Conjugation support — Intermediate vectors carrying T-DNA are often conjugation-deficient. Which helper plasmid is classically used to mediate conjugation into Agrobacterium?

Introduction / Context:
Triparental mating is a classical way to move plasmids from E. coli into Agrobacterium. A mobilizable but non-self-transmissible plasmid (the intermediate or binary vector) needs transfer functions supplied in trans by a helper plasmid.

Given Data / Assumptions:

• Intermediate vectors often lack tra genes.
• Helper plasmids provide mob/tra functions.
• Efficient conjugation is routine in plant transformation pipelines.

Concept / Approach:
pRK2013 is a widely used helper plasmid that carries transfer genes allowing mobilization of vectors bearing an origin of transfer (oriT). In a triparental setup, donor (vector), helper (pRK2013), and recipient (Agrobacterium) strains are mixed, enabling conjugative transfer of the vector into Agrobacterium.

Step-by-Step Solution:

Verification / Alternative check:
Method sections in plant transformation protocols consistently cite pRK2013 as the standard helper for conjugation.

Why Other Options Are Wrong:

• pRN 3: not a standard helper plasmid in this context.
• “Either (a) or (b)” fails because only (a) is correct.
• “None of these” and pUC19: pUC19 is a cloning vector without tra functions.

Common Pitfalls:
Assuming any plasmid can act as a helper; transfer requires specific tra/mob machinery and oriT compatibility.

Final Answer:
pRK 2013