Plant hairy roots: Induction, applications, limitations and prospects

Hairy roots (HRs) are highly branched adventitious roots generated by the infection of plants with Agrobacterium rhizogenes. Due to the fast growth rate, genetic stability, strong biosynthetic ability, hormone autotrophy, and low cultivation cost, hairy roots have become an excellent base for the biosynthesis of plant secondary metabolites, recombinant proteins (such as vaccines, antibodies, antibody derivatives, and pharmaceutical proteins), and industrial products. In particular, hairy roots are considered to be fast, efficient, and the most promising bioreactors for the production of plant secondary metabolites. Interestingly, the use of hairy root induction can produce composite plants (composed of transgenic roots and wild-type shoots) and whole-plant transgenic plants with stable gene expression, thus providing new tools for gene function research and crop improvement. In addition, the research value and application prospects of hairy roots in phytoremediation have gradually attracted attention in recent years. This review elaborates on the mechanism and factors influencing the induction of hairy roots by A. rhizogenes. It also provides a detailed review of the application of hairy roots in the biosynthesis of beneficial substances (such as plant secondary metabolites, recombinant proteins, and industrial products), genetic transformation of plants, and environmental remediation. This article provides a reference and basis for in-depth research on the application of hairy roots and also calls on more researchers to conduct further research and exploration on the application of hairy roots.