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Plant defense involves a complex array of biochemical interactions, many of which occur in the extracellular environment. The apical 1- to 2-mm root tip housing apical and root cap meristems is resistant to infection by most pathogens, so growth and gravity sensing often proceed normally even when other sites on the root are invaded. The mechanism of this resistance is unknown but appears to involve a mucilaginous matrix or \"slime\" composed of proteins, polysaccharides, and detached living cells called \"border cells.\" Here, we report that extracellular DNA (exDNA) is a component of root cap slime and that exDNA degradation during inoculation by a fungal pathogen results in loss of root tip resistance to infection. Most root tips (>95%) escape infection even when immersed in inoculum from the root-rotting pathogen Nectria haematococca. By contrast, 100% of inoculated root tips treated with DNase I developed necrosis. Treatment with BAL31, an exonuclease that digests DNA more slowly than DNase I, also resulted in increased root tip infection, but the onset of infection was delayed. Control root tips or fungal spores treated with nuclease alone exhibited normal morphology and growth. Pea (Pisum sativum) root tips incubated with [³²P]dCTP during a 1-h period when no cell death occurs yielded root cap slime containing ³²P-labeled exDNA. Our results suggest that exDNA is a previously unrecognized component of plant defense, an observation that is in accordance with the recent discovery that exDNA from white blood cells plays a key role in the vertebrate immune response against microbial pathogens.

Newly generated plant tissue is inherently sensitive to infection. Yet, when pea (Pisum sativum) roots are inoculated with the pea pathogen, Nectria haematococca, most newly generated root tips remain uninfected even though most roots develop lesions just behind the tip in the region of elongation. The resistance mechanism is unknown but is correlated spatially with the presence of border cells on the cap periphery. Previously, an array of >100 extracellular proteins was found to be released while border cell separation proceeds. Here we report that protein secretion from pea root caps is induced in correlation with border cell separation. When this root cap secretome was proteolytically degraded during inoculation of pea roots with N. haematococca, the percentage of infected root tips increased from 4% ± 3% to 100%. In control experiments, protease treatment of conidia or roots had no effect on growth and development of the fungus or the plant. A complex of >100 extracellular proteins was confirmed, by multidimensional protein identification technology, to comprise the root cap secretome. In addition to defense-related and signaling enzymes known to be present in the plant apoplast were ribosomal proteins, 14-3-3 proteins, and others typically associated with intracellular localization but recently shown to be extracellular components of microbial biofilms. We conclude that the root cap, long known to release a high molecular weight polysaccharide mucilage and thousands of living cells into the incipient rhizosphere, also secretes a complex mixture of proteins that appear to function in protection of the root tip from infection.

Hypocreales represents one of the most successful orders of ascomycetes on mosses and hepatics, and more than 30 obligately bryophilous species belonging to seven genera of Bionectriaceae and Nectriaceae are known. These fungi have a remarkably wide range of ascospore types that differ in form, size and septation. Especially heterogeneous are the ascospores of the six hypocrealean parasites recorded on European populations of Frullania dilatata. Patterns of distribution of bryophilous Hypocreales on this host appear to follow the principles of island biogeography. Two new leaf-perforating species of Nectria with unusual ascospores are described. Nectria foertheri Döbbeler sp. nov. grows biotrophically on Porella sp. in Guatemala, and N. lagodes Döbbeler sp. nov. is a necrotroph on Frullania dilatata in Italy and Greece.

Ergosterol is an important fungal-specific biomarker, but its use for fungal biomass estimation is still varied. It is important to distinguish between free and esterified ergosterols, which are mainly located on the plasma membrane and the cytosolic lipid particles, respectively. The present study analyzes free and esterified ergosterol contents in: (1) the fifty-nine strains of culturable fungi isolated from mangrove soil, (2) the broken spores of the fungus Ganoderma lucidum stored in capsule for more than 12 years, and (3) the mangrove soil and nearby campus wood soil samples by high performance liquid chromatography (HPLC). The results show that the contents of free and esterified ergosterols varied greatly in fifty-nine strains of fungi after 5 days of growth, indicating the diversity of ergosterol composition in fungi. The average contents of free and total ergosterols from the fifty-nine strains of fungi are 4.4 ± 1.5 mg/g and 6.1 ± 1.9 mg/g dry mycelia, respectively, with an average ergosterol esterification rate of 27.4%. The present study suggests that the fungi might be divided into two classes, one is fungi with high esterification rates (e.g., more than 27%) such as Nectria spp. and Fusarium spp., and the other is fungi with low esterification rates (e.g., less than 27%) such as Penicillium spp. and Trichoderma spp. Moreover, the ergosterol esterification rate in the spores of G. lucidum is 91.4% with a very small amount of free ergosterol (0.015 mg/g), compared with 41.9% with a higher level of free ergosterol (0.499 mg/g) reported in our previous study in 2007, indicating that free ergosterol degrades more rapidly than esterified ergosterol. In addition, the ergosterol esterification rates in mangrove soil and nearby campus wood soil samples range from 0 to 39.0%, compared with 80% in an old soil organic matter reported in a previous study, indicating the potential relationship between aging degree of fungi or soil and esterification rate. The present study proposes that both free and esterified ergosterols should be analyzed for fungal biomass estimation. When the ergosterol esterification rates in soils are higher, free ergosterol might be a better marker for fungal biomass. It is speculated that the ergosterol esterification rate in soils might contain some important information, such as the age of old-growth forests over time scales of centuries to millennia, besides the senescence degree of fungal mycelia in soils.Key points• Fungi might be divided into two classes depending on ergosterol esterification rates.• Ergosterol esterification rate of broken spores stored for long time raised evidently.• Both free and esterified ergosterols should be analyzed for fungal biomass estimate.• Free ergosterol is a better marker for fungal biomass with a high esterification rate.

The genus Thelonectria and closely related species with cylindrocarpon-like asexual states are a group of perithecial ascomycetes in the family Nectriaceae that occur as saprobes and in few cases as pathogens of hardwood trees, shrubs or other plants. Although a key component of forest ecosystems around the world, species relationships and distributions of these fungi are largely unknown. The objectives of this study were to: 1) infer species rank phylogenetic relationships of the genus Thelonectria and closely related species with cylindrocarpon-like asexual states and test the monophyly of each of the groups studied; 2) delimit taxa establishing taxon circumscriptions; 3) resolve nomenclatural issues by identifying redundantly used names and synonyms; and 4) provide an updated outline to the genus, geographical distributions data and identification tools, specifically diagnostic keys and molecular data that can be used as molecular barcodes. The recovered consensus phylogeny resulted in a narrow circumscription of the genus Thelonectria , based on the type T. discophora , excluding one of the common species T. jungneri . According to the phylogenetic analyses, T. jungneri belongs in a segregate clade that should be recognized as a different genus. In the genus Thelonectria , a total of four new species and three new combinations are recognized. Additionally, three new genera, closely related to Thelonectria , are described to accommodate species displaying a morphological resemblance to those of Thelonectria : Cinnamomeonectria gen. nov. with C. cinnamomea as type species, Macronectria gen. nov. with M. jungneri as type species and including four additional newly described species, and Tumenectria gen. nov. with T. laetidisca as type species.

Nayarit ranks first in national soursop production (Annona muricata L.). However, the soursop fruits are perishable and susceptible to microorganisms attack, reaching up to 60% of the postharvest losses. Due to the previously mentioned points, the objective of the present study was to isolate, identify, and determine the pathogenicity of fungi related to postharvest diseases in soursop fruits in the main producing areas of Nayarit, Mexico. Several fungi belonging to the genera Fusarium sp., Rhizopus, Lasiodiplodia, Gliocladium, and Colletotrichum were isolated and morphologically identified. Further, bioinformatics sequence analysis of the ITS1-5.8S-ITS2 region of the rDNA identified that most pathogen species were Lasiodiplodia theobromae, Lasiodiplodia pseudotheobromae, and Nectria haematococca, which cause postharvest diseases in soursop fruit, affecting their quality. Lasiodiplodia causes the highest postharvest damage in soursop among the pathogenic species identified.

Root infection in susceptible host species is initiated predominantly in the zone of elongation, whereas the remainder of the root is resistant. Nectria haematococca infection of pea (Pisum sativum) was used as a model to explore possible mechanisms influencing the localization of root infection. The failure to infect the root tip was not due to a failure to induce spore germination at this site, suppression of pathogenicity genes in the fungus, or increased expression of plant defense genes. Instead, exudates from the root tip induce rapid spore germination by a pathway that is independent of nutrient-induced germination. Subsequently, a factor produced during fungal infection and death of border cells at the root apex appears to selectively suppress fungal growth and prevent sporulation. Host-specific mantle formation in response to border cells appears to represent a previously unrecognized form of host-parasite relationship common to diverse species. The dynamics of signal exchange leading to mantle development may play a key role in fostering plant health, by protecting root meristems from pathogenic invasion.

The diversity of symbiotic fungi associated with the gorgonian coral Echinogorgia rebekka from the Weizhou coral reef in the South China Sea was investigated. Combined with morphologic traits, ITS-rDNA sequences revealed 18 fungal strains from this gorgonian. All of the 18 fungi belonged to the phylum Ascomycota and were distributed among seven genera in five orders: Eurotiales (Aspergillus and Penicillium), Pleosporales (Alternaria), Capnodiales (Cladosporium), Trichosphaeriales (Nigrospora) and Hypocreales (Hypocrea and Nectria). Antibacterial activities of these fungal strains were investigated with five pathogenic bacteria. All of the 18 fungal strains displayed different levels of antibacterial activities, most of which exhibited moderate to high antibacterial activities to the Gram-positive pathogens Staphylococcus aureus and Micrococcus tetragenus, and showed relatively low bioactivities to other three pathogenic bacteria. Several fungal strains in the genera Penicillium and Cladosporium with strong antibacterial activities provide potential for further research on isolation of bioactive secondary metabolites.

Fungal pathogens usually have multiple genes that encode extracellular hydrolytic enzymes that may degrade the physical barriers in their hosts during the invasion process. Nectria hematococca, a plant pathogen, has two inducible pectate lyase (PL) genes (pel) encoding PL that can help degrade the carbohydrate barrier in the host. pelA is induced by pectin, whereas pelD is induced only in planta. We show that the disruption of either the pelA or pelD genes alone causes no detectable decrease in virulence. Disruption of both pelA and pelD drastically reduces virulence. Complementation of the double disruptant with pelD gene, or supplementation of the infection droplets of the double disruptant with either purified enzyme, PLA, or PLD, caused a recovery in virulence. These results show that PL is a virulence factor. Thus, we demonstrate that disruption of all functionally redundant genes is required to demonstrate the role of host barrier-degrading enzymes in pathogenesis and that dismissal of the role of such enzymes based on the effects of single-gene disruption may be premature.