Characterization of a novel dsRNA element in the pine endophytic fungus Diplodia scrobiculata.

Diplodia scrobiculata and Diplodia pinea are endophytic fungi associated with dieback and cankers of mainly Pinus spp. in many parts of the world. These two fungi are closely related and have, in the past, been considered to represent two morphological forms (A and B morphotypes) of D.

Molecular and morphological characterization of Dothiorella casuarini sp. nov. and other Botryosphaeriaceae with diplodia-like conidia.

After recent changes to the taxonomy of the Botryosphaeriaceae species with diplodia-like (= dark, ovoid, often pigmented) conidia are considered to belong to at least three genera including Diplodia, Lasiodiplodia and Dothiorella. In a recent molecular phylogenetic study it became apparent that two groups of isolates with diplodia-like conidia required taxonomic revision. One group of isolates originated from Cupressus sempervirens in Greece and Cyprus and had been identified as D.

Characterization of South African Cryphonectria cubensis Isolates Infected with a C. parasitica Hypovirus.

ABSTRACT Cryphonectria cubensis is the causal agent of a serious canker disease of Eucalyptus spp. in tropical and subtropical parts of the world. In this study, a South African C.

Phylogeny of the Botryosphaeriaceae reveals patterns of host association.

Three anamorph genera of the Botryosphaeriaceae namely Diplodia, Lasiodiplodia and Dothiorella have typically dark, ovoid conidia with thick walls, and are consequently difficult to distinguish from each other. These genera are well-known pathogens of especially pine species. We generated a multiple gene genealogy to resolve the phylogenetic relationships of Botryosphaeriaceae with dark conidial anamorphs, and mapped host associations based on this phylogeny.

A population genetics pedigree perspective on the transmission of Helicobacter pylori.

The inference of transmission pathways for medicinally important bacteria is important to our understanding of pathogens. Here we report analyses of transmission in Helicobacter pylori, a major carcinogen. Our study is novel in that the focal community comprises detailed family pedigrees and has a high prevalence of H.

Phenotypic and DNA sequence data comparisons reveal three discrete species in the Ceratocystis polonica species complex.

Ceratocystis polonica and C. laricicola are two morphologically similar species that occur on conifers and reside in the Ceratocystis coerulescens species complex. They, however, represent two ecologically distinct entities.

Relative Pathogenicity of Cryphonectria cubensis on Eucalyptus Clones Differing in Their Resistance to C. cubensis.

Cryphonectria cubensis causes a destructive canker disease of Eucalyptus species. Management of this disease is primarily through breeding and selection of disease resistant trees. One means of selecting such trees is by artificial inoculation with the pathogen.

Multiple gene genealogies and microsatellite markers reflect relationships between morphotypes of Sphaeropsis sapinea and distinguish a new species of Diplodia.

Sphaeropsis sapinea is an opportunistic pathogen causing serious damage to conifers, pre-disposed by adverse environmental conditions or mechanical damage. Three different morphological forms of the fungus have been described and are commonly referred to as the A, B and C morphotypes. Isolates of the different morphotypes have also been separated based on differences in pathogenicity and molecular characteristics.

Transfection of Diaporthe perjuncta with Diaporthe RNA virus.

Diaporthe perjuncta is a pathogen of grapevines worldwide. A positive-strand RNA virus, Diaporthe RNA virus (DaRV), occurs in hypovirulent isolates of this fungus. A virus-free isolate from a South African grapevine was transfected with in vitro-transcribed positive strands of DaRV.

Bacterial Blight and Dieback of Eucalyptus Species, Hybrids, and Clones in South Africa.

During 1998, a new disease appeared on trees representing a Eucalyptus grandis × E. nitens (GN) hybrid in a nursery in KwaZulu/Natal. The disease has subsequently spread to other Eucalyptus species, hybrids, and clones in nurseries and plantations throughout South Africa.

A novel RNA mycovirus in a hypovirulent isolate of the plant pathogen Diaporthe ambigua.

Hypovirulent isolates of the fruit tree fungal pathogen Diaporthe ambigua have previously been shown to harbour a double-stranded (ds)RNA genetic element of about 4 kb. In this study, we established the complete cDNA sequence of this dsRNA, which represents a replicative form of a positive-strand RNA virus that we have named D. ambigua RNA virus (DaRV).

Coinfection of a fungal pathogen by two distinct double-stranded RNA viruses.

Unsegmented double-stranded (ds)RNA viruses belonging to the family Totiviridae persistently infect protozoa and fungi. In this study, two totiviruses were found to coinfect the filamentous fungus Sphaeropsis sapinea, a well known pathogen of pines. Isometric, virus-like particles approximately 35 nm in diameter were isolated from extracts of this fungus.

Bradyrhizobium japonicum FixK2, a crucial distributor in the FixLJ-dependent regulatory cascade for control of genes inducible by low oxygen levels.

Bradyrhizobium japonicum possesses a second fixK-like gene, fixK2, in addition to the previously identified fixK1 gene. The expression of both genes depends in a hierarchical fashion on the low-oxygen-responsive two-component regulatory system FixLJ, whereby FixJ first activates fixK2, whose product then activates fixK1. While the target genes for control by FixK1 are unknown, there is evidence for activation of the fixNOQP, fixGHIS, and rpoN1 genes and some heme biosynthesis and nitrate respiration genes by FixK2.

The Bradyrhizobium japonicum fixGHIS genes are required for the formation of the high-affinity cbb3-type cytochrome oxidase.

We report structural and functional analyses of the Bradyrhizobium japonicum fixGHIS genes, which map immediately downstream of the fixNOQP operon for the symbiotically essential cbb3-type heme-copper oxidase complex. Expression of fixGHIS, like that of fixNOQP, is strongly induced in cells grown microaerobically or anaerobically. A fixGHI deletion led to the same prominent phenotypes as those known from a fixNOQP deletion: defective symbiotic nitrogen fixation (Fix-) and decreased cytochrome oxidase activity in cells grown under oxygen deprivation.

Assembly and function of the cytochrome cbb3 oxidase subunits in Bradyrhizobium japonicum.

The Bradyrhizobium japonicum cbb3-type cytochrome oxidase, which supports microaerobic respiration, is a multisubunit enzyme encoded by the genes of the fixNOQP operon. We investigated the contribution of the individual subunits to function and assembly of the membrane-bound complex. In-frame deletion mutants of fixN, fixO, and fixQ, and an insertion mutant of fixP were constructed.

A high-affinity cbb3-type cytochrome oxidase terminates the symbiosis-specific respiratory chain of Bradyrhizobium japonicum.

It has been a long-standing hypothesis that the endosymbiotic rhizobia (bacteroids) cope with a concentration of 10 to 20 nM free O2 in legume root nodules by the use of a specialized respiratory electron transport chain terminating with an oxidase that ought to have a high affinity for O2. Previously, we suggested that the microaerobically and anaerobically induced fixNOQP operon of Bradyrhizobium japonicum might code for such a special oxidase. Here we report the biochemical characteristics of this terminal oxidase after a 27-fold enrichment from membranes of anaerobically grown B.

The ccoNOQP gene cluster codes for a cb-type cytochrome oxidase that functions in aerobic respiration of Rhodobacter capsulatus.

The genes for a new type of a haem-copper cytochrome oxidase were cloned from Rhodobacter capsulatus strain 37b4, using the Bradyrhizobium japonicum fixNOQP gene region as a hybridizing probe. Four genes, probably organized in an operon (ccoNOQP), were identified; their products share extensive amino acid sequence similarity with the FixN, O, Q and P proteins that have recently been shown to be the subunits of a cb-type oxidase. CcoN is a b-type cytochrome, CcoO and CcoP are membrane-bound mono- and dihaem c-type cytochromes and CcoQ is a small membrane protein of unknown function.

Genes for a microaerobically induced oxidase complex in Bradyrhizobium japonicum are essential for a nitrogen-fixing endosymbiosis.

We report the discovery of a Bradyrhizobium japonicum gene cluster (fixNOQP) in which mutations resulted in defective soybean root-nodule bacteroid development and symbiotic nitrogen fixation. The predicted, DNA-derived protein sequences suggested that FixN is a heme b and copper-binding oxidase subunit, FixO a monoheme cytochrome c, FixQ a polypeptide of 54 amino acids, and FixP a diheme cytochrome c and that they are all membrane-bound. The isolation and analysis of membrane proteins from B.

Genes for a second terminal oxidase in Bradyrhizobium japonicum.

Bradyrhizobium japonicum possesses a mitochondria-like respiratory chain terminating with an aa3-type cytochrome c oxidase. The gene for subunit I of this enzyme (coxA) had been identified and cloned previously via heterologous hybridization using a Paracoccus denitrificans DNA probe. In the course of these studies, another B.