Hirschfeldia incana, is a pseudometallophyte belonging to the Brassicaceae family, widespread in the Mediterranean region and a medium perennial shrub. This plant has good ability to grow on soils contaminated by lead (Pb). We used Hirschfeldia incana as a model for molecular characterization of Pb tolerance and accumulation in plants.

Microarrays comparison of gene expression between H. incana and a susceptible plant to Pb (Arabidopsis thaliana) , enabled the identification of a set of specific genes expressed in response to lead exposure. The number of genes specifically regulated by Pb in H. incana was higher in shoots than in roots, with 602 and 341 genes, respectively. Four groups of genes were particularly over-represented due to the Pb exposure and are categorized into biological processes as photosynthesis, cell wall, transport and metal handling.

Expression profile of a subset of differentially regulated genes involved specifically in transport and metal handling was also checked by qRT-PCR in H. incana.

Our results suggest a possible scenario of Pb tolerance and accumulation mechanisms in H. incana. In roots, Pb is probably chelated with defensins at the cytosol level and interact with membrane transporters. Then, HMA4 a P-type ATPase transporter may play a role in Pb translocation to aerial parts through the xylem. Once in the leaves, ferritin and Metalothinein can play an essential role in Pb distribution in leaves and Pb binding and sequestration in cells. MRP14 transporter can be involved in the Pb storage in the vacuoles probably in a conjugate form (glutathione-Pb). Another transporter, GCN2 from the ABCF family, can contributed in Pb storage in chloroplast.

This study provided new insights into the molecular mechanisms of Pb tolerance and accumulation in plants and opens new ways for the study and the selection of heavy metals tolerant plants.