Vir gene induction (tobacco) — Which plant phenolic signal molecules regulate expression of <i>vir</i>B, <i>vir</i>C, <i>vir</i>D, and <i>vir</i>E in Agrobacterium during infection of tobacco?

Introduction / Context:
Agrobacterium senses plant wound signals to activate its virulence regulon. Phenolic compounds exuded at wound sites bind the VirA/VirG two-component system, upregulating operons such as virB–virE that are essential for T-DNA processing and transfer.

Given Data / Assumptions:

• Tobacco and many dicots release phenolics upon wounding.
• Acetosyringone is the classic inducer of Agrobacterium vir genes in lab protocols.
• Alpha-hydroxy-syringone is also an effective inducer in species like tobacco.

Concept / Approach:
Vir gene activation is not restricted to a single phenolic. Multiple related syringyl compounds can trigger VirA autophosphorylation, which then activates VirG to turn on the downstream vir operons. Therefore, both listed molecules act as regulators/inducers in this context.

Step-by-Step Solution:

Verification / Alternative check:
Plant transformation media often include acetosyringone to enhance T-DNA delivery; literature shows α-hydroxy-syringone is active especially in tobacco systems.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming a single universal inducer; induction spectrum varies with plant species and Agrobacterium strain.

Final Answer:
Both (a) and (b).