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#Agrobacterium

16 public questions tagged with this topic.

Plant tissue culture 3

Hairy root inducing plasmid is called:

Agrobacterium plasmids determine disease phenotype. Ti plasmid, tumor-inducing, contains T-DNA with iaaM, iaaH, and ipt genes overproducing auxin and cytokinin, causing undifferentiated gall. Ri plasmid, root-inducing, carries TL and TR T-DNA regions in agropine strains; TL harbors rol cluster essential for hairy root syndrome and TR carries auxin genes and agropine synthesis. Virulence region mediates T-strand excision and transfer via type IV secretion. Upon integration, rol gene expression modifies host signaling, stimulating root proliferation rather than callus. Laboratory disarmed Ri vectors retain vir functions but delete oncogenes for transformation purposes. Naming convention Ri originates from root inducing ability, distinguishing it from Ti. Knowing plasmid identities enables selection of appropriate strain for either crown gall studies or hairy root induction, forming foundation of plant genetic engineering vector development history. Comparative genomics shows Ri plasmid TL-DNA size approximately 20 kb harboring rolA-D, while TR-DNA carries aux1, aux2 and opine synthase. Sequence analysis distinguishes agropine, mannopine, and cucumopine Ri types based on opine signature. Agrobacterium rhizogenes strain selection influences virulence and host range, critical for successful transformation of recalcitrant legumes and woody species requiring optimized co-cultivation conditions.

Ref: White & Nester J Bacteriol 1980 Ri structure; Nilsson & Olsson Physiol Plant 1997 rol; NCBI NBK21414 Ti vs Ri; https://www.ncbi.nlm.nih.gov/books/NBK21414/

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Plant tissue culture 3

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.

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Gene and Genome

Acquisition of new genes by Agrobacterium is an example of:

Horizontal gene transfer refers to non-vertical transmission of genetic material between unrelated organisms via transformation, transduction, conjugation or vectors. Agrobacterium tumefaciens exemplifies natural inter-kingdom transfer, possessing Ti plasmid bearing T-DNA flanked by border repeats. Virulence proteins excise T-DNA and deliver it through type IV secretion system into plant nucleus where it integrates, expressing oncogenes inducing crown gall formation. This natural gene delivery system underlies plant transgenesis. Acquisition of novel genes through such mechanisms spreads antibiotic resistance among bacteria and introduces foreign functions outside Mendelian inheritance.

Ref: Chilton et al., Cell 1977: Agrobacterium T-DNA Transfer as Example of Horizontal Gene Transfer

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