Azoxystrobin (AZY), a systemic broad-spectrum fungicide, is applied on crops to control soil-borne pathogenic fungi. This study aimed to determine the effects of AZY on non-target plant species and Glomus intraradices Schenck & Smith, an arbuscular mycorrhizal fungus (AMF) associated with plants' roots. We hypothesized that AZY negatively affects AMF viability; and that, if the plants were dependent on this symbiosis, AZY exerts an indirect detrimental effect on plant growth. To test this, three mycotrophic (Phalaris arundinacea L., Solidago canadense L., Geum canadense Jacq.) and one non-mycotrophic (Chenopodium album L.) native plant species were subjected to five AZY doses with or without AMF. Plants were grown for 60 days in a greenhouse, in individual pots, (4 plants X 2 AMF X 5 AZY X 6 replicates), and mesocosms (1 mes. X 2 AMF X 5 AZY X 6 replicates), and harvested 30 days after spraying, and dry mass was taken. Fresh root samples were used for microscopic assessment of AMF colonization. The results from the individual pot experiment show that the effects of AZY on biomass varied across plant species. AZY led to a significant increase in shoot and root mass of P. arundinacea, and a decrease in shoot mass of AMF inoculated G. canadense. The presence of AMF resulted in a significant increase in root and shoot mass of P. arundinacea, and an increase in root mass of S. canadense and shoot mass of C. album. In the mesocosm experiment AZY did not have a significant effect on the measured parameters, although the presence of AMF significantly increased root, shoot, and total dry mass of G. canadense and P. arundinacea. Conversely, AMF significantly decreased shoot and total dry mass of S. canadense. The results suggest that both direct and indirect effects should be taken into account when assessing the impact of pesticides on non-target plant species.

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In Freiland- und Gefäßversuchen sollten Aufnahme der Schwermetalle (SM) und Wuchsverhalten an Kulturpflanzen im Hinblick auf die Wirkung von arbuskulären Mykorrhizapilzen (AM) Glomus intraradices, des Bakterienstammes Pseudomonas fluorescens (RA56) und als Dualinokulation auf Schwermetall belasteten Böden untersucht werden. Als Versuchspflanzen wurden Mais (Zea maize L.) und Weidelgras (Lolium multiflorum L.) und zusätzlich die Sonnenblume (Helianthus annuus L.) in Gefäßversuchen eingesetzt. Die Schwermetallkonzentrationen in den Böden lagen zwischen 0,5 und 56 mg Cd/kg TS, 17 und 650 mg Cu/kg TS und 110 und 1870 mg Zn/kg TS. Der Sonnenblumenertrag konnte im Gefäßversuch auf dem hoch belasteten Boden mit 36 mg Cd/kg TS, 556 mg Cu/kg TS und 1270 mg Zn/kg TS durch den AM-Pilz um 220 % und in der Dualinokulation um 348 % signifikant zur Kontrolle gesteigert werden. Gleichzeitig erhöhte die AM die Cd-Aufnahme um 29 % und die Dualinokulation um 66 %. Trotz der hohen Cd-Konzentrationen wiesen die Pflanzen mit Pilzbehandlungen keine Schäden auf. Der Maisertrag wurde durch AM und Bakterien im Feldversuch und als Dualinokulation in den ersten beiden Versuchsjahren bis zu 47 % gefördert. Im dritten Versuchsjahr kam es zu einer Ausbreitung der Mykorrhiza auf der gesamten Fläche, so dass eine Wuchsförderung auch auf den Kontrollparzellen statt fand. Durch die Variabilität der Cd -Gesamtgehalte auf der Versuchsfläche war der Vergleich der Aufnahmeraten zwischen den Varianten nur über den Cd-Transferfaktor möglich. In den oberirdischen Pflanzenteilen des Maises zeichneten deutlich eine Abnahme und in die Wurzeln eine Zunahme des Cd-Transfers ab. Gleichzeitig wurden die Mykorrhizainfektionen an den Maiswurzeln erhöht. Durch die Anwendung der Mykorrhiza in Kombination mit den Pseudomonaden können im Mais über mehrere Anbaujahre das Cd in das Erntegut reduziert werden mit gleichzeitiger Ertragserhöhung. / Influence of Mycorrhiza fungi and associate bacteria on the availability of nutrients and heavy metal in culture plants on heavy metal soils The heavy metal uptake and the influence on plant growing in culture plants is analysed in this study. Field- and pot experiments were done. An emphasis of this study was focused on the effect of the arbuscular Mycorrhiza (AM) fungi Glomus intraradices, the bacteria Pseudomonas fluorescens (RA56) and as dual inoculation. Maize (Zea maize L.) and Italien rye (Lolium multiflorum L.) were used and in addition sunflowers (Helianthus annuus L.) in the pot experiments. The concentrations of heavy metals in the soil were measured between 0.5 and 56 mg Cd/kg dry weight (d.w.), 17 and 650 mg Cu/kg d.w. and 110 and 1870 mg Zn/kg d.w. The yield of sunflowers was increased significantly up to 220% with AM fungi in the pot experiments. Cd-absortion increased by 29% in the soil with 36 mg Cd/kg d.w., 556 mg Cu/kg d.w. and 1270 mg Zn/kg d.w. in those pot experiments. With AM and Pseudomonades the yield was increased significantly up to 348% compared to the control group, the Cd-absortion increased by 66%. In spite of high Cd-concentrations, the plants showed no damages. The yield of maize was increased up to 47% due to AM fungi and Pseudomonades in singular and dual inoculation in the field experiments during the first and second year. In the third year, the AM fungi were spread over the whole area and no differences of yield were found. Because of the heterogeneous concentrations of Cd in the field area the comparison of Cd assimilation was allowed only by analysis of the transfer factor in the variants. Within the experimental years, the AM infection rate and the Cd-transfer was increased in the maize roots. On the other hand, the Cd translocation rate was decreased in the shoots. The reduction of Cd rate in monocotyledonous plants and an increase of yield are estimated for long term application of the AM fungi with Pseudomonades.

L’association mycorhizienne à arbuscules (AM) est le résultat d’une interaction compatible entre les génomes des deux partenaires symbiotiques. Dans ce contexte, le but de mes recherches a été de mieux caractériser le rôle des gènes de pois liés aux stades tardifs de la symbiose, PsSym36, PsSym33 and PsSym40, dans le fonctionnement de la symbiose MA (i) en étudiant l’effet des mutations de ces trois gènes sur l’expression des gènes de la plante et du champignon, et (ii) en créant les conditions pour positionner deux de ces gènes, PsSym36 and PsSym40, sur la carte génétique afin d’envisager leur clonage futur. L’expression d’un groupe de dix gènes fongiques et de huit gènes de plante, déjà décrits pour être activés durant le développement de la mycorhize, a été comparée dans les racines de pois inoculées avec G. intraradices chez les plantes de génotypes sauvages, ou les mutants Pssym36, Pssym33 et Pssym40. L’expression de la plupart des gènes fongiques a été inhibée dans les racines du mutant Pssym36 où la formation des arbuscules est avortée, tandis que l’expression de plusieurs d’entre eux a été activée lorsqu’il existe un développement plus rapide du champignon dans les racines du mutant Pssym40. Des microdisséquats obtenus à partir de racines mycorhizées du mutant PsSym40 confirment l’expression préférentielle de trois gènes de G. intraradices (SOD, DESAT et PEPISOM) dans les cellules contenant les arbuscules. L’inactivation du gène PsSym36 provoque également une inhibition des gènes de plante alors que la mutation des gènes PsSym33 and PsSym40 affecte l’expression des gènes de plante plutôt de façon temporelle. Les résultats indiquent ainsi une implication des gènes SYM de pois dans la modulation des interactions moléculaires entre la plante et le champignon impliquées au niveau de la signalisation, des échanges nutritifs ou de la régulation des réponses au stress durant la formation et/ou le fonctionnement de la symbiose AM. Les conditions pour la localisation des gènes PsSym36 and PsSym40 sur la carte génétique du pois ont été développées pour leur clonage basé sur la cartographie. En utilisant les marqueurs moléculaires obtenus, il a été possible de conclure que la localisation du gène PsSym40 réside vraisemblablement à l’extérieur des groupes de liaison I, II, III ou V de la carte génétique du pois. / The arbuscular mycorrhizal (AM) association results from a successful interaction between the genomes of the two symbiotic partners. In this context, the aim of my research was to better characterize the role of the late stage symbiosis-related pea genes PsSym36, PsSym33 and PsSym40 in the functional AM (i) by investigating the effect of mutations in the three genes on fungal and plant gene responses and (ii) by creating conditions for the localization of two of the genes, PsSym36 and PsSym40, on the pea genetic map for future map-based cloning. 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 roots of wild type and Pssym36, Pssym33 and Pssym40 mutant pea plants. Most of the fungal genes were down-regulated in roots of the Pssym36 mutant where arbuscule formation is defective, and several were upregulated with more rapid fungal development in roots of the Pssym40 mutant. Microdissection of mycorrhizal PsSym40 roots corroborated preferential expression of the three G. intraradices genes SOD, DESAT and PEPISOM in arbuscule-containing cells. Inactivation of PsSym36 also resulted in down regulation of plant genes whilst mutation of the PsSym33 and PsSym40 genes affected plant gene responses in a more time-dependent way. Results thus indicate an implication of the investigated pea SYM genes in the modulation of plant and fungal molecular interactions linked to signaling, nutrient exchange or stress response regulation during AM symbiosis formation and functioning. Conditions for localization of the PsSym36 and PsSym40 genes on the pea genetic map were developed for their future map-based cloning. Based on the molecular markers obtained, it was possible to conclude that localization of the PsSym40 gene most likely resides outside the linkage groups I, II, III or V of the genetic map of pea. / Формирование арбускулярной микоризы (АМ) является результатом успешного взаимодействия между геномами двух симбиотических партнёров. Целью моего исследования являлось изучение роли поздних симбиотических генов гороха PsSym36, PsSym33 и PsSym40 в формировании функционального АМ симбиоза. Для этого было проведено исследование эффекта мутаций в генах PsSym36, PsSym33 и PsSym40 на экспрессию грибных и растительных генов, предположительно (по литературным данным) вовлечённых в процессы формирования АМ, а так же проведена работа по локализации генов PsSym36 и PsSym40 на генетической карте гороха для последующего более точного картирования и позиционного клонирования данных генов. Экспрессия десяти грибных и восьми растительных генов была определена в корнях растений дикого типа и PsSym36, PsSym33 и PsSym40 мутантов, инокулированных G. intraradices. В корнях PsSym36 мутанта, имеющего дефект развития арбускул, большая часть грибных генов была супрессирована, в то время как в корнях PsSym40 мутанта, для которого характерна более быстрая по сравнению с диким типом микоризация, был отмечен более высокий уровень экспрессии грибных генов. Использование метода микродиссекций позволило выделить клетки, содержащие арбускулы, из микоризованных корней мутанта PsSym40 и подтвердить, что гены G. intraradices SOD, DESAT и PEPISOM преимущественно экспрессируются в клетках, содержащих арбускулы. Мутация в гене PsSym36 также привела к подавлению экспрессии большинства вовлечённых в анализ растительных генов, тогда как мутации в генах PsSym33 и PsSym40 оказали влияние на ксперессию растительных генов в меньшей степени. Полученные результаты свидетельствуют о роли исследуемых SYM генов гороха в контролировании растительно-грибных молекулярных взаимодействий, связанных с сигналингом, обменом питательными веществами и стрессовыми реакциями в процессе формирования и функционирования АМ симбиоза. Проведённое генетическое картирование не привело к локализации генов PsSym36 и PsSym40 на генетической карте гороха. Однако разработка и использование молекулярных маркеров для картирования позволили исключить локализацию гена PsSym40 в I, II, III и V группах сцепления с высокой долей вероятности.

RESUME : Le Sud-Est du Niger est soumis au phénomène dérosion éolienne. Dans la zone de Gouré, les cuvettes oasiennes, principales sources de productions agricoles et de revenus, sont menacées de disparition à cause de lensablement. Des opérations de fixation de dunes sont entreprises pour sauver ce capital productif. Lévaluation de la technique de fixation mécanique des dunes utilisée dans la zone a montré que celle-ci est efficace dans la restauration écologique du milieu. Trois années après la mise en place des palissades anti-érosives, à base des branchages de Leptadenia pyrotechnica, une végétation spontanée, comprenant 58 espèces (20 familles), dont 17 pérennes, sétait installée à lintérieur du clayonnage, soit 42 espèces de plus que dans les zones non traitées. Au fil des ans, la composition floristique sest progressivement stabilisée, témoignant ainsi dune réduction notable des perturbations du milieu engendrées par laction érosive des vents. Dans une expérimentation de fixation biologique de dunes, sept espèces ligneuses, dont cinq autochtones (Acacia senegal, A. tortilis, A. nilotica, Bauhinia rufescens, Balanites aegyptiaca), et deux allochtones (Prosopis juliflora et P. chilensis) ont été testées. En pépinière, les espèces ont subi un stress hydrique par interruption darrosage durant six jours. Les taux dhydratation foliaire ont été déterminés, afin dévaluer leur capacité respective à limiter les pertes deau par transpiration. Dans un essai de terrain, les espèces ont été plantées sur un cordon dunaire, préfixé mécaniquement, en vue de tester leur aptitude à la stabilisation des dunes. Les taux de survie sur trois années ont été calculés et la croissance en hauteur mesurée. Les résultats en pépinière ont montré, quaprès six jours de stress hydrique, Acacia senegal, A. tortilis, Prosopis chilensis et A. nilotica sont les quatre espèces limitant le mieux les pertes en eau. Les résultats sur site ont montré que la meilleure combinaison en matière de fixation de dunes dans cette zone serait dassocier lespèce de Prosopis chilensis (fort taux de survie et croissance rapide) avec A. tortilis et/ou A. nilotica (survie et croissance relativement appréciables et intérêt économique plus important). Dans loptique dun essai dinoculation mycorhizienne, des échantillons de sols de Gouré ont été récoltés sous dix espèces ligneuses locales et exotiques, avec lobjectif didentifier les différents types de champignons mycorhiziens à arbuscules (CMA) et de produire un inoculum indigène par le biais de trois plantes-pièges locales ; le mil, le sorgho et le niébé. Les résultats ont mis en évidence la présence de deux familles de Glomales dans les sols du département de Gouré, Glomaceae (appartenant au genre Glomus) et Gigasporaceae. Avec plus de 56 % des spores, le genre Glomus est le plus abondant des Glomales identifiées et aussi le plus viable (55,80 % des spores vivantes). La croissance en hauteur des parties aériennes du sorgho et du niébé a été significativement stimulée par linoculation. Les trois cultures sont équivalentes dans le piégeage des spores. Un inoculum mycorhizien composite de souches indigènes a été produit à partir de cette culture sporale. Lefficacité de la mycorhization naturelle a été comparée à celles des apports de ce complexe mycorhizien indigène et du Glomus intraradices. Un substrat de culture naturel, non stérilisé, a été inoculé par le complexe mycorhizien de souches indigènes ou par du Glomus intraradices. Les effets de linoculation ont été observés sur cinq espèces ligneuses, dont trois Acacias (A. nilotica, A. tortilis, A. senegal), Bauhinia rufescens et Prosopis chilensis, en pépinière et en sol dunaire. En pépinière, les espèces ont subi un stress hydrique par interruption darrosage durant six jours. Les taux dhydratation foliaire ont été calculés, afin dévaluer les effets de la mycorhization sur la limitation des pertes deau par transpiration. Les différents taux de mycorhization ont été déterminés, ainsi que la croissance des plants et la production de la biomasse totale. Dans un essai de terrain, les espèces inoculées et non inoculées ont été plantées sur un cordon dunaire, préfixé mécaniquement, en vue dévaluer les effets des différents apports mycorhiziens au champ sur la croissance en hauteur des plants. Les résultats en pépinière ont montré que (i) le sol de pépinière non stérilisé contient des CMA (champignon mycorhizien à arbuscules) endogènes aussi infectifs que les souches contrôlées ; (ii) lapport du Glomus intraradices est efficace dans la stimulation de la production de biomasse totale et (iii) la mycorhization naturelle est quasi aussi efficace que les deux apports mycorhiziens dans la stimulation de la croissance en hauteur et dans la limitation de la perte deau des espèces par transpiration. Les résultats sur site confirment lefficacité comparable de la mycorhization naturelle et de celle des apports mycorhiziens. Bien que leffet du G. intraradices apparaisse être bénéfique en certains points chez quelques espèces, les effets observés ne justifient pas doffice de le préférer à linoculum composite de souches indigènes, ni à la mycorhization naturelle dans cette zone. -------------------------------------------------------------------------------- SUMMARY: The Southeastern of Niger Republic is subjected to the phenomenon of wind erosion. In Gouré, the oasis basins, which are the main source of agricultural productions and incomes, are threatened to disappear because of the sand silting up. Operations of sand dunes fixation are taken to save this productive capital. Assessment of the mechanical sand dunes fixation technique, used in this area, showed that this technique is effective in the ecological restoration of the environment. Three years after the implementation of the anti erosive fences, made of Leptadenia pyrotechnica branches, spontaneous floral vegetation, including 58 species (20 families) of which 17 perennials, had settled down inside the fences, owing 42 species more than in the untreated areas. Over the years, the floral composition gradually stabilized proving then a considerable reduction of the environmental disturbances caused by the erosive winds action. In a biological sand dunes fixation experiment, seven woody species, of which five natives (Acacia senegal, A. tortilis, A. nilotica, Bauhinia rufescens and Balanites aegyptiaca) and two exotic (Prosopis juliflora and P. chilensis) have been tested in that zone of the Southeastern of Niger Republic. In nursery, species underwent a water stress by interrupting the watering during six days. Foliar hydration has been determined in order to evaluate their capacity to limit water loss. In a field experiment, species have been planted on a mechanically prefixed sand dune cord in order to test their ability in sand dunes stabilization. Survival rates during the first three years have been calculated and height growth was measured. In nursery, results showed that, after six days of water stress, Acacia senegal, A. tortilis, P. chilensis and A. nilotica are the four species limiting the best the losses in water. Results on site showed that the best combination in sand dunes fixation, in this zone, would be the association of Prosopis chilensis specie (high survival rate and fast growth) with A. tortilis and/or A. nilotica (survival and growth relatively substantial and more important economic interest). In the optics of a further mycorrhizal inoculation essay, soil samples from Gouré department were collected beneath ten mature native and exotic tree species in order to identify the types of associated arbuscular mycorrhizal (AM) fungi and to produce an indigenous inoculum by growing three local trap cultures including millet, sorghum and cowpea. The results highlighted the presence of two families of Glomales in the soils including Glomaceae (belonging to the genus Glomus) and Gigasporaceae. With more than 56 % of spores, the genus Glomus is the most abundant of the identified Glomales and the most viable (55, 80 % of the live spores). The length growth of sorghum and cowpea plants was significantly stimulated by inoculation. The three trap cultures species are equivalent in the spores trapping. An indigenous mycorrhizal complex was produced from this spore culture. Effects of the natural mycorhization were compared with those of the addition of this indigenous mycorrhizal complex and Glomus intraradices. A natural unsterile culture substrate was inoculated with the indigenous inoculum or with G. Intraradices. Inoculation effects were assessed on five woody species, among which three Acacias species (A. nilotica, A. tortilis, A. senegal), Bauhinia rufescens and Prosopis chilensis, in a tree nursery and on a sand dune of Gouré. In the nursery, species underwent a water stress by interrupting the watering during six days. Foliar hydration has been determined in order to evaluate the respective effects of the mycorrhizal inoculation on the water loss limitation. Mycorrhizal root colonization has been determined as well as plant height and total biomass. In a field experiment, inoculated and non inoculated species have been planted on a mechanically prefixed sand dune portion in order to evaluate the effects of mycorrhizal inoculations on growth in the field. Results in nursery showed that (i) the non sterile soil would contain some endogenous AMF (arbuscular mycorrhizal fungi) as infectious as those in soils with mycorrhizal additions; (ii) addition of Glomus intraradices would be efficient to stimulate total biomass and (iii) natural mycorhization would be as efficient as both mycorrhizal addition in growth stimulation and water loss limitation by transpiration. Results on site confirm the comparable effectiveness of the natural mycorhization and mycorrhizal additions. Although the addition of G. intraradices appears to be slightly superior by some aspects on some species, the observed effects do not justify preferring it, when compared to indigenous composite inoculum or to natural mycorhization in this zone.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Pas de résumé en français / In plants, long distance transport of sugars from photosynthetic source leaves to sink organs comprises different crucial steps depending on the species and organ types. Sucrose, the main carbohydrate for long distance transport is synthesized in the mesophyll and then loaded into the phloem. After long distance transport through the phloem vessels, sucrose is finally unloaded towards sink organs. Alternatively, sugar can also be transferred to non‐plant sinks and plant colonization by heterotrophic organisms increases the sink strength and creates an additional sugar demand for the host plant. These sugar fluxes are coordinated by transport systems. Main sugar transporters in plants comprise sucrose (SUTs) and monosaccharide (MSTs) transporters which constitute key components for carbon partitioning at the whole plant level and in interactions with fungi. Although complete SUTs and MSTs gene families have been identified from the reference Dicot Arabidopsis thaliana and Monocot rice (Oriza sativa), sugar transporter families of the leguminous plant Medicago truncatula, which represents a widely used model for studying plant-fungal interactions in arbuscular mycorrhiza (AM), have not yet been investigated.With the recent completion of the M. truncatula genome sequencing as well as the release of transcriptomic databases, monosaccharide and sucrose transporter families of M. truncatula were identified and now comprise 62 MtMSTs and 6 MtSUTs. I focused on the study of the newly identified MtSUTs at a full family scale; phylogenetic analyses showed that the 6 members of the MtSUT family distributed in all three Dicotyledonous SUT clades; they were named upon phylogenetic grouping into particular clades: MtSUT1-1, MtSUT1-2, MtSUT1-3, MtSUT2, MtSUT4-1 and MtSUT4-2. Functional analyses by yeast complementation and expression profiles obtained by quantitative RT-PCR revealed that MtSUT1-1 and MtSUT4-1 are H+/sucrose symporters and represent key members of the MtSUT family. Conservation of transport capacity between orthologous leguminous proteins, expression profiles and subcellular localization compared to previously characterized plant SUTs indicate that MtSUT1-1 is the main protein involved in phloem loading in source leaves whilst MtSUT4-1 mediates vacuolar sucrose export for remobilization of intracellular reserve.The AM symbiosis between plants and fungi from the phylum Glomeromycota is characterized by trophic exchanges between the two partners. The fungus supplies the autotrophic host with nutrients and thereby promotes plant growth. In return, the host plant provides photosynthate (sugars) to the heterotrophic symbiont. Here, sugar fluxes from plant source leaves towards colonized sink roots in the association between the model leguminous plant M. truncatula and the arbuscular mycorrhizal fungus (AMF) Glomus intraradices were investigated. Sugar transporter candidates from both the plant and fungal partners presenting differential expression profiles using available transcriptomic tools were pinpointed. Gene expression profiles of MtSUTs and sugar quantification analyses upon high and low phosphorus nutrient supply and inoculation by the AMF suggest a mycorrhiza-driven stronger sink in AM roots with a fine-tuning regulation of MtSUT gene expression. Conserved regulation patterns were observed for orthologous SUTs in response to colonization by glomeromycotan fungi.In parallel, a non-targeted strategy consisting in the development of a M. truncatula - G. intraradices expression library suitable for yeast functional complementation and screening of symbiotic marker genes, similar to the approach that led to the identification of the first glomeromycotan hexose transporter (GpMST1), has been developed in this study. [...]

The arbuscular mycorrhizal (AM) association results from a successful interaction between the genomes of the two symbiotic partners. In this context, the aim of my research was to better characterize the role of the late stage symbiosis-related pea genes PsSym36, PsSym33 and PsSym40 in the functional AM (i) by investigating the effect of mutations in the three genes on fungal and plant gene responses and (ii) by creating conditions for the localization of two of the genes, PsSym36 and PsSym40, on the pea genetic map for future map-based cloning. 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 roots of wild type and Pssym36, Pssym33 and Pssym40 mutant pea plants. Most of the fungal genes were down-regulated in roots of the Pssym36 mutant where arbuscule formation is defective, and several were upregulated with more rapid fungal development in roots of the Pssym40 mutant. Microdissection of mycorrhizal PsSym40 roots corroborated preferential expression of the three G. intraradices genes SOD, DESAT and PEPISOM in arbuscule-containing cells. Inactivation of PsSym36 also resulted in down regulation of plant genes whilst mutation of the PsSym33 and PsSym40 genes affected plant gene responses in a more time-dependent way. Results thus indicate an implication of the investigated pea SYM genes in the modulation of plant and fungal molecular interactions linked to signaling, nutrient exchange or stress response regulation during AM symbiosis formation and functioning. Conditions for localization of the PsSym36 and PsSym40 genes on the pea genetic map were developed for their future map-based cloning. Based on the molecular markers obtained, it was possible to conclude that localization of the PsSym40 gene most likely resides outside the linkage groups I, II, III or V of the genetic map of pea.