Transgenic hairy roots: recent trends and applications

Agrobacterium rhizogenes causes hairy root disease in plants. The neoplasti c roots produced by A. rhizogenes infection is characterized by high growth rate and genetic stability. These genetically transformed root cultures ca n produce higher levels of secondary metabolites or amounts comparable to t hat of intact plants. Hairy root cultures offer promise for production of v aluable secondary metabolites in many plants. The main constraint for comme rcial exploitation of hairy root cultures is their scaling up, as there is a need for developing a specially designed bioreactor that permits the grow th of interconnected tissues unevenly distributed throughout the vessel. Rh eological characteristics of heterogeneous system should also be taken into consideration during mass scale culturing of hairy roots. Development of b ioreactor models for hairy root cultures is still a recent phenomenon. It i s also necessary to develop computer-aided models for different parameters such as oxygen consumption and excretion of product to the medium. Further, transformed roots are able to regenerate genetically stable plants as tran sgenics or clones. This property of rapid growth and high plantlet regenera tion frequency allows clonal propagation of elite plants. In addition, the altered phenotype of hairy root regenerants (hairy root syndrome) is useful in plant breeding programs with plants of ornamental interest. In vitro tr ansformation and regeneration from hairy roots facilitates application of b iotechnology to tree species. The ability to manipulate trees at a cellular and molecular level shows great potential for clonal propagation and genet ic improvement. Transgenic root system offers tremendous potential for intr oducing additional genes along with the Ri T-DNA genes for alteration of me tabolic pathways and production of useful metabolites or compounds of inter est, This article discusses various applications and perspectives of hairy root cultures and the recent progress achieved with respect to transformati on of plants using A. rhizogenes, (C) 2000 Elsevier Science Inc, All rights reserved.