Hairy root cultures are induced by infection with:
Hairy root syndrome originates when wounded dicot tissue is invaded by soil bacterium carrying root inducing plasmid. Transfer of T-DNA segment harboring rolA, rolB, rolC, rolD loci plus opine synthesis genes into host chromosome rewires hormone balance. rolB encodes tyrosine phosphatase increasing auxin sensitivity, rolC cytokinin glucosidase adjusting growth, together triggering extensive adventitious root emergence directly from callus. Roots grow plagiotropically, highly branched, hormone independent, and genetically stable for decades. In contrast Agrobacterium tumefaciens produces crown gall tumors via cytokinin and auxin genes. Distinguishing pathogens is vital for biotechnology applications: rhizogenes-mediated transformation provides root-specific secondary metabolite factories exploited for alkaloid, ginsenoside, and flavonoid production. Therefore Agrobacterium rhizogenes is identified as causal agent inducing hairy root cultures used worldwide in metabolic engineering research. Mechanism includes virD2 mediated T-strand processing and integration via non-homologous end joining, expression of rol genes altering auxin signal transduction via tyrosine phosphatase activity. Resulting roots produce opines like agropine used by bacteria as carbon source. Cultures maintained on hormone-free medium for years retain biosynthetic capacity for root-specific metabolites, validating Agrobacterium rhizogenes as natural genetic engineer.
Ref: Chilton Nature 1982 Ri plasmid; Tepfer PNAS 1984 hairy root; NCBI NBK21344 rol genes; PubMed 17302573 hairy root review 2014.