Nuclear DNA content of 11 fungal species in Glomales

Hosny, Michel; Gianinazzi‐Pearson, Vivienne; Dulieu, H.

doi:10.1139/gen-41-3-422

Cited by 28 publications

(27 citation statements)

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“…Calculations with Clarke and Carbon's equation (13) indicated that 2,000 primary recombinants are needed to represent the Burkholderia genome with 99% probability. To calculate this value it was considered that in each spore of G. margarita there are 2,000 to 3,000 fungal nuclei (7) of about 10 8 bp each (23) and 250,000 bacteria with a genome of approximately 10 6 bp (9). Therefore, about 30% of recombinant clones in the library should be prokaryotic.…”

Section: Methodsmentioning

confidence: 99%

Nitrogen Fixation Genes in an Endosymbiotic Burkholderia Strain

Minerdi

Fani

Gallo

et al. 2001

Appl Environ Microbiol

131

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In this paper we report the identification and characterization of a DNA region containing putative nif genes and belonging to a Burkholderia endosymbiont of the arbuscular mycorrhizal fungus Gigaspora margarita. A genomic library of total DNA extracted from the fungal spores was also representative of the bacterial genome and was used to investigate the prokaryotic genome. Screening of the library with Azospirillum brasilense nifHDK genes as the prokaryotic probes led to the identification of a 6,413-bp region. Analysis revealed three open reading frames encoding putative proteins with a very high degree of sequence similarity with the two subunits (NifD and NifK) of the component I and with component II (NifH) of nitrogenase from different diazotrophs. The three genes were arranged in an operon similar to that shown by most archaeal and bacterial diazotrophs. PCR experiments with primers designed on the Burkholderia nifHDK genes and Southern blot analysis demonstrate that they actually belong to the genome of the G. margarita endosymbiont. They offer, therefore, the first sequence for the nif operon described for Burkholderia. Reverse transcriptase PCR experiments with primers designed on the Burkholderia nifH and nifD genes and performed on total RNA extracted from spores demonstrate that the gene expression was limited to the germination phase. A phylogenetic analysis performed on the available nifK sequences placed the endosymbiotic Burkholderia close to A. brasilense.

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Section: Methodsmentioning

confidence: 99%

Nitrogen Fixation Genes in an Endosymbiotic Burkholderia Strain

Minerdi

Fani

Gallo

et al. 2001

Appl Environ Microbiol

131

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“…Their hyphae are coenocytic, and asexual spores form on the termini of hyphae (8). These spores contain hundreds to thousands of nuclei per spore (1,11,29). In the species Scutellospora castanea, one spore contains approximately 800 nuclei (11).…”

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confidence: 99%

“…These spores contain hundreds to thousands of nuclei per spore (1,11,29). In the species Scutellospora castanea, one spore contains approximately 800 nuclei (11). The spores are the only form by which individual species can be identified on the basis of morphological characteristics (33).…”

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confidence: 99%

Identification and Isolation of Two Ascomycete Fungi from Spores of the Arbuscular Mycorrhizal Fungus Scutellospora castanea

Hijri

Redecker

Petetot

et al. 2002

Appl Environ Microbiol

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Two filamentous fungi with different phenotypes were isolated from crushed healthy spores or perforated dead spores of the arbuscular mycorrhizal fungus (AMF) Scutellospora castanea. Based on comparative sequence analysis of 5.8S ribosomal DNA and internal transcribed spacer fragments, one isolate, obtained from perforated dead spores only, was assigned to the genus Nectria, and the second, obtained from both healthy and dead spores, was assigned to Leptosphaeria, a genus that also contains pathogens of plants in the Brassicaceae. PCR and randomly amplified polymorphic DNA-PCR analyses, however, did not indicate similarities between pathogens and the isolate. The presence of the two isolates in both healthy spores and perforated dead spores of S. castanea was finally confirmed by transmission electron microscopy by using distinctive characteristics of the isolates and S. castanea. The role of this fungus in S. castanea spores remains unclear, but the results serve as a strong warning that sequences obtained from apparently healthy AMF spores cannot be presumed to be of glomalean origin and that this could present problems for studies on AMF genes.The order Glomales (class Zygomycota) comprises arbuscular mycorrhizal fungi (AMF) that are able to form mutualistic symbioses with roots of approximately 60% of all plant species (25). AMF are important for plants because they assist plants in absorbing nutrients, especially phosphate (14), and have a protective role against plant-pathogenic fungi (10, 17). It has also been shown that the diversity of AMF is an important determinant of plant diversity and productivity (26,27,28). AMF are obligate biotrophs. Their hyphae are coenocytic, and asexual spores form on the termini of hyphae (8). These spores contain hundreds to thousands of nuclei per spore (1,11,29). In the species Scutellospora castanea, one spore contains approximately 800 nuclei (11). The spores are the only form by which individual species can be identified on the basis of morphological characteristics (33).Because of the symbiotic function of AMF, there is great interest in identifying AMF genes that are involved in the establishment and functioning of the symbiosis. However, at present, very few genes other than rRNA genes have been studied in these fungi. Several studies have shown that genetic diversity of the internal transcribed spacer (ITS) exists among and within single spores (9,16,22). Six different ITS1-5.8S-ITS2 types (T1 to T6) from S. castanea were reported (8). The 5.8S sequences published by Hijri et al. (9) were subsequently used in a phylogenetic analysis of Glomales and other fungi (20). This analysis showed that the highly divergent sequences T1, T3, T5, and T6 clustered within the ascomycetes (with Phoma-Leptosphaeria as the closest relatives to T1 and T3). Other studies have also reported sequences of rRNA genes obtained from glomalean spores that clustered in the ascomycetes in phylogenetic analyses (4,12,18). The question therefore arises as to what is the true origin of these s...

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“…It is largely accepted that AM fungi are asexual, haploid, multinucleated organisms, with a wide range of genome sizes (Hosny et al 1998). In contrast, a debate is currently focused on the question whether AM fungi have a multigenomic structure or by contrast they have a homokaryotic organization including intra-individual genetic variation (Bever & Wang 2005).…”

Section: Discussionmentioning

confidence: 99%