Fusaric Acid Production Research Articles

Pathogen-driven Pseudomonas reshaped the phyllosphere microbiome in combination with Pseudostellaria heterophylla foliar disease resistance via the release of volatile organic compounds

BackgroundContinuous monocropping obstacles are common in plants, especially medicinal plants, resulting in disease outbreaks and productivity reductions. Foliar disease, mainly caused by Fusarium oxysporum, results in a severe decrease in the yield of Pseudostellaria heterophylla annually. Determining an effective biomethod to alleviate this disease is urgently needed to improve its productivity and quality.ResultsThis study screened thirty-two keystone bacterial genera induced by pathogens in P. heterophylla rhizosphere soil under continuous monocropping conditions. Pseudomonas, Chryseobacterium, and Flavobacterium, referred to as the beneficial microbiota, were significantly attracted by pathogen infection. The P. palleroniana strain B-BH16-1 can directly inhibit the growth and spore formation of seven primary pathogens of P. heterophylla foliar disease by disrupting fusaric acid production via the emission of volatile organic compounds (VOCs). In addition, strain B-BH16-1 enhances the disease resistance of P. heterophylla by obliterating the pathogen and assembling beneficial microbiota.ConclusionPathogen-induced Pseudomonas reshaped phyllosphere microbial communities via direct antagonism of pathogens and indirect disruption of the pathogen virulence factor biosynthesis to enhance disease suppression and improve yields. These results show that inhibiting pathogen virulence biosynthesis to reshape the plant microbial community using disease-induing probiotics will be an innovative strategy for managing plant disease, especially under continuous monoculture conditions.

Fusaric acid mediates the assembly of disease-suppressive rhizosphere microbiota via induced shifts in plant root exudates

The plant health status is determined by the interplay of plant-pathogen-microbiota in the rhizosphere. Here, we investigate this tripartite system focusing on the pathogen Fusarium oxysporum f. sp. lycopersici (FOL) and tomato plants as a model system. First, we explore differences in tomato genotype resistance to FOL potentially associated with the differential recruitment of plant-protective rhizosphere taxa. Second, we show the production of fusaric acid by FOL to trigger systemic changes in the rhizosphere microbiota. Specifically, we show this molecule to have opposite effects on the recruitment of rhizosphere disease-suppressive taxa in the resistant and susceptible genotypes. Last, we elucidate that FOL and fusaric acid induce changes in the tomato root exudation with direct effects on the recruitment of specific disease-suppressive taxa. Our study unravels a mechanism mediating plant rhizosphere assembly and disease suppression by integrating plant physiological responses to microbial-mediated mechanisms in the rhizosphere.

Modes of action of Trichoderma virens Gl006 and Bacillus velezensis Bs006: decoding the arsenal of the microbial consortium

The consortium based on Trichoderma virens Gl006 and Bacillus velezensis Bs006 was selected in a previous study because the high effectiveness against Fusarium wilt of cape gooseberry (Fusarium oxysporum f. sp. physali—Foph). The compatibility among the strains was determined previously, but the modes of action exerted by the consortium remained unknown. In this study, the modes of action displayed by the Gl006 and Bs006 consortium against the Foph strain Map5 were determined and compared with the modes of action of the single microorganisms. Production of cell wall degrading enzymes (CWDE), cyclic lipopeptides (CLPs) by Bs006 and gliotoxin by Gl006, and fusaric acid (FA) production by Foph were evaluated in the co-culture of the strains in several culture media. Furthermore, the survival of the strains in the soil, the colonization of plant tissues and the induction of systemic responses through a split root model bioassay were evaluated. While Bs006 showed protease, β-1,3-glucanase, and chitobiosidase enzymatic activities, and production of CLPs, Gl006 showed β-N-acetylglucosaminidase, chitobiosidase, total chitinase, β-1,3-glucanase, and protease activities. All the metabolites produced by the single strains were also found in the consortium, but in a culture medium dependent manner. The FA was found in the experiment on the interaction of the consortium with Foph Map5 in the minimal basal medium and in potato dextrose broth. The population of Foph was reduced by the consortium in vitro, under the synthetic media that favored the production of all the CWDE tested. In soil conditions, the consortium reduced the population of Foph by 63% in a synergistic way. Bs006 was recovered from the inner tissues of the plant, where Gl006 prevented the entry of Foph to the roots and reduced the incidence of the disease under the split root model. These results suggest that the consortium of Gl006 and Bs006 displays modes of action through CWDE and CLP´s and indirectly through induction of systemic resistance, which could act complementary since neither of them were enhanced in consortium. Here we characterized a consortium capable of reducing the population of Foph in soil and control the disease in a synergistic way.

In vitro production of gibberellic acid and fusaric acid by Fusarium spp. and their role in bakanae disease development

Gibberellic acid (GA3) and fusaric acid (FA) are directly correlated with the symptom development of bakanae disease in rice plants. The role of GA3 and FA, produced in vitro by several Fusarium species associated with bakanae disease, was studied to understand the disease’s etiology and its impact on symptom development. In total, 121 Fusarium strains were obtained from bakanae-infected rice plants collected from various rice cultivation regions in Bangladesh. Finally, 18 highly virulent Fusarium strains were selected based on virulence assay and further evaluated for GA3 and FA production through ultra-performance liquid chromatography analysis. Among the Fusarium strains, Fusarium fujikuroi strains produced a high amount of GA3 and a low amount of FA. In contrast, Fusarium proliferatum and Fusarium verticillioides strains produced a high amount of FA and a low amount of GA3. In exception, the Fusarium strain BD117R of F. fujikuroi produced no GA3 but a high amount of FA. Interestingly, Fusarium commune produced only FA in high concentration. In bakanae disease development, GA3 production was positively related to elongation symptoms whereas FA contributes to stunting symptoms. This is the first record of the production of GA3 and FA by Fusarium species causing bakanae disease of rice in Bangladesh.

Involvement of FoVEL1 and FoLAE1 in conidiation, virulence and secondary metabolism of Fusarium oxysporum f. sp. Niveum

The velvet protein family plays a key factor in coordinating development and secondary metabolism in many pathogenic fungi. However, no previous research has investigated the function of the velvet protein family in Fusarium oxysporum f. sp. Niveum (FON), which causes a highly destructive disease on watermelon. In this study, ∆fovel1 and ∆folae1 deletion mutants and ∆fovel1-C and ∆folae1-C corresponding complementation mutants of FON were confirmed. Meanwhile, effects of phenotype, biochemistry and virulence of the deletion mutants were protected. Compared with the wild-type strains, the ∆fovel1 and ∆folae1 mutants showed different mycelia phenotype, depressed of conidiation and reduced production of bikaverin and fusaric acid. Moreover, their virulence on watermelon plant roots was significant decreased. In addition, all of these alterations in mutants were restored in corresponding complementation strains. Importantly, yeast two hybrid results indicated an interaction relationship between FoVel1 and FoLae1. The results of this study indicated that FoVEL1 and FoLAE1 play critical roles in secondary metabolisms, conidiation, and virulence in FON. These information will deepen our understanding on the genetic and functional roles of the VEL1 and LAE1 in pathogenic fungi.

Repression of autocrine pheromone signaling leads to fusaric acid over-production

Fusaric acid (FA), a picolinic acid derivative, is a natural substance produced by a wide variety of fungal plant pathogens belonging to the Fusarium genus. As a metabolite, fusaric acid exerts several biological activities including metal chelation, electrolyte leakage, repression of ATP synthesis, and direct toxicity on plants, animals and bacteria. Prior studies on the structure of fusaric acid revealed a co-crystal dimeric adduct between FA and 9,10-dehydrofusaric acid. During an ongoing search for signaling genes differentially regulating FA production in the fungal pathogen Fusarium oxysporum (Fo), we found that mutants lacking pheromone expression have an increased production of FA compared to the wild type strain. Noteworthy, crystallographic analysis of FA extracted from Fo culture supernatants showed that crystals are formed by a dimeric form of two FA molecules (1:1 molar stoichiometry). Overall, our results suggest that pheromone signaling in Fo is required to regulate the synthesis of fusaric acid.

Production profile and comparison analysis of main toxin components of Fusarium oxysporum f. sp. sesami isolates with different pathogenicity levels

Fusarium wilt is a common fungal disease in sesame caused by Fusarium oxysporum f. sp. sesami (FOS). To determine the toxin production profiles of the FOS isolates with different pathogenicity levels under various culture conditions, we assessed the content variation of fusaric acid (FA) and 9, 10-dehydrofusaric acid (9, 10-DFA) produced by the four representative FOS isolates. Results indicated that the concentration of FA reached to a maximum of 2848.66 ​μg/mL in Czapek medium, while 9, 10-DFA was mainly produced in Richard and Low-carbon Richard medium. The concentration of 9, 10-DFA on Richard culture medium varied from 0 ​μg/mL to 716.89 ​μg/mL. Of the five culture media used in this study, Czapek culture medium was the most conductive to produce FA. FA production was significantly affected by culture medium, culture time, and their interactions. Results suggest that there is no correlation between toxin production and pathogenicity level of FOS isolates. These findings provide key information for the mechanism analysis of FOS- sesame interaction and pathogen control.

Antifungal effects and biocontrol potential of lipopeptide-producing Streptomyces against banana Fusarium wilt fungus Fusarium oxysporum f. sp. cubense.

Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4), presents the foremost menace to the global banana production. Extensive efforts have been made to search for efficient biological control agents for disease management. Our previous study showed that Streptomyces sp. XY006 exhibited a strong inhibitory activity against several phytopathogenic fungi, including F. oxysporum. Here, the corresponding antifungal metabolites were purified and determined to be two cyclic lipopeptide homologs, lipopeptin A and lipopeptin B. Combined treatment with lipopeptin complex antagonized Foc TR4 by inhibiting mycelial growth and conidial sporulation, suppressing the synthesis of ergosterol and fatty acids and lowering the production of fusaric acid. Electron microscopy observation showed that lipopeptide treatment induced a severe disruption of the plasma membrane, leading to cell leakage. Lipopeptin A displayed a more pronounced antifungal activity against Foc TR4 than lipopeptin B. In pot experiments, strain XY006 successfully colonized banana plantlets and suppressed the incidence of FWB, with a biocontrol efficacy of up to 87.7%. Additionally, XY006 fermentation culture application improved plant growth parameters and induced peroxidase activity in treated plantlets, suggesting a possible role in induced resistance. Our findings highlight the potential of strain XY006 as a biological agent for FWB, and further research is needed to enhance its efficacy and mode of action in planta.

An explanation of the mystifying bakanae disease narrative for tomorrow's rice.

Rice production is severely hampered by the bakanae disease (Fusarium fujikuroi), formerly recognized as Fusarium moniliforme. F. moniliforme was called the F. fujikuroi species complex (FFSC) because it was later discovered that it had some separate species. The FFSC's constituents are also well recognized for producing phytohormones, which include auxins, cytokinin, and gibberellins (GAs). The normal symptoms of bakanae disease in rice are exacerbated by GAs. The members of the FFSC are responsible for the production of fumonisin (FUM), fusarins, fusaric acid, moniliformin, and beauvericin. These are harmful to both human and animal health. This disease is common around the world and causes significant yield losses. Numerous secondary metabolites, including the plant hormone gibberellin, which causes classic bakanae symptoms, are produced by F. fujikuroi. The strategies for managing bakanae, including the utilization of host resistance, chemical compounds, biocontrol agents, natural goods, and physical approaches, have been reviewed in this study. Bakanae disease is still not entirely preventable, despite the adoption of many different tactics that have been used to manage it. The benefits and drawbacks of these diverse approaches are discussed by the authors. The mechanisms of action of the main fungicides as well as the strategies for resistance to them are outlined. The information compiled in this study will contribute to a better understanding of the bakanae disease and the development of a more effective management plan for it.

Effect of Abiotic Conditions on Growth, Mycotoxin Production, and Gene Expression by Fusarium fujikuroi Species Complex Strains from Maize.

Fusarium fujikuroi species complex (FFSC) strains are a major concern for food quantity and quality due to their strong ability to synthesize mycotoxins. The effects of interacting conditions of water activity, temperature, and incubation time on the growth rate, toxin production, and expression level of biosynthetic genes were examined. High temperature and water availability increased fungal growth. Higher water activity was in favor of toxin accumulation. The maximum amounts of fusaric acid (FA) and fumonisin B1 (FB1) were usually observed at 20-25 °C. F. andiyazi could produce a higher content of moniliformin (MON) in the cool environment than F. fujikuroi. The expression profile of biosynthetic genes under environmental conditions varied wildly; it was suggested that these genes might be expressed in a strain-dependent manner. FB1 concentration was positively related to the expression of FUM1, while a similar correlation of FUB8 and FUB12 with FA production could be observed in F. andiyazi, F. fujikuroi, and F. subglutinans. This study provides useful information in the monitoring and prevention of such toxins entering the maize production chain.

4-Vinyl Guaiacol exists widely in rhizosphere soil of Lanzhou lily (Lilium davidii var. unicolor) and has a strong negative effect on lily planting

Phenolics from the rhizosphere soil are a key factor that leads to obstacles in the continuous cropping system. While we tested the phenolics in the rhizosphere soil of Lanzhou lily (Lilium davidii var. unicolor), a high relative content 4-Vinyl Guaiacol (4-VG) was firstly detected. Therefore, we attempted to explore the role of 4-VG stress in Lanzhou lily physiology and disease, and the potential enhanced effects of pathogenicity in Fusarium oxysporum B4 (F. oxysporum B4). The effects of different concentrations of 4-VG (0, 0.01, 0.05, 0.1, 0.2, 0.5, 1 mM) on the growth of F. oxysporum B4 and the production of fusaric acid were examined. The result indicated that 4-VG inhibited the growth of F. oxysporum B4 hypha, promoted spore germination, and increased fusaric acid content. Furthermore, transcriptome sequencing of F. oxysporum B4 hypha after stress mediated by 0.5 mM 4-VG was performed to help characterize the response mechanism to 4-VG. Compared with the control group, differentially expressed genes (DEGs) were mainly related to the growth and fusaric acid synthesis of F. oxysporum B4. Except that, the increase of infection area formed after F. oxysporum B4 infected the squama of Lanzhou lily under the high concentration of 4-VG was measured and indicated that 4-VG played a role in the F. oxysporum B4 infection. The exogenous addition of 4-VG significantly inhibited the growth and health of Lanzhou lily. Under the dual stress of F. oxysporum B4 and different concentrations of 4-VG, it significantly enhanced the incidence and disease index of Lanzhou lily. These results suggest the key role of 4-VG from rhizosphere soil in the occurrence of Lanzhou lily Fusarium wilt.

Fusaric Acid Production by Different Isolates of Fusarium oxysporum f. sp. ciceris and Effect of Selected Culture Filtrate Containing Fusaric Acid on Dynamics of Plant Pigments in Chickpea

Background: Biochemical variation with respect to fusaric acid (FA) production by various isolates of Fusarium oxysporum f. sp. ciceris (Foc) was not known and the effect of FA on the pigment dynamics of chickpea was not studied earlier. Methods: The quantity of FA production by 14 isolates of Foc was estimated through HPLC. Further, the effect of culture filtrate (CF) containing FA of ITCC 7682 and ITCC 7681 on the dynamics of plant pigments was studied on resistant cv. WR315 and susceptible cv. JG 62 under Phytotron growing conditions during 2019-2021. Result: Isolate ITCC 7681 was recorded to produce the lowest quantity of FA (126.88±5.56 mg L-1); whereas isolate ITCC 7682 produced the highest quantity of FA (820.51±13.37 mgL-1). Isolates ITCC 7682 and ITCC 7680 were recorded to be highly virulent initiating wilt symptoms within 19-24 hours of inoculation in chickpea seedlings of susceptible cv. JG 62. Culture filtrates of ITCC 7682 and ITCC 7681 caused a reduction of chlorophyll a (15.13-72.38% and 9.24-72.38%), chlorophyll b (16.28-89.83% and 13.95-97.74%), total chlorophyll (48.68-73.17% and 38.87-70.33%) and carotenoid (58.33-88.23% and 48.14-82.56%) contents 3 and 6 days after inoculation respectively. Reduction of all these pigments was significantly higher in susceptible cv. JG 62 than resistant cv. WR 315.

FoRSR1 Is Important for Conidiation, Fusaric Acid Production, and Pathogenicity in Fusarium oxysporum f. sp. ginseng.

The root rot disease caused by Fusarium oxysporum f. sp. ginseng is one of the most destructive diseases of ginseng, an economically important herb. However, little is known about the pathogen's toxin biosynthesis or the molecular mechanisms regulating infection of ginseng. In this study we identified and functionally characterized the FoRSR1 gene that encodes a Ras-related (RSR) small GTPase homologous to yeast Rsr1 in F. oxysporum f. sp. ginseng. Disruption of FoRSR1 resulted in a significant reduction in mycelial dry weight in liquid cultures, although vegetative growth rate was not affected on culture plates. Notably, the Forsr1 mutant exhibited blunted and swollen hyphae with multi-nucleated compartments. It produced fewer and morphologically abnormal conidia and was defective in chlamydospore formation. In infection assays with ginseng roots, the Forsr1 mutant was significantly less virulent and caused only limited necrosis at the wounding sites. Deletion of FoRSR1 also affected pigmentation, autophagy, and production of fusaric acid. Furthermore, the expression of many candidate genes involved in secondary metabolism was significantly downregulated in the mutant, suggesting that FoRSR1 is also important for secondary metabolism. Overall, our results indicated that FoRSR1 plays important roles in conidiation, vacuolar morphology, secondary metabolism, and pathogenesis in F. oxysporum f. sp. ginseng.

Alkaline pH, Low Iron Availability, Poor Nitrogen Sources and CWI MAPK Signaling Are Associated with Increased Fusaric Acid Production in Fusarium oxysporum

Fusaric acid (FA) is one of the first secondary metabolites isolated from phytopathogenic fungi belonging to the genus Fusarium. This molecule exerts a toxic effect on plants, rhizobacteria, fungi and animals, and it plays a crucial role in both plant and animal pathogenesis. In plants, metal chelation by FA is considered one of the possible mechanisms of action. Here, we evaluated the effect of different nitrogen sources, iron content, extracellular pH and cellular signalling pathways on the production of FA siderophores by the pathogen Fusarium oxysporum (Fol). Our results show that the nitrogen source affects iron chelating activity and FA production. Moreover, alkaline pH and iron limitation boost FA production, while acidic pH and iron sufficiency repress it independent of the nitrogen source. FA production is also positively regulated by the cell wall integrity (CWI) mitogen-activated protein kinase (MAPK) pathway and inhibited by the iron homeostasis transcriptional regulator HapX. Collectively, this study demonstrates that factors promoting virulence (i.e., alkaline pH, low iron availability, poor nitrogen sources and CWI MAPK signalling) are also associated with increased FA production in Fol. The obtained new insights on FA biosynthesis regulation can be used to prevent both Fol infection potential and toxin contamination.

Antifungal activity of volatile compounds generated by endophytic fungi Sarocladium brachiariae HND5 against Fusarium oxysporum f. sp. cubense.

The soil-born filamentous fungal pathogen Fusarium oxysporum f. sp. cubense (FOC), which causes vascular wilt disease in banana plants, is one of the most economically important Fusarium species. Biocontrol using endophytic microorganisms is among the most effective methods for controlling banana Fusarium wilt. In this study, volatile organic compounds (VOCs) showed strong antifungal activity against FOC. Seventeen compounds were identified from the VOCs produced by endophytic fungi Sarocladium brachiariae HND5, and three (2-methoxy-4-vinylphenol, 3,4-dimethoxystyrol and caryophyllene) showed antifungal activity against FOC with 50% effective concentrations of 36, 60 and 2900 μL/L headspace, respectively. Transmission electron microscopy (TEM) and double fluorescence staining revealed that 2-methoxy-4-vinylphenol and 3,4-dimethoxystyrol damaged the plasma membranes, resulting in cell death. 3,4-dimethoxystyrol also could induce expression of chitin synthases genes and altered the cell walls of FOC hyphae. Dichloro-dihydro-fluorescein diacetate staining indicated the caryophyllene induced accumulation of reactive oxygen species (ROS) in FOC hyphae. FOC secondary metabolism also responded to active VOC challenge by producing less fusaric acid and expressions of genes related to fusaric acid production were interrupted at sublethal concentrations. These findings indicate the potential of S. brachiariae HND5 as a biocontrol agent against FOC and the antifungal VOCs as fumigants.

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.

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.

FocSge1 in Fusarium oxysporum f. sp. cubense race 1 is essential for full virulence

BackgroundFusarium wilt disease of banana is one of the most devastating diseases and was responsible for destroying banana plantations in the late nineteenth century. Fusarium oxysporum f. sp. cubense is the causative agent. Presently, both race 1 and 4 strains of Foc are creating havoc in the major banana-growing regions of the world. There is an urgent need to devise strategies to control this disease; that is possible only after a thorough understanding of the molecular basis of this disease.ResultsThere are a few regulators of Foc pathogenicity which are triggered during this infection, among which Sge1 (Six Gene Expression 1) regulates the expression of effector genes. The protein sequence is conserved in both race 1 and 4 strains of Foc indicating that this gene is vital for pathogenesis. The deletion mutant, FocSge1 displayed poor conidial count, loss of hydrophobicity, reduced pigmentation, decrease in fusaric acid production and pathogenicity as compared to the wild-type and genetically complemented strain. Furthermore, the C-terminal domain of FocSge1 protein is crucial for its activity as deletion of this region results in a knockout-like phenotype.ConclusionThese results indicated that FocSge1 plays a critical role in normal growth and pathogenicity with the C-terminal domain being crucial for its activity.

Effects of water activity and temperature on fusaric and fusarinolic acid production by Fusarium temperatum

Fusaric acid (FA) is a secondary metabolite produced by several Fusarium species that commonly is isolated from maize and maize-based foods and feeds, and is toxic to some plants and animals, most notably cotton. Fusarinolic acid (FnA) is closely related to FA and is enzymatically derived from it, but much less is known about its toxicity to humans and other animals. We determined the effects of water activity (aW – 0.95, 0.98 and 0.995), temperature (15°, 25° and 30 °C), incubation time (7, 14, 21 and 28 days) and their interactions on FA and FnA production by two strains of F. temperatum isolated from maize growing on sterile maize grain. The amount of FA and FnA accumulated was measured by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). Both compounds were accumulated by both strains of F. temperatum under all evaluated conditions. The amount of FnA produced always exceeded the amount of FA produced (max 50,000 ng/g and 4,500 ng/g, respectively). Temperature, aW, incubation time, and the two- and three-way interactions amongst them all significantly impacted FA and FnA accumulation. Factors favouring fungal growth and mycotoxin production include insect damage, high humidity, delays in harvest, and improper (wet) storage. Grain colonization by F. temperatum begins in the field, but fungal growth and mycotoxin production can easily continue in storage if conditions are right. Thus, from a toxicological point of view, F. temperatum represents a risk for maize under both field and storage conditions. Our data enable better risk estimates and strategies to reduce FA and FnA in the food and feed chains. The highest level of FA was detected at 0.995aW and was independent of temperature and length of incubation, suggesting that there is a limit to the amount of FA that can be accumulated by F. temperatum growing under laboratory conditions. Strikingly high amounts of FnA were observed under all incubation conditions, often exceeding FA levels by 20× to 200× . This result suggests that FnA is more important to the fungus than is FA, and that FA might be little more than an intermediate in a pathway to FnA. The role of the accumulated FnA is unknown, but its role as a toxin may have been discounted since studies to date report limited toxicity. However, if FnA is tested for toxicity at higher levels, such as those identified in this study, then it could have significant toxicological, or other effects that have not previously been considered.