Nitrogen (and phosphorus) nutrition of a woody plant and its root associates: a post-genomic perspective
Trees differ fundamentally from annual plant species in that they are adapted to survive on a long time-scale. The sequencing of the poplar genome and the use of appropriate functional tools offer an unprecedented opportunity to highlight key and specific mechanisms that characterize woody species. Most particularly, the isolation and characterization of complete sets of genes encoding transporters for inorganic / organic N and for P will bring fundamental knowledge that will be used to tackle changes in capacities for N and P uptake and assimilation under natural conditions. Additionally, under natural conditions the majority of trees are believed to have ectomycorrhizal (ECM) associations (intimate symbiotic association between fungi and roots), which can have a significant role in the worldwide nitrogen and/or phosphorus cycle. This mycorrhizal status relies 1) on efficient uptake processes by the fungal partner 2) on the bidirectional transfer of nutrients between the two symbionts, which was first demonstrated by Melin and Nilsson >50 years ago. The recent sequencing of the Laccaria bicolor genome, together with that of poplar, will probably reveals key genes that are essential for symbiotic functions, and hence for tree physiology.