Hairy Root Culture and Rhizosecretion

The use of hairy roots for the production of biopharmaceuticals has been studied extensively and has been discussed in Chapter 1 of this book. To date, over 116 different plant species have been induced to produce hairy roots in culture (Guillon, 2006). Originally, an expression system was developed for protein production based on the natural secretion from roots of intact plants. In order to take up nutrients from the soil, interact with other soil organisms, and defend themselves against numerous pathogens, plant roots have developed sophisticated mechanisms based upon 

Biopharmaceuticals in Plants Toward the Next Century of Medicine 

Rhizosecretion is easy to scale up and very cost effective with respect to isolation and purification. However, the bioreactor systems used for hairy root cultures differ from those used for plant cell suspensions. Traditional bioreactor systems have recently been adapted for root culture, and this technology is now being taken to commercial scales. The most traditional system is the airlift bioreactor used for microorganisms or plant cells. This system is adapted for the culturing of roots in liquid medium. Mist culture systems have also been developed. For this technology, the volume of the culture medium is reduced and the concentration of the secreted therapeutic protein is increased. If the protein to be produced is known to be quite stable, then a less expensive hydroponic culture can be designed in a manner suitable for scale-up. 

The production of pharmaceutical proteins using hairy roots and rhizosecretion technology represents a safe and viable alternative to the use of whole plants for molecular pharming. As an example of the efficiency of this system, Medina-Bolivar and Cramer (2004) expressed the reporter protein GFP in tobacco hairy root cultures using a plastic sleeve bioreactor with a 5 L volume. Yields of 500 pg GFP/L after 21 days of incubation or 20% of total secreted protein were produced using this expression system, suggesting that rhizosecretion offers a promising production system for the production of biopharmaceuticals. 

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