Question

Production of hairy roots due to agrobacterium rhizogenes

Answer 1

Toshiya Muranaka, Kazuki Saito, inComprehensive Natural Products II, 2010

3.17.2.2 Hairy Root Cultures

When Agrobacterium rhizogenes, a Gram-negative soil bacterium, infects plants, adventitious roots called ‘hairy roots’ are induced from the infected site.110,111This event occurs due to the transfer of the particular DNA region called transfer DNA (T-DNA) comprising the loci between the TR and TL regions of the root-inducing (Ri) plasmid of the bacterium into the plant genome. The basic molecular mechanism of T-DNA trimming from the Ri plasmid, transfer to plant cells, and integration into the plant genome is known, although the functions of several genes on the T-DNA have not yet been elucidated. The hairy roots are aseptically cultured in vitrowithout added phytohormones.

As described in Section 3.17.2.1, undifferentiated plant cell cultures are successfully used to produce valuable secondary metabolites such as shikonin and paclitaxel, but many researchers have realized that plant cell culture is not always successful for the purpose of their production. Even if the cultured cells produced the desired compounds, the concentration was often very low compared to that of intact plants.

Several secondary metabolites of pharmaceutical interest are accumulated in plant roots. Hairy root cultures, in contrast to undifferentiated cell cultures, can usually synthesize the same compounds as the roots of the intact plant. In 1986, three laboratories independently demonstrated the production of secondary metabolites by hairy root cultures, including the production of tropane alkaloids by Atropa belladonna43 and Scopolia,112 and nicotine by Nicotiana rustica.113

Agrobacterium rhizogenes-mediated transformation has several features desirable for the production of secondary metabolites. The rapid and efficient induction of hairy roots from explant tissues in a wide variety of plant species, including medicinal plants, has been reported. These hairy roots are characterized by a high growth rate and high root branching without added phytohormones. Furthermore, they often produce secondary metabolites for a long period of time, unlike intact roots. For these reasons, switching from undifferentiated cell culture to hairy root culture is considered an attractive alternative for the production of many valuable secondary metabolites that originally accumulated in root tissues. In Table 1, the hairy root culture of medicinal plants is listed as ‘HR’.