Fungal Endophytes of Grasses: Detrimental and Beneficial Associations

Siegel, Malcolm R.; Schardl, Christopher L.

doi:10.1007/978-1-4612-3168-4_10

Cited by 28 publications

(15 citation statements)

References 77 publications

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“…Unravelling the interactions in endophytic mutualism at sistance and leads to changes of grass morphology, growth rate and growth yield (Scott & Schardl, 1993;Siegel & Schardl, 1991 ;West, 1994). In contrast, our understanding of the interactions leading to these effects between plant and fungus the cellular and molecular level is-a-challenging experimental task: the very processes one wants to study only take place during the association of the participating organisms which cannot easily be separated for analysis or manipulation.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative Assessment of in Planta Distribution of Metabolic Activity and Gene Expression of an Endophytic Fungus

et al. 1997

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Using perennial ryegrass infected with an Acremonium transformant carrying the Escherichis coli ED-glucuronidase gene (gusA) (GUS system) under control of a constitutive promoter, we have developed methods for the quantitative extraction of endophyte-associated GUS activity from plant material. Fluorometric assays of these extracts allow quantitative assessment of the distribution of endophyte-associated GUS activity within single plants (tillers) with high resolution. Fluorescence microscopy with the dye lmagene Green can in addition visualize individual GUS-expressing hyphae. Since the transformant expresses the GUS gene constitutively, GUS activity can be used as an indicator of in planta endophyte metabolic activity. Using this approach we found that (i) the concentration of endophyte metabolic activity in plant tissue decreases with increasing plant size, (ii) approximately 7 0 % of endophyte metabolic activity present in a plant is located in the leaf Sheaths, (iii) basal-apical gradients and lateral (younger to older tissue) gradients of endophyte metabolic activity exist and (iv) basal-apical gradients are established early in leaf development. Our data suggest that the concentration of endophyte in each part of the plant is regulated so that a predetermined threshold of total endophyte activity per plant is not exceeded and a consistent distribution pattern is maintained.

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Section: Introductionmentioning

confidence: 99%

“…is very limitea and mainly based on &direct evidence such as observations of the fungus in uitro or extrapolation from other systems (Porter, 1994;Siegel & Schardl, 1991 ;West, 1994).…”

Section: Introductionmentioning

confidence: 99%

Quantitative Assessment of in Planta Distribution of Metabolic Activity and Gene Expression of an Endophytic Fungus

et al. 1997

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“…Their presence confers upon the grass a number of physiological characteristics such as drought resistance, enhanced growth, and protection from herbivores, through the synthesis of feeding deterrents and toxins. In return, the plant provides nutrients and propagates the endophyte via its seeds (17,28,34,35,46,47).We have recently used a Neotyphodium endophyte, transformed with the Escherichia coli ␤-glucuronidase gene (GUS reporter gene system [14]), under the control of a heterologous constitutive promoter, to estimate the in planta distribution of endophyte metabolic activity (as GUS activity) (12). We found that GUS activity followed well-defined patterns, established during the growth of ryegrass leaves (12).…”

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confidence: 99%

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confidence: 99%

In Planta Regulation of Extension of an Endophytic Fungus and Maintenance of High Metabolic Rates in Its Mycelium in the Absence of Apical Extension

Tan¹,

Spiering²,

Scott³

et al. 2001

Appl Environ Microbiol

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The fungus Neotyphodium lolii is an endophytic symbiont. It grows in the intercellular spaces of the perennial ryegrass Lolium perenne, producing secondary metabolites which enhance the fitness of the association over that of uninfected L. perenne. We report that the average number of hyphal strands in a given section of a leaf remains constant during the life of a leaf, indicating synchrony of leaf and hyphal extension, including cessation of hyphal extension when leaf extension ceases. We used a constitutively expressed reporter gene as an indicator of the mycelium's metabolic activity during and after hyphal extension. Reporter gene activity decreased when the mycelium stopped extending in liquid culture but not in planta. This indicates that in planta endophyte hyphae remain metabolically highly active when extension has ceased and throughout the life of the leaf they are colonizing. The behavior of the fungus in planta indicates the existence of signaling pathways which (i) synchronize the extension of leaf and hypha by regulating hyphal extension, (ii) suppress hyphal branching, and (iii) stop apical extension of fungal hyphae, without reducing the mycelium's metabolic activity. These signals may be crucial for the symbiosis, by allowing the endophyte to switch the focus of its metabolic activity from extension to the production of secondary metabolites.Neotyphodium endophytes are mutualistic symbionts of grasses, living in their intercellular spaces. Their presence confers upon the grass a number of physiological characteristics such as drought resistance, enhanced growth, and protection from herbivores, through the synthesis of feeding deterrents and toxins. In return, the plant provides nutrients and propagates the endophyte via its seeds (17,28,34,35,46,47).We have recently used a Neotyphodium endophyte, transformed with the Escherichia coli ␤-glucuronidase gene (GUS reporter gene system [14]), under the control of a heterologous constitutive promoter, to estimate the in planta distribution of endophyte metabolic activity (as GUS activity) (12). We found that GUS activity followed well-defined patterns, established during the growth of ryegrass leaves (12). The endophyte metabolic activity in plant tissue measured in such experiments depends on (i) the number of endophyte hyphae present, (ii) the rate of gene expression in these hyphae, and (iii) the half-life of the GUS enzyme. Thus, while the existence of these patterns was intriguing, these experiment allowed only limited conclusions as to how they are generated. We have now determined directly the in planta distribution of endophyte hyphal biomass. In parallel, we have determined the endophyte's constitutive GUS expression in the same ryegrass tillers. We have also determined GUS activity in exponentially growing and stationary laboratory cultures of the same endophyte strain. Together, these data allow us to draw conclusions regarding the endophyte's metabolic state in different parts of the ryegrass tiller. MATERIALS AND METHODSStrains and plant ...

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“…Endophytic infection of grasses by fungi of the tribe Balansieae is widespread in nature (for reviews, see Siegel and Schardl, 1991;Siegel, 1993). Many commercially important turf and forage grasses are naturally infected with endophytes of the genus Acrernonium (Morgan-Jones and Gams, 1982), which is related to the teleomorphic genus Epichloe.…”

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Mutualistic Fungal Endophytes Express a Proteinase that Is Homologous to Proteases Suspected to Be Important in Fungal Pathogenicity

1996

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Many cultivated and wild grass species are hosts to mutualistic fungal endophytes. These associations are ecologically and agronomically significant, yet little is known regarding the physiological aspects of the interaction. In the Poa amp/a/Acremonium typhinum interaction, a fungal serine proteinase, Atl, is surprisingly abundant and may constitute 1 to 2% of the total leaf-sheath protein. Sequence analysis of cDNA and genomic clones indicates that proteinase Atl is a member of the eukaryotic subtilisin-like protease family. It is homologous to proteases suspected to be virulence factors in fungal pathogens of insects, nematodes, and other fungi. Cel blot analysis of RNA extracted from infected leaf-sheath tissue indicates that the proteinase Atl transcript leve1 is extremely high. RNA gel blots and immunoblots of purified enzymes indicate that similar proteinases are produced by Epichloe festucae and Acremonium lolii, the fungal endophytes infecting Festuca rubra subsp. rubra and Lolium perenne, respectively. Fungal expression of proteinase Atl-like enzymes may be a general feature of endophyte infection.

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Fungal Endophytes of Grasses: Detrimental and Beneficial Associations

Cited by 28 publications

References 77 publications

Quantitative Assessment of in Planta Distribution of Metabolic Activity and Gene Expression of an Endophytic Fungus

Quantitative Assessment of in Planta Distribution of Metabolic Activity and Gene Expression of an Endophytic Fungus

In Planta Regulation of Extension of an Endophytic Fungus and Maintenance of High Metabolic Rates in Its Mycelium in the Absence of Apical Extension

Mutualistic Fungal Endophytes Express a Proteinase that Is Homologous to Proteases Suspected to Be Important in Fungal Pathogenicity

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