Phylogenetic Analysis of a Dataset of Fungal 5.8S rDNA Sequences Shows That Highly Divergent Copies of Internal Transcribed Spacers Reported from Scutellospora castanea Are of Ascomycete Origin

Redecker, Dirk; Hijri, Mohamed; Dulieu, H.; Sanders, Ian R.

doi:10.1006/fgbi.1999.1173

Cited by 83 publications

(64 citation statements)

References 21 publications

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“…With the internal consistency of these experiments, it is unnecessary and non-parsimonious to invoke the action of any undetected pathogens to explain the negative feedback observed in the test experiment ( gure 2). The possibility remains that microorganisms that have been observed living within spores of AM fungi (see Walley & Germida 1996;Redecker et al 1999) could contribute to the impact of these fungi on plant growth. However, for these microorganisms to play a part in the observed negative feedback, they would have to be stably inherited with individual AM fungal species to account for the internal consistency of these results.…”

Section: Discussionmentioning

confidence: 99%

Negative feedback within a mutualism: host–specific growth of mycorrhizal fungi reduces plant benefit

Bever

2002

Proc. R. Soc. Lond. B

361

351

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A basic tenet of ecology is that negative feedback on abundance plays an important part in the coexistence of species within guilds. Mutualistic interactions generate positive feedbacks on abundance and therefore are not thought to contribute to the maintenance of diversity. Here, I report evidence of negative feedback on plant growth through changes in the composition of their mutualistic fungal symbionts, arbuscular mycorrhizal (AM) fungi. Negative feedback results from asymmetries in the delivery of bene t between plant and AM fungal species in which the AM fungus that grows best with the plant Plantago lanceolata is a poor growth promoter for Plantago. Growth of Plantago is, instead, best promoted by the AM fungal species that accumulate with a second plant species, Panicum sphaerocarpon. The resulting community dynamic leads to a decline in mutualistic bene t received by Plantago, and can contribute to the coexistence of these two competing plant species.

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Section: Discussionmentioning

confidence: 99%

Negative feedback within a mutualism: host–specific growth of mycorrhizal fungi reduces plant benefit

Bever

2002

Proc. R. Soc. Lond. B

361

351

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“…Therefore, we believe that only GmPMA1 and GmHA5 H ϩ -ATPases belong to the fungus G. mosseae, although we do not exclude that other yet unknown isozymes might exist. GmHA1, -2, -3, and -4 could belong to one of the associated ascomycetes that often cohabit within spores of AM fungi (Redecker et al, 1999). It is interesting that the catalytic domain from the AM isoforms GmPMA1 and GmHA5 appear more closely related to those from plant H ϩ -ATPases than to the catalytic domain of the fungal isoforms.…”

Section: Discussionmentioning

confidence: 99%

Symbiotic Status, Phosphate, and Sucrose Regulate the Expression of Two Plasma Membrane H+-ATPase Genes from the Mycorrhizal Fungus Glomus mosseae

Requena

Breuninger²,

Franken

et al. 2003

Plant Physiology

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The establishment of the arbuscular mycorrhizal symbiosis results in a modification of the gene expression pattern in both plant and fungus to accomplish the morphological and physiological changes necessary for the bidirectional transfer of nutrients between symbionts. H+-ATPase enzymes play a key role establishing the electrochemical gradient required for the transfer of nutrients across the plasma membrane in both fungi and plants. Molecular analysis of the genetic changes in arbuscular mycorrhizal fungi during symbiosis allowed us to isolate a fungal cDNA clone encoding a H+-ATPase, GmPMA1, from Glomus mosseae (BEG12). Despite the high conservation of the catalytic domain from H+-ATPases, detailed analyses showed that GmPMA1 was strongly related only to a previously identified G. mosseae ATPase gene, GmHA5, and not to the other four ATPase genes known from this fungus. A developmentally regulated expression pattern could be shown for both genes, GmPMA1 and GmHA5. GmPMA1 was highly expressed during asymbiotic development, and its expression did not change when entering into symbiosis, whereas the GmHA5 transcript was induced upon plant recognition at the appressorium stage. Both genes maintained high levels of expression during intraradical development, but their expression was reduced in the extraradical mycelium. Phosphate, a key nutrient to the symbiosis, also induced the expression of GmHA5 during asymbiotic growth, whereas sucrose had a negative effect. Our results indicate that different fungal H+-ATPases isoforms might be recruited at different developmental stages possibly responding to the different requirements of the life in symbiosis.

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“…Three possibilities were suggested by Redecker et al (20): (i) that these sequences were from contaminating fungi on the surface of the AMF spores, (ii) that they were sequences from ascomycetes which were living inside S. castanea spores, and (iii) that they originated from the S. castanea genome. The first two possibilities were seen as the most likely explanations (20).In this study, we have addressed the question of whether ascomycete fungi live inside healthy S. castanea spores or only on the surface of the spores. This is an important question, because if other fungi are able to live inside healthy AMF, then they pose a serious problem for studies of AMF genes.…”

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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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Phylogenetic Analysis of a Dataset of Fungal 5.8S rDNA Sequences Shows That Highly Divergent Copies of Internal Transcribed Spacers Reported from Scutellospora castanea Are of Ascomycete Origin

Cited by 83 publications

References 21 publications

Negative feedback within a mutualism: host–specific growth of mycorrhizal fungi reduces plant benefit

Negative feedback within a mutualism: host–specific growth of mycorrhizal fungi reduces plant benefit

Symbiotic Status, Phosphate, and Sucrose Regulate the Expression of Two Plasma Membrane H+-ATPase Genes from the Mycorrhizal Fungus Glomus mosseae

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

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