Phylogenetic analysis, fumonisin production and pathogenicity of Fusarium fujikuroi strains isolated from rice in the Philippines

Sensitivity Testing of Natural Antifungal Agents on Fusarium fujikuroi to Investigate the Potential for Sustainable Control of Kiwifruit Leaf Spot Disease

Kiwifruit is a nutritious and economically important fruit that is widely cultivated in China. In 2021, leaf spot disease of kiwifruit was discovered in the main kiwifruit-producing area of Xifeng County, Guizhou Province, China. Leaf spot disease weakens plant photosynthesis and reduces nutrient synthesis, thereby affecting plant growth. We studied the morphological characteristics and performed a combined analysis of EF-1α, RPB2, and TUB2 genes of Fusarium fujikuroi, a fungus associated with leaf spot disease. The pathogenicity of F. fujikuroi followed Koch’s hypothesis, confirming that this fungus is the cause of kiwifruit leaf spot disease. The sensitivity of seven natural antifungal agents against F. fujikuroi was measured using the mycelial growth rate method. Honokiol, cinnamaldehyde, and osthol showed good antifungal effects against F. fujikuroi, with EC50 values of 18.50, 64.60, and 64.86 μg/mL, respectively. The regression coefficient of cinnamaldehyde was the largest at 2.23, while that of honokiol was the smallest at 0.408. Fusarium fujikuroi was the most sensitive to cinnamaldehyde.

Biosynthesis, regulation, and biological significance of fumonisins in fungi: current status and prospects

Fumonisins are one of the most important mycotoxin classes due to their widespread occurrence and potential health threat to humans and animals. Currently, most of the research focuses on the control of fumonisin contamination in the food supply chain. In recent years, significant progress in biochemistry, enzymology, and genetic regulation of fumonisin biosynthesis has been achieved using molecular technology. Furthermore, new insights into the roles of fumonisins in the interaction between fungi and plant hosts have been reported. This review provides an overview of the current understanding of the biosynthesis and regulation of fumonisins. The ecological significance of fumonisins to Fusarium species that produce the toxins is discussed, and the complex regulatory networks of fumonisin synthesis is proposed.

Plant defence mechanisms against mycotoxin Fumonisin B1

Fumonisin B1 (FB1) is the most harmful mycotoxin which prevails in several crops and affects the growth and yield as well. Hence, keeping the alarming consequences of FB1 under consideration, there is still a need to seek other more reliable approaches and scientific knowledge for FB1-induced cell death and a comprehensive understanding of the mechanisms of plant defence strategies. FB1-induced disturbance in sphingolipid metabolism initiates programmed cell death (PCD) through various modes such as the elevated generation of reactive oxygen species, lipid peroxidation, cytochrome c release from the mitochondria, and activation of specific proteases and nucleases causing DNA fragmentation. There is a close interaction between sphingolipids and defence phytohormones in response to FB1 exposure regulating PCD and defence. In this review, the model plant Arabidopsis and various crops have been presented with different levels of susceptibility and resistivity exposed to various concentration of FB1. In addition to this, regulation of PCD and defence mechanisms have been also demonstrated at the physiological, biochemical and molecular levels to help the understanding of the role and function of FB1-inducible molecules and genes and their expressions in plants against pathogen attacks which could provide molecular and biochemical markers for the detection of toxin exposure.

Frequency of three mutations in the fumonisin biosynthetic gene cluster of Fusarium fujikuroi that are predicted to block fumonisin production

Fusarium fujikuroi is the most prominent pathogen found in rice. In addition to gibberellin, F. fujikuroi produces various secondary metabolites, including the polyketide mycotoxins, fumonisins. Fumonisin production is conferred by the fumonisin biosynthetic gene (FUM) cluster consisting of 15-17 genes. F. fujikuroi is phylogenetically subclassified into one group with fumonisin production (F-group) and another group in which fumonisin production is undetectable (G-group). In a previous study, a G-to-T substitution (FUM21_G2551T) in the FUM cluster transcription factor gene, FUM21, was identified as a cause of fumonisin-non-production in a G-group strain. In the current study, further analysis of G-group strains identified two additional mutations that involved FUM-cluster genes essential for fumonisin production: (1) a 22.4-kbp deletion in the FUM10-FUM19 region; and (2) a 1.4-kbp insertion in FUM6. PCR analysis of 44 G-group strains, indicated that 84% had the FUM21_G2551T mutation, 50% had the 22.4-kbp FUM10-FUM19 deletion, and 32% had the 1.4-kbp insertion in FUM6, and some strains had two or all the mutations. None of the mutations were detected in the 51 F-group strains examined. Each of the three mutations alone could account for the lack of fumonisin production in G-group strains. However, one G-group strain did not have any of the mutations. Therefore, another mutation(s) is likely responsible for the lack of fumonisin production in some G-group strains of F. fujikuroi.

Fusarium fujikuroi Species Complex Associated With Rice, Maize, and Soybean From Jiangsu Province, China: Phylogenetic, Pathogenic, and Toxigenic Analysis

Species belonging to the Fusarium fujikuroi species complex (FFSC) are of vital importance and are a major concern for food quantity and quality worldwide, as they not only cause serious diseases in crops but also produce various mycotoxins. To characterize the population structure and evaluate the risk of poisonous secondary metabolites, a total of 237 candidate strains were isolated from rice, maize, and soybean samples in Jiangsu Province, China. Species identification of the individual strain was accomplished by sequencing the translation elongation factor 1α gene (TEF-1α) and the fumonisin (FB) synthetic gene (FUM1). The distribution of Fusarium species among the different crops was observed. The maize seeds were dominated by F. proliferatum (teleomorph, Gibberella intermedia) and F. verticillioides (teleomorph, G. moniliformis), whereas F. fujikuroi (teleomorph, G. fujikuroi) was the most frequently isolated species from rice and soybean samples. In addition, phylogenetic analyses of these strains were performed, and the results suggested clear groups showing no obvious relationship with the origin source. FFSC species pathogenicity and toxigenicity were studied. All of the species reduced the rice seed germination rate, with no significant differences. F. fujikuroi showed two distinct patterns of influencing the length of rice seedlings, which were correlated with FBs and gibberellic acid synthesis. FBs were mainly produced by F. verticillioides and F. proliferatum. F. proliferatum and F. fujikuroi also produced moniliformin and beauvericin. The toxigenicity of F. andiyazi (teleomorph, G. andiyazi) was extremely low. Further analysis indicated that the sequence variations in TEF-1α and the differences in the expression levels of the toxin synthesis genes were associated with the diversity of secondary metabolites in F. fujikuroi strains. These findings provide insight into the population-level characterization of the FFSC and might be helpful in the development of strategies for the management of diseases and mycotoxins.

Different Phenotypes, Similar Genomes: Three Newly Sequenced Fusarium fujikuroi Strains Induce Different Symptoms in Rice Depending on Temperature

Bakanae, caused by the hemibiotrophic fungus Fusarium fujikuroi, is one of the most important diseases of rice and is attributed to up to 75% of losses, depending on the strain and environmental conditions. Some strains cause elongation and thin leaves, whereas others induce stunting and chlorotic seedlings. Differences in symptoms are attributed to genetic differences in the strains. F. fujikuroi strains Augusto2, CSV1, and I1.3 were sequenced with Illumina MiSeq, and pathogenicity trials were conducted on rice cultivar Galileo, which is susceptible to bakanae. By performing gene prediction, single nucleotide polymorphism (SNP) calling, and structural variant analysis with a reference genome, we show how an extremely limited number of polymorphisms in genes not commonly associated with bakanae disease can cause strong differences in phenotype. CSV1 and Augusto2 were particularly close, with only 21,887 SNPs between them, but they differed in virulence, reaction to temperature, induced symptoms, colony morphology and color, growth speed, fumonisin, and gibberellin production. Genes potentially involved in the shift in phenotype were identified. Furthermore, we show how temperature variation may result in different symptoms even in rice plants inoculated with the same F. fujikuroi strain. Moreover, all of the F. fujikuroi strains became more virulent at higher temperatures. Significant differences were likewise observed in gibberellic acid production and in the expression of both fungal and plant gibberellin biosynthetic genes.

Clonality, spatial structure, and pathogenic variation in Fusarium fujikuroi from rain-fed rice in southern Laos

Bakanae disease, caused by the fungal phytopathogen Fusarium fujikuroi, can be detected in most rice (Oryza sativa L.) growing areas worldwide. In this study, we investigated the population structure of this fungus in southern Lao PDR, a country located near the geographic origin of rice domestication. Microsatellites (SSRs) and mating type (MAT) analyses, pathogenicity and fungicide sensitivity tests were integrated in the study. The first key finding is that the population genetic structure of F. fujikuroi in Lao PDR is consistent with high clonal reproduction. Indeed, (i) “true” clones were identified; (ii) within populations, MAT types were frequently skewed from 1:1 ratio, (iii) linkage disequilibrium (among SSRs as also among SSRs and MAT) was present, and (iv) gene-flow between opposite MAT types within the same population is restricted. The presence of genetic divergence among areas and populations and the occurrence of positive spatial autocorrelation of genetic variation, indicate that migration is restricted, and that genetic drift plays an important role in the evolution of this fungus. Two main well-defined groups of isolates were detected (F_ST = 0.213) that display a non-random spatial distribution. They differ in the ability to induce seedlings death but not seedlings elongation (the typical Bakanae symptom) suggesting that the pathogen’s ability to induce the two symptoms is under different genetic control. Finally, we compared two agroecosystems with contrasting characteristics: low-input and traditional (Lao PDR) vs high-input and modern (Italy). We found differences in the level of population structuring and of spatial autocorrelation. This suggests that the evolutionary potential of the fungus not only depends on its intrinsic characteristics, but is strongly influenced by other external factors, most likely by the dynamics of infested seed exchange. Thus, quarantine and chemical treatments are a way to reduce population connectivity and hence the evolutionary potential of this pathogen.

Mycotoxigenic Fungi and Mycotoxins in Agricultural Crop Commodities in the Philippines: A Review

The tropical, warm, and humid conditions that are favorable to the growth and development of mycotoxigenic fungi put the Philippines at a high risk of mycotoxin contamination. To date, seven mycotoxigenic Aspergillus species, four Fusarium species, and one Penicillium species have been isolated from various agricultural crop commodities in the country. There are five mycotoxin groups (aflatoxin, fumonisin, ochratoxin, nivalenol, and zearalenone) that have been detected in both the raw form and the by-products of major crops grown in the country. Since the first scientific report of aflatoxin contamination in the Philippines in 1972, new information has been generated on mycotoxins and mycotoxigenic fungi, but little has been known of other mycotoxins until the last two decades. Further, despite the increase in the understanding of mycotoxigenic fungi and mycotoxins in the country, very limited knowledge exists on practices and measures that control both the fungi and the toxins. This paper reviews the current literature on mycotoxigenic fungi and mycotoxins in the Philippines with emphasis on the last two decades and on other mycotoxins.

A Natural Variation of Fumonisin Gene Cluster Associated with Fumonisin Production Difference in Fusarium fujikuroi

Fusarium fujikuroi, a member of the Fusarium fujikuroi species complex, stands out as a rice bakanae disease pathogen with a high production of gibberellic acid. Not all, but some F. fujikuroi strains are known to produce a carcinogenic mycotoxin fumonisin. Fumonisin biosynthesis is dependent on the FUM cluster composed of 16 FUM genes. The FUM cluster was detected not only from a fumonisin producing strain, but also from a fumonisin nonproducing strain that does not produce a detectable level of fumonisin. Genetic mapping indicated the causative mutation(s) of fumonisin nonproduction is present in the FUM cluster of the fumonisin nonproducing strain. Comparative analyses of FUM genes between the fumonisin producing and the nonproducing strains and gene complementation indicated that causative mutation of fumonisin nonproduction is not a single occurrence and the mutations are distributed in FUM21 and FUM7. Our research revealed a natural variation in the FUM cluster involving fumonisin production difference in F. fujikuroi.

Genetic Differentiation Associated with Fumonisin and Gibberellin Production in Japanese Fusarium fujikuroi

Fusarium fujikuroi is a pathogenic fungus that infects rice. It produces several important mycotoxins, such as fumonisins. Fumonisin production has been detected in strains of maize, strawberry, and wheat, whereas it has not been detected in strains from rice seedlings infested with bakanae disease in Japan. We investigated the genetic relationships, pathogenicity, and resistance to a fungicide, thiophanate-methyl (TM), in 51 fumonisin-producing strains and 44 nonproducing strains. Phylogenetic analyses based on amplified fragment length polymorphism (AFLP) markers and two specific genes (a combined sequence of translation elongation factor 1α [TEF1α] and RNA polymerase II second-largest subunit [RPB2]) indicated differential clustering between the fumonisin-producing and -nonproducing strains. One of the AFLP markers, EATMCAY107, was specifically present in the fumonisin-producing strains. A specific single nucleotide polymorphism (SNP) between the fumonisin-producing and nonproducing strains was also detected in RPB2, in addition to an SNP previously found in TEF1α. Gibberellin production was higher in the nonproducing than in the producing strains according to an in vitro assay, and the nonproducing strains had the strongest pathogenicity with regard to rice seedlings. TM resistance was closely correlated with the cluster of fumonisin-nonproducing strains. The results indicate that intraspecific evolution in Japanese F. fujikuroi is associated with fumonisin production and pathogenicity. Two subgroups of Japanese F. fujikuroi, designated G group and F group, were distinguished based on phylogenetic differences and the high production of gibberellin and fumonisin, respectively.IMPORTANCE Fusarium fujikuroi is a pathogenic fungus that causes rice bakanae disease. Historically, this pathogen has been known as Fusarium moniliforme, along with many other species based on a broad species concept. Gibberellin, which is currently known as a plant hormone, is a virulence factor of F. fujikuroi Fumonisin is a carcinogenic mycotoxin posing a serious threat to food and feed safety. Although it has been confirmed that F. fujikuroi produces gibberellin and fumonisin, production varies among strains, and individual production has been obscured by the traditional appellation of F. moniliforme, difficulties in species identification, and variation in the assays used to determine the production of these secondary metabolites. In this study, we discovered two phylogenetic subgroups associated with fumonisin and gibberellin production in Japanese F. fujikuroi.

Evolution and Diversity of Biosynthetic Gene Clusters in Fusarium

Plant pathogenic fungi in the Fusarium genus cause severe damage to crops, resulting in great financial losses and health hazards. Specialized metabolites synthesized by these fungi are known to play key roles in the infection process, and to provide survival advantages inside and outside the host. However, systematic studies of the evolution of specialized metabolite-coding potential across Fusarium have been scarce. Here, we apply a combination of bioinformatic approaches to identify biosynthetic gene clusters (BGCs) across publicly available genomes from Fusarium, to group them into annotated families and to study gain/loss events of BGC families throughout the history of the genus. Comparison with MIBiG reference BGCs allowed assignment of 29 gene cluster families (GCFs) to pathways responsible for the production of known compounds, while for 57 GCFs, the molecular products remain unknown. Comparative analysis of BGC repertoires using ancestral state reconstruction raised several new hypotheses on how BGCs contribute to Fusarium pathogenicity or host specificity, sometimes surprisingly so: for example, a gene cluster for the biosynthesis of hexadehydro-astechrome was identified in the genome of the biocontrol strain Fusarium oxysporum Fo47, while being absent in that of the tomato pathogen F. oxysporum f.sp. lycopersici. Several BGCs were also identified on supernumerary chromosomes; heterologous expression of genes for three terpene synthases encoded on the Fusarium poae supernumerary chromosome and subsequent GC/MS analysis showed that these genes are functional and encode enzymes that each are able to synthesize koraiol; this observed functional redundancy supports the hypothesis that localization of copies of BGCs on supernumerary chromosomes provides freedom for evolutionary innovations to occur, while the original function remains conserved. Altogether, this systematic overview of biosynthetic diversity in Fusarium paves the way for targeted natural product discovery based on automated identification of species-specific pathways as well as for connecting species ecology to the taxonomic distributions of BGCs.

Species composition of and fumonisin production by the Fusarium fujikuroi species complex isolated from Korean cereals

To assess the risk of fumonisin contamination in Korean cereals, we isolated colonies of the Fusarium fujikuroi species complex (FFSC) from barley, maize, rice and soybean samples from 2011 to 2015. A total of 878 FFSC strains were isolated mostly from maize and rice, and species identity of the isolates were determined using the DNA sequence of the translation elongation factor 1-α (TEF-1α) and RNA polymerase II (RPB2) genes. Fusaria recovered from Korean cereals included F. fujikuroi (317 isolates and a frequency of 36%), F. proliferatum (212 isolates and 24.1%), F. verticillioides (170 isolates and 19.4%), F. concentricum (86 strains and 9.8%), F. andiyazi (56 isolates and 6.4%), F. subglutinans (28 isolates and 3.2%), F. thapsinum (5 isolates and 0.6%), and F. circinatum (2 isolates and 0.2%). The rice samples were dominated by F. fujikuroi (47.4%), F. proliferatum (27.3%), and F. concentricum (15.1%), whereas maize samples were dominated by F. verticillioides (33.9%), F. fujikuroi (25.3%), and F. proliferatum (21.1%). A phylogenetic analysis of 70 representative isolates demonstrated that each species was resolved as genealogically exclusive in the ML tree. Fumonisin production potential was evaluated using a PCR assay for the fumonisin biosynthesis gene, FUM1 in all of the isolates. Most of the isolates tested (94%) were positive for FUM1. All of the isolates assigned to F. fujikuroi, F. proliferatum, F. verticillioides and F. thapsinum were positive for FUM1 irrespective of their host origin. Seventy-seven representative isolates positive for FUM1 were examined for fumonisin production in rice medium. The majority of F. proliferatum (26/27, 96.3%), F. verticillioides (16/17, 94.1%) and F. fujikuroi (19/25, 76.0%) produced both FB₁ and FB₂. Notably, 16 of 19 fumonisin-producing F. fujikuroi produced >1000μg/g of fumonisins (FB₁+FB₂) in rice medium, which is higher than that in previous reports. These results suggest that F. fujikuroi can produce high levels of fumonisins similar to F. verticillioides and F. proliferatum.

A Novel Population of Fusarium fujikuroi Isolated from Southeastern U.S. Winegrapes Reveals the Need to Re-Evaluate the Species' Fumonisin Production

Mycotoxins pose a challenge to a safe food supply worldwide, and their threat is expected to worsen with our changing climate. The need for diligence is exemplified by the discovery of fumonisin B2 in wine, which joins ochratoxin A as a mycotoxin of concern in the grape-wine chain. To elucidate the mycotoxin risk in southeastern American wine, grape samples were collected from vineyards during harvest in 2013 and potentially mycotoxigenic fungi (Fusarium and Aspergillus) were isolated from the samples. Numerous Fusarium isolates were recovered and identified to the species level by comparison of translation elongation factor 1-α gene sequences to verified strains. Fusariumfujikuroi was the most abundant species recovered (239 isolates), followed by F. proliferatum (52), F. incarnatum-equiseti (14), F. oxysporum (7), F. concentricum (1), and F. solani (1). In vitro assays quantified fumonisin production for representative isolates via liquid chromatography-tandem mass spectrometry. Surprisingly, nearly all F. fujikuroi isolates produced fumonisins B1, B2, and B3 at levels comparable to both the F. proliferatum isolates and the positive control, Fusariumverticillioides. Such capacity for fumonisin production refutes the generally accepted notion that F.fujikuroi produces undetectable or low levels of fumonisins and provides evidence to reconsider this species as a mycotoxigenic threat to economically significant crops.

Multi-Homologous Recombination-Based Gene Manipulation in the Rice Pathogen Fusarium fujikuroi

Gene disruption by homologous recombination is widely used to investigate and analyze the function of genes in Fusarium fujikuroi, a fungus that causes bakanae disease and root rot symptoms in rice. To generate gene deletion constructs, the use of conventional cloning methods, which rely on restriction enzymes and ligases, has had limited success due to a lack of unique restriction enzyme sites. Although strategies that avoid the use of restriction enzymes have been employed to overcome this issue, these methods require complicated PCR steps or are frequently inefficient. Here, we introduce a cloning system that utilizes multi-fragment assembly by In-Fusion to generate a gene disruption construct. This method utilizes DNA fragment fusion and requires only one PCR step and one reaction for construction. Using this strategy, a gene disruption construct for Fusarium cyclin C1 (FCC1 ), which is associated with fumonisin B1 biosynthesis, was successfully created and used for fungal transformation. In vivo and in vitro experiments using confirmed fcc1 mutants suggest that fumonisin production is closely related to disease symptoms exhibited by F. fujikuroi strain B14. Taken together, this multi-fragment assembly method represents a simpler and a more convenient process for targeted gene disruption in fungi.

Giberella fujikuroi species complex isolated from maize and wheat in Iran: distribution, molecular identification and fumonisin B1 in vitro biosynthesis

BACKGROUND

Contamination of food and agricultural crops by Fusarium species is a major concern of food spoilage and a potential public health hazard. In the present study, natural contamination of maize and wheat samples from main cultivation areas of Iran by Fusarium species belonging to the Giberella fujikuroi species complex was evaluated, with special attention to the ability of the isolates to produce fumonisin B1 (FB1 ).

RESULTS

A total of 55 Fusarium isolates were obtained from 27/32 maize samples (84.4%) and 11/15 wheat samples (73.3%). They were identified as F. verticillioides (47.3%), F. proliferatum (47.3%), F. fujikuroi (1.8%), F. nygamai (1.8%) and F. redolens (1.8%) by sequence analysis of translation elongation factor 1-α (TEF1-α). Twenty-two of 55 Fusarium isolates belonging to F. proliferatum (23.6%), F. verticillioides (14.5%) and F. fujikuroi (1.8%) produced FB1 in the concentration range 230.4-9565.0 µg mL(-1) . The dendrogram resulting from the TEF1-α profile showed that the genotypes were divided into clusters I, II and III, of which cluster III contained only F. redolens, its first report from Iran.

CONCLUSION

On the basis of in vitro FB1 biosynthesis of the analyzed strains, the high degree of contamination of maize and wheat with Fusarium strains reported here should be considered as a potential public health threat, because a meaningful number of the isolates were found to produce hazardous levels of carcinogenic FB1 .

Interplay between pathway-specific and global regulation of the fumonisin gene cluster in the rice pathogen Fusarium fujikuroi

The rice pathogenic fungus Fusarium fujikuroi is known to produce a large variety of secondary metabolites. Besides the gibberellins, causing the bakanae effect in infected rice seedlings, the fungus produces several mycotoxins and pigments. Among the 47 putative secondary metabolite gene clusters identified in the genome of F. fujikuroi, the fumonisin gene cluster (FUM) shows very high homology to the FUM cluster of the main fumonisin producer Fusarium verticillioides, a pathogen of maize. Despite the high level of cluster gene conservation, total fumonisin FB1 and FB2 levels (FBx) produced by F. fujikuroi were only 1-10 % compared to F. verticillioides under inducing conditions. Nitrogen repression was found to be relevant for wild-type strains of both species. However, addition of germinated maize kernels activated the FBx production only in F. verticillioides, reflecting the different host specificity of both wild-type strains. Over-expression of the pathway-specific transcription factor Fum21 in F. fujikuroi strongly activated the FUM cluster genes leading to 1000-fold elevated FBx levels. To gain further insights into the nitrogen metabolite repression of FBx biosynthesis, we studied the impact of the global nitrogen regulators AreA and AreB and demonstrated that both GATA-type transcription factors are essential for full activation of the FUM gene cluster. Loss of one of them obstructs the pathway-specific transcription factor Fum21 to fully activate expression of FUM cluster genes.