Gibberella konza (Fusarium konzum) sp. nov. from prairie grasses, a new species in the Gibberella fujikuroi species complex

The Gibberella fujikuroi species complex (Fusarium section Liseola and allied taxa) is composed of an increasingly large number of morphological, biological and phylogenetic species. Most of the known species in this group have been isolated from agricultural ecosystems or have been described from a small number of isolates. We sampled Fusarium communities from native prairie grasses in Kansas and recovered a large number of isolates that superficially resemble F. anthophilum. We used a combination of morphological, biological and molecular characters to describe a new species, Gibberella konza (Gibberella fujikuroi mating population I [MP-I]), from native prairie grasses in Kansas. Although female fertility for field isolates of this species appears to be low, G. konza is heterothallic, and we developed reliably female fertile mating population tester strains for this species. The F. konzum anamorph is differentiated from F. anthophilum and from other Fusarium species in section Liseola by mating compatibility, morphology, AFLP fingerprint profile and differences in β-tubulin DNA sequence.     

PCR-based identification of MAT-1 and MAT-2 in the Gibberella fujikuroi species complex

All sexually fertile strains in the Gibberella fujikuroi species complex are heterothallic, with individual mating types conferred by the broadly conserved ascomycete idiomorphs MAT-1 and MAT-2. We sequenced both alleles from all eight mating populations, developed a multiplex PCR technique to distinguish these idiomorphs, and tested it with representative strains from all eight biological species and 22 additional species or phylogenetic lineages from this species complex. In most cases, either an approximately 800-bp fragment from MAT-2 or an approximately 200-bp fragment from MAT-1 is amplified. The amplified fragments cosegregate with mating type, as defined by sexual cross-fertility, in a cross of Fusarium moniliforme (Fusarium verticillioides). Neither of the primer pairs amplify fragments from Fusarium species such as Fusarium graminearum, Fusarium pseudograminearum, and Fusarium culmorum, which have, or are expected to have, Gibberella sexual stages but are thought to be relatively distant from the species in the G. fujikuroi species complex. Our results suggest that MAT allele sequences are useful indicators of phylogenetic relatedness in these and other Fusarium species.     

Distribution of gibberellin biosynthetic genes and gibberellin production in the Gibberella fujikuroi species complex

Gibberella fujikuroi is a species-rich monophyletic complex of at least nine sexually fertile biological species (mating populations, MP-A to MP-I) and more than 30 anamorphs in the genus Fusarium. They produce a variety of secondary metabolites, such as fumonisins, fusaproliferin, moniliformin, beauvericin, fusaric acid, and gibberellins (GAs), a group of plant hormones. In this study, we examined for the first time all nine sexually fertile species (MPs) and additional anamorphs within and outside the G. fujikuroi species complex for the presence of GA biosynthetic genes. So far, the ability to produce GAs was described only for Fusarium fujikuroi (G. fujikuroi MP-C), which contains seven clustered genes in the genome all participating in GA biosynthesis. We show that six other MPs (MPs B, D, E, F, G, and I) and most of the anamorphs within the species complex also contain the entire gene cluster, except for F. verticillioides (MP-A), and F. circinatum (MP-H), containing only parts of it. Despite the presence of the entire gene cluster in most of the species within the G. fujikuroi species complex, expression of GA biosynthetic genes and GA production were detected only in F. fujikuroi (MP-C) and one isolate of F. konzum (MP-I). We used two new molecular marker genes, P450-4 from the GA gene cluster, and cpr, encoding the highly conserved NADPH cytochrome P450 reductase to study phylogenetic relationships within the G. fujikuroi species complex. The molecular phylogenetic studies for both genes have revealed good agreement with phylogenetic trees inferred from other genes. Furthermore, we discuss the role and evolutionary origin of the GA biosynthetic gene cluster.     

Identification of airborne propagules of the Gibberella fujikuroi species complex during maize production

The airborne dispersal of the anamorphs of the Gibberella fujikuroi species complex was studied under pre- and postharvest maize (corn) production conditions using a 3-stage Andersen sampler. The aim of this study was to identify and analyse the size distribution of such species in air samples. Differences were observed between the concentration of large- and small-sized propagules (identified as aggregates and single microconidia, respectively), but the difference was only significant during a high concentration period (October 2007, P = 0.009). No correlation was found between the concentration of fusaria found at different sampling heights (10 and 150 cm above ground level). Fusarium isolates were collected and identified based on morphological characters and using species-specific PCR assays. The PCR analysis confirmed morphological identification of F. verticillioides, F. proliferatum and F. subglutinans. High concentrations were found during the maize harvest, loading and corn shelling. Our results showed that the monitoring of F. verticillioides should be performed at a single sampling height.     

Heritability of fumonisin B1 production in Gibberella fujikuroi mating population A.

Fumonisins are mycotoxins produced by strains belonging to several different mating populations of Gibberella fujikuroi (anamorphs, Fusarium section Liseola), a major pathogen of maize and sorghum worldwide. We studied the heritability of fumonisin production in mating population A by crossing fumonisin-producing strains collected from maize and sorghum in the United States with fumonisin-nonproducing strains collected from maize in Nepal. Random ascospore and tetrad progeny from three of these crosses were analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography for their ability to produce fumonisins on autoclaved cracked maize. In all three crosses, the ability to produce fumonisins, predominately fumonisin B1, segregated as a single gene or group of closely linked genes. Intercrosses between appropriate progeny and parents were poorly fertile, so we could not determine if the apparent single genes that were segregating in each of these crosses were allelic with one another. Mating type and spore-killer traits were scored in some crosses, and each segregated, as expected, as a single gene that was unlinked to the ability to produce fumonisins. We conclude that G. fujikuroi mating population A provides a powerful genetic system for the study of this important fungal toxin.     

Heritability of fumonisin B1 production in Gibberella fujikuroi mating population A.

Fumonisins are mycotoxins produced by strains belonging to several different mating populations of Gibberella fujikuroi (anamorphs, Fusarium section Liseola), a major pathogen of maize and sorghum worldwide. We studied the heritability of fumonisin production in mating population A by crossing fumonisin-producing strains collected from maize and sorghum in the United States with fumonisin-nonproducing strains collected from maize in Nepal. Random ascospore and tetrad progeny from three of these crosses were analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography for their ability to produce fumonisins on autoclaved cracked maize. In all three crosses, the ability to produce fumonisins, predominately fumonisin B1, segregated as a single gene or group of closely linked genes. Intercrosses between appropriate progeny and parents were poorly fertile, so we could not determine if the apparent single genes that were segregating in each of these crosses were allelic with one another. Mating type and spore-killer traits were scored in some crosses, and each segregated, as expected, as a single gene that was unlinked to the ability to produce fumonisins. We conclude that G. fujikuroi mating population A provides a powerful genetic system for the study of this important fungal toxin.     

串珠镰孢菌种名的废弃及其与腾仓赤霉复合种的关系

<正>通常所说的串珠镰孢菌Fusarium moniliforme Sheld.是镰孢菌属Fusarium Link中最重要的植物病原菌之一,可侵染多种作物引起严重病害,特别是在禾谷类作物上,如玉米穗腐病、小麦赤霉病、水     

赤霉菌分子生物学研究进展

过去 1 0年中 ,由于基因克隆、遗传转化等分子生物学方法与技术的应用 ,对赤霉菌中赤霉素生物合成基因的克隆、鉴定、异源表达及其表达调控等分子生物学研究取得了很大进展。现从赤霉菌的转化系统、赤霉素生物合成基因克隆、合成机理及其基因表达调控等方面的研究进展进行综述     

Linkage among genes responsible for fumonisin biosynthesis in Gibberella fujikuroi mating population A.

Most naturally occurring strains of the fungus Gibberella fujikuroi mating population A produce high levels of the mycotoxin fumonisin B1 (FB1), which is oxygenated at both carbons C-5 and C-10. Some strains, however, produce only FB2 or FB3, suggesting that they lack the ability to hydroxylate position C-10 or C-5, respectively. Genetic analysis indicates that these different phenotypes are due to single gene defects at closely linked loci designated fum2 and fum3. Further allellism tests indicate that both fum2 and fum3 are closely linked to fum1, a previously identified gene that regulates fumonisin production. The recovery frequency of FB1-producing progency from cross 510 between fum1 and fum2 mutations suggests a map distance of approximately 6.2 cM between these two loci. Amplified fragment length polymorphism analysis of parents and progeny of cross 510 was employed to confirm that the FB1-producing strains are recombinant progeny. We conclude that fum1, fum2, and fum3 constitute a fumonisin biosynthetic gene cluster on chromosome 1 of the restriction fragment length-map of G. fujikuroi.     

Gibberella fujikuroi mating population E is associated with maize and teosinte

Isolates of Fusarium subglutinans mating population E are usually found on maize. This fungus forms part of the so-called Gibberella fujikuroi species complex. Previously, F. subglutinans has been associated with two additional mating populations (B and H) and a variety of plant hosts. This was mainly due to a lack of diagnostic morphological characters, but the use of DNA sequence information showed that the strains making up mating populations B, E and H, as well as those associated with the different plant hosts, represent separate species. Recently, another putative mating population has been reported on the wild teosinte relatives of maize. Based on sexual compatibility studies, these isolates were apparently closely related to the pitch canker fungus, F. subglutinans f. sp. pini (= F. circinatum;G. fujikuroi mating population H). The aim of the current study was to determine whether the population of F. subglutinans from teosinte constitutes a new or an existing lineage within the G. fujikuroi complex. For this purpose, portions of the mitochondrial small subunit ribosomal DNA, calmodulin and β-tubulin genes from the fungi were sequenced. Phylogenetic analyses and comparison with sequences from public domain databases indicated that the F. subglutinans isolates from teosinte are most closely related to strains of G. fujikuroi mating population E. These results were confirmed using sexual compatibility studies. The putative mating population from the wild relatives of maize therefore forms part of the existing E-mating population and does not constitute a new lineage in the G. fujikuroi species complex.     

Molecular organization of mating type loci in heterothallic, homothallic, and asexual Gibberella/Fusarium species

Mating type (MAT) genes were cloned from three members of the Gibberella/Fusarium complex that differ in reproductive mode: heterothallic G. fujikuroi, homothallic G. zeae, and asexual F. oxysporum. The G. fujikuroi MAT locus organization is typical of other heterothallic pyrenomycetes characterized to date; i.e., there are three genes at MAT1-1 and one at MAT1-2. G. zeae has homologues of all four genes encoded by the two G. fujikuroi MAT idiomorphs, tightly linked on the same chromosome, interspersed with sequences unique to G. zeae. Field isolates of F. oxysporum, although asexual, have either the MAT1-1 or the MAT1-2 genes found in sexual species and these genes are highly similar to those of heterothallic G. fujikuroi. RT-PCR analysis proved that the F. oxysporum MAT genes are expressed and that all putative introns found in each of the four MAT genes in G. fujikuroi and F. oxysporum are removed. Apparent failure of F. oxysporum to reproduce sexually could not be attributed to mutations in the MAT genes themselves.     

Fusarium ananatum sp. nov. in the Gibberella fujikuroi species complex from pineapples with fruit rot in South Africa

Pineapple (Ananas comosus) is native to South America and widely planted as a fruit crop in the tropics and sub-tropics. This plant is susceptible to a number of fungal diseases of which the most severe is fusariosis. The disease is caused by Fusarium guttiforme and occurs only in South and Central America. The occurrence of a similar disease on pineapples in South Africa has prompted a re-evaluation of the Fusarium sp. associated with pineapple fruit rot. Phylogenetic relationships of isolates from pineapples collected in Brazil and South Africa were assessed based on sequence data for the translation elongation factor-1-α, histone H3 and β-tubulin gene regions. Analyses showed that the South African isolates represent a species distinct from Brazilian isolates. The South African isolates are characterised by a concentration of aerial mycelium at the centres of the colonies, different to the Brazilian isolates that have an even distribution of aerial mycelium. Both phylogenetic and morphological data show that the disease on pineapple in South Africa is caused by a new Fusarium species described here as F. ananatum sp. nov.     

Molecular Standardization of Mating Type Terminology in the Gibberella fujikuroi Species Complex

Mating type in the Gibberella fujikuroi species complex is controlled by a single locus with two alleles and is usually identified following sexual crosses with standard, female-fertile tester isolates. The mating type alleles have been arbitrarily designated “+” and “−” within each biological species, and the nomenclature is tied to the standard tester strains. We developed a pair of PCR primers that can be used to amplify a unique fragment of one of the mating type alleles (MAT-2) from at least seven of the biological species in this species complex. Based on the amplification pattern, we propose a replacement for the existing, arbitrary +/− terminology that is presently in use. The new terminology is based on DNA sequence similarities between the mating type allele fragments from the biological species of the G. fujikuroi species complex and the corresponding fragments from other filamentous ascomycetes.     

Fusarium subglutinans f. sp. Pini represents a distinct mating population in the gibberella fujikuroi species complex

Fusarium strains in the Gibberella fujikuroi species complex cause diseases on a variety of economically important plants. One of these diseases, pitch canker of Pinus spp., is caused by strains identified as Fusarium subglutinans f. sp. pini. Fertile crosses were detected between F. subglutinans f. sp. pini strains from South Africa, California, and Florida. F. subglutinans f. sp. pini strains were not cross-fertile with the standard tester strains of six of the seven other mating populations of G. fujikuroi. Sporadic perithecia with ascospores were obtained in two crosses with the mating population B tester strains. These perithecia were homothallic, and the ascospores derived from these perithecia were vegetatively compatible with the mating population B tester strain parent. We concluded that fertile F. subglutinans f. sp. pini isolates represent a new mating population (mating population H) of G. fujikuroi and that they belong to a unique biological species in a distinct taxon.     

Assessment ofGibberella fujikuroi mating type by PCR

Mating type (MAT)-specific fragments of the two idiomorphs ofGibberella fujikuroi (anamorph,Fusarium moniliforme) were obtained by PCR amplification using primers to conserved regions ofMAT homologs from other fungal species and used to assign mating type by molecular criteria rather than the arbitrary historical designation. Mating type—strains of mating populations A-E and a mating type+strain of mating population F carry an α-box motif and should therefore be designatedMAT-1. Mating type+strains of mating populations A-E and a mating type—strain of mating population F carry an HMG-box motif and should be designatedMAT-2. Thus, assessment of mating type ofG. fujikurol strains can be easily achieved usingMAT-specific primers.