Agrobacterium-mediated gene transfer methods In plant biotechnology workflows that use Agrobacterium tumefaciens, the transfer of an ‘‘intermediate’’ cloning vector constructed in Escherichia coli into Agrobacterium cells is most commonly accomplished by which method?

Introduction / Context:
Agrobacterium tumefaciens is a cornerstone of plant genetic engineering because it naturally transfers T-DNA to plant cells. Before plant transformation, researchers often need to move an intermediate vector (assembled in Escherichia coli) into Agrobacterium. Understanding the classical method used to mobilize these plasmids clarifies historical and practical lab procedures.

Given Data / Assumptions:

• Intermediate vectors are typically mobilizable but not self-transmissible.
• Agrobacterium accepts plasmids via conjugation if transfer (tra/mob) functions are supplied.
• Multiple laboratory routes exist today (e.g., electroporation), but the question targets the canonical approach.

Concept / Approach:

Triparental mating uses three partners: (1) an E. coli donor carrying the intermediate vector, (2) an E. coli helper strain carrying a broad-host-range transfer/helper plasmid that supplies tra/mob functions, and (3) the Agrobacterium recipient. The helper plasmid enables conjugative mobilization of the intermediate vector into Agrobacterium where it can replicate or recombine, enabling subsequent plant transformation.

Step-by-Step Solution:

Verification / Alternative check:

Many legacy protocols (prevalent before routine electroporation of Agrobacterium) describe mixing donor, helper, and recipient on filters/plates, recovering transconjugants with appropriate antibiotic selection—consistent with triparental mating being the standard historical method.

Why Other Options Are Wrong:

Transformation of Agrobacterium without specialized methods is inefficient. Biparental mating lacks the helper's tra/mob functions for non-self-transmissible plasmids. Transduction in Agrobacterium is not a routine route for plant vectors. Electroporation is possible but was not the classical mainstay implied by ‘‘intermediate vector’’ mobilization.

Common Pitfalls:

Confusing modern electroporation convenience with the historically dominant conjugation-based mobilization strategy requiring a helper plasmid.

Final Answer:

Triparental mating (helper plasmid provides mobilization functions)