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The research of the team SYM focuses on the Alnus/Frankia complex. They combine laboratory approaches (complex recreated under controlled conditions, "in-vitro") and field approaches (complex isolated from its natural ecosystem, "in-natura"). In addition, they target particular strains of the Frankia partner capable of sporulating in-planta (Sp+) or non-sporulating in-planta (Sp-).

Theme 1. Mechanisms of interaction between the bacterium and its eukaryotic host

This theme aims to elucidate the molecular mechanisms involved in establishing the symbiotic relationship between the bacterium Frankia and its host Alnus glutinosa, using global "-omics" approaches.

• Genomics and transcriptomics approaches: 

RNAseq approaches on bacteria (in collaboration with Génoscope), plants and nodules (BGI project).

• Metabolomics and proteomics approaches: 

Comparison of the metabolic content of a non-nodulated root versus nodulation and identification of biomarker metabolites involved in plant/bacteria interactions.
Proteomic approaches to understanding the effect of osmotic stress in Frankia and, more recently, monitoring the first plant-bacteria contacts at 64 h.

• Physiological analyses on both partners: 

Growth monitoring, Frankia N-fixation...
Significant changes between the two types of nodules.

• Gain-of-function approaches in other bacterial hosts (Frankia model not yet transformable).

Theme 2. Ecology and evolution of the symbiosis 

This theme aims to study Frankia's genetic diversity in order to understand the mechanisms that generate and maintain it, and explain Frankia's spatio-temporal distribution and ecological role.

• Diversity and phylogeography of Frankia populations associated with alder :

Multi-Locus-Sequence-Analysis (MLSA) approach of over 600 Frankia strains/nodules, including symbionts from 22 alder species representing the genus' worldwide distribution.

• Diversity, ecology and evolution of Sp+ strains of Frankia :

Sequencing of the first genomes of Sp+ strains despite the absence of cultivated strains.
Understanding the evolution of these strains using comparative genomics approaches.

• Impact of the alder/Frankia symbiotic complex on ecosystem functioning :

Alders, trees comprising the genus Alnus, are essential in their ecosystem due to their nitrogen inputs. We are interested in the ecological role of the Alnus/Frankia complex in ecosystem functioning and its evolution, particularly in a context of global warming. We are developing projects on green alder (A. viridis), which is expanding in sub-alpine/boreal zones (due to changes in agro-pastoral practices and global warming), and on black alder (A. glutinosa) in wetlands (populations heavily impacted by declining water resources). Our projects are based on metabarcoding approaches to characterize soil microbial communities, in particular populations involved in the nitrogen cycle, coupled with in-situ activity measurements (DFMA team collaboration).