Study of the evolutionary dynamics of plant beneficial bacteria

Résumé

Plants are in association with microbial communities that strongly influence their development and their adaptation to the environment in which they evolve. Within the plant microbiota, certain bacteria, known as PGPR (Plant Growth-Promoting Rhizobacteria), are capable of stimulating plant growth and protecting the plant against diseases (Vacheron et al., 2013a). They are in fact capable of expressing a set of plant beneficial properties involved in the improvement of the plant's mineral nutrition (nitrogen fixation, phosphate solubilisation, production of siderophors, etc.), the modulation of plant hormonal balances, the production of antimicrobial compounds and the induction of plant defence responses (Lemanceau et al., 2017; Vacheron et al., 2013b). Although these bacteria produce a wide variety of beneficial plant functions, their inoculation does not always lead to significant beneficial effects on the host. Indeed, the mechanisms favouring the establishment of PGPRs in the rhizosphere and the expression of their properties are still largely unknown. In order to better understand the functioning of plant-PGPR symbioses (be it root colonisation or the expression of phytobeneficial functions), we have set up an experimental evolutionary approach. In the literature, experimental evolution studies have generally been carried out by inoculating a single microorganism into a plant (Guan et al., 2013; Marchetti et al., 2017; Meaden and Koskella, 2017; Perrier et al., 2016). However, the functioning of bacterial populations in the rhizosphere depends on networks of interactions that they share with other microbial populations colonising plant roots (Karimi et al., 2017; Mas et al., 2016). We have therefore developed an experimental evolutionary approach with a synthetic community composed of 10 PGPR strains with a high or moderate number of plant beneficial functions, inoculated on a plant of agronomic interest, maize (axis 1), in order to study the evolutionary dynamics of our initial assembly (modification of population balances) as well as the genetic modifications undergone at the level of the genomes (axis 2).

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