Hairy Root Cultures: A Novel Way to Mass Produce Plant Secondary Metabolites

The in vitro method of transformation of root cultures using natural soil-borne bacterium Rhizobium rhizogenes (earlier known as Agrobacterium rhizogenes) is considered as a novel biotechnological tool to overproduce plant secondary metabolites from diverse plant species. The characteristic neoplastic roots that appear at the infection site owing to the transfer DNA insertion from Ri plasmid exhibit several unique characters such as rapid growth rate without the need of growth hormones, high genetic stability, and biosynthesis of plant secondary metabolites at levels even higher or comparable to their natural counterparts. The ease of hairy root culture in liquid system has escalated the platforms for large-scale production of various therapeutical, cosmeceutical, and nutraceutical metabolites in controlled bioreactor systems. The technology also offers the additional advantage of overexpression of tailor-made metabolites through metabolic engineering of plant biosynthetic pathways. Recently, the application of elicitors (signal molecules) in hairy root cultures has further kindled the robustness of this technique for the large-scale synthesis of specific plant metabolites. Thus, the present appraisal aims to discuss the recent progress, achievements, and future trends of hairy root technology, a pioneering expression system to meet the large-scale demand of valuable phytochemicals.