Plasmid tools — In Agrobacterium-mediated plant transformation workflows, which statement is NOT true about helper plasmids?

Introduction / Context:Helper plasmids are central to both co-integrative and binary vector systems used with Agrobacterium. Distinguishing their real properties from misconceptions helps avoid design errors in cloning and conjugation steps.

Given Data / Assumptions:

• Helper plasmids typically carry transfer (tra) functions and sometimes vir genes.
• They replicate in Agrobacterium and can mediate mobilization of non-self-transmissible vectors.
• Intermediate vectors may be conjugation-deficient and need a helper.

Concept / Approach:By definition, helper plasmids are compatible replicons in Agrobacterium that provide necessary functions for conjugation and/or virulence in trans. Therefore, the claim that they cannot replicate in Agrobacterium is incorrect.

Step-by-Step Solution:

Verification / Alternative check:Widely used helpers like pRK2013 function in Agrobacterium, enabling triparental mating and plasmid mobilization.

Why Other Options Are Wrong:

• Replicate in Agrobacterium: correct.
• Mediate conjugation: correct.
• Provide vir in trans (in some systems): correct.
• “All of the above”: cannot be correct because one choice is false.

Common Pitfalls:Confusing helper plasmids with E. coli-only cloning plasmids that lack replication origins compatible with Agrobacterium.

Final Answer:These can't replicate in Agrobacterium