The complete mitochondrial genome of the important phytopathogen Nectria cinnabarina (Hypocreales, Ascomycota).

The complete nucleotide sequence of the mitochondrial genome of the important phytopathogic fungus Nectria cinnabarina was determined using the next-generation sequencing technology. The circular molecule is 69 895 bp long with a GC content of 28.71%. Gene prediction revealed 42 genes encoding 15 conserved proteins, 25 tRNAs, the large and small ribosomal RNAs. All genes are located on the same strand. Compared with previously sequenced mitochondrial genomes of the other members of Nectriaceae, the composition and order of the protein and rRNA genes are highly conserved; however, the quantity and order of tRNA genes are different. The phylogenetic analysis confirmed N. cinnabarina as a basal lineage in Nectriaceae. The mitochondrial genome of N. cinnabarina will contribute to the understanding of phylogeny and evolution of Nectriaceae and Hypocreales.

Origin of pisatin demethylase (PDA) in the genus Fusarium.

Host specificity of plant pathogens can be dictated by genes that enable pathogens to circumvent host defenses. Upon recognition of a pathogen, plants initiate defense responses that can include the production of antimicrobial compounds such as phytoalexins. The pea pathogen Nectria haematococca mating population VI (MPVI) is a filamentous ascomycete that contains a cluster of genes known as the pea pathogenicity (PEP) cluster in which the pisatin demethylase (PDA) gene resides. The PDA gene product is responsible for the detoxification of the phytoalexin pisatin, which is produced by the pea plant (Pisum sativum L.). This detoxification activity allows the pathogen to evade the phytoalexin defense mechanism. It has been proposed that the evolution of PDA and the PEP cluster reflects horizontal gene transfer (HGT). Previous observations consistent with this hypothesis include the location of the PEP cluster and PDA gene on a dispensable portion of the genome (a supernumerary chromosome), a phylogenetically discontinuous distribution of the cluster among closely related species, and a bias in G+C content and codon usage compared to other regions of the genome. In this study we compared the phylogenetic history of PDA, beta-tubulin, and translation elongation factor 1-alpha in three closely related fungi (Nectria haematococca, Fusarium oxysporum, and Neocosmospora species) to formally evaluate hypotheses regarding the origin and evolution of PDA. Our results, coupled with previous work, robustly demonstrate discordance between the gene genealogy of PDA and the organismal phylogeny of these species, and illustrate how HGT of pathogenicity genes can contribute to the expansion of host specificity in plant-pathogenic fungi.

Nectria eustromatica sp. nov., an exceptional species with a hypocreaceous stroma.

A new species with remarkable morphology, Nectria eustromatica, is described, based on morphology of the teleomorph and anamorph, ecology and molecular phylogenetic analyses. Nectria eustromatica is characterized by sphaeroid perithecia immersed in pseudoparenchymatous stromata formed singly or collectively on a subiculum. Despite its deviating teleomorph morphology, it is placed within Nectria sensu stricto in phylogenetic analyses of a combined dataset of LSU, ITS, rpb2 and tef1 sequences with high internal support. Nectria eustromatica has been collected specifically on Hippocrepis (Coronilla) emerus in southern Europe. The anamorph of N. eustromatica shares morphological traits with the genera Stilbella and Tubercularia but produces non-phialidic macroconidia in addition to phialoconidia.

The genome of Nectria haematococca: contribution of supernumerary chromosomes to gene expansion.

The ascomycetous fungus Nectria haematococca, (asexual name Fusarium solani), is a member of a group of >50 species known as the "Fusarium solani species complex". Members of this complex have diverse biological properties including the ability to cause disease on >100 genera of plants and opportunistic infections in humans. The current research analyzed the most extensively studied member of this complex, N. haematococca mating population VI (MPVI). Several genes controlling the ability of individual isolates of this species to colonize specific habitats are located on supernumerary chromosomes. Optical mapping revealed that the sequenced isolate has 17 chromosomes ranging from 530 kb to 6.52 Mb and that the physical size of the genome, 54.43 Mb, and the number of predicted genes, 15,707, are among the largest reported for ascomycetes. Two classes of genes have contributed to gene expansion: specific genes that are not found in other fungi including its closest sequenced relative, Fusarium graminearum; and genes that commonly occur as single copies in other fungi but are present as multiple copies in N. haematococca MPVI. Some of these additional genes appear to have resulted from gene duplication events, while others may have been acquired through horizontal gene transfer. The supernumerary nature of three chromosomes, 14, 15, and 17, was confirmed by their absence in pulsed field gel electrophoresis experiments of some isolates and by demonstrating that these isolates lacked chromosome-specific sequences found on the ends of these chromosomes. These supernumerary chromosomes contain more repeat sequences, are enriched in unique and duplicated genes, and have a lower G+C content in comparison to the other chromosomes. Although the origin(s) of the extra genes and the supernumerary chromosomes is not known, the gene expansion and its large genome size are consistent with this species' diverse range of habitats. Furthermore, the presence of unique genes on supernumerary chromosomes might account for individual isolates having different environmental niches.

Molecular assays reveal the presence and diversity of genes encoding pea footrot pathogenicity determinants in Nectria haematococca and in agricultural soils.

AIM: The aim of this study was to develop molecular assays for investigating the presence and diversity of pathogenicity genes from the pea footrot pathogen Nectria haematococca (anamorph Fusarium solani f.sp. pisi) in soils. METHODS AND RESULTS: Polymerase chain reaction (PCR) assays were developed to amplify four N. haematococca pathogenicity genes (PDA, PEP1, PEP3 and PEP5) from isolates and soil-DNA from five agricultural fields with a prior footrot history. A collection of 15 fungi isolated on medium selective for Fusarium spp. exhibited variation in their virulence to peas as assessed via a disease index (DI: 0-5; no virulence to the highest virulence). PCR analyses showed that three isolates in which all four pathogenicity genes were detected resulted in the highest DI (>3.88). All four pathogenicity genes were detected in soil-DNA obtained from all five fields with a footrot disease history, but were not amplified from soils, which had no footrot history. Denaturing gradient gel electrophoresis and/or sequence analysis revealed diversity amongst the pathogenicity genes. CONCLUSION: The PCR assays developed herein enable the specific detection of pathogenic N. haematococca in soils without recourse to culture. SIGNIFICANCE AND IMPACT OF THE STUDY: Molecular assays that specifically target pathogenicity genes have the capacity to assess the presence of the footrot-causing pathogen in agricultural soils.