The mycorrhizal symbiosis is among the most widespread species interactions on Earth. This thesis focuses on orchid mycorrhiza, a unique mycorrhizal type that has caught scientists’ attention for... Show moreThe mycorrhizal symbiosis is among the most widespread species interactions on Earth. This thesis focuses on orchid mycorrhiza, a unique mycorrhizal type that has caught scientists’ attention for centuries. By merging the concepts and approaches of molecular phylogenetics, microbial community ecology, and plant ecophysiology, this thesis provides an overview of the evolution and ecology of orchid mycorrhizal interactions from both the fungal and plant perspective, and from the global to the local scale. In this thesis, the variation in fungal associations in space and in time is a central topic, which was inferred by analyses on phylogenetic signals and variation in fungal community structure and also captured by empirical experiments using metabarcoding approaches and quantitative ddPCR. Based on the insights gained in this thesis and that of previous studies, this thesis proposes several directions for future studies to deepen our understanding of the evolution, ecophysiology, and molecular biology of mycorrhizal symbiosis, and thus to benefit orchid conservation and ecosystem restoration. Show less
To gain more insight into the evolutionary development of orchid flowers and fruits, the orchid species Erycina pusilla was studied. The evolutionary origin of the median petaloid sepal, the callus... Show moreTo gain more insight into the evolutionary development of orchid flowers and fruits, the orchid species Erycina pusilla was studied. The evolutionary origin of the median petaloid sepal, the callus on the labellum, and the stelidia was studied. These organs were found to be derived from a sepal, a stamen that gained petal identity, and stamens that became staminodes, respectively. The “Oncidiinae” model was proposed, explaining the duplications, diversifying selection and changes in spatial expression of different MADS-box genes that shaped the perianth, enabling the rewardless flowers of E. pusilla to mimic an unrelated rewarding flower for pollinator attraction.After pollination the inferior orchid ovary develops into a fruit. This process is described for E. pusilla up to fruit dehiscence. The fruit associated MADS-box genes and proteins together with other dehiscence-related genes were analyzed in order to propose a first “orchid fruit developmental protein and gene network” model. Fruit development was further studied by transcriptome analyses presenting data obtained from different developmental phases.By analyzing the anatomy of ripe fruits of different orchid species, possible correlations were found between fruit valve lignification patterns, life form, growth strategy, ecology, fruit orientation, dehiscence type, number of valves and slits, and phylogenetic relationships. Show less
In this thesis, I targeted the orchid genus Lepanthes, one of the six genera of angiosperms that surpasses 1,000 species in the Neotropics, as a study model to investigate the evolutionary... Show moreIn this thesis, I targeted the orchid genus Lepanthes, one of the six genera of angiosperms that surpasses 1,000 species in the Neotropics, as a study model to investigate the evolutionary processes that promoted species diversifications. To investigate this, we improved the taxonomy of the group integrating a solid phylogenetic framework with morphological evolution, assessing inter-specific relationships in species complexes with hundreds of DNA markers using anchored hybrid enrichment approach, and describing new species. In addition, we addressed the pollination of Trichosalpinx through the study of floral anatomy, pollinator behavior, and floral traits. Trichosalpinx flowers are pollinated exclusively by female biting midges that are attracted by the small quantities of proteins secreted on the flowers. Finally, we inferred the biogeographical history and diversification dynamics of the two largest Neotropical orchid groups (Cymbidieae and Pleurothallidinae), using densely sampled phylogenies coupled with geological datasets and discussed the impact of biogeographical events and orogeny on the species richness of Lepanthes. Species diversification is correlated with Andean orogeny, and multiple migrations and recolonizations across the Andes indicate that mountains do not constrain orchid dispersal over long timescales. This thesis provides new insights into the complex evolution of one of the most species-rich angiosperm. Show less
Background and Aims Partially mycoheterotrophic plants are enriched in 13C and 15N compared to autotrophic plants. Here, it is hypothesized that the type of mycorrhizal fungi found in orchid roots... Show moreBackground and Aims Partially mycoheterotrophic plants are enriched in 13C and 15N compared to autotrophic plants. Here, it is hypothesized that the type of mycorrhizal fungi found in orchid roots is responsible for variation in 15N enrichment of leaf tissue in partially mycoheterotrophic orchids.Methods The genus Epipactis was used as a case study and carbon and nitrogen isotope abundances of eight Epipactis species, fungal sporocarps of four Tuber species and autotrophic references were measured. Mycorrhizal fungi were identified using molecular methods. Stable isotope data of six additional Epipactis taxa and ectomycorrhizal and saprotrophic basidiomycetes were compiled from the literature. Key Results The 15N enrichment of Epipactis species varied between 3·2 ± 0·8 ‰ (E. gigantea; rhizoctonia-associated) and 24·6 ± 1·6 ‰ (E. neglecta; associated with ectomycorrhizal ascomycetes). Sporocarps of ectomycorrhizal ascomycetes (10·7 ± 2·2 ‰) were significantly more enriched in 15N than ectomycorrhizal (5·2 ± 4·0 ‰) and saprotrophic basidiomycetes (3·3 ± 2·1 ‰).Conclusions As hypothesized, it is suggested that the observed gradient in 15N enrichment of Epipactis species is strongly driven by 15N abundance of their mycorrhizal fungi; i.e. ɛ15N in Epipactis spp. associated with rhizoctonias < ɛ15N in Epipactis spp. with ectomycorrhizal basidiomycetes < ɛ15N in Epipactis spp. with ectomycorrhizal ascomycetes and basidiomycetes < ɛ15N in Epipactis spp. with ectomycorrhizal ascomycetes. Show less
Vanilla planifolia, a flowering epiphytic orchid, is the major natural source of vanilla flavour. Largely used in dairy products, beverages, bakeries and perfume, vanilla flavour is obtained after... Show moreVanilla planifolia, a flowering epiphytic orchid, is the major natural source of vanilla flavour. Largely used in dairy products, beverages, bakeries and perfume, vanilla flavour is obtained after a long process: from eight to nine months after flower pollination, mature pods are harvested and then prepared during about one year in order to release the characteristic vanilla aroma. Nowadays, more than half of vanilla pods world production comes from Madagascar. To face the concurrence, a solution could be to develop higher quality pods. Selection of the most aromatic vanilla plant is then preferred. Nevertheless, amelioration program are facing up to a lack of knowledge in vanilla plant physiology. It is now essential to understand more the physiological and biochemical mechanisms implied in the aromatic production of V. planifolia pods. In this thesis, a metabolomic analysis of vanilla green pods and leaves has been performed by nuclear magnetic resonance. This technique has allowed the qualitative and quantitative analysis of primary (sugar, amino and organic acids__) and secondary metabolites (phenolic compounds__) present in vanilla plant according to various physiological conditions: developing pods, viral infection, inter-accession or seasonal variation. Show less
