Résumé
The aim of this work was to initiate a functional genomic approach in order to characterized the Arabidopsis thaliana PTR gene family. An in silico analysis allows us to identify 51 PTR genes. The functions of most of these genes remains unknown. Transcript profiling of a large number of putative NO3 – transporters (PTR and NRT2 family) and NH4 + (AMT family) has been done using a dedicated GST (Gene Sequence Tag) macro-array. A large numbers of PTR genes are expressed in roots. Some PTR genes are regulated by the N source, the N status, light and sugars or potassium availability. The functions of two genes AtNRT1.2 and AtNRT1.5 have been investigated using KO mutants. The phenotype of AtNRT1.2 mutant confirms a role of the gene in cLATS (constitutive Low Affinity Transport System) of nitrate. Results concerning AtNRT1.5 show that the gene has a unique role in nitrate transport. The AtNRT1.5 transcript accumulation is localized specifically in root stele. Inactivation of AtNRT1.5 is correlated with a deficiency in the export of NO3 - from root to shoot when plants are grown on NH4NO3 as sole N source. AtNRT1.5 is the 1st NO3 - transporter known to be involved in this function. This influx transporter may favor the NO3 - secretion into the xylem sap by reabsorbing ions present in the apoplasm into the stele symplasm. Transcript profiles of the mutant and the wild type have been compared using the dedicated macro-array. Inactivation of AtNRT1.5 has important consequences on the expression of PTR and AMT genes. The significance of these molecular responses remains to be understood.