Mycorrhizal Fungus Glomus Versiforme Research Articles

Arbuscular mycorrhizal fungi enhance disease resistance of Salvia miltiorrhiza to Fusarium wilt.

Salvia miltiorrhiza Bunge (Danshen in Chinese) is vulnerable to Fusarium wilt, which severely affects the quality of the crude drug. Mycorrhizal colonization enhances resistance to fungal pathogens in many plant species. In this study, pre-inoculation of S. miltiorrhiza with the arbuscular mycorrhizal fungi (AMF) Glomus versiforme significantly alleviated Fusarium wilt caused by Fusarium oxysporum. Mycorrhizal colonization protected S. miltiorrhiza from pathogen infection, thereby preventing a loss of biomass and photosynthesis. There were greater defense responses induced by pathogen infection in AMF pre-inoculated plants than those in non-treated plants. AMF pre-inoculation resulted in systemic responses upon pathogen inoculation, including significant increases in the protein content and activities of phenylalanine ammonia-lyase (PAL), chitinase, and β-1,3-glucanase in S. miltiorrhiza roots. In addition, mycorrhizal pre-inoculation caused upregulation of defense-related genes, and jasmonic acid (JA) and salicylic acid (SA) signaling pathway genes after pathogen infection. The above findings indicate that mycorrhizal colonization enhances S. miltiorrhiza resistance against F. oxysporum infection by enhancing photosynthesis, root structure, and inducing the expression of defense enzymes and defense-related genes on the other hand.

Fungal association and utilization of phosphate by plants: success, limitations, and future prospects.

Phosphorus (P) is a major macronutrient for plant health and development. The available form of P is generally low in the rhizosphere even in fertile soils. A major proportion of applied phosphate (Pi) fertilizers in the soil become fixed into insoluble, unavailable forms, which restricts crop production throughout the world. Roots possess two distinct modes of P uptake from the soil, direct and indirect uptake. The direct uptake of P is facilitated by the plant’s own Pi transporters while indirect uptake occurs via mycorrhizal symbiosis, where the host plant obtains P primarily from the fungal partner, while the fungus benefits from plant-derived reduced carbon. So far, only one Pi transporter has been characterized from the mycorrhizal fungus Glomus versiforme. As arbuscular mycorrhizal fungi cannot be cultured axenically, their Pi transporter network is difficult to exploite for large scale sustainable agriculture. Alternatively, the root-colonizing endophytic fungus Piriformospora indica can grow axenically and provides strong growth-promoting activity during its symbiosis with a broad spectrum of plants. P. indica contains a high affinity Pi transporter (PiPT) involved in improving Pi nutrition levels in the host plant under P limiting conditions. As P. indica can be manipulated genetically, it opens new vistas to be used in P deficient fields.

Arbuscular mycorrhizal fungi and biological control of Verticillium-wilted cotton plants

The interaction of arbuscular mycorrhizal fungi (Glomus etunicatum, Glomus intraradices, and Glomus versiforme) with a wilt-causing soil-borne pathogen, Verticillium dahliae, was studied in cotton. It was found that establishment by arbuscular mycorrhizal fungi reduced disease index. In diseased cotton plants colonised by G. etunicatum, the disease index was less than other diseased mycorrhizal and non-mycorrhizal ones. In diseased cotton plants, chlorophyll content was lower than others. Three Glomus species significantly increased content of sugar and protein in shoot and root. Pathogen-infected plants had higher proline concentration in shoot and root than healthy plants. On the other hand, the increased content of proline as stress sensor showed that Verticillium accelerates senescence and reduces yield. These results suggest that the beneficial effects of mycorrhiza can alleviate the pathogenesis effects of V. dahliae partly, and also there is a competitive interaction between the pathogenic and symbiotic fungi.

Effects of Arbuscular Mycorrhizal Fungi and Ammonium: Nitrate Ratios on Growth and Pungency of Onion Seedlings

ABSTRACT A pot experiment was conducted to study the growth and pungency of Allium cepa L. grown in Perlite as affected by colonization by the arbuscular mycorrhizal (AM) fungi Glomus versiforme and Glomus intraradices BEG141 and by ammonium:nitrate (NH4 +:NO3 −) ratios of 3:1, 1:1, and 1:3 in 4 mM solutions. Plants were harvested when bulb formation commenced. In general, mycorrhizal colonization resulted in increased shoot dry weight, shoot length, sheath diameter, root nitrogen (N) and phosphorus (P) content (except with G. intraradices and a NH4 +:NO3 − ratio of 1:3), shoot N and P concentrations (except with G. versiforme and a NH4 +:NO3= ratio of 3:1) and content. Plants inoculated with G. versiforme had higher growth parameters and N and P content than those with G. intraradices, whereas N and P concentrations showed the opposite trends. Growth parameters and N and P content of non-mycorrhizal plants were highest at a NH4 +:NO3= ratio of 1:3, while those of plants inoculated with G. versiforme or G. intraradices were highest at a ratio of NH4 +:NO3 − 3:1 or 1:1. Neither mycorrhizal colonization nor proportion of inorganic N species significantly affected bulb enzyme-produced pyruvate or total or organic sulfur (S) concentrations in plant shoots. Colonization by AM fungi made a substantial contribution to onion growth and may not have been directly related to bulb pungency at early stages of plant growth. However, the influence of AM fungi on plant N and P metabolism may have implications for onion flavor at later stages of plant growth.

Microtubule organization in root cells of Medicago truncatula during development of an arbuscular mycorrhizal symbiosis with Glomus versiforme.

The colonization of plants by arbuscular mycorrhizal fungi has been shown to induce changes in cytoplasmic organization and morphology of root cells. Because of their role in a variety of cellular functions in plants, it is likely that microtubules are involved either in the signaling events leading to the establishment of the symbiosis or in changes in host cell morphology and cytoplasmic architecture. Recent studies of the arbuscular mycorrhizal symbiosis have shown that root cortical cells reorganize their microtubules upon colonization. These studies, however, have focused primarily on the cells containing hyphal coils or arbuscules and did not include descriptions of microtubule changes in adjacent cells. To probe further into the potential role of the microtubule cytoskeleton in the establishment of arbuscular mycorrhizal symbiosis, we examined the three-dimensional arrangement of microtubules in roots of the model legume Medicago truncatula colonized by the arbuscular mycorrhizal fungus Glomus versiforme by indirect immunofluorescence and confocal microscopy. Our data show extensive remodeling of the microtubule cytoskeleton from the early stages of arbuscule development until arbuscule collapse and senescence. While confirming some of the microtubule patterns shown in other mycorrhizal systems, our results also reveal that cortical cells adjacent to those containing arbuscules or adjacent to intercellular hyphae reorganize their microtubules. This indicates that the cortical cells initiate the modification of their cytoskeleton prior to entry of the fungus and is consistent with signal exchange between the symbionts prior to fungal penetration of the cells.

FACTORS AFFECTING ARBUSCULAR MYCORRHIZAL DEPENDENCY OF WHEAT GENOTYPES WITH DIFFERENT PHOSPHORUS EFFICIENCIES

Three wheat (Triticum aestivum L.) genotypes with high, intermediate and low phosphorus (P) efficiency were grown in a pot experiment with low P supply and adequate P supply either inoculated with the arbuscular mycorrhizal fungus Glomus versiforme or uninoculated. The mycorrhizal dependency of the genotype with relatively high P efficiency was lower than that of the genotypes with lower P efficiencies. Linear correlation analysis revealed that mycorrhizal dependency was primarily controlled by P uptake efficiency. More carbohydrate was translocated to the roots of genotypes with low P efficiency than of those with high P efficiency. In a second pot experiment the same three genotypes were grown in low P soils. Higher hyphal length density arising from carbohydrate translocation led to more P uptake, and this may account for higher mycorrhizal dependency.

Chitin synthase genes in the arbuscular mycorrhizal fungusGlomus versiforme: full sequence of a gene encoding a class IV chitin synthase

Chitin synthase genes of the arbuscular mycorrhizal fungus Glomus versiforme were sought in an investigation of the molecular basis of fungal growth. Three DNA fragments (Gvchs1, Gvchs2 and Gvchs3) corresponding to the conserved regions of distinct chitin synthase (chs) genes were amplified by means of the polymerase chain reaction (PCR) with two sets of degenerate primers. Gvchs1 and Gvchs2 encode two class I chitin synthases, whereas Gvchs3 encodes a class IV chitin synthase. A genomic library was used to obtain the Gvchs3 complete gene (1194 amino acids), which shows a very close similarity to the class IV chitin synthase from Neurospora crassa.

Chitin synthase genes in the arbuscular mycorrhizal fungus Glomus versiforme: full sequence of a gene encoding a class IV chitin synthase

Chitin synthase genes of the arbuscular mycorrhizal fungus Glomus versiforme were sought in an investigation of the molecular basis of fungal growth. Three DNA fragments ( Gvchs1, Gvchs2 and Gvchs3) corresponding to the conserved regions of distinct chitin synthase ( chs) genes were amplified by means of the polymerase chain reaction (PCR) with two sets of degenerate primers. Gvchs1 and Gvchs2 encode two class I chitin synthases, whereas Gvchs3 encodes a class IV chitin synthase. A genomic library was used to obtain the Gvchs3 complete gene (1194 amino acids), which shows a very close similarity to the class IV chitin synthase from Neurospora crassa.

A cDNA from the arbuscular mycorrhizal fungus Glomus versiforme with homology to a cruciform DNA-binding protein from Ustilago maydis

A cDNA clone (Gv1) was isolated from a Medicago truncatula/Glomus versiforme root cDNA library by a differential screening technique. Gv1 represents a full-length G. versiforme mRNA encoding a 99-amino-acid polypeptide. This shares regions of identity with HMP1, a non-histone, cruciform DNA-binding protein from Ustilago maydis. Northern blot analysis indicated that Gv1 transcripts were present in mycorrhizal roots of M. truncatula and M. sativa (alfalfa), but absent in uncolonized roots of both species. A reverse transcription/polymerase chain reaction (RT-PCR) technique detected transcripts in the roots of the M. sativa non-mycorrhizal genotype MN NN-1008 colonized with G. versiforme, as well as in external hyphae collected from the roots of M. sativa colonized with G. versiforme. A genomic copy of Gv1 was detected by PCR in DNA isolated from the roots of M. truncatula colonized with G. versiforme and in DNA isolated from spores of G. versiforme. The PCR product identified in the mycorrhizal DNA preparation was identical in sequence to the cDNA, except for the presence of two introns. A homologue of Gv1 was detected in a second arbuscular mycorrhizal fungus, Glomus intraradices. (Less)

Partial Purification and Characterization of a Lipolytic Enzyme from Spores of the Arbuscular Mycorrhizal Fungus Glomus versiforme

Partial Purification and Characterization of a Lipolytic Enzyme from Spores of the Arbuscular Mycorrhizal Fungus Glomus versiforme

Partial purification and characterization of a lipolytic enzyme from spores of the arbuscular mycorrhizal fungus Glomus versiforme

The lypolytic activity of extracts from G. versiforme spores was detected and measured in in vitro assays using triolein as a substrate. Among the different subcellular fractions assayed, a membrane-rich one showed the greatest lipolytic activity. Like other membrane-bound enzymes, G. versiforme lipase was well extracted in presence of detergent. The time-course of triolein hydrolysis by several lipase preparations was studied. The partial purification of the lipase from the total homogenate revealed increasing enzyme specific activities in the following order: homogenate < sediment at 13 000 g for 30 min < acetone powder < fraction obtained by gel permeation chromatography. The molecular mass of the enzyme was estimated to be 30 kDa as determined by gel filtration column chromatography.

Variations in the lipid composition of alfalfa roots during colonization with the arbuscular mycorrhizal fungus Glomus versiforme

Lipids and their fatty acids were characterized and quantified during the development of the arbuscular mycorrhizal fungus Glomus versiforme in roots of alfalfa (Medicago sativa). A net increase in root total lipids was observed and was proportional to the development of arbuscular mycorrhizal fungus colonization. Triacylglycerols were the main lipid class in colonized roots and appear to have been synthesized by fungi. The increase of palmitoleic acid (characteristic of triacylglycerols from arbuscular mycorrhizal fungus) in roots colonized with G. versiforme reinforced this suggestion. Phosphatidylethanolamine and to a minor extent phosphatidylcholine also increased during the endophyte growth. Variations in the lipid classes of external mycelia isolated from one-, two- and three-mo old colonized roots with G. versiforme were also analyzed. Despite the continuous increase of triacylglycerols and phosphatidylethanolamine observed, the polar lipid class predominated in the external mycelia isolated from one-mo old colonized roots and the neutral lipid class prevailed in the external mycelia obtained from three-mo old mycorrhizal roots. Biosynthesis of triacylglycerols in intra- and extramatrical mycelia as well as an induced synthesis of polar lipids in roots are suggested as the consequence of fungi colonization.

Variations in the Lipid Composition of Alfalfa Roots during Colonization with the Arbuscular Mycorrhizal Fungus Glomus versiforme

Lipids and their fatty acids were characterized and quantified during the development of the arbuscular mycorrhizal fungus Glomus versiforme in roots of alfalfa (Medicago sativa). A net increase in root total lipids was observed and was proportional to the development of arbuscular mycorrhizal fungus colonization. Triacylglycerols were the main lipid class in colonized roots and appear to have been synthesized by fungi. The increase of palmitoleic acid (characteristic of triacylglycerols from arbuscular mycorrhizal fungus) in roots colonized with G. versiforme reinforced this suggestion. Phosphatidylethanolamine and to a minor extent phosphatidylcholine also increased during the endophyte growth. Variations in the lipid classes of external mycelia isolated from one-, two- and three-mo old colonized roots with G. versiforme were also analyzed. Despite the continuous increase of triacylglycerols and phosphatidylethanolamine observed, the polar lipid class predominated in the external mycelia isolated from one-mo old colonized roots and the neutral lipid class prevailed in the external mycelia obtained from three-mo old mycorrhizal roots. Biosynthesis of triacylglycerols in intra- and extramatrical mycelia as well as an induced synthesis of polar lipids in roots are suggested as the consequence of fungi colonization.

In vitro mass-production of the arbuscular mycorrhizal fungus, Glomus versiforme, associated with Ri T-DNA transformed carrot roots

The rate of in vitro spore formation of the arbuscular mycorrhizal fungus Glomus versiforme was followed in Petri dishes, using mycorrhizal root-segment inoculum associated with Ri T-DNA transformed carrot roots. Three phases of sporulation were observed: a lag phase, a period of intensive spore production and a plateau phase. An average of 9500 spores per Petri dish was produced after 5 months of dual culture. The root-organ culture system supported extensive root colonization, with many arbuscules and vesicles being formed. The fungus, both within root-segments and as spores produced, was viable and able to complete its life cycle in vitro. The mycorrhizal root-segments, however, exhibited higher inoculum potential due to the numerous vesicles and extensive intraradical mycelium.

Phosphate transporters from the higher plant Arabidopsis thaliana.

Two cDNAs (AtPT1 and AtPT2) encoding plant phosphate transporters have been isolated from a library prepared with mRNA extracted from phosphate-starved Arabidopsis thaliana roots, The encoded polypeptides are 78% identical to each other and show high degree of amino acid sequence similarity with high-affinity phosphate transporters of Saccharomyces cerevisiae, Neurospora crassa, and the mycorrhizal fungus Glomus versiforme. The AtPT1 and AtPT2 polypeptides are integral membrane proteins predicted to contain 12 membrane-spanning domains separated into two groups of six by a large charged hydrophilic region. Upon expression, both AtPT1 and AtPT2 were able to complement the pho84 mutant phenotype of yeast strain NS219 lacking the high-affinity phosphate transport activity. AtPT1 and AtPT2 are representatives of two distinct, small gene families in A. thaliana. The transcripts of both genes are expressed in roots and are not detectable in leaves. The steady-state level of their mRNAs increases in response to phosphate starvation.

Molecular Responses of Plants to Phosphate Starvation

Phosphate deficiency is wide spread in the nature. The deficiency results in several morphological and biochemical changes in plants. Some of these changes have been shown to involve altered gene expression. We have isolated two full--length cDNAs (AtPT1 and AtPT2), showing significant amino acid sequence similarity with the high-affinity phosphate transporters of yeast, Neurospora and the mycorrhizal fungi Glomus versiforme, from a phosphate-starved Arabidopsis root library. The transcripts of both genes are highly induced under Pi starvation and they are expressed in roots. Using Arabidopsis cDNAs as probes, we have isolated several tomato root cDNA clones representing the two different genes. The expression characteristics of the tomato isoforms of the putative high affinity phosphate transporter genes will be discussed. The northern blots of RNA isolated from phosphate-deficient and phosphate-sufficient roots of tomato indicated that both genes are strongly induced in response to Pi starvation in roots. Furthermore, by the method of differential display of mRNA, we have cloned and characterized a full-length cDNA representing a Pi starvation induced gene (TPSI1) from tomato. The gene is expressed as a specific response to Pi starvation in roots and leaves. The TPSI1 is an intron-less gene represented by a single copy in the tomato genome. The structure, expression, and functional significance of these genes will be discussed. This research has been supported, in part, by USDA grant 94-37100-0834 to KGR.

Spatial patterns of expression of flavonoid/isoflavonoid pathway genes during interactions between roots of Medicago truncatula and the mycorrhizal fungus Glomus versiforme

SummaryA combination of Northern blot analysis and in situ hybridization was used to measure and localize changes in the levels of transcripts encoding five enzymes of phenylpropanoid/flavonoid/isoflavonoid metabolism in Medicago truncatula roots following colonization with the mycorrhizal fungus Glomus versiforme. In colonized roots, elevated levels of phenylalanine ammonia‐lyase (PAL) and chalcone synthase (CHS) transcripts were detected specifically in the cortical cells containing arbuscules. This localization was discrete, and elevated levels of transcripts were not observed in adjacent, non‐colonized cells. In contrast, isoflavone reductase (IFR) transcripts, which were detected at relatively high levels in the cortical cells of non‐colonized roots, were almost undetectable in the colonized cortical cells containing arbuscules and were also lowered in adjacent cells. The expression of chalcone isomerase (CHI) and isoliquiritigenin 2′‐O‐methyltransferase (ChalOMT) was unaffected by colonization, and the tissue‐specific patterns of gene expression were the same as in non‐colonized roots. It is concluded that the establishment of the mycorrhizal interaction results in cell type‐specific differential expression of genes of phenylpropanoid/flavonoid/isoflavonoid biosynthesis, which may be causally related to arbuscule development.

Triacylglycerol consumption during spore germination of vesicular‐arbuscular mycorrhizal fungi

AbstractLipids and fatty acids of spores of the vesicular‐arbuscular mycorrhizal fungusGlomus versiforme were identified and quantitatively determined at different times of germination. Triacylglycerols were, by far, the most abundant lipid (38% on a wet‐weight basis). Phosphatidylethanolamine, together with minor quantities of other phospholipids, was the main polar lipid. Palmitoleic, palmitic and oleic acids were quantitatively the most important fatty acids in total lipids, and even more so in the triacylglycerol fraction. Minor percentages of fatty acids, identified as ω3 and ω6 polyunsaturated, completed the fatty acid spectra. Germination ofG. versiforme spores evokes a continuous decrease of triacylglycerols and an increase of phospholipids. The balance of fatty acids during germination suggests either a degradation or a transference of fatty acids from triacylglycerols to phospholipids.

Rapid methods for quantifying VAM fungal infections in maize roots

Roots of maize (Zea mays cv W64A × W182E) infected by vesicular arbuscular mycorrhizal (VAM) fungi (Glomus versiforme (Karst) Berch or a Glomus species isolated from an alfalfa soil) exhibit a bright yellow pigmentation. The percentage of pigmented roots can be quantified by a rapid visual estimate or by a grid intersect method. Both methods gave similar estimates of VAM infection to those obtained using a grid intersect count on cleared roots stained with chlorazol black E. Thus for experimental or field evaluation where speed and quantity are important, the rapid visual estimate (less than one minute for each washed root system) yields reliable results. The yellow root intersect method takes longer (5–15 minutes per root system) but gives more reproducible results. The yellow root pigmentation is light sensitive However, root systems can be reliably assayed after 1 week when stored at 5°C in the dark or after 1 year if dried.

Occurrence of trehalose in vesicular-arbuscular mycorrhizal fungi and in mycorrhizal roots

Summary The presence of trehalose was investigated in sporocarps of the vesicular-arbuscular mycorrhizal fungus Glomus versiforme and in roots of Tagetes tenuifolia and Glycine max infected by Glomus mosseae . Trehalose was the main soluble carbohydrate in sporocarps; it was present also in mycorrhizal roots, whereas in nonmycorrhizal roots it was absent or detected only in traces. Soybean plants were inoculated with G. mosseae and grown under different conditions of light regimen and phosphate availability. P fertilization and light deprivation reduced root mycorrhizal infection. The trehalose content of mycorrhizal roots increased concurrently with the course of fungal infection, and decreased both upon P fertilization and light deprivation. The content of total soluble carbohydrates, on the contrary, decreased only upon light deprivation.