Fernanda De Carvalho-Niebel
Terrestrial plants have the remarkable ability to establish symbiotic associations with soil microorganisms to acquire essential nutrients for their growth. In some specialized endosymbiotic interactions, the plant hosts its microbial partners inside cells to allow efficient acquisition of nutrients (e.g. phosphorus, nitrogen) in exchange for carbon sources.
However, this requires the formation of new symbiotic exchange structures at the root level, such as unique structures called arbuscules, formed in the root cortex during association with mycorrhizal fungi belonging to the Glomeromycetes, or root nodules colonized by nitrogen-fixing bacteria. Despite significant differences in their mode of nutrient acquisition and host spectrum, the establishment of these symbioses, from the oldest (arbuscular mycorrhizae) to the most recent (nitrogen-fixing symbioses), is guided by an ancestral signaling pathway that allows intracellular accommodation of their symbiont.
The exchange of specific signals between the plant and the micro-organism is necessary for the activation of a calcium-dependent symbiotic signaling pathway. Specific symbiotic transcription factors then orchestrate the establishment of symbiotic programs allowing root penetration and intracellular accommodation of symbionts.
Although we have acquired a great deal of knowledge about the genetic pathways and key players in these root endosymbioses, important questions remain about the mechanisms that govern endosymbiotic infection and the coordinated formation of a new organ.
The researchers of the SYMBIPHYT network aim to understand the molecular and cellular mechanisms underlying endosymbiotic colonization, as well as the coordinated development of nodules. For this, they use a variety of model systems (e.g. Medicago, Mimosa, Lupinus, Soya, Arachis, Casuarina, etc.) capable of establishing symbioses with different microorganisms (e.g. Glomeromycota fungi, Frankia bacteria or rhizobia). A deeper understanding of these mechanisms and their modulation is essential to exploit their potential in future applications for a more sustainable agriculture.