Résumé
Hairy roots in plants are the manifestation of infection caused by Agrobacterium rhizogenes, a gram negative soil bacterium. This phytopathogen transfers its large root-inducing (Ri) plasmid carrying a set of genes into plant genome and thereby encoding enzymes capable of modifying the plant hormonal metabolism. Such new hormonal balances induce the formation of proliferating roots, called hairy roots that emerge at the wounding site. Hairy root cultures, owing to their stable and high productivity, have been investigated from several decades to produce the valuable metabolites present in wild-type roots. The emergence of key molecules for overcoming the limiting culture parameters for the regulation of the metabolic pathways has made possible improvements in the production of secondary metabolites by hairy roots. Secretion and harvesting of these metabolites with the aid of trapping systems enhance the interest in such cultures. The use of hairy roots to produce recombinant animal proteins represents an attractive system that may be extrapolated for industrial exploitation. Equally, a good understanding of the underlying molecular mechanism, based on the transfer of the plasmid T-DNA of A. rhizogenes, opens a route for developing new strategies in metabolic engineering. Indeed, hairy root systems allow gene gain- or loss-of-function techniques and transcriptome analyses for the discovery of new metabolic genes. Because of the prolific proliferation of the roots, hairy roots could be promising tools for phytoremediation. The hairy root system must be scaled up if they are to be used in industry for the mass production of secondary metabolites.