Os fungos micorrízicos arbusculares (FMA) têm papel fundamental na absorção de nutrientes, sobrevivência vegetal e na estruturação dos solos. Recentemente uma série de pesquisadores verificou que plantas associadas com FMA também podem se associar com os fungos de micélio escuro (DSE do inglês, dark septate endophytes). Embora de estudo recente, já se observou que os endófitos de micélio escuro igualmente podem promover o crescimento de plantas em diversos ambientes. O objetivo desse trabalho é realizar um levantamento de espécies de FMA e DSE em áreas de Mata Atlântica em um gradiente altitudinal, podendo advir respostas de relevância ecológica maior, como a influência da planta hospedeira, dos parâmetros do solo, da sazonalidade e da altitude sobre a ocorrência e diversidade desses fungos. Espera-se também esclarecer melhor a lacuna existente no conhecimento dos benefícios dos DSE para as plantas e dar o primeiro passo para a compreenção da interação dos FMA com os DSE. Avaliaram-se os atributos químicos, físicos e microbiológicos do solo e, entre estes, a ocorrência e diversidade dos FMA e DSE na raiz e solo rizosférico de diferentes espécies arbóreas da Mata Atlântica do Parque Estadual da Serra do Mar, Estado de São Paulo, Brasil, em um gradiente altitudinal: 80m, 600m e 1000m. As coletas de solo e raízes foram realizadas em quatro estações. Os dados foram submetidos à análise de variância ANOVA, teste LSD, análise canônica discriminante (ACD) e análise de redundância (RDA). Uma vez que muitas espécies de DSE são conhecidas por serem patogênicas sobre certas plantas, os isolados de DSE foram avaliados quanto à sua eventual patogenicidade. Os isolados não patogênicos foram selecionados para um bio-teste, sozinhos ou em combinação com um FMA em plantas de arroz. Foram identificadas no solo rizosférico 58 espécies de FMA e os gêneros Acaulospora e Glomus foram dominantes, enquanto que nas raízes, apenas 14 grupos de FMA foram encontrados e todos apresentaram elevada similaridade com a família Glomeraceae. Foram encontrados 251 isolados de DSE que se agruparam em 35 UTO. A maioria dos isolados de DSE foram patogênicos para as plantas de arroz. A época de amostragem teve efeito sobre a colonização radicular e diversidade dos FMA. A altitude foi importante em selecionar espécies de FMA e também agiu sobre o número de esporos e colonização por DSE e FMA. A maioria dos FMA e DSE ocorreu de forma generalizada nas diferentes espécies hospedeiras, apesar de existirem algumas espécies fúngicas com preferências para certas árvores. Os atributos do solo tiveram forte influência sobre a colonização pelos FMA, enquanto que para os DSE as diferenças na colonização foram pouco infuenciadas pelos parâmetros do solo. No entanto, as propriedades do solo foram responsáveis por dirigir a ocorrência de certas espécies de FMA e DSE. A interação entre FMA e DSE e os seus benefícios para as plantas hospedeiras ainda necessita de maiores estudos principalmente com relação a compreenção das condições fornecidas em experimentos que favoreçam ambas as associações. / Arbuscular mycorrhizal fungi (AMF) play a fundamental role in the absorption of nutrients, plant survival and soil structure. Recently a number of researchers found that plants associated with AMF may also be associated with dark mycelium fungi. In a recent study, it was observed that the dark septate endophytes (DSE), usually Ascomycetes, can promote the growth of plants in different environments. The aim of this study was to survey the diversity of AMF and DSE in Atlantic Forest areas in altitudinal gradients, which result in responses of greater ecological relevance, as the influence of the host plant, soil attributes, seasonality and altitude on occurrence and diversity of these fungi. We also expect to clarify the gap in the knowledge of the benefits of DSE for plants and take the first step towards the comprehension of the interaction of AMF and DSE. We evaluated the chemical, physical and microbiological attributes, and among these, the occurrence and diversity of AMF and DSE in the root and rhizospheric soil of different tree species of the Atlantic Forest of Serra do Mar State Park, State of Sao Paulo, Brazil, along an altitudinal gradient: 80m, 600m and 1000m. Samplings of the soil and roots were performed in four seasons. The data were submitted to ANOVA, LSD test, canonical discriminant analysis (CDA) and redundancy discriminant analysis (RDA). Since many species of DSE are known to be pathogenic on certain plants, DSE fungal isolates were evaluated for their eventual pathogenic activity. The isolates non-pathogenic were used in a bio-test to either alone or in combination with the AMF in rice plants. In the rhizosphere 58 AMF species were identified. The genera Acaulospora and Glomus were predominant. However, in the roots, only 14 AMF sequences were found and all had high similarity to the family Glomeraceae. In an analysis of the DNA ITS sequences of the 251 DSE isolates we found that they clustered into 35 UTOs. Most DSE found were considered pathogenic for rice. The season had no effect on root colonization and AMF diversity. Altitude was important in selecting AMF species and also acted on the number of spores and colonization by AMF and DSE. Most of the AMF and DSE were generalists, without a specificity for host plants, although there are some fungal species with preferences for certain trees. The soil properties had a strong influence on colonization by AMF while, for the DSE, differences in colonization do not seem to be related to soil attributes. However, soil attributes were responsible for directing the diversity of AMF and also of DSE species. The interaction between AMF and DSE and their benefits to the host plants require further studies to comprehend the conditions that favor both associations.

Les plantes terrestres vivent en association avec des champignons du sol, formant ce que l’on appelle des symbioses mycorhiziennes. Elles échangent du carbone (photosynthétats) contre de l’eau et des minéraux. Ce mutualisme est toutefois troublé par certaines plantes, appelées mycohétérotrophes, capables de soutirer du carbone à leurs symbiontes fongiques. Le plus souvent non photosynthétiques, elles dépendent alors entièrement des champignons mycorhiziens. Certaines ont en revanche conservé la photosynthèse et obtiennent leur carbone par ces deux voies, on les appelle mixotrophes. Cette thèse est consacrée à l’étude des plantes mycohétérotrophes et mixotrophes chez les orchidées, avec des éléments de comparaison chez les éricacées. Les différents travaux qui la structurent précisent la phylogénie de certains groupes clés, s’intéressent aux évolutions génomiques, métaboliques et physiologiques accompagnant ces modes de nutrition originaux, et à leur sensibilité face aux conditions environnementales. / Terrestrial plants live in collaboration with soil fungi, forming associations called mycorrhizal symbioses. They exchange carbon (photosynthates) for water and nutrients. This mutualism is however disrupted by some plants, called mycoheterotrophs, which are able to obtain carbon from their fungal symbionts. Non-photosynthetic most of the time, then they entirely depend on mycorrhizal fungi. Some yet have retained photosynthesis and acquire carbon from these two ways, we called them mixotrophs. This PhD thesis is dedicated to the study of mycoheterotrophic and mixotrophic plants in orchids, with points of comparison in Ericaceae. This dissertation is structured around different kinds of work, which clarify the phylogeny of some key lineages, provide insights into the genomic, metabolic and physiologic evolution going along with these unusual nutrition types, and question how they respond to environmental parameters.

Os fungos micorrízicos arbusculares (FMA) têm papel fundamental na absorção de nutrientes, sobrevivência vegetal e na estruturação dos solos. Recentemente uma série de pesquisadores verificou que plantas associadas com FMA também podem se associar com os fungos de micélio escuro (DSE do inglês, dark septate endophytes). Embora de estudo recente, já se observou que os endófitos de micélio escuro igualmente podem promover o crescimento de plantas em diversos ambientes. O objetivo desse trabalho é realizar um levantamento de espécies de FMA e DSE em áreas de Mata Atlântica em um gradiente altitudinal, podendo advir respostas de relevância ecológica maior, como a influência da planta hospedeira, dos parâmetros do solo, da sazonalidade e da altitude sobre a ocorrência e diversidade desses fungos. Espera-se também esclarecer melhor a lacuna existente no conhecimento dos benefícios dos DSE para as plantas e dar o primeiro passo para a compreenção da interação dos FMA com os DSE. Avaliaram-se os atributos químicos, físicos e microbiológicos do solo e, entre estes, a ocorrência e diversidade dos FMA e DSE na raiz e solo rizosférico de diferentes espécies arbóreas da Mata Atlântica do Parque Estadual da Serra do Mar, Estado de São Paulo, Brasil, em um gradiente altitudinal: 80m, 600m e 1000m. As coletas de solo e raízes foram realizadas em quatro estações. Os dados foram submetidos à análise de variância ANOVA, teste LSD, análise canônica discriminante (ACD) e análise de redundância (RDA). Uma vez que muitas espécies de DSE são conhecidas por serem patogênicas sobre certas plantas, os isolados de DSE foram avaliados quanto à sua eventual patogenicidade. Os isolados não patogênicos foram selecionados para um bio-teste, sozinhos ou em combinação com um FMA em plantas de arroz. Foram identificadas no solo rizosférico 58 espécies de FMA e os gêneros Acaulospora e Glomus foram dominantes, enquanto que nas raízes, apenas 14 grupos de FMA foram encontrados e todos apresentaram elevada similaridade com a família Glomeraceae. Foram encontrados 251 isolados de DSE que se agruparam em 35 UTO. A maioria dos isolados de DSE foram patogênicos para as plantas de arroz. A época de amostragem teve efeito sobre a colonização radicular e diversidade dos FMA. A altitude foi importante em selecionar espécies de FMA e também agiu sobre o número de esporos e colonização por DSE e FMA. A maioria dos FMA e DSE ocorreu de forma generalizada nas diferentes espécies hospedeiras, apesar de existirem algumas espécies fúngicas com preferências para certas árvores. Os atributos do solo tiveram forte influência sobre a colonização pelos FMA, enquanto que para os DSE as diferenças na colonização foram pouco infuenciadas pelos parâmetros do solo. No entanto, as propriedades do solo foram responsáveis por dirigir a ocorrência de certas espécies de FMA e DSE. A interação entre FMA e DSE e os seus benefícios para as plantas hospedeiras ainda necessita de maiores estudos principalmente com relação a compreenção das condições fornecidas em experimentos que favoreçam ambas as associações. / Arbuscular mycorrhizal fungi (AMF) play a fundamental role in the absorption of nutrients, plant survival and soil structure. Recently a number of researchers found that plants associated with AMF may also be associated with dark mycelium fungi. In a recent study, it was observed that the dark septate endophytes (DSE), usually Ascomycetes, can promote the growth of plants in different environments. The aim of this study was to survey the diversity of AMF and DSE in Atlantic Forest areas in altitudinal gradients, which result in responses of greater ecological relevance, as the influence of the host plant, soil attributes, seasonality and altitude on occurrence and diversity of these fungi. We also expect to clarify the gap in the knowledge of the benefits of DSE for plants and take the first step towards the comprehension of the interaction of AMF and DSE. We evaluated the chemical, physical and microbiological attributes, and among these, the occurrence and diversity of AMF and DSE in the root and rhizospheric soil of different tree species of the Atlantic Forest of Serra do Mar State Park, State of Sao Paulo, Brazil, along an altitudinal gradient: 80m, 600m and 1000m. Samplings of the soil and roots were performed in four seasons. The data were submitted to ANOVA, LSD test, canonical discriminant analysis (CDA) and redundancy discriminant analysis (RDA). Since many species of DSE are known to be pathogenic on certain plants, DSE fungal isolates were evaluated for their eventual pathogenic activity. The isolates non-pathogenic were used in a bio-test to either alone or in combination with the AMF in rice plants. In the rhizosphere 58 AMF species were identified. The genera Acaulospora and Glomus were predominant. However, in the roots, only 14 AMF sequences were found and all had high similarity to the family Glomeraceae. In an analysis of the DNA ITS sequences of the 251 DSE isolates we found that they clustered into 35 UTOs. Most DSE found were considered pathogenic for rice. The season had no effect on root colonization and AMF diversity. Altitude was important in selecting AMF species and also acted on the number of spores and colonization by AMF and DSE. Most of the AMF and DSE were generalists, without a specificity for host plants, although there are some fungal species with preferences for certain trees. The soil properties had a strong influence on colonization by AMF while, for the DSE, differences in colonization do not seem to be related to soil attributes. However, soil attributes were responsible for directing the diversity of AMF and also of DSE species. The interaction between AMF and DSE and their benefits to the host plants require further studies to comprehend the conditions that favor both associations.

O Estado do Cearà vem se destacando na Ãrea de produÃÃo de flores e plantas ornamentais nos Ãltimos anos e tem apresentado crescimento em vÃrios aspectos, influenciando, dessa maneira, no desenvolvimento da economia cearense. No entanto, apesar da grande importÃncia econÃmica das rosas no Cearà como tambÃm em outras regiÃes do Brasil, hà carÃncia de pesquisas sobre essas flores no paÃs. As informaÃÃes sÃo escassas quanto, por exemplo, Ãs exigÃncias nutricionais de roseiras nas condiÃÃes de produÃÃo no Brasil, bem como sobre as possÃveis associaÃÃes benÃficas estabelecidas com microrganismos edÃficos. Objetiva-se neste trabalho avaliar o efeito da colonizaÃÃo micorrÃzica arbuscular sobre o desenvolvimento de minirosa em um Neossolo QuartzarÃnico do municÃpio de EusÃbio no Estado do CearÃ. O experimento foi conduzido, inicialmente, em estufa e teve continuidade em condiÃÃes de campo apÃs o transplantio. O trabalho foi realizado na empresa Exotic Paisagismo, no municÃpio de EusÃbio-Ce. O solo utilizado foi um Neossolo QuartzarÃnico o qual foi coletado para anÃlises quÃmicas e microbiolÃgicas. As estacas de minirosa, variedade branca, foram plantadas em bandejas contendo solo estÃril ou natural onde foram mantidas por um perÃodo de 30 dias para o enraizamento. Estas estacas tambÃm receberam Ãgua de lagoa estÃril ou natural durante o perÃodo de formaÃÃo de raÃzes. A fase de enraizamento ocorreu em estufa. ApÃs este perÃodo, as mudas foram transplantadas para vasos plÃsticos contendo somente solo natural. Estas plantas, apÃs transplantio, passaram a receber Ãgua da lagoa apenas natural e dois nÃveis de fÃsforo. O experimento foi destrutivo, com duas Ãpocas de coleta, aos 60 (coleta 1) e 90 (coleta 2) DAT, onde foram retiradas trÃs repetiÃÃes de cada tratamento para a realizaÃÃo de anÃlises. O experimento obedeceu a um delineamento experimental inteiramente casualizado, em esquema fatorial 2 ( dois nÃveis de fÃsforo) x 2 (enraizamento em solo estÃril ou natural) x 2 (irrigaÃÃo com Ãgua da lagoa natural ou Ãgua da lagoa estÃril), com 3 repetiÃÃes. Os parÃmetros a serem avaliados foram: massa da matÃria seca da parte aÃrea MSPA, altura da planta, diÃmetro do caule, nÃmero de rosas, determinaÃÃo de P da parte aÃrea, colonizaÃÃo micorrÃzica arbuscular, densidade de esporos e diversidade de FMA no solo e respiraÃÃo basal do solo. Na coleta 2, nas plantas que receberam o nÃvel subÃtimo de P (P2), a colonizaÃÃo precoce aumentou de forma significativa a produÃÃo de MSPA de plantas enraizadas em solo natural em relaÃÃo Ãs plantas enraizadas em solo estÃril. Os FMA podem ter sido estimulados pelo menor suprimento de fÃsforo. Na coleta 2, o aumento da altura das plantas, influenciado pelas condiÃÃes de enraizamento, pode ter sido promovido pelo enraizamento em solo natural, ou seja, pela presenÃa de FMA durante o perÃodo de formaÃÃo de raÃzes. Na coleta 1, as plantas que receberam os tratamentos T5 e T6 foram as Ãnicas parcelas a nÃo apresentarem rosas aos 60 DAT, sendo que, ambos os tratamentos foram compostos pelo fator enraizamento em solo estÃril, ou seja, na ausÃncia de FMA. Na coleta 2, as plantas que receberam os tratamentos T3 e T4 e que, portanto, foram enraizadas em solo natural (prÃ-colonizadas) apresentaram o maior nÃmero de rosas no momento da coleta e, subseqÃente, contagem das rosas. Em relaÃÃo a colonizaÃÃo micorrÃzica, tanto na coleta 1 quanto na coleta 2 o fÃsforo foi, estatÃsticamente, o Ãnico fator a influenciar nos resultados. O enraizamento em solo natural promoveu um maior desenvolvimento da minirosa no solo com menos P disponÃvel. As estacas de minirosas quando enraizadas em solo apresentaram um menor nÃmero de estacas perdidas, maior sobrevivÃncia ao transplantio e melhor crescimento e vigor do que as plantas cultivadas, comercialmente, em pà de coco e casca de arroz carbonizada. / The state of Cearà has been highlighted in the production of flowers and ornamental plants in recent years and has been growing in many ways influencing in the developing the economy of CearÃ. However, despite the great economic importance of roses in Cearà as well as in other regions of Brazil, there is a lack of research on these flowers in the country. Information is scarce as, for example, the nutritional requirements of roses under the conditions of production in Brazil, as well as the possible beneficial associations established with edaphic microorganisms. The objective of this work was to evaluate the effect of arbuscular mycorrhizal colonization on the development of in a Neosoil Quartzarenic in the EusÃbio county in Cearà state. The experiment was initially conducted under greenhouse conditions and was continued in field conditions after transplanting. The study was conducted at Exotic Landscaping company in the Eusebio county. The soil collected was used for chemical and microbiological analysis. The cuttings rose miniature, white variety, were planted in trays containing sterile soil or natural soil, where they were kept for a period of 30 days for rooting. These cuttings also received sterile water or natural water during the formation of roots. The rooting phase was conducted in greenhouse conditions. After this period, the seedlings were transplanted to plastic pots containing only natural soil. These plants after transplanting began to receive only natural lake water and two different levels of phosphorus. The experiment was destructive, with two samplings periods, to 60 and 90 days after transplanting, and three replicates for each treatment. A factorial completely randomized design 2 (two phosphorus levels) x 2 (roots in sterile soil or natural) x 2 (irrigation with natural pond water or sterile pond water) with four replicates was adopted. The parameters evaluated were: shoot dry matter, plant height, diameter of stalk, number of roses, determination of P in the plant, arbuscular mycorrhizal colonization, spore density and diversity of AMF species and basal soil respiration. To 90 days after transplanting, the plants that received suboptimal levels of P (P2), the early colonization significantly increased the production of shoot dry matter of plants rooted in natural soil when compared to plants rooted in sterile soil. The FMA may have been stimulated by the low supply of phosphorus. To 90 days after transplanting, increased plant height, influenced by the rooting conditions, may have been promoted by the roots in natural soil, or by the presence of AMF during the formation of roots. To 60 days after transplanting, the plants that received the treatments T5 and T6 were the only plots that there were no roses at the this period both treatments were made up by a factor of rooting in sterile soil, eg. in the absence of AMF. To 90 days after transplanting period, the plants that received the treatments T3 and T4 and therefore were rooted in natural soil (pre-colonized) had the largest number of roses at the time of sampling and subsequent counting of roses. Related to mycorrhizal colonization, in both periods, the P factor was, statistically, the only factor to influence the results. Rooting in natural soil promoted the further development of the rose miniature in soil with less P available. The cuttings of rose miniature when rooted in soil had less lost cuttings, increased survival to transplanting and better growth and vigor when compared to plants grown commercially in powder coconut and rice shell.

Abstract Mycorrhizal symbiosis is generally advantageous for plants in nutrient-poor soils. Arcto-alpine areas are relatively nutrient-poor, but abundantly inhabited by non-mycorrhizal species. Possibly, mycorrhizal symbiosis is not favoured due to the harsh climatic conditions and the short growing season, which constrain the photosynthetic gain and growth of the arcto-alpine plants. This hypothesis was theoretically evaluated by assuming that optimal mycorrhizal colonization maximizes the net carbon gain of the host plant. In addition, the prevalence of arbuscular mycorrhizal (AM) and dark-septate endophytic (DSE) fungi along an altitudinal gradient was studied in the field, and their effects on the plant performance were tested in the laboratory. In the model, the photosynthetic nutrient use efficiency (PNUE) had a key role in determining whether mycorrhizal strategy would be optimal for the plant net carbon gain. The model generated several colonization patterns depending on possible changes in PNUE and soil nutrient concentrations along altitudinal gradients. Field studies indicated that species-level colonizations do not yield a consistent pattern along the altitude except for fine endophyte, which increased along an altitudinal gradient. In a high-alpine field site root fungal colonizations were rare. Seasonal shifts in colonizations in low-alpine conditions were not found. DSE fungi were common root-associates in the field. In the laboratory, AM had a positive impact on the performance of Gnaphalium norvegicum at 15°C, but not at 8°C. DSE-inoculation did not colonize the roots, but it had a positive impact on seedling performance, which may be due to the saprophytic activity of the fungus in the substrate. Additionally, mycorrhizal inoculum was found to decrease the performance of a non-mycorrhizal plant in a competition experiment. Species-level mycorrhizal colonization patterns may differ from community-level pattern along altitudinal gradients and the relative abundance of different fungal symbionts may change along with the altitude. The performance of mycorrhizal plants in high-alpine conditions may be decreased due to several factors e.g. low temperature constraints on plant and fungal physiology and allocation, soil disturbances and low availability of inoculum. Climatic constraints for plant photosynthesis may thus affect the mycorrhizal colonization patterns in arcto-alpine conditions, but are not necessarily the primary cause for lower performance of mycorrhizal plants at higher altitudes.

This study addressed the effects of salinity and pot size on the interaction between leguminous plant hosts and arbuscular mycorrhizal fungi in four pine rockland soils using a shade house trap-plant experiment. Little is known about the belowground diversity of pine rocklands and the interactions between aboveground and belowground biota – an increased understanding of these interactions could lead to improved land management decisions, conservation and restoration efforts. Following twelve weeks of growth, plants were measured for root and shoot dry biomass and percent colonization by arbuscular mycorrhizal fungi. Overall, arbuscular mycorrhizal fungi had positive fitness effects on the four legume species (Cajanus cajan, Chamaecrista fasciculata, Tephrosia angustissima and Abrus precatorius), improving their growth rate, shoot and root biomass; pot size influenced plant-fungal interactions; and percent colonization by arbuscular mycorrhizal fungi was influenced by soil type as well as salinity.

La symbiose endomycorhizienne à arbuscules (SMA) a une importance écologique et agronomique majeure car elle permet à la majorité des plantes terrestres, via une association avec des champignons du phylum des Glomeromycota, une meilleure acquisition de nutriments du sol. Les champignons grâce à un large réseau mycélien dans le sol, collectent et echangent des nutriments avec les plantes qui leurs fournissent des substrats carbonés issus de la photosynthèse. Le champignon mycorhizienne à arbuscules (CMA) Rhizophagus irregularis, capable de coloniser les racines de la plupart des plantes terrestres, sécrète des lipo-chitooligosaccharides (Myc-LCOs) et des chitooligosaccharides à chaîne courte (Myc-COs). L’ajout exogène de Myc-LCO stimule la colonisation de plusieurs espèces par des CMAs. Ces Myc-LCOs et les Myc-COs sont capables d’activer une voie de signalisation symbiotique requise pour l’établissement de la SMA. Cependant, le rôle de ces molécules et leur importance dans l’établissement de la symbiose restent à ce jour inconnu. Au cours de ma thèsej’ao étudié la SMA chez la plante modèle pour les monocotylédones tempérées, Brachypodium distachyon. Je me suis intéressé, tout d’abord, à la perception des signaux fongiques (Myc-LCOs et Myc-COs). Un mécanisme possible par lequel les Myc-LCOs pourraient stimuler la SMA, est leur capacité à induire une augmentation du nombre de racines latérales (RL), montrée chez la légumineuse modèle Medicago truncatula ainsi que chez la monocotylédone Oriza sativa (riz). Les réponses transcriptionnelles aux Myc-LCOs chez M. truncatula suggèrent une interaction entre la perception de Myc-LCOs et la signalisation auxine. Par ailleurs, l’ajout d’auxine stimule la SMA chez M. truncatula et le riz. Pendant mes travaux de thèse, nous avons pu montrer que des LCOs induisent aussi la formation de RLs chez B. distachyon. De plus, nous avons pu montrer un effet des LCOs sur l’homéostasie de l’auxine. Finalement, nous avons pu confirmer un rôle positif de l’auxine dans la mise en place de la SMA grâce à l’étude d’un mutant surproduisant de l’auxine. Par ailleurs, des travaux dans l’équipe ont permis d’identifier BdLYR1, un récepteur kinase contenant des motifs lysin (LysM-RLK) capable de lier les LCOs à haute affinité. Cependant, un mutant dans ce gène ne présente aucun phénotype mycorhizien suggérant une redondance fonctionnelle au niveau des récepteurs et/ou des signaux pour l’activation de la voie de signalisation symbiotique. J’ai initié la caractérisation du LysM-RLK BdLYR4, un récepteur potentiel de COs. Enfin, il a été observé que la réponse de croissance des plantes à la colonisation par les CMA est à la fois dépendantes de l’environnement, de la souche de champignon utilisée ainsi que du génotype de plante. Très peu d’études ont été réalisées dans le but d’identifier les mécanismes moléculaires qui régissent ces réponses de croissance. Pour pouvoir le faire, j’ai initié la caractérisation de la variabilité génétique pour les réponses de croissance aux CMAs chez B. distachyon dans le but d’identifier des génotypes contrastés ainsi que les variables phénotypiques les plus pertinentes à analyser. Ces travaux ont permis de trouver des conditions de culture qui permettent l’analyse de la réponse croissance chez B. distachyon. / The endomycorrhizal symbiosis with arbuscules (AM) is of major ecological and agronomic importance because it allows the majority of terrestrial plants, via an association with phylum fungi of Glomeromycota, to facilitate their acquisition of nutrients and water. Fungi through a large soil exchange surface collect and provide nutrients to plants that provide fungi with carbonaceous substrates derived from photosynthesis. The fungus AM Rhizophagus irregularis, capable of colonizing the roots of most terrestrial plants, secretes lipo-chitooligosaccharides (Myc-LCOs) and short-chain chitooligosaccharides (Myc-COs). These molecules are capable of activating a signaling pathway required for the establishment of the AM symbiosis. However, their role and relevance for AM symbiosis is completely unkown. During my phD, I studied perception of fungal signals (Myc-LCOs and Myc-COs) in B.distachyon. Myc-LCOs stimulate AM symbiosis in several plants and induce an increase in the number of lateral roots (RL) in legume plant Medicago truncatula, as well as in Oriza sativa (rice).Transcriptional responses to LCO in M.truncatula suggest a crosstalk between auxin and LCO. Moreover, the addition of auxin also stimulates AM symbiosis in M. truncatula and rice. During my phD, we showed that LCOs stimulates also lateral root formation in B.distachyon. In addition, we showed that these developmental effects are linked to a regulation of auxin biosyntheses and homeostasis. Finally, I could confirm the positive role of auxin in AM thanks to an auxin-overproducer mutant. In the team, BdLYR1, a high-affinity LCO binding protein has been identified. However, the mutant Bdlyr1 is not affected in mycorrhization, as it was also shown for its ortholog in rice. This can be explained by functional redundancy of the receptors but also by redundancy of fungal signals (Myc-CO). During my phD, I focused on BdLYR4, which is a good candidate for Myc-COs receptor. It has been reported mycorrhizal growth responses (MGR) in colonized plants. These growth responses depend on environmental conditions, fungal strain and plant genotype. To date, very few studies have been done in order to identify molecular mechanisms controlling MGRs. To do so, I initiate the characterization of natural variability for MGRs in B.distachyon in order to identify contrasted genotypes and the more convenient phenotipical and physiological traits to analyze. All this work leads us to identify good conditions that maximize differences between genotypes.

A continuously growing world population with a projected size of more than 9 billion inhabitants in the year 2040 requires huge efforts in food production while concurrently avoiding adverse side effects such as the use of pesticides or fertilizers. Among them phosphorous (P) is an important mineral fertilizer for which only few renewable sources exist and which is becoming increasingly scarce. Therefore, methods to reduce P fertilization or enhance fertilization efficiency are urgently needed. One idea is to look how plants in natural ecosystems cope with the problem of nutrient limitation. A strategy, found in almost all plant species is interaction with mycorrhizal fungi. Plants usually deliver carbohydrates (C) to the fungi and get nutrients, like phosphorous (P), in exchange. In natural ecosystems, plants usually interact with multiple fungi which perform differently in their P delivery. However, in agro-ecosystems not all these fungi are helpful. Fungi which are carbon demanding but deliver just few P, might even result in lower plant growth. Therefore a deep knowledge of the mechanisms driving the P and C dynamics is necessary. This can be gained by a computer simulation model which is possible to examine the influence of different nutrient exchange strategies in detail and make prediction how they perform. In this PhD thesis, a spatially explicit simulation model of arbuscular mycorrhizal fungi (AMF) was developed and specific laboratory experiments have been conducted and used for model calibration. This model has been used to evaluate the performance of different nutrient exchange strategies by the emerging maximum achievable fungal biomass, the C uptake rate from the plant and the P delivery rate to the plant. On this basis, three functional types could be identified: parasitic type, intermediate type, mutualistic type. In further steps these functional types have been used to investigate their performance to smooth temporal P pulses (i.e., by transforming them into a continuous P flux delivered to the plant) and to take up spatially heterogeneously distributed P. In both cases, the mutualistic type was found to perform worst and parasitic type best. Two key mechanisms for efficient resource use in spatiotemporally heterogeneous environments could be identified. By the ability of quick fungal biomass growth, AMF can efficiently explore space and store P inside the fungal mycelium. By the creation of spores that do not need C for 6 maintenance, AMF can use the saved C to grow new hypha for further spatial exploration. Through these two mechanisms AMF are able to adapt their mycelium to the spatial and temporal conditions of the P distribution and thus have the potential to largely enhance Puse efficiency. This finally might reduce the application of P fertilizers.

Mycorrhizal associations are very important to plant growth. This is mainly due to the hyphal stands that are able to utilize concentrations of nutrients that would normally be considered unavailable for plant growth, especially phosphorus. These associations are of great importance in soils that have been disturbed by mineral extraction and are consequently low in available nutrients. The ability of mycorrhizal fungi to form associations on disturbed sites may be dictated by a number of factors: moisture, soil pH, soil fertility (including heavy metal ions), salinity, and plant response. Two factorial experiments were conducted with the legume Hedysarum boreale cv utahensis and the mycorrhizal fungus Glomus mosseae. The first to observe the effects of three factors: fungi level (mycorrhizal or non-mycorrhizal), type of phosphate (P) (monocalcium or superphosphate), and irrigation intervals (2, 4, or 8 day) on root and shoot dry weights. The second experiment was conducted to observe the effects of three factors: fungi level, type of P and level of P on root and shoot dry weights, root and shoot P concentration, nodulation and nitrogen fixation. In the first experiment, the combination of fungi level and type of P had a significant effect on root /shoot ratio (weight ). In the second experiment, the interaction of fungi level, type of P and level of P had a significant effect on nodulation. The interaction of P type and P level had a significant effect on the amount of phosphorus found in plant roots and shoots. The factor, fungi level, had a significant effect on shoot dry weight, with mycorrhizal plant's shoots having a significantly greater dry weight than non-mycorrhizal shoots. Mycorrhizal infection may have been greatly reduced by the adverse soil conditions found in the mine spoil (i.e. low pH, high salinity , and high heavy metal concentration). What infection did occur may have been great enough to produce changes in the shoot dry weight, but not great enough to significantly enhance plant P uptake. The reintroduction of mycorrhizae into disturbed areas for reclamation purposes may be important for rapid establishment of plant cover and to speed up succession. Before mycorrhizae can be reestablished in a disturbed area, many potential stress factors need to be addressed and, if possible, overcome.

<p>Plants and mycorrhizal fungi form a mutualism in which plants donate carbon to the fungus and, in return, receive benefits such as increased nutrient uptake and water. Mycorrhizal fungi colonize plant roots, forming nutrient exchange structures. The fungi also colonize the soil by growing long strands of hyphae that forage for nutrients and attach plants, forming a common mycorrhizal network (CMN). Plants attached to a well-supported CMN will receive greater benefits than those attached to a lesser CMN because the more carbon donations the fungal partner receives, the more it can grow and colonize the soil, accessing hard to reach soil nutrients. Kin selection theory predicts that relatives should donate more carbon to the fungal partner than non-relatives because benefits gained by neighbouring relatives through the CMN lead to inclusive fitness gains. Thus, social environment, i.e. relatedness of the group, could affect the mycorrhizal mutualism. Moreover, the presence of mycorrhizal fungi in the soil could affect plant responses to their social environment.</p> <p>For my PhD thesis I have investigated whether mycorrhizal fungi respond to plant social environment and whether the presence of mycorrhizal fungi affects plant responses to relatedness. I have addressed these topics in three greenhouse studies and two field studies, using herbaceous plants and trees. I have found strong evidence that siblings have an increased association with their mycorrhizal partner compared to strangers, resulting in greater benefits for siblings. Taken together, the results from this thesis demonstrate that the ability for plants to recognize kin has implications beyond intra-specific competitive interactions and that plant social environment has important effects on a widespread inter-specific mutualism. Additionally, the recently discovered phenomenon of plant kin recognition has been put into the context of mycorrhizae, and I have shown that mycorrhizal plants respond differently to their social environment than non-mycorrhizal plants.</p> / Doctor of Philosophy (PhD)