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International audience; Modern agriculture is currently undergoing rapid changes in the face of the continuing growth of world population and many ensuing environmental challenges. Crop quality is becoming as important as crop yield and can be characterised by several parameters. For fruits and vegetables, quality descriptors can concern production cycle (e.g. conventional or organic farming), organoleptic qualities (e.g. sweet taste, sugar content, acidity) and nutritional qualities (e.g. mineral content, vitamins). For other crops, however, the presence of secondary metabolites such as anthocyanins or certain terpenes in the targeted tissues is of interest as well, especially for their human health properties. All plants are constantly interacting with microorganisms. These microorganisms include arbuscular mycorrhizal fungi as well as certain soil bacteria that provide ecosystem services related to plant growth, nutrition and quality parameters. This review is an update of current research on the single and combined (co-inoculation) use of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria in crop production, with a focus on their positive impacts on crop quality traits (e.g. nutritional value, organoleptic properties). We also highlight the need to dissect mechanisms regulating plant-symbionts and symbiont-symbiont interactions, to develop farming practices and to study a broad range of interactions to optimize the symbiotic potential of root-associated microorganisms.

Arbuscular mycorrhizal (AM) fungi, symbionts of most land plants, increase plant fitness in metal contaminated soils. To further understand the mechanisms of metal tolerance in the AM symbiosis, the expression patterns of the maize Heavy Metal ATPase (HMA) family members and the ionomes of non-mycorrhizal and mycorrhizal plants grown under different Cu supplies were examined. Expression of ZmHMA5a and ZmHMA5b, whose encoded proteins were predicted to be localized at the plasma membrane, was up-regulated by Cu in non-mycorrhizal roots and to a lower extent in mycorrhizal roots. Gene expression of the tonoplast ZmHMA3a and ZmHMA4 isoforms was up-regulated by Cu-toxicity in shoots and roots of mycorrhizal plants. AM mitigates the changes induced by Cu toxicity on the maize ionome, specially at the highest Cu soil concentration. Altogether these data suggest that in Cu-contaminated soils, AM increases expression of the HMA genes putatively encoding proteins involved in Cu detoxification and balances mineral nutrient uptake improving the nutritional status of the maize plants.

Modern agriculture is currently undergoing rapid changes in the face of the continuing growth of world population and many ensuing environmental challenges. Crop quality is becoming as important as crop yield and can be characterised by several parameters. For fruits and vegetables, quality descriptors can concern production cycle (e.g. conventional or organic farming), organoleptic qualities (e.g. sweet taste, sugar content, acidity) and nutritional qualities (e.g. mineral content, vitamins). For other crops, however, the presence of secondary metabolites such as anthocyanins or certain terpenes in the targeted tissues is of interest as well, especially for their human health properties. All plants are constantly interacting with microorganisms. These microorganisms include arbuscular mycorrhizal fungi as well as certain soil bacteria that provide ecosystem services related to plant growth, nutrition and quality parameters. This review is an update of current research on the single and combined (co-inoculation) use of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria in crop production, with a focus on their positive impacts on crop quality traits (e.g. nutritional value, organoleptic properties). We also highlight the need to dissect mechanisms regulating plant-symbionts and symbiont-symbiont interactions, to develop farming practices and to study a broad range of interactions to optimize the symbiotic potential of root-associated microorganisms.

International audience; Arbuscular mycorrhiza, one of the oldest interactions on earth (~ 450 million years old) and a first-class partner for plants to colonize emerged land, is considered one of the most pervasive ecological relationships on the globe. Despite how important and old this interaction is, its discovery was very recent compared to the long story of land plant evolution. The story of the arbuscular mycorrhiza cannot be addressed apart from the history, controversies, and speculations about mycorrhiza in its broad sense. The chronicle of mycorrhizal research is marked by multiple key milestones such as the initial description of a “persistent epiderm and pellicular wall structure” by Hartig; the introduction of the “Symbiotismus” and “Mycorrhiza” concepts by Frank; the description of diverse root-fungal morphologies; the first description of arbuscules by Gallaud; Mosse’s pivotal statement of the beneficial nature of the arbuscular mycorrhizal symbiosis; the impact of molecular tools on the taxonomy of mycorrhizal fungi as well as the development of in vitro root organ cultures for producing axenic arbuscular mycorrhizal fungi (AMF). An appreciation of the story – full of twists and turns – of the arbuscular mycorrhiza, going from the roots of mycorrhiza history, along with the discovery of different mycorrhiza types such as ectomycorrhiza, can improve research to help face our days’ challenge of developing sustainable agriculture that integrates the arbuscular mycorrhiza and its ecosystem services.

International audience; Crop inoculation with Glomus cubense isolate (INCAM-4, DAOM-241198) promotes yield in banana, cassava, forages, and others. Yield improvements range from 20 to 80% depending on crops, nutrient supply, and edaphoclimatic conditions. However, it is difficult to connect yield effects with G. cubense abundance in roots due to the lack of an adequate methodology to trace this taxon in the field. It is necessary to establish an accurate evaluation framework of its contribution to root colonization separated from native arbuscular mycorrhizal fungi (AMF). A taxon-discriminating primer set was designed based on the ITS nrDNA marker and two molecular approaches were optimized and validated (endpoint PCR and quantitative real-time PCR) to trace and quantify the G. cubense isolate in root and soil samples under greenhouse and environmental conditions. The detection limit and specificity assays were performed by both approaches. Different 18 AMF taxa were used for endpoint PCR specificity assay, showing that primers specifically amplified the INCAM-4 isolate yielding a 370 bp-PCR product. In the greenhouse, Urochloa brizantha plants inoculated with three isolates (Rhizophagus irregularis, R. clarus, and G. cubense) and environmental root and soil samples were successfully traced and quantified by qPCR. The AMF root colonization reached 41–70% and the spore number 4–128 per g of soil. This study demonstrates for the first time the feasibility to trace and quantify the G. cubense isolate using a taxon-discriminating ITS marker in roots and soils. The validated approaches reveal their potential to be used for the quality control of other mycorrhizal inoculants and their relative quantification in agroecosystems.

International audience; De manière générale, un couvert végétal se définit par une espèce ou une communauté d’espèces végétales recouvrant le sol de manière permanente ou temporaire. L’agriculteur a la possibilité de semer ces couverts, selon un choix raisonné, ou bien de laisser la végétation spontanée se développer. Il existe 3 types de couverts semés avec des objectifs différents pour l’exploitant : le couvert hivernal, installé pour faire face au phénomène d’érosion du sol important pendant cette période de repos végétatif ; les engrais verts, installés avec l’objectif d’amender naturellement la parcelle, en détruisant et en enfouissant les résidus du couvert qui libèrent ainsi de la matière organique plus ou moins rapidement, qui servira à alimenter la plante au cycle suivant, après des étapes de minéralisation ; les cultures intermédiaires pièges à nitrate (CIPAN), installées au tout début de l’automne pour capter dans le sol les nitrates en excès et des quantités d’eau importantes dans le but de limiter la lixiviation et la contamination des eaux souterraines et de surfaces par les nitrates.Les couverts et leurs intérêts en production végétaleLes espèces végétales les plus couramment utilisées dans ces couverts font essentiellement partie de trois familles présentant chacune différents avantages quant à leur utilisation. Nous retrouvons : les graminées (avoine, seigle, ray grass, brome, fétuque, orge…), avantageuses avec un rapport C/N élevé, produisent une biomasse (figure 1) importante bénéfique lors de la destruction ; les brassicacées (anciennement « crucifères ») (moutarde, navette fourragère, radis chinois, colza fourrager…) servent couramment de « pompe à azote » mais aussi de biofumigateur (figure 1), ce qui peut avoir un impact négatif sur certains champignons bénéfiques du sol (champignons mycorhiziens) si la proportion est trop importante. Elles présentent l’avantage de s’implanter rapidement, empêchant le développement important des adventices (appelées également fréquemment mauvaises herbes) ; les légumineuses (vesce, féverole, trèfle, luzerne…) sont de plus en plus utilisées, seules ou en mélange, pour leur capacité à réaliser une symbiose avec des bactéries du sol, leur permettant ainsi de fixer le diazote atmosphérique. Avec un rapport C/N alors très faible, le relargage de l’azote assimilé et des nutriments se fait très rapidement, et ceux-ci deviennent donc disponibles pour la culture.Les plantes de couvert sont fortement plébiscitées en polyculture pour couvrir les parcelles lorsqu’elles ne sont pas utilisées par une culture d’intérêt. L’utilisation de ces couverts d’interculture s’est développée notamment pour contrer des phénomènes de battance et d’érosion des sols, qualifiés d’anthropogènes car liés à l’exploitation, parfois intensive, des milieux agricoles et à la destruction de la couverture végétale naturelle.

Native arbuscular mycorrhizal fungi (AMF) associated to cassava (Manihot esculenta), a globally important food crop have been shown to enhance its growth, nutrition and productivity. In order to better characterize levels of AMF diversity and identify species relevant to cassava productivity, deeper sequencing depth of cassava field soils is needed. In this paper, we hypothesise that community composition could be linked to specific edaphic factors within contrasted soils. The arbuscular mycorrhizal fungi (AMF) communities of Manihot esculenta rhizosphere soils was investigated by Illumina MiSeq technology. We analyzed the possible correlation between soil characteristics and AMF community composition in cassava field soils within three different agro-ecological zones. Principal Coordinate Analysis (PCoA) and Permutational Multivariate Analysis of Variance were used to test the relative contribution of each agro-ecological zone in explaining the variation in AMF community composition within cassava field soils. Pearson correlations were used to identify the soil properties that significantly explained AMF community compositions within the three zones. The results have shown that despite the fact that the three zones exhibited contrasted soils, AMF community in cassava field soils was dominated by Glomeraceae (Rhizophagus, Glomus, Funneliformis and Septoglomus), with Rhizophagus as the most dominant core genus. Soil type determined the distribution of AMF communities in cassava field soils, and this effect was attributed to soil properties related to organic matter, three micronutrients (available phosphorus, Ca2+, Mg2+), V% and clay. It was shown that high available phosphorus contents (50-100ppm) reduce diversity but did not affect the dominance of the genus Rhizophagus.

Background: Wetlands in Neotropics harbor high fungal diversity, including arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE). This study describes the interaction of plant roots with AMF and DSE in a freshwater wetland belonging to a hotspot of biodiversity. Hypothesis: Differential root colonization between arbuscular mycorrhizal and dark septate endophyte fungi is influenced by plant species and abiotic conditions in a freshwater wetland. Studied species: Plant species colonized by arbuscular mycorrhizal and dark septate endophyte fungi. Methods: Properties of soils and the water column, floristic composition, root colonization by AMF and DSE, and molecular identification of AMF inside roots were studied. Results: Soils were Gleysol and flooded during the rainy season. Most of identified plant species were herbaceous, with Cyperus articulatus and Mimosa pigra as the dominant species. Seven of 8 analyzed plant species exhibited differential co-colonization between AMF and DSE. Repeated sampling for one year under flooding/dry conditions demonstrated that C. articulatus and M. pigra were mainly associated with DSE and AMF, respectively. A positive correlation between dissolved O2 in the water column and fungal colonization was observed in C. articulatus . Glomerales and Archaeosporales were molecularly identified inside roots containing arbuscules of M. pigra . Conclusions: Findings highlight differential coexistence between AMF and DSE in plant roots; fungal colonization was influenced by flooding/dry conditions in a neotropical wetland; the community of AMF inside arbusculated roots of M. pigra includes at least four clades.

International audience; Pesticide contamination of the environment can result from agricultural practices. Persistence of pesticide residues is a threat to the soil biota including plant roots and beneficial microorganisms, which support an important number of soil ecosystem services. Arbuscular mycorrhizal fungi (AMF) are key symbiotic microorganisms contributing to plant nutrition. In the present study, we assessed whether AMF could indicate eventual side effects of pesticides when directly applied to field soils. We evaluated the ecotoxicological impact of a cocktail of three commonly used agricultural pesticides (fenhexamid, folpel, deltamethrin) on the abundance and composition of the AMF community in vineyard (Montagne de Saint-Emilion) and arable (Martincourt) soils subjected to different agricultural practices. The dissipation of applied pesticides was monitored by multiresidual analyses to determine the scenario of exposure of the AMF community. Diversity analysis before application of the pesticide cocktail showed that the AMF communities of vineyard soils, subjected to mechanical weeding or grass cover, and of the arable soil subjected to intensive agriculture, were dominated by Glomerales. Ribotypes specific to each soil and to each agricultural practice in the same soil were found, with the highest abundance and diversity of AMF being observed in the vineyard soil with a grass-cover. The abundance of the global AMF community (Glomeromycota) and of three taxa of AMF (Funneliformis mosseae, Claroideoglomus etunicatum/C. claroideum) was evaluated after pesticide application. The abundance of Glomeromycota decreased in both soils after pesticide application while the abundance of Claroideoglomus and F. mosseae decreased only in the arable soil. These results show that higher doses of pesticide exposure did not affect the global abundance, but altered the composition, of the AMF community. Resilience of the AMF community composition was observed only in the vineyard soil, where F. mosseae was the most tolerant taxon to pesticide exposure.

SPE UB IPM BIOME; Utilizing a European transect of 54 soil samples, comprising of grasslands, arable and forest sites, we analyzed community composition of Arbuscular Mycorrhizal Fungi (AMF, Glomeromycota) using pyrosequencing of the Internal Transcribed Spacer region. We found a significant influence of environmental factors (soil pH and organic carbon or land use) on the community composition, but these factors did not fully explain the overall amount of AMF diversity. Geographical distance of sites also significantly affected community structure, indicating significant dispersal limitations of Glomeromycota at the European scale. Indicator species have been proposed by land use and physicochemical soil parameters. Generalist species were also identified, that were found occurring in a large proportion of the sample sites. By co-occurrence analysis of species pairs we show that, at this spatial scale, closely-related species are more likely to co-occur than distantly-related ones. This suggests that environmental filtering is a more dominant driving force in community assembly than fungal competition.

Prod ? SPE IPM INRA UB; We developed a new protocol to study arbuscular mycorrhizal fungal (AMF) communities in Bordeaux vineyards in a standardized way, in order to compare results obtained over years and between locations. To this end, we first used grapevine root samples instead of soil samples to avoid AMF spores or hyphae interacting with cover plants. We next increased the number of grapevine samples to obtain more representative coverage of AMF communities while decreasing variability intra-vineyard, especially for the larger parcels. In addition, we adapted the DNA extraction protocol dedicated to soil samples to grapevine roots, as a way to increase the yield and the purity of samples. These features, coupled to the choice of the LSU-D2 region as the molecular marker for highthroughput sequencing (MiSeq® technology), further allowed us to assess the AMF populations of Bordeaux vineyards.

Prod ? SPE IPM INRA UB; It is well established that arbuscular mycorrhiza (AM) symbiotic fungi contribute to the scavenging of soil mineral nutrients in exchange for photosynthetically fixed organic carbon in the large majority of land plants. However, plants are naturally interconnected by a common mycorrhizal network (CMN), and the terms of trade as well as developmental interactions between plants connected with a shared fungal partner are still poorly understood. To facilitate the decrypting of such complex relationships, model systems allowing the study of two or more interconnected plants have been developed. Compartmented microcosms were designed to physically separate the roots of studied plants (using meshes) that can in fact only interact through a CMN the integrity of which can be controlled. Here, we report on recently published results relative to the implementation of various specifically designed microcosms to better understand the role in plant-plant relationships of the CMN and that of the AM fungal species involved.

prod ? SPE IPM UB INRA; Arbuscular mycorrhizal symbiosis occurs between obligate biotrophic fungi of the phylum Glomeromycota and most of land plants. The exchange of nutrients between host plants and arbuscular mycorrhizal fungi is presumed to be the main benefit for the two symbiotic partners. In this review article, we outline the current concepts of nutrient exchanges within this symbiosis (mechanisms and regulation). First, we focus on phosphorus and nitrogen transfer from the fungal partner to the host plant and on the reciprocal transfer of carbon compounds, with a highlight on a possible interplay between nitrogen and phosphorus nutrition during arbuscular mycorrhizal symbiosis. We further discuss potential mechanisms of regulation of these nutrient exchanges linked to membrane dynamics. The review finally addresses the common mycorrhizal networks formed by arbuscular mycorrhizal fungi, which inter-connect plants from similar and/or different species. Then the best way to integrate this knowledge and the ensuing potential benefits of arbuscular mycorrhiza in a sustainable agriculture is discussed. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Arbuscular mycorrhizal fungi (AMF) play a major role as biofertilizer for sustainable agriculture. Nevertheless, it is still poorly documented whether inoculated AMF can successfully establish in field soils as exotic AMF and improve plant growth and productivity. Further, the fate of an exogenous inoculum is still poorly understood. Here, we pre-inoculated two cultivars (Tasset and Gola) of the fruit tree Ziziphus mauritiana (jujube) with the exotic AM fungus Rhizophagus irregularis isolate IR27 before transplantation in the field. In two experiments, tracking and quantification of R. irregularis IR27 were assessed in a 13-month-old jujube and an 18-month-old jujube in two fields located in Senegal. Our results showed that the inoculant R. irregularis IR27 was quantitatively traced and discriminated from native R. irregularis isolates in roots by using a qPCR assay targeting a fragment of the RNA polymerase II gene (RPB1), and that the inoculum represented only fractions ranging from 11 to 15% of the Rhizophagus genus in the two plantations 13 and 18 months after transplantation, respectively. This study validates the use of the RPB1 gene as marker for a relative quantification of a mycorrhizal inoculant fungus isolate in the field.

SPE IPM INRA UB; Aim : To improve knowledge of arbuscular fungal communities for a sustainable management in vineyards. Methods and results : In 16 plots across Burgundy under contrasted soil properties and agricultural practices, we assessed arbuscular mycorrhizal fungal (AMF) diversity in vine roots, using pyrosequencing of ribosomal Internal Transcribed Spacers (ITS). AMF sequences could be retrieved from all plots across Burgundy, both in organic and in conventional vineyards with high chemical inputs. Sequences from the survey were almost exclusively affiliated to molecular taxa in the Glomerales, including six “core species” found in all plots, corresponding to 77% of all sequences, suggesting a relatively low species diversity in vine roots. A large part of the molecular taxa had no close similarity to previously-reported sequences. Conclusion : AMF diversity observed in vine roots was relatively low and a significant proportion of molecular taxa shared between the sites. Nevertheless, some differences in the AMF community composition were observed between the plots. Significance and impact of the study: This is the first large-scale study of AMF diversity in French vineyards using high-throughput sequencing, which will contribute to a better understanding of ecology of these fungi in vine roots, thus providing essential knowledge for future applications in sustainable agriculture in vineyards.; Objectif : Améliorer les connaissances sur la communauté des champignons mycorhiziens à arbuscules pour une gestion durable des vignes. Méthodes et résultats : Nous avons évalué la diversité des champignons mycorhiziens à arbuscules (CMA) dans les racines de vignes, en utilisant un pyroséquençage basé sur le marqueur ITS (espaceurs internes transcrits), dans 16 parcelles à travers la Bourgogne ayant des propriétés du sol et des pratiques culturales contrastées. Les résultats montrent que les CMA peuvent être trouvés dans toutes les parcelles de Bourgogne, aussi bien dans les parcelles biologiques que dans les vignes conventionnelles avec de hauts niveaux d’intrants chimiques. Les séquences de l’étude ont été presque exclusivement affiliées à des taxons moléculaires au sein des Glomerales, dont 6 espèces structurantes, c’est à dire des espèces trouvées dans toutes les parcelles, correspondant à 77% des séquences totales, suggérant ainsi une diversité relativement faible d’espèces dans les racines de vigne. Une grande partie des taxons moléculaires n’avaient pas de similitude avec des séquences précédemment décrites. Conclusion : La diversité observée était relativement faible et une proportion significative de taxons moléculaires étaient communs entre les sites. Néanmoins, quelques différences dans la composition de la communauté des CMA ont été observées entre les parcelles. Signification et impact de l’étude : Il s’agit de la première analyse à grande échelle de la diversité des CMA dans les vignobles français en utilisant un séquençage à haut débit, et cela contribue à mieux comprendre l’écologie de ces champignons dans les racines de vigne, fournissant ainsi une connaissance essentielle pour de futures applications pour une gestion durable des vignobles.

The authors of the above-mentioned published article inadvertently omitted Dirk Redecker, Dioumacor Fall and Diaminatou Sanogo from the list of authors. The names and their affiliations presented in this paper.

The soil-borne nepovirus Grapevine fanleaf virus (GFLV), causal agent of grapevine fanleaf degeneration disease, spreads mainly via the nematode vector Xiphinema index. Since the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices can induce local and systemic protection against X. index (Hao et al., 2012), therefore, the objective of the present study was to investigate if AM may represent a means for limiting GFLV infection by reducing nematode vector attack. Three-week-old mycorrhizal or nonmycorrhizal grapevine rootstock SO4 (Vitis berlandieri × V. riparia) plants were inoculated with 10 or 100 viruliferous nematodes per plant under glasshouse conditions. Plants were harvested 35 and 90 days after inoculation with X. index (DAIN), prior to and after the appearance of fanleaf degeneration symptoms, respectively. Both levels of viruliferous X. index inhibited root growth of nonmycorrhizal plants at 90 DAIN, while the presence of arbuscular mycorrhizal colonization significantly decreased gall formation on roots at both time points and reduced nematode reproduction in soil at 90 DAIN. GFLV was not detected by one-step reverse transcription PCR in the roots of any plant at 35 DAIN after viruliferous X. index inoculation. At 90 DAIN with 10 viruliferous nematodes per plant, the virus was present in nonmycorrhizal roots but absent from mycorrhizal grapevine. The virus was detected in both mycorrhizal and nonmycorrhizal plants 90 DAIN. It is suggested that inhibition of X. index proliferation and penetration by AM may protect grapevine against GFLV at a low abundance of the viruliferous nematode in soils and so contribute to virus control under these conditions.

Prod 2017-372 SPE IPM INRA UB; National audience

Arbuscular mycorrhizal symbiosis is an important plant root–fungal partnership/interaction that affects the growth response of crops. We have investigated the molecular diversity of arbuscular mycorrhizal fungi (AMF) colonizing cowpea roots and the associated rhizosphere soil to test the hypothesis that community diversity in rhizosphere soil is similar to that in cowpea (Vigna unguiculata) roots. Cowpea plants were grown in farmers’ fields located in seven agro-ecological zones of Benin, and soil and root samples were collected. The molecular diversity of the AMF in these samples was assessed after amplification of the large ribosomal subunit of DNA extracted from the soil and the root samples. At fruition, the frequency of mycorrhizal infection was unaffected by the agro-ecological zone, but there were significant differences in the intensity of AMF colonization among the zones. Multiple regression analysis showed that the main factor affecting mycorrhizal frequency at flowering was available phosphorus. Phylogenetic analysis revealed 25 operational taxonomic units belonging to two fungal families (Glomeraceae and Gigasporaceae). The diversity of AMF colonizing roots of cowpea in Benin was high and fairly similar to that in the rhizosphere soil but with a prevalence of the Glomeraceae. Despite the absence of strict host specificity in mycorrhizal symbiosis, there was a preferential association between some AMF species and cowpea cultivar IT96D-610.

We have enriched a 47-kDa polypeptide (p47) from Neurospora crassa on the basis of its affinity to calmodulin. The p47 was purified to homogeneity by chromatography on a Mono S cation exchange column and evidence is presented that the polypeptide co-sediments specifically with F-actin. The intracellular distribution of p47 and actin was also examined using indirect double immunofluorescence staining of cells at different stages of development. Our results suggest that by altering the conformation binding site of actin to p47, calmodulin could play a regulatory role in the polarized hyphal growth of N. crassa.

SPE IPM INRA SUPDAT CT EJ; As functional diversity influences the benefits conferred on host plants by arbuscular mycorrhizal fungi (AMF) and large scale commercial inoculation is currently impracticable, strategies are required to manage communities of indigenous AMF associated with different hosts within agricultural cropping systems. In a non-sterilized soil, using 454 pyrosequencing of the LSU-D2 rDNA gene, host plant AMF diversity was assessed following successions of different plant species, grown with or without prior soil disturbance. Diversity present in the roots of two species of the Fabaceae (Ornithopus compressus and Trifolium subterraneum) was compared with those of two species of Poaceae (Lolium rigidum and Triticum aestivum). When spores and colonised root fragments formed were the main propagules source (disturbed soil), the communities of AMF present in the two legumes were clearly different from those of the two members of the Poaceae but were similar for plants within each family, consistent with there being preferential symbioses existing within an AMF population for host classes. Significantly, wheat grown in undisturbed soil immediately after the legume O. compressus acquired a mycorrhizal fungal community closely related to that of the previous host plant, and different to that found when the soil was disturbed or not cropped prior to the growth of the wheat. Parallel effects were seen in the succession from L rigidum to T subterraneum, indicating that these effects are not unique to the legume wheat sequence. These results also suggest that, under no-till cropping, selected cover crops or crops in rotation could help build mycorrhizal communities that function throughout a sequence of several main crops. .

Phytostabilisation can benefit from phytostimulatory rhizobacteria. Forty-three bacterial strains were isolated from the roots of the metallicolous legume Anthyllis vulneraria ssp. carpatica grown in a highly contaminated mine tailing (total Cd, Pb and Zn were up to 1200; 34,000; and 170,000 mg kg(-1), respectively). We aimed at evaluating their phytostimulatory effects on the development of leguminous metallophytes. Strains were screened for fluorescent siderophores and auxin synthesis, inorganic P solubilisation and 1-amino-cyclopropane-1-carboxylate deaminase (ACCd) activity to define a subset of 11 strains that were inoculated on the leguminous metallophytes A. vulneraria and Lotus corniculatus grown in diluted mine spoil (Zn 34,653; Pb 6842; and Cd 242, all in mg kg-1). All strains were affiliated to Pseudomonas spp. (except two), synthetised auxins and siderophores and solubilised P (except three), and seven of them were ACCd positive. The inoculation effects (shoot-root-nodule biomass, chlorophyll content) depended on legume species and bacterial strain genotype. Phytostimulation scores were unrelated to siderophore/auxin synthesis and P solubilisation rates. Inoculations of the strain nos. 17-43 triggered a 1.2-fold significant increase in the chlorophyll content of A. vulneraria. Chlorophyll content and root biomass of L. corniculatus were significantly increased following the inoculations of the strain nos. 17-22 (1.5-1.4-fold, respectively). The strongest positive effects were related to increases in the nodule biomass of L. corniculatus in the presence of three ACCd-positive strains (1.8-fold), one of which was the highest auxin producer. These data suggest to focus on interactions between ACCd activity and auxin synthesis to enhance nodulation of metallicolous legumes.

The cessation of mowing in subalpine grasslands promotes the dominance of Festuca paniculata leading to the reduction in plant diversity. Moreover, it affects positively the abundance of Epichloe sp. inhabiting F. paniculata leaves and negatively the soil density of arbuscular mycorrhizal fungi (AMF). We explored how the cessation of mowing influences root AMF communities in F. paniculata and the neighboring plants, and Epichloe sp alkaloids. Thirteen AMF operational taxonomical units were found. The neighboring plants affected positively the abundances of Aalpin and GLOM_7 whereas the interaction plant/management type influenced significantly Claroide_1 , GLOM_1 and GLOM_7 . The N-formylnorloline, produced by Epichloe sp. increased in unmown grassland. Hence, the cessation of mowing, coinciding with the high abundance of endophyte alkaloid, affected root-associated AMF with differential responses at the abundance level. The N-formylnorloline could be one compound underpinning the dynamic of plant diversity with a resulting structuration of AMF in subalpine grasslands.

SPE IPM INRA SUPDAT; International audience; Many of the non-pathogenic endophytic bacteria that reside in plant roots promote plant growth as well as protection against pathogens attack. However, little is known about their mode of action in wheat. We have previously demonstrated the potential of Paenibacillus sp. strain B2 (PB2) to stimulate plant defense mechanisms via its paenimyxin lipo-polypeptide elicitor. Recently, we isolated the Curtobacterium plantarum strain EDS (EDS) from seeds of almost all wheat cultivars. In the present work, the ability of PB2 and EDS to promote wheat growth and protection against Septoria leaf blotch (SLB) was investigated. Results showed that PB2 is a general root external colonizer and cultivar-dependent endophyte. In the endophytic state and only in co-inoculation, it significantly increased the internal root colonization by EDS, resulting in an increase of root and aerial part fresh weights. qPCR analysis showed that, in the endophytic and nonendophytic states, PB2 conferred >= 59% protection against SLB by inducing systemic resistance which is characterized by the over expression of the pr1, lox, Aos, peroxidase, oxo and gst genes. Paenimyxin conferred 76% local protection characterized by the overexpression of the glu, lox, aos, pal, chs, oxo, and gst genes, and 82% systemic protection by chs. It was concluded that PB2 is potentially very interesting in the biocontrol of SLB and, in a mixture with EDS, in the wheat growth promoting. Genes involved in the flavonoid, salicylic acid, jasmonic acid, reactive oxygen species and basal defense pathways seem to play an important role in the resistance against SLB.

Paenibacillus sp. strain B2, isolated from the mycorrhizosphere of Sorghum bicolor , was previously shown to possess antagonistic activity against fungi and bacteria due to the secretion of the peptide paenimyxin. The effects of strain B2 and paenimyxin were assessed against grapevine pathogens as they potentially represent a non-polluting complement or an alternative biocontrol agent to existing disease management strategies. In this study, the effects of Paenibacillus sp. strain B2 and paenimyxin were analyzed in vitro or in planta on the aerial or root pathogens of grapevine Botrytis cinerea , Plasmopara viticola and Xiphinema index . The bacterium significantly reduced B. cinerea development in vitro , and substantially decreased X. index numbers in soil and gall formation in the root system of grapevine plants. In vitro , paenimyxin inhibited the mycelial growth of B. cinerea , the mobility of the zoospores of P. viticola and X . index activity. Supplying paenimyxin at the time of inoculation of leaf tissue with P. viticola decreased infection sites, compared to application prior to fungal inoculation. Using the P. viticola /grapevine pathosystem, we showed that paenimyxin acts as a biopesticide against the oomycete but does not trigger plant defense. Conversely, Paenibacillus sp. strain B2 can induce the expression of the defense genes CHI (chitinase), PR-3 (proteinase inhibitor) and LOX (lipoxygenase). Altogether, the results obtained highlight the interest of Paenibacillus sp. strain B2 and paenimyxin for the biocontrol of different grapevine diseases.

International audience; The arbuscular mycorrhiza association results from a successful interaction between genomes of the plant and fungal symbiotic partners. In this study, we analyzed the effect of inactivation of late-stage symbiosis-related pea genes on symbiosis-associated fungal and plant molecular responses in order to gain insight into their role in the functional mycorrhizal association. The expression of a subset of ten fungal and eight plant genes, previously reported to be activated during mycorrhiza development, was compared in Glomus intraradices-inoculated wild-type and isogenic genotypes of pea mutated for the PsSym36, PsSym33, and PsSym40 genes where arbuscule formation is inhibited or fungal turnover modulated, respectively. Microdissection was used to corroborate arbuscule-related fungal gene expression. Molecular responses varied between pea genotypes and with fungal development. Most of the fungal genes were downregulated when arbuscule formation was defective, and several were upregulated with more rapid fungal development. Some of the plant genes were also affected by inactivation of the PsSym36, PsSym33, and PsSym40 loci, but in a more time-dependent way during root colonization by G. intraradices. Results indicate a role of the late-stage symbiosis-related pea genes not only in mycorrhiza development but also in the symbiotic functioning of arbuscule-containing cells.

The symbiosis between plant roots and arbuscular mycorrhizal (AM) fungi has been shown to affect both the diversity and productivity of agricultural communities. In this study, we characterized the AM fungal communities of Solanum tuberosum L. (potato) roots and of the bulk soil in two nearby areas of northern Italy, in order to verify if land use practices had selected any particular AM fungus with specificity to potato plants. The AM fungal large-subunit (LSU) rRNA genes were subjected to nested PCR, cloning, sequencing, and phylogenetic analyses. One hundred eighty-three LSU rRNA sequences were analyzed, and eight monophyletic ribotypes, belonging to Glomus groups A and B, were identified. AM fungal communities differed between bulk soil and potato roots, as one AM fungal ribotype, corresponding to Glomus intraradices , was much more frequent in potato roots than in soils (accounting for more than 90% of sequences from potato samples and less than 10% of sequences from soil samples). A semiquantitative heminested PCR with specific primers was used to confirm and quantify the AM fungal abundance observed by cloning. Overall results concerning the biodiversity of AM fungal communities in roots and in bulk soils from the two studied areas suggested that potato roots were preferentially colonized by one AM fungal species, G. intraradices .

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Molecular responses to Cd were studied in roots of three pea genotypes (cv. Frisson, VIR4788, VIR7128) growing in a polluted substrate. Root and shoot fresh biomass was decreased by Cd pollution in all genotypes. Gene expression profiling after one weeks' exposure to Cd revealed that genes encoding stress-related proteins (heat-shock protein, pI206, chitinase, chalcone isomerase), a metallothionein, γ -glutamylcysteine synthetase and glutathione reductase were up-regulated in the pea genotypes. A glutathione synthetase gene was activated only in VIR4788 but a homoglutathione synthetase gene was unaffected by Cd, and concomitantly glutathione/homoglutathione accumulation in plant roots did not change with Cd stress. However, the overall concentration of thiol groups, which indicate the presence of phytochelatins and/or homophytochelatins, increased more than 2-fold.

Applying sewage sludges to agricultural land is a widespread practice because of the sludges’ agronomic value as a source of plant nutrients and organic matter. Nevertheless, sludges often contain micropollutants that can constitute a menace for health and the environment. Arbuscular mycorrhizal fungi are sensitive to sewage sludges that have been spiked, or not, with metallic trace elements (MTE). Here we have investigated if MTE in sewage sludges could be responsible for effects on mycorrhizal development betweenGlomus mosseae andMedicago truncatula. The impact of a dehydrated or composted urban sewage sludge spiked or not with MTE, was tested on spore germination and root colonization byG. mosseae. The sewage sludges depressed both the presymbiotic andin planta stages of development of the mycorrhizal fungus. This negative effect was more related to the metallic pollutant contents of the sludges than to the presence of antagonistic microorganisms or phosphorus.

International audience; Arbuscular mycorrhizal (AM) symbiosis that associates roots of most land plants with soil-borne fungi (Glomeromycota), is characterized by reciprocal nutritional benefits. Fungal colonization of plant roots induces massive changes in cortical cells where the fungus differentiates an arbuscule, which drives proliferation of the plasma membrane. Despite the recognized importance of membrane proteins in sustaining AM symbiosis, the root microsomal proteome elicited upon mycorrhiza still remains to be explored. In this study, we first examined the qualitative composition of the root membrane proteome of Medicago truncatula after microsome enrichment and subsequent in depth analysis by GeLC-MS/MS. The results obtained highlighted the identification of 1226 root membrane protein candidates whose cellular and functional classifications predispose plastids and protein synthesis as prevalent organelle and function, respectively. Changes at the protein abundance level between the membrane proteomes of mycorrhizal and nonmycorrhizal roots were further monitored by spectral counting, which retrieved a total of 96 proteins that displayed a differential accumulation upon AM symbiosis. Besides the canonical markers of the periarbuscular membrane, new candidates supporting the importance of membrane trafficking events during mycorrhiza establishment/functioning were identified, including flotillin-like proteins. The data have been deposited to the ProteomeXchange with identifier PXD000875. Biological significance During arbuscular mycorrhizal symbiosis, one of the most widespread mutualistic associations in nature, the endomembrane system of plant roots is believed to undergo qualitative and quantitative changes in order to sustain both the accommodation process of the AM fungus within cortical cells and the exchange of nutrients between symbionts. Large-scale GeLC-MS/MS proteomic analysis of the membrane fractions from mycorrhizal and nonmycorrhizal roots of M. truncatula coupled to spectral counting retrieved around one hundred proteins that displayed changes in abundance upon mycorrhizal establishment. The symbiosis-related membrane proteins that were identified mostly function in signaling/membrane trafficking and nutrient uptake regulation. Besides extending the coverage of the root membrane proteome of M. truncatula, new candidates involved in the symbiotic program emerged from the current study, which pointed out a dynamic reorganization of microsomal proteins during the accommodation of AM fungi within cortical cells

International audience; Sulfur plays an essential role in plants' growth and development and in their response to various abiotic and biotic stresses despite its leachability and its very low abundance in the only form that plant roots can uptake (sulfate). It is part of amino acids, glutathione (GSH), thiols of proteins and peptides, membrane sulfolipids, cell walls and secondary products, so reduced availability can drastically alter plant growth and development. The nutritional benefits of symbiotic interactions can help the plant in case of S deficiency. In particular the arbuscular mycorrhizal (AM) interaction improves N, P and S plant nutrition, but the mechanisms behind these exchanges are not fully known yet. Although the transcriptional changes in the leguminous model plant Medicago truncatula have been already assessed in several biotic and/or abiotic conditions, S deficiency has not been considered so far. The aim of this work is to get a first overview on S-deficiency responses in the leaf and root tissues of plants interacting with the AM fungus Rhizophagus irregularis. Several hundred genes displayed significantly different transcript accumulation levels. Annotation and GO ID association were used to identify biological processes and molecular functions affected by sulfur starvation. Beside the beneficial effects of AM interaction, plants were greatly affected by the nutritional status, showing various differences in their transcriptomic footprints. Several pathways in which S plays an important role appeared to be differentially affected according to mycorrhizal status, with a generally reduced responsiveness to S deficiency in mycorrhized plants.

Polymorphism of the internal transcribed spacers (ITS) of the ribosomal DNA inScutellospora castanea(Glomales, Zygomycota) and its organization among spores were evaluated. Polymerase chain reaction (PCR) amplification with ITS1/ITS4 primers yielded several fragments of different lengths, even from single spores. Fragments produced from multisporal DNA were cloned and grouped into 6 ITS types by PCR-RFLP and sequence analysis. Five type-specific primers were designed. Spores were then analyzed by PCR and amplification profiles revealed that they were qualitatively different one from another due to the presence or absence of some ITS types. Intrasporal segregation of ITS variant length types was also shown, by PCR experiments, utilizing diluted fractions of nuclear suspensions from single spores. The results demonstrate the mainly multikaryotic condition of the spores ofS. castanea.

For almost 2 centuries it has been disputed whether Tuber aestivum and Tuber uncinatum constitute two different species of truffles. Molecular markers have been applied previously to contribute to resolving this question, coming to different conclusions. In this study, we address this question by analyzing the genetic structure of truffles assigned to either of the two putative species from a geographically broad sampling across Europe. We used an approach involving multigene phylogenies and coalescent analyses of nine regions from five genes. All tests conducted supported the conspecificity of Tuber aestivum and Tuber uncinatum.

Fluctuations in intracellular calcium levels generate signalling events and regulate different cellular processes. Whilst the implication of Ca2+ in plant responses during arbuscular mycorrhiza (AM) interactions is well documented, nothing is known about the regulation or role of this secondary messenger in the fungal symbiont. The spatio-temporal expression pattern of putatively Ca2+-related genes of Glomus intraradices BEG141 encoding five proteins involved in membrane transport and one nuclear protein kinase, was investigated during the AM symbiosis. Expression profiles related to successful colonization of host roots were observed in interactions of G. intraradices with roots of wild-type Medicago truncatula (line J5) compared to the mycorrhiza-defective mutant dmi3/Mtsym13. Symbiotic fungal activity was monitored using stearoyl-CoA desaturase and phosphate transporter genes. Laser microdissection based-mapping of fungal gene expression in mycorrhizal root tissues indicated that the Ca2+-related genes were differentially upregulated in arbuscules and/or in intercellular hyphae. The spatio-temporal variations in gene expression suggest that the encoded proteins may have different functions in fungal development or function during symbiosis development. Full-length cDNA obtained for two genes with interesting expression profiles confirmed a close similarity with an endoplasmic reticulum P-type ATPase and a Vcx1-like vacuolar Ca2+ ion transporter functionally characterized in other fungi and involved in the regulation of cell calcium pools. Possible mechanisms are discussed in which Ca2+-related proteins G. intraradices BEG141 may play a role in mobilization and perception of the intracellular messenger by the AM fungus during symbiotic interactions with host roots. (C) 2012 The British Mycological Society. Published by Elsevier Ltd. All rights reserved.

International audience; The mutualistic symbiosis involving Glomeromycota, a distinctive phylum of early diverging Fungi, is widely hypothesized to have promoted the evolution of land plants during the middle Paleozoic. These arbuscular mycorrhizal fungi (AMF) perform vital functions in the phosphorus cycle that are fundamental to sustainable crop plant productivity. The unusual biological features of AMF have long fascinated evolutionary biologists. The coenocytic hyphae host a community of hundreds of nuclei and reproduce clonally through large multinucleated spores. It has been suggested that the AMF maintain a stable assemblage of several different genomes during the life cycle, but this genomic organization has been questioned. Here we introduce the 153-Mb haploid genome of Rhizophagus irregularis and its repertoire of 28,232 genes. The observed low level of genome polymorphism (0.43 SNP per kb) is not consistent with the occurrence of multiple, highly diverged genomes. The expansion of mating-related genes suggests the existence of cryptic sex-related processes. A comparison of gene categories confirms that R. irregularis is close to the Mucoromycotina. The AMF obligate biotrophy is not explained by genome erosion or any related loss of metabolic complexity in central metabolism, but is marked by a lack of genes encoding plant cell wall-degrading enzymes and of genes involved in toxin and thiamine synthesis. A battery of mycorrhiza-induced secreted proteins is expressed in symbiotic tissues. The present comprehensive repertoire of R. irregularis genes provides a basis for future research on symbiosis-related mechanisms in Glomeromycota.

Les mycorhizes arbusculaires constituent le type d'association le plus général et probablement le plus ancien entre les plantes et les champignons, avec lequel la grande majorité des plantes terrestres ont évolué en développant un système de compatibilité envers les symbiotes fongiques. Les interactions cellulaires conduisant à l'intégration morphofonctionnelle entre les symbiontes, au cours de la formation de la mycorhize, sont complexes. Certains gènes de la plante ainsi que certains événements cellulaires pourraient être communs avec ceux des processus de nodulation, mais il y a déjà des preuves qu'il existe des modifications moléculaires spécifiques aux mycorhizes arbusculaires. Les réactions de défense des plantes qui sont normalement faiblement activées à l'état symbiotique, sont fortement élicitées par les champignons mycorhizogènes arbusculaires chez des hôtes génétiquement modifiés et résistants; cela suggère qu'il y aurait un contrôle de l'expression des mécanismes de défense au cours de la formation d'une symbiose normale. On observe également des modifications induites chez les symbiontes fongiques au cours de la colonisation des tissus hôtes, lesquelles se manifestent par des changements du métabolisme pariétal et de l'expression de protéines. Rien n'est connu de la constitution génétique des champignons mycorhizogènes arbusculaires qui ne peuvent être mis en culture pure. Le clonage récent de l'ADN de ces champignons ouvre la possibilité d'identifier des gènes fonctionnels en vue d'étudier leur régulation et leur rôle dans la symbiose.

We identified de novo sucrose transporter (SUT) genes involved in long-distance transport of sucrose from photosynthetic source leaves towards sink organs in the model leguminous species Medicago truncatula. The iden- tification and functional analysis of sugar transporters provide key information on mechanisms that underlie carbon partitioning in plant-microorganism interactions. In that way, full-length sequences of the M. truncatula SUT (MtSUT) family were retrieved and biochemical characterization of MtSUT members was performed by heterologous expression in yeast. The MtSUT family now comprises six genes which distribute among Dicotyledonous clades. MtSUT1-1 and MtSUT4-1 are key members in regard to their expression profiles in source leaves and sink roots and were characterized as functional H +/sucrose transporters. Physiological and molecular responses to phosphorus supply and inoculation by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied by gene expression and sugar quantification analyses. Sucrose represents the main sugar transport form in M. truncatula and the expression profiles of MtSUT1-1, MtSUT2, and MtSUT4-1 highlight a fine-tuning regulation for beneficial sugar fluxes towards the fungal symbiont. Taken together, these results suggest distinct functions for proteins from the SUT1, SUT2, and SUT4 clades in plant and in bio- trophic interactions.

Cadmium is a serious environmental pollution threats to the planet. Its accumulation in plants affects many cellular functions, resulting in growth and development inhibition, whose mechanisms are not fully understood. However, some fungi forming arbuscular mycorrhizal symbiosis with the majority of plant species have the capacity to buffer the deleterious effect of this heavy metal. In the present work we investigated the capacity of Rhizophagus irregularis (syn. Glomus irregularis) to alleviate cadmium stress in Medicago truncatula. In spite of a reduction in all mycorrhizal parameters, plants colonized for 21 days by R. irregularis and treated by 2 mg kg(-1) cadmium displayed less growth inhibition in comparison to plants grown without cadmium. Cadmium strongly increased the accumulation of some isoflavonoids and their derivates: formononetin, malonylononin, medicarpin 3-O-beta-(6'-malonylglucoside), medicarpin and coumestrol. Interestingly, in plants colonized by R. irregularis we noticed a strong reduction of the cadmium-induced accumulation of root isoflavonoids, a part for medicarpin and coumestrol. Moreover, transcripts of chalcone reductase, a protein that we reported previously as being down-regulated in R. irregularis-colonized M. truncatula roots, revealed a similar expression pattern with a strong increase in response to cadmium and a reduced expression in cadmium-treated mycorrhizal roots

International audience; The ectoparasitic dagger nematode (Xiphinema index), vector of Grapevine fanleaf virus (GFLV), provokes gall formation and can cause severe damage to the root system of grapevines. Mycorrhiza formation by Glomus (syn. Rhizophagus) intraradices BEG141 reduced both gall formation on roots of the grapevine rootstock SO4 (Vitis berlandierixV. riparia) and nematode number in the surrounding soil. Suppressive effects increased with time and were greater when the nematode was post-inoculated rather than co-inoculated with the arbuscular mycorrhizal (AM) fungus. Using a split-root system, decreased X. index development was shown in mycorrhizal and non-mycorrhizal parts of mycorrhizal root systems, indicating that both local and systemic induced bioprotection mechanisms were active against the ectoparasitic nematode. Expression analyses of ESTs (expressed sequence tags) generated in an SSH (subtractive suppressive hybridization) library, representing plant genes up-regulated during mycorrhiza-induced control of X. index, and of described grapevine defence genes showed activation of chitinase 1b, pathogenesis-related 10, glutathione S-transferase, stilbene synthase 1, 5-enolpyruvyl shikimate-3-phosphate synthase, and a heat shock proein 70-interacting protein in association with the observed local and/or systemic induced bioprotection against the nematode. Overall, the data suggest priming of grapevine defence responses by the AM fungus and transmission of a plant-mediated signal to non-mycorrhizal tissues. Grapevine gene responses during AM-induced local and systemic bioprotection against X. index point to biological processes that are related either to direct effects on the nematode or to protection against nematode-imposed stress to maintain root tissue integrity

Chapitre 1; International audience; All fungi forming a mutualistic symbiosis with plant roots called arbuscular mycorrhiza were formerly grouped together in one order, the Glomales, placed in the Zygomycota (Morton 1993). Based on molecular analyses suggestingthat arbuscular mycorrhizal fungi should be separated from other fungal taxa, they were transferred a decade ago to the Glomeromy-cota , a new phylum created specifically for them (Schu¨ ssler et al. 2001). Whilst members of this monophyletic group originated from the same common ancestor as the Ascomycota and Basidiomycota, they have no obvious affinity to other major extant phylogenetic groups in the kingdom Fungi (James et al. 2006) and they probably diverged from the other fungal lineages several hundred million years before plants colonized terrestrial habitats 400–500 million years ago (mya) (Heckman et al. 20 01). Glomeromycotan fungi are complex but extremely successful organisms. They establish a compatible interaction with plants by either avoiding or suppressing plant defence reactions whilst redirecting host metabolic flow to their benefit without being detrimental to their host. The mechanisms by which this bio-trophy is achieved are largely unknown but the Glomeromycota have accompanied land plants through evolution and survived across periods of important environmental change to become ecologically and agriculturally impor-tant symbionts which improve the overall fit-ness of very different plant taxa in terrestrial ecosystems world-wide (Smith and Read 2008 ). Substantial evidence has accumulated about how a rational use of the microsymbiont proper-ties should significantly contribute to decreasing fertilizer and pesticide use in agriculture (Gianinazzi et al. 20 10). Although the Glomeromycota show consid-erable diversity between or within morphologi-cally recognizable species (Rosendahl 2008), they share some singular biological traits which limit experimental approaches that can be exploited to characterize their complexity. One particularity is their reproduction through large asexual spores , each of which is a single cell harbouring several hundreds or thousands of nuclei. The main mechanism for filling a spore with so many nuclei appears to be a massive influx of nuclei from subtending myce-lium into the developing spore (Jany and Pawlowska 2010). No sexual stage is known for these fungi but, although they are assumed to only reproduce asexually, recent transcrip-tome analyses indicate that they do possess genetic information essential for sexual repro-duction and meiosis (Tisserant et al. 2012 ). Absence of a sexual cycle raises questions about how Glomeromycota deal with deleteri-ous mutations usually eliminated through meiosis and how they have adapted to new hosts or habitats during evolution. High poly-ploidy, with multiple gene copies in the same genome, has been speculated as a possible mechanism to buffer against mutational events (Pawlowska and Taylor 2004 ), whilst nuclear exchange through hyphal anastomosis between different individuals of a same species (Casana and Bonfante 1988; Giovannetti et al. 2001 ) provides the possibility for genetic flux and recombination events (Croll et al. 2009 ; Angelard and Sanders 2011). However, basic information concerning ploidy, karyosis, num-ber of chromosomes or whether meiosis does occur in the Glomeromycota is still lacking, and evidence for genetic exchange, recombination or segregation is very limited. Another particularity is that all glomeromy-cotan fungi are obligate symbionts which have so far proved to be incalcitrant to pure culture in the absence of a host root on which they depend as a carbon source. This introduces inherent limitations in the application of standard tech-niques like genetic transformation or mutant generation/characterization, and it greatly hin-ders advances in the knowledge about gene function in these organisms. As previously pointed out (Gianinazzi-Pearson et al. 2001), there is converging evidence that the Glomero-mycota are an unusual group of fungi, and information about their genome structure, com-plexity and function is essential to understand-ing the processes regulating their symbiotic attributes, their reproductive biology and their apparent stability during coevolution in symbi-osis with many different plant taxa. Despite the fact that the biology of glomeromycotan fungi makes them extremely difficult to manipulate experimentally, the advent of powerful molecu-lar techniques has considerably furthered research during the past decade. The present chapter updates on the state of the art on Glo-meromycota genomics within the past decade (Gianinazzi-Pearson et al. 20 01), as well as on progress made through targeted and high-throughput sequencing programmes into an understanding of their basic biology.

A more diverse arbuscular mycorrhiza (AM) fungal community should be more versatile and resilient to variation in environmental conditions over space and time. To evaluate the effect of no-till and conventional tillage systems, AM fungal diversity was assessed as part of a long term field experiment by sequencing of DNA, extracted from soil, that encoded the large ribosomal sub-unit and was obtained by nested-PCR. In comparison with no-till, conventional tillage decreased AM fungal diversity by 40%. Differences between treatments in the frequency of the operational taxonomic units (OTUs) present in soil, confirm that AM fungi are differently vulnerable to soil disturbance.

Although plant biotisation with arbuscular mycorrhizal fungi (AMF) is a promising strategy for improving plant health, a better knowledge regarding the molecular mechanisms involved is required. In this context, we sought to analyse the root proteome of grapevine rootstock Selection Oppenheim 4 (SO4) upon colonisation with two AMF. As expected, AMF colonisation stimulates plant biomass. At the proteome level, changes in protein amounts due to AMF colonisation resulted in 39 differentially accumulated two-dimensional electrophoresis spots in AMF roots relative to control. Out of them, 25 were co-identified in SO4 roots upon colonisation by Glomus irregulare and Glomus mosseae supporting the existence of conserved plant responses to AM symbiosis in a woody perennial species. Among the 18 proteins whose amount was reduced in AMF-colonised roots were proteins involved in glycolysis, protein synthesis and fate, defence and cell rescue, ethylene biosynthesis and purine and pyrimidine salvage degradation. The six co-identified proteins whose amount was increased had functions in energy production, signalling, protein synthesis and fate including proteases. Altogether these data confirmed that a part of the accommodation program of AMF previously characterized in annual plants is maintained within roots of the SO4 rootstock cuttings. Nonetheless, particular responses also occurred involving proteins of carbon metabolism, development and root architecture, defence and cell rescue, anthocyanin biosynthesis and P remobilization, previously reported as induced upon P-starvation. This suggests the occurrence of P reprioritization upon AMF colonization in a woody perennial plant species with agronomical interest.