NUtrient signals in forest Trees Regulating Root growth and Ecto-mycorrhizal SYMbiosis

PI : Clémence Bonnot (UMR 1136 Interactions Arbres/Micro-organismes – IAM)

Co-applicants : Annegret KOHLER, Francis MARTIN (UMR 1136 Interactions Arbres/Micro-organismes – IAM), Marie-Béatrice BOGEAT, Pascale MAILLARD, Dominique GERANT (UMR 1434 Silva)

Context — Forest trees acquire mineral nutrients from their root systems and via symbiotic interactions with ectomycorrhizal fungi. The development and functioning of roots and symbiotic organs have an energetic cost for the plant, which divert a large part of its carbon resources towards them. In forest soils, mineral nutrients are scarce. To invest their resources efficiently and maintain optimal growth, trees increase root growth and ectomycorrhizal symbioses formation in nutrients rich zones but repress them in zones poor in nutrients. This suggests that trees perceive and integrate environmental and metabolic nutritional cues to trigger responses supporting the development of the adequate organs. The molecular mechanisms supporting these regulatory processes are unknown. However, it is known that nutrient signals in Legumes involve Small-Secreted Proteins (SSP). Translocated throughout the plant, SSPs trigger changes in the expression of genes involved in nitrogen and phosphorus acquisition, root growth and symbiotic associations.

Objectives — We aim to characterize the molecular mechanisms allowing trees to compute the trade-offs between nutrient needs and growth costs by investigating the role of SSPs and carbon fluxes in the regulation of ectomycorrhizal symbiosis and roots growth by nutrient signals in poplar.

Approaches — We will identify by transcriptomics the SSPs regulated by nutritive stresses and will assess the putative correlation of their expression with the regulation of ectomycorrhizal symbiosis and root growth. Finally, we will verify whether a reorientation of the plant carbon fluxes toward the growing roots and the ectomycorrhizal occur from these signals.

Expected results and impacts — By providing a better understanding of the molecular mechanisms governing the integration of environment and metabolic nutritive cues that regulates tree growth and symbiotic interactions, NUTRRESYM will improve our knowledge on the impact of changes in forest soil nutrients content on tree growth and nutrition in forest affected by human activities.