Fusarium tupiense sp. nov., a member of the Gibberella fujikuroi complex that causes mango malformation in Brazil.

Fusarium tupiense, the main causal agent of mango malformation in Brazil, is described through a combination of morphological, biological and molecular markers. This new species belongs to the Gibberella fujikuroi species complex (GFSC) and has an anamorph morphologically similar to Fusarium mangiferae and F. sterilihyphosum. F. tupiense can be differentiated from other species in the G. fujikuroi species complex on the basis of sexual crosses, amplified fragment length polymorphism (AFLP) markers and partial sequences of the tef1 and tub2 genes. Female fertility for field isolates of F. tupiense appears to be low. PCR with primers specific for the mating type (MAT) alleles and sexual crosses identified this species as heterothallic with two idiomorphs. Female-fertile tester strains were developed for the identification of field strains of this species through sexual crosses.

Functional analyses of regulators of G protein signaling in Gibberella zeae.

Regulators of G protein signaling (RGS) proteins make up a highly diverse and multifunctional protein family that plays a critical role in controlling heterotrimeric G protein signaling. In this study, seven RGS genes (FgFlbA, FgFlbB, FgRgsA, FgRgsB, FgRgsB2, FgRgsC, and FgGprK) were functionally characterized in the plant pathogenic fungus, Gibberella zeae. Mutant phenotypes were observed for deletion mutants of FgRgsA and FgRgsB in vegetative growth, FgFlbB and FgRgsB in conidia morphology, FgFlbA in conidia production, FgFlbA, FgRgsB, and FgRgsC in sexual development, FgFlbA and FgRgsA in spore germination and mycotoxin production, and FgFlbA, FgRgsA, and FgRgsB in virulence. Furthermore, FgFlbA, FgRgsA, and FgRgsB acted pleiotropically, while FgFlbB and FgRgsC deletion mutants exhibited a specific defect in conidia morphology and sexual development, respectively. Amino acid substitutions in Gα subunits and overexpression of the FgFlbA gene revealed that deletion of FgFlbA and dominant active GzGPA2 mutant, gzgpa2(Q207L), had similar phenotypes in cell wall integrity, perithecia formation, mycotoxin production, and virulence, suggesting that FgFlbA may regulate asexual/sexual development, mycotoxin biosynthesis, and virulence through GzGPA2-dependent signaling in G. zeae.

Meiotic silencing in the homothallic fungus Gibberella zeae.

The homothallic ascomycete fungus Gibberella zeae is an important pathogen on major cereal crops. The objective of this study was to determine whether meiotic silencing occurs in G. zeae. Cytological studies demonstrated that GFP and RFP-fusion proteins were not detected during meiosis, both in heterozygous outcrosses and homozygous selfings. The deletion of rsp-1, a homologue used for studies on meiotic silencing of Neurospora crassa, triggered abnormal ascospores from selfing, but outcrosses between the mutant and wild-type strain resulted in some ascospores with mutant phenotype (low occurrence of ascus dominance). When the ectopic mutants that carried an additional copy of rsp-1 were selfed, they primarily produced ascospores with normal shape but a few ascospores (0.23 %) were abnormal, in which both endogenous and ectopically integrated genes contained numerous point mutations. The ectopic mutants showed low occurrence of ascus dominance in outcrosses with strains that carried the wild-type allele. Approximately 10 % of ascospores were abnormal but all of the single-ascospore isolates produced normal-shaped ascospores from selfing. However, no ascus dominance was observed when the mutants were outcrossed with a sad-1 deletion mutant, which lacks the putative RNA-dependent RNA polymerase essential for meiotic silencing in N. crassa. All results were consistent with those generated from an additional gene, roa, required for ascospore morphogenesis. This study demonstrated that G. zeae possesses a functional meiotic silencing mechanism which is triggered by unpaired DNA, as in N. crassa.

Gibberella musae (Fusarium musae) sp. nov., a recently discovered species from banana is sister to F. verticillioides.

Several strains of Fusarium isolated from banana were identified previously as F. verticillioides (Sacc.) Nirenberg but described as unable to produce fumonisin. Here we report biochemical and morphological evidence, as well as multilocus phylogenetic analyses based on elongation factor (EF-1α), calmodulin, ß-tubulin, and the second largest subunit of RNA polymerase II (RPB2) sequences, indicating that these isolates represent a unique lineage in the Gibberella fujikuroi species complex related to but distinct from F. verticillioides. Together with previous results of molecular studies, as well as with results of metabolite analyses, crossing experiments, pathogenicity tests and morphological characterization, these new data indicate that these strains isolated from banana represent a new species, Gibberella musae Van Hove et al. sp. nov. (anamorph: Fusarium musae Van Hove et al. sp. nov.), which is described herein.

Effect of silicone oil on the gibberellic acid production by Gibberella fujikuroi and Aspergillus niger.

The effect of silicone oil on gibberellic acid production was investigated using Gibberella fujikuroi and Aspergillus niger fungi. Silicone oil was used as an oxygen vector in the gibberellic acid production process. When silicone oil was used, gibberellic acid concentration increased with respect to the control run having A. niger and G. fujikuroi microorganisms 4.6 and 6.7 times, respectively.

Functional analysis of the polyketide synthase genes in the filamentous fungus Gibberella zeae (anamorph Fusarium graminearum).

Polyketides are a class of secondary metabolites that exhibit a vast diversity of form and function. In fungi, these compounds are produced by large, multidomain enzymes classified as type I polyketide synthases (PKSs). In this study we identified and functionally disrupted 15 PKS genes from the genome of the filamentous fungus Gibberella zeae. Five of these genes are responsible for producing the mycotoxins zearalenone, aurofusarin, and fusarin C and the black perithecial pigment. A comprehensive expression analysis of the 15 genes revealed diverse expression patterns during grain colonization, plant colonization, sexual development, and mycelial growth. Expression of one of the PKS genes was not detected under any of 18 conditions tested. This is the first study to genetically characterize a complete set of PKS genes from a single organism.

Description of Gibberella sacchari and neotypification of its anamorph Fusarium sacchari.

We described the teleomorph of Fusarium sacchari as Gibberella sacchari, sp. nov. This species can be separated from other species of Gibberella on the basis of the longer, narrower ascospores found in G. sacchari and by sexual cross fertility. Female-fertile mating type tester strains were developed that can be used for making sexual crosses with this heterothallic fungus under laboratory conditions. The anamorph, Fusarium sacchari, was neotypified.