LUE - Etude du rôle des petits peptides sécrétés de l'arbre dans la régulation de la symbiose ectomycorhizienne en réponse au signaux nutritionnels biotiques et abiotiques.

école doctorale

équipe

ECOGENOMIQUE DES INTERACTIONS

contexte

As the largest land carbon dioxide sink, forests constitute an important leverage to mitigate the effect of the anthropogenic carbon dioxide emissions. In forests, carbon-sequestration mainly occurs in trees and soil microbiota. Therefore, trees' associations to soil microorganisms and the effect of these associations on trees' growth and health have a major impact on the carbon-sink capacity of forests 1-3. Ectomycorrhizal (ECM) symbiosis is the main mutualistic association formed between soil fungi and boreal or temperate forests trees 4,5. Providing limiting mineral nutrients for organic-carbon fixed during photosynthesis, these associations ensure trees growth and health and are pivotal for carbon-sequestration and nutrient-cycling 6,7. However, ECM symbioses are sensitive to changes in nutrient availability. In forest soils, such changes mainly result from anthropogenic activities (pollutions) 8,9. Trees regulate their ECM association in response to their nutritive environment. For instance, nitrate (NO3-) represses ECM associations between Eucalyptus grandis and Pisolithus albus, and between Populus x canescens and Laccaria bicolor 10 (Bonnot et al., in prep). The signalling pathways leading to the regulation of ECM symbiosis in response to nutrient cues are unknown. Identifying them would allow a better understanding of the dynamics of tree nutrition thought its ECM associates in response to human pressures, and is the first stone towards prediction of the impact on forest health and functions. In herbaceous, some Small Secreted Peptides (SSPs) (<250 amino acids) mediate local and systemic signals regulating symbiotic associations with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi in response to nutrient stresses 11-13. SSPs are produced from short open reading frames or through proteolytic cleavage of pre-proteins and secreted in the apoplast. Belonging to different phylogenetic families, their functions range from antimicrobial to signalling molecules 14-16. More than 4,000 putative SSP families exists in plants of which 68 are functionally characterised in herbaceous. Amongst, 21 have members involved in the regulation of, or transcriptionally regulated by, symbiosis and nutrient cues 17-20. The roles of trees' SSPs in regulating ECM symbiosis in response to nutrient signals are unexplored. Focusing on the tree model P. x canescens, we established its genetic repertoire of the 21 SSP families. Using transcriptomics and in vitro activity-screens, we identified three P. X canescens SSPs (PcCLE08, PcPIPL19, PcIDL16) affecting its ECM association to L. bicolor, and transcriptionally regulated in response to NO3-. In herbaceous, members of the CLE, PIPL and IDL families are signalling-SSPs transducing cell-cell developmental and adaptive signals through the binding of LRR-RLK or -RLP cell-surface receptors 16,21,22. Thus, we hypothesised that trees use signalling-SSPs to regulate ECM symbiosis in response to nutrient cues. The objective of this PhD is to functionally characterize PcCL08, PcPIPL19 and PcIDL16 to understand their role in the regulation of ECM associations in response to nitrogen-cues in poplar. The PhD student will determine the steps of the ECM association they target, the circumstances in which they are produced by P. x canescens, if they are necessary to regulate its association to L. bicolor and their modes of action. This work will identify for the 1st time some of the molecular mechanisms used by trees to control their ECM associations.

spécialité

Biologie et écologie des forêts et des agrosystèmes

laboratoire

IAM - Interactions Arbres Microrganismes