycotoxins, and the liver is an important site of mycotoxin metabolism. The objective of the present research was to determine histopathological changes, apoptosis, and proliferation in the liver of gilts fed with Fusarium mycotoxin-contaminated feed for a prolonged time at the end of their pregnancy and until weaning of their piglets. Additionally, the same parameters were evaluated in the liver of their piglets to determine whether Fusarium mycotoxins would affect the offspring. The results revealed increased hepatocellular necrosis and apoptosis as well as sinusoidal leukocytosis with inflammatory infiltrates of hepatic lobules in experimental gilts, but no significant changes were observed in the piglet livers, implying that the utilized concentrations and duration of exposure did not cause detrimental effects on them. Interestingly, the amount of interlobular connective tissue in the liver of experimental gilts was significantly decreased. The obtained results emphasized the need to evaluate Fusarium mycotoxin concentrations in feed because even at low concentrations, they can cause adverse effects, but there is less concern for severe detrimental effects on the offspring.Mycotoxins are common fungal secondary metabolites in both animal feed and human food, representing widespread toxic contaminants that cause various adverse effects. Co-contamination with different mycotoxins is frequent; therefore, this study focused on feed contaminated with Fusarium mycotoxins, namely, deoxynivalenol (5.08 mg/kg), zearalenone (0.09 mg/kg), and fusaric acid (21.6 mg/kg). Their effects on the liver of gilts and their piglets were chosen as the research subject as pigs are one of the most sensitive animal species that are also physiologically very similar to humans. The gilts were fed the experimental diet for 54 ± 1 day, starting late in their pregnancy and continuing until roughly a week after weaning of their piglets. Livers of gilts and their piglets were assessed for different histopathological changes, apoptosis, and proliferation activity of hepatocytes. On histopathology, gilts fed the experimental diet had a statistically significant increase in hepatocellular necrosis and apoptosis (p = 0.0318) as well as sinusoidal leukocytosis with inflammatory infiltrates of hepatic lobules (p = 0.0004). The amount of interlobular connective tissue in the liver of experimental gilts was also significantly decreased (p = 0.0232), implying a disruption in the formation of fibrous connective tissue. Apoptosis of hepatocytes and of cells in hepatic sinusoids, further assessed by the terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assay, showed a statistically significant increase (p = 0.0224 and p = 0.0007, respectively). No differences were observed in piglet livers. These results indicated that Fusarium mycotoxins elicited increased apoptosis, necrosis, and inflammation in the liver of gilts, but caused no effects on the liver of piglets at these concentrations.

Identification of secondary metabolites in mycoparasites Fusarium strains and antifungal activity of fusaric acid against Plasmopara viticola

Fusarium delphinoides M1, F. brachygibbosum M2, F. pseudonygamai M10, M12_1 and Fusarium species novo M12_2 have been reported as mycoparasites of Plasmopara viticola, a causal agent of downy mildew disease of grapes. This study focused on screening of biocontrol potential of secondary metabolites produced by Fusarium strains using UHPLC-QTOF-MS coupled with UNIFI software. Furthermore, multivariate analysis was performed to analyze discriminant metabolites. The thirty-nine metabolites were identified based on their precursor, fragments ions matching with fungal secondary metabolite database. Among the metabolites, the identity of fusaric acid was the most common and dominant metabolite in extract of five strains. Leaf disc bioassay showed that extract of these strains inhibited >80% sporangia production in P. viticola and IC50 of fusaric acid was <0.61 µG/mL against P. viticola. Fusarium strains can be further explored to commercial production of fusaric acid to facilitate management of grapevine downy mildew disease.

Diversity and Biocontrol Potential of Culturable Endophytic Fungi in Cotton.

Healthy cotton samples were collected and 93 endophytic fungal strains were isolated: 23 strains from the roots and 70 strains from the stems. Morphological characterization and ITS sequence analysis were used for the identification of these isolates. The results showed that the 93 strains including 20 species were highly diverse in terms of their taxonomy. Simpson’s and Shannon’s diversity indices were 0.915 and 3.848, respectively. Fusarium and Alternaria were the two dominant genera, constituting 19.4% of the total strains. Then, 72 spore-producing strains were tested for the suppression of cotton Verticillium wilt (CVW) caused by Verticillium dahliae in a greenhouse. Five strains exhibited effective suppression of CVW with average efficacy values higher than 50%. One of the effective strains, namely, Fusarium proliferatum 10R-7, was selected for the investigation of the role of fusaric acid, a secondary metabolite of strain 10R-7, in the suppression of V. dahliae and CVW. The results showed that F. proliferatum 10R-7 could produce fusaric acid, and this metabolite exhibited 100% inhibition of mycelial growth of V. dahliae at concentrations higher than 20 μg/ml. However, fusaric acid at 2.5 to 80 μg/ml was not effective in the suppression of CVW, compared with the control treatment with V. dahliae alone. F. proliferatum 10R-7 was labeled with green fluorescent protein (GFP), and the GFP-tagged strain was found to be able to colonize inside the taproots of cotton, suggesting that F. proliferatum 10R-7 is a true endophyte of cotton and endophytic colonization may play a role in the suppression of infection of cotton by V. dahliae.

Physiological Response of Cape Gooseberry Plants to Fusarium oxysporum f. sp. physali, Fusaric Acid, and Water Deficit in a Hydrophonic System.

Cape gooseberry production has been limited by vascular wilt caused by Fusarium oxysporum f. sp. physali (Foph). Fusaric acid (FA) is a mycotoxin produced by many Fusarium species such as F. oxysporum formae speciales. The effects of the interaction between this mycotoxin and plants (such as cape gooseberry) under biotic stress (water deficit, WD) have been little explored. Three experiments were carried out. The objectives of this study were to evaluate (i) different Foph inoculum densities (1 × 104 and 1 × 106 conidia ml−1; experiment (1); (ii) the effect of times of exposure (0, 6, 9, and 12 h) and FA concentrations (0, 12.5, 25, 50, and 100 mg L−1; experiment (2), and (iii) the interaction between Foph (1 × 104 conidia mL−1) or FA (25 mg L−1 × 9 h), and WD conditions (experiment 3) on the physiological (plant growth, leaf stomatal conductance (gs), and photochemical efficiency of PSII (Fv/Fm ratio) and biochemical [malondialdehyde (MDA) and proline] responses of cape gooseberry seedling ecotype Colombia. The first experiment showed that Foph inoculum density of 1 × 106 conidia ml−1 caused the highest incidence of the disease (100%). In the second experiment, gs (~40.6 mmol m−2 s−1) and Fv/Fm ratio (~0.59) decreased, whereas MDA (~9.8 μmol g−1 FW) increased in plants with exposure times of 9 and 12 h and an FA concentration of 100 mg L−1 compared with plants without FA exposure or concentrations (169.8 mmol m−2 s−1, 0.8, and 7.2 μmol g−1 FW for gs, Fv/Fm ratio and MDA, respectively). In the last experiment, the interaction between Foph or FA and WD promoted a higher area under the disease progress curve (AUDPC) (Foph × WD = 44.5 and FA × WD = 37) and lower gs (Foph × WD = 6.2 mmol m−2 s−1 and FA × WD = 9.5 mmol m−2 s−1) compared with plants without any interaction. This research could be considered as a new approach for the rapid scanning of responses to the effects of FA, Foph, and WD stress not only on cape gooseberry plants but also on other species from the Solanaceae family.

Co-Occurrence of 35 Mycotoxins: A Seven-Year Survey of Corn Grain and Corn Silage in the United States.

Mycotoxins contaminate crops worldwide and play a role in animal health and performance. Multiple mycotoxins may co-occur which may increase the impact on the animal. To assess the multiple mycotoxin profile of corn (Zea mays), we conducted a 7-year survey of new crop corn grain and silage in the United States. A total of 711 grain and 1117 silage samples were collected between 2013 and 2019 and analyzed for the simultaneous presence of 35 mycotoxins using ultra-performance liquid chromatography–tandem mass spectrometry. The measured mean number of mycotoxins per sample were 4.8 (grain) and 5.2 (silage), ranging from 0 to 13. Fusaric acid (FA) was most frequently detected in 78.1 and 93.8% of grains and silages, respectively, followed by deoxynivalenol (DON) in 75.7 and 88.2% of samples. Fumonisin B1 (FB1), fumonisin B2 and 15-acetyl-deoxynivalenol (15ADON) followed. The greatest (p < 0.05) co-occurrence was between FA and DON in 59.1% of grains and 82.7% of silages, followed by FA with FB1, DON with 15ADON, and FA with 15ADON. Although many samples had lower mycotoxin concentrations, 1.6% (grain) and 7.9% (silage) of tested samples had DON ≥ 5000 µg/kg. Fumonisins were detected ≥ 10,000 µg/kg in 9.6 and 3.9% of grain and silage samples, respectively. Concentrations in grain varied by year for eight mycotoxin groups (p < 0.05), while all 10 groups showed yearly variations in silage. Our survey suggest that multiple mycotoxins frequently co-occur in corn grain and silage in the United States, and some of the more prevalent mycotoxins are those that may not be routinely analyzed (i.e., FA and 15ADON). Assessment of multiple mycotoxins should be considered when developing management programs.

Integrated analysis of transcriptome and proteome for exploring the mechanism of guaiacol production by Alicyclobacillus acidoterrestris

Alicyclobacillus spp. can cause commercially pasteurized fruit juices/beverages to spoil and the spoilage is characterized by the formation of a distinct medicinal or antiseptic off-odor attributed to guaiacol. The aim of this study was to reveal the mechanism of guaiacol production in A. acidoterrestris by combining transcriptomic and proteomic approaches. RNA-sequencing and iTRAQ analyses were conducted to investigate differences in expression levels of genes and proteins in A. acidoterrestris when producing (with 500 μM vanillic acid) and not producing (without vanillic acid) guaiacol. A total of 225 differentially expressed genes and 77 differentially expressed proteins were identified. The transcription of genes vdcBCD encoding subunits of vanillic acid decarboxylase were 626.47, 185.01 and 52.81-fold up-regulated, respectively; they were the most up-regulated genes involved in guaiacol production. Expressions of the benzoate membrane transport protein, fusaric acid resistance protein, resistance-nodulation- division transporter, some ATP-binding cassette transporters and major facilitator superfamily transporters were increased at either mRNA, protein or both levels, indicating that they participated in the uptake of vanillic acid and extrusion of guaiacol. In the metabolic process of vanillic acid to guaiacol in A. acidoterrestris, genes related to the pathway of tricarboxylic acid cycle and ribosome were up-regulated, while the expression of some genes associated with valine, leucine and isoleucine biosynthesis was decreased. These findings provide novel insight to understand the mechanism of guaiacol production in A. acidoterrestris, which will serve as an important guide for developing strategies for the control of A. acidoterrestris problems in the fruit juice industry.

Plant Growth-Promoting Rhizobacteria HN6 Induced the Change and Reorganization of Fusarium Microflora in the Rhizosphere of Banana Seedlings to Construct a Healthy Banana Microflora.

Streptomyces aureoverticillatus HN6 was isolated in our previous study and effectively controlled banana Fusarium wilt. We explored the role of HN6 in constructing a healthy rhizosphere microflora of banana seedlings. The method of antibiotic resistance was used to determine the colonization ability of HN6. The effect of HN6 on the rhizosphere microbial communities was assessed using culture-dependent and high-throughput sequencing. The effect of HN6 on the infection process of the pathogen was evaluated using a pot experiment and confocal laser scanning microscopy. The results showed that HN6 could prevent pathogen infection; it increased the nutrient content and diversity of the bacterial community in the rhizosphere, promoted plant growth, and decreased the mycotoxin fusaric acid content and abundance of pathogens in the banana rhizosphere. Thus, HN6 decreased the relative abundance of Fusarium species, increased the diversity of fungi, and increased the relative abundance of bacteria in the rhizosphere. HN6 induced the change and reorganization of the microbial community dominated by Fusarium in the rhizosphere of banana seedlings, and it evolved into a community dominated that was not conducive to the occurrence of diseases, shaping the rhizosphere microflora and promoting the growth of banana.

Nitrate mediated resistance against Fusarium infection in cucumber plants acts via photorespiration.

Fusarium wilt is one of the major biotic factors limiting cucumber (Cucumis sativus L.) growth and yield. The outcomes of cucumber-Fusarium interactions can be influenced by the form of nitrogen nutrition (nitrate [NO3- ] or ammonium [NH4+ ]); however, the physiological mechanisms of N-regulated cucumber disease resistance are still largely unclear. Here, we investigated the relationship between nitrogen forms and cucumber resistance to Fusarium infection. Our results showed that on Fusarium infection, NO3- feeding decreased the levels of the fungal toxin, fusaric acid, leaf membrane oxidative, organelle damage and disease-associated loss in photosynthesis. Metabolomic analysis and gas-exchange measurements linked NO3- mediated plant defence with enhanced leaf photorespiration rates. Cucumber plants sprayed with the photorespiration inhibitor isoniazid were more susceptible to Fusarium and there was a negative correlation between photorespiration rate and leaf membrane injury. However, there were positive correlations between photorespiration rate, NO3- assimilation and the tricarboxylic acid (TCA) cycle. This provides a potential electron sink or the peroxisomal H2 O2 catalysed by glycolate oxidase. We suggest that the NO3- nutrition enhanced cucumber resistance against Fusarium infection was associated with photorespiration. Our findings provide a novel insight into a mechanism involving the interaction of photorespiration with nitrogen forms to drive wider defence.

Mycorrhizal fungi induced activation of tomato defense system mitigates Fusarium wilt stress.

The fungus Fusarium oxysporum f. sp. lycopersici (FOL) is known to cause vascular wilt on tomato almost over the world. Inoculation of FOL reduced plant growth and increased wilt of tomato. The following study examined the possible role of arbuscular mycorrhizal fungi (AMF) consortium comprising of Rhizophagus intraradices, Funneliformis mosseae and Claroideoglomus etunicatum against FOL in tomato and explored in an inducing plant systemic defense. AMF inoculation reduced the wilt disease within vascular tissue and in vivo production of fusaric acid was observed which may be responsible in reduced wilting. FOL had an antagonistic effect on AMF colonization, reduced the number of spores, arbuscules and vesicles. AMF also inhibited the damage induced by Fusarium wilt through increasing chlorophyll contents along with the activity of phosphate metabolising enzymes (acid and alkaline phosphatases). Moreover, tomato plants with mycorrhizal inoculation showed an increase in the level of antioxidant enzymes including glutathione reductase, catalase, and etc. with an ultimate influence on the elimination of reactive oxygen species. Moreover, rise in phosphatase along with antioxidant enzymatic systems and enhanced photosynthetic performance contributed to induced resistance against FOL in tomato.

Deciphering the effect of FUB1 disruption on fusaric acid production and pathogenicity in Fusarium circinatum

Fusarium circinatum is an important pathogen of pine trees. However, little is known regarding the molecular processes underlying its pathogenesis. We explored the potential role of the phytotoxin fusaric acid (FA) in the pathogenicity of the fungus. FA is produced by products of the FUB biosynthesis gene cluster, containing FUB1-12. Of these, FUB1 encodes the core polyketide synthase, which we disrupted. We used the resulting mutant strain to investigate whether FUB1 and FA production play a role in the virulence of F. circinatum on pine. Our results showed that FA production was abolished both in vitro and in planta. However, bikaverin production was increased in the knockout mutant. FUB1 disruption also corresponded with downregulation of a F. circinatum homologue of LaeA, a master transcriptional regulator of secondary metabolism. Lesion lengths produced by the FUB1 knockout mutant on inoculated Pinus patula seedlings were significantly smaller than those produced by the wild type strain. Collectively, these results show that FUB1 plays a role in FA production in F. circinatum, and that this gene contributes to the aggressiveness of F. circinatum on P. patula. This study will contribute to the limited knowledge we have about the molecular basis of pathogenicity in this fungus.

Ethylene-dependent effects of fusaric acid on the photosynthetic activity of tomato plants

Fusaric acid (FA) is one of the potential toxins produced by pathogenic Fusarium species which exerts oxidative stress and cell death in plants. In this work, the effects of different concentrations of FA were investigated on the photosynthetic activity in leaves of wild type and Never ripe (Nr) tomato plants to reveal the potential role of ethylene under mycotoxin exposure. FA induced a significant ethylene emission from leaves in a concentration- and time-dependent manner. FA (1 mM) decreased the maximal and effective quantum yields of PSII and PSI in both tomato genotypes but photoprotective processes, such as the nonphotochemical quenching and the cyclic electron flow, were activated more effectively in Nr plants. However, the lipid peroxidation was higher in leaves of Nr. Our result confirmed that Nr plants were more sensitive to FA phytotoxicity suggesting the key role of ethylene in the activation of defense responses.

Pre-selection of banana somaclones resistant to Fusarium oxysporum f. sp. cubense, subtropical race 4

– Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most destructive diseases affecting banana crops worldwide. Therefore, the development of resistant cultivars is a promising alternative to mitigate the effects of the disease on banana plantations. The objectives of this study were to induce somaclonal variation in banana cultivars of the Silk and Cavendish types and to select somaclones resistant to subtropical race 4, thereby enabling the production of fruit in areas where this race is present. Shoot clump apexes of the Grand Naine and Maçã (Silk) cultivars were grown in MS medium. The cultures were subcultured four times. They were then challenged with fusaric acid (FA) in an experiment consisting of four treatments with different concentrations (0.1, 0.2, 0.3, and 0.4 mM) and five repetitions, each consisting of a Petri dish containing seven multiple shoot clumps in MS culture medium supplemented with 2.5 mg/L benzylamine purine. Multiple shoot clumps without the addition of FA were also used in the experiment, and were subcultured three times and maintained in a dark room. The multiple shoot clumps that survived the treatment with FA were transferred to MS medium and maintained in the growth chamber in the presence of light. The regenerated plants were later planted in tanks containing soil infested with an isolate classified as Foc subtropical race 4 (Foc STR4), and were evaluated for resistance to the pathogen at 90 days after inoculation (d.a.i.). Pathogen structures were confirmed by root clarification and root staining technique. All somaclones of the Maçã (Silk) cultivar were susceptible to Fusarium wilt and two somaclones of the Grand Naine cultivar were selected as resistant. The addition of FA as a selective agent was effective in the selection of somaclones among plants of the Grand Naine cultivar, as shown by the selection of two somaclones resistant to Foc STR4. The next step will consist of the agronomic and market potential validation of the selected somaclones, aiming to confirm their potential use by producers.

Kynurenine pathway as alternative biosynthetic pathway for fusaric acid in Fusarium oxysporum f.sp. cubense

Banana fusarium wilt caused by Fusarium. oxysporum f.sp. cubense race 4, has already become one of the main diseases in banana production. Previous research suggests that Foc can secrete two phytotoxins, respectively, fusaric acid and beauvericin, to contribute to its pathogenicity when it infects bananas. A gene cluster FUB consisting of 12 genes has been identified for fusaric acid biosynthesis in several Fusarium spp, including Fusarium. oxysporum f.sp. cubense race 4, F. oxysporum f.sp. lycopersici etc. In the present study, using reverse genetic research methods, we report the evidence for the kynurenine pathway as alternative biosynthetic pathways of fusaric acid in F. oxysporum f.sp. cubense 4. In the meanwhile, our experiments suggests that the beauvericin might not directly contribute to the pathogenicity to banana of F. oxysporum f.sp. cubense 4.

A Transcriptomic Analysis of Gene Expression in Chieh-Qua in Response to Fusaric Acid Stress

Fusarium wilt results in undesirable effects on the quality and production of chieh-qua (Benincasa hispida Cogn. var. Chieh-qua How). Fusaric acid (FA), a secondary metabolite of biotin produced by pathogens of genus Fusarium, induced resistant responses in chieh-qua; however, the physiological and molecular mechanism(s) of FA resistance remains largely unknown. In our study, ‘A39’ (FA-resistant cultivar) exhibited decreased malondialdehyde (MDA) content and increased superoxide dismutase (SOD) enzyme activity when exposed to FA compared with ‘H5’ (FA-susceptible cultivar). More apoptosis cells existed in ‘H5’ than ‘A39’ after 2 days of FA treatment. RNA-seq results revealed that a total of 2968 and 3931 differentially expressed genes (DEGs) were detected under normal conditions (1562 up-regulated and 1406 down-regulated) and FA treatment (2243 up-regulated and 1688 down-regulated), respectively. Interestingly, DEGs associated with pathogen-related protein and ethylene (ET) biosynthesis and signal pathways were most significantly changed during FA stress. Notably, several crucial genes encoding pathogenesis-related protein (CL4451.Contig2, CL2175.Contig4), peroxidase (Unigene49615 and CL11695.Contig2), and ET-responsive transcription factors (TFs) (CL9320.Contig1, CL9849.Contig3, CL6826.Contig2, CL919. Contig6, and CL518.Contig7) were specifically induced after FA treatment. Collectively, the study provides molecular data for isolating candidate genes involved in FA resistance, especially ET related genes in chieh-qua.

Deletion of Rv2571c confers resistance to arylamide compounds in Mycobacterium tuberculosis.

Tuberculosis, caused by Mycobacterium tuberculosis, is an urgent global health problem requiring new drugs, new drug targets and an increased understanding of antibiotic resistance. We have determined the mode of resistance to a series of arylamide compounds in M. tuberculosis We isolated M. tuberculosis resistant mutants to two arylamide compounds which are inhibitory to growth under host-relevant conditions (butyrate as a sole carbon source). Thirteen mutants were characterized, and all had mutations in Rv2571c; mutations included a premature stop codon and frameshifts as well as non-synonymous polymorphisms. We isolated a further ten strains with mutations in Rv2571c with resistance. Complementation with a wild-type copy of Rv2571c restored arylamide sensitivity. Over-expression of Rv2571c was toxic in both wild-type and mutant backgrounds. We constructed M. tuberculosis strains with an unmarked deletion of the entire Rv2571c gene by homologous recombination and confirmed that these were resistant to the arylamide series. Rv2571c is a member of the aromatic amino acid transport family and has a fusaric acid resistance domain which is associated with compound transport. Since loss or inactivation of Rv2571c leads to resistance, we propose that Rv2571c is involved in the import of arylamide compounds.

Phytotoxic Metabolites Produce by Fusarium oxysporum f. sp. cubense Race 2.

Banana is a major tropical fruit crop but banana production worldwide is seriously threatened due to Fusarium wilt. Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Fusarium wilt of banana (also referred as Panama disease) is an asexual, soil inhabiting facultative parasite. Foc isolates can be classified into three races that are not defined genetically, but for their pathogenicity to different banana cultivars. Despite mycotoxins being some of the best studied virulence factors of phytopathogenic fungi and these have been useful for the prediction of Foc virulence on banana plants, toxins produced by Foc race 2 strains have not been previously identified. The aim of this contribution was to identify the phytotoxic metabolites closely related to banana wilt caused by a Foc race 2 strain. We used an in vitro bioassay on detached banana leaves to evaluate the specificity of the microbial culture filtrates before a partial purification and further identification of Foc race 2 phytotoxins. A 29-day-old host-specific culture filtrate was obtained but specificity of culture filtrate was unrecovered after partial purification. The non-specific phytotoxins were characterized as fusaric acid, beauvericin, and enniatin A. Whereas some, if not all, of these phytotoxins are important virulence factors, a proteinaceous fraction from the specific 29-day-old culture filtrate protected the leaves of the resistant banana cultivar from damage caused by such phytotoxic metabolites.