Trends in Biotechnology
ReviewHarnessing the potential of hairy roots: dawn of a new era
Section snippets
Underground resources of plants: a paradigm shift
Several secondary metabolites of pharmaceutical interest are accumulated in plant roots [1]. However, harvesting roots is destructive for the plants and hence there has been a growing interest to generate hairy roots from medicinal plant species (Table 1; Box 1). Hairy roots develop as the consequence of the interaction between Agrobacterium rhizogenes, a Gram-negative soil bacterium, and the host plant (Box 2). To generate hairy roots, wounded plant tissues are inoculated with A. rhizogenes,
Transcriptome analysis of elicited hairy roots and T-DNA activation tagging are used for metabolic gene discovery
Valuable secondary metabolites are often synthesized by plants for defence against pathogens, and the corresponding biosynthesis pathways are known to be induced by pathogen cell-wall-derived molecules called elicitors. Several elicitors have been successfully tested to increase the production or the secretion of secondary metabolites in hairy roots from different plant species (Table 2). For example, the stress hormone methyl jasmonate (MeJa), which often has a role as secondary messenger in
The metabolic engineering of hairy roots
Sometimes the biosynthesis of a valuable metabolite by hairy roots is limited by the availability of its precursor. One solution to address this problem is to add the desired product to the culture medium, but this can be costly if the precursor is difficult to synthesize or to obtain from other natural sources. In this context, the co-culture system (see Glossary) has proven to be a judicious alternative for the production of the anti-tumor drug podophyllotoxin by Podophyllum hexandrum cell
Genetic transformation of hairy roots can help to design metabolic traps
When the produced metabolites are secreted into the culture medium, a trapping system can enhance the biosynthesis of them, opening the way to design continuously producing culture systems. Metabolite trapping (see Glossary) depends on the chemical nature of the metabolite considered. The addition to the culture medium of an alumina:silica (ratio 1:1) trap made it possible to recover 97.2% of betalaines, the red natural pigments produced by Beta vulgaris hairy roots [23]. Similarly, adding
Hairy roots for molecular farming
The possibility to express functional animal proteins in hairy roots makes this plant material attractive for molecular farming (see Glossary), with several advantages compared with field-cultured plants. These advantages are mostly based on the fact that hairy roots are cultured in confined recipients, avoiding transgene or pharmacologically active protein dissemination in the environment, and in controlled conditions of growth, avoiding pollution of the produced proteins. Recombinant proteins
Scale-up and integration of technology to industry
When fast-growing, properly engineered hairy roots and their culture medium have been optimized, it remains to scale-up the culture for industrial production. Different bioreactor systems are suitable for hairy root cultures. The most traditional system is to adopt the airlift bioreactors used for microorganisms or plant cells to culture the transformed roots in liquid medium, as reported for the hairy roots of Beta vulgaris, Artemisia annua and Astragalus membranaceus 30, 31, 32, 33.
Hairy roots: centre stage of pharmaceutical biotechnologies
The hairy root culture is entering into a new phase, drawing benefit from the progress made in the field of the natural biodiversity of plants, metabolic engineering, animal protein expression in plant system and the conception of new bioreactor systems adapted to root culture. Concerning the natural metabolite production, the discovery of transcription factors regulating several genes of a biosynthetic pathway will stimulate the improvement of hairy roots to produce molecules that are normally
Glossary
- Airlift system
- the medium is mixed and gassed by introducing air, or another gas mixture, inside a tube placed at the base of the reactor.
- Airlift mesh draught reactor
- an airlift system equipped with a concentric draft-tube internal-loop. Gas sparging is carried out on the draft-tube bottom so that the liquid circulation is driven from riser to down corner.
- Basket bubble bioreactor
- a co-culture system with two identical glass domes separated by a silicon gasket. Cultures are immobilized inside the
References (54)
‘Radicle’ biochemistry: the biology of root-specific metabolism
Trends Plant Sci.
(1999)Agrobacterium T-DNA integration: molecules and models
Trends Genet.
(2004)- et al.
Plant ‘hairy root’ culture
Curr. Opin. Biotechnol.
(1999) Elicitation of different Panax ginseng-transformed root phenotypes for an improved ginsenoside production
Plant Physiol. Biochem.
(2003)Characterization of lucidin formation in Rubia tinctorum L
Plant Physiol. Biochem.
(2005)The use of genetics to dissect plant secondary pathways
Curr. Opin. Plant Biol.
(2005)Alkaloid production in Duboisia hybrid hairy roots and plants overexpressing the h6h gene
Plant Sci.
(2003)- et al.
Determination of metabolic rate-limitations by precursor feeding in Catharanthus roseus hairy root cultures
J. Biotechnol.
(2000) Metabolic engineering of the indole pathway in Catharanthus roseus hairy roots and increased accumulation of tryptamine and serpentine
Metab. Eng.
(2004)- et al.
Transhinone production and isoprenoid pathways in Salvia miltiorrhiza hairy roots induced by Ag+ and yeast elicitor
Plant Sci.
(2005)