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Abstract:

Mutualisms can have an important impact on ecosystem functioning. One of the most prevalent examples is the interaction between symbiotic microorganisms and flowering plants. Such partnerships can increase plant biomass production by providing extra nutrients (e.g. nitrogen-fixation by rhizobia) or by fortifying plant defence mechanisms (e.g. endophytes can produce alkaloids that protect the host against herbivores). Most research concentrates on the plant-bacteria interactions with immediate applications. This restricted vision entails the risk of overlooking associations that might be beneficial in the future. In the Rubiaceae family, several plant species interact with Burkholderia bacteria that are located in the leaves. In the plant genus Psychotria, the endophytes can either be found in specialized leaf nodules or freely distributed among the mesophyll cells. The host specificity of the bacteria seems to indicate the obligatory nature of the interaction, but the advantages of the symbiosis to the host remain enigmatic. One of the main goals of the present research is to cultivate Burkholderia-free plants in order to elucidate the purpose and the advantages of this interaction. Due to the host specificity, the transmission of the endophytes to the next plant generation is hypothesised to be vertical. Our aim is to clarify the location of the endophyte throughout the floral and seed development and to investigate the vertical transmission. The location of the endophytes will be investigated using Fluorescence In Situ Hybridisation. This microscopic technique maximises the contrast and specifically stains the endophytes within the plant organs. The location of the endophytes during the floral and seed development is essential to understand the obligatory nature of the endosymbiosis and is required to cultivate Burkholderia-free plants. This key knowledge will also be used to inoculate a plant with non-host bacteria and will eventually help us determine the specificity and the function of the symbiosis.