Explanation of the hormone’s role

• Acetosyringone is a phenolic compound released by wounded dicot tissues. It serves as a signal that induces the vir (virulence) genes on Agrobacterium’s Ti plasmid.

• Activation of the vir operon is essential for processing T‑DNA, forming the T‑strand, and assembling the transfer machinery, which greatly increases transformation efficiency.

Option‑by‑option analysis

1. Helps in anchorage of bacteria to plant cell wall – Incorrect

• Bacterial attachment mainly involves proteins like VirA, VirB, and surface polysaccharides, but acetosyringone’s primary known role is as a chemical inducer of vir genes, not as a glue that anchors cells.

2. Activates vir operon of bacteria – Correct

• Acetosyringone binds to the VirA/VirG two‑component regulatory system, leading to transcriptional activation of vir genes required for T‑DNA transfer. This is exactly why it is added during co‑cultivation.

3. Helps in integration of T‑DNA in plant genome – Incorrect

• T‑DNA integration uses plant DNA repair and recombination machinery. Acetosyringone does not catalyze integration directly; it acts earlier, at the stage of vir gene induction and T‑DNA processing.

4. Promotes bacterial growth by activating genes in plant – Incorrect

• Acetosyringone does not stimulate plant genes to feed the bacterium. In fact, at certain conditions it can even inhibit Agrobacterium growth; its key function in transformation protocols is vir‑gene induction, not growth promotion.

SEO‑oriented introduction (for article use)

In Agrobacterium‑mediated plant transformation, acetosyringone is a crucial additive because it activates the vir operon of Agrobacterium, which in turn drives T‑DNA processing and transfer into plant cells. Without this phenolic inducer, vir gene expression remains low and transformation efficiency drops, whereas adding acetosyringone significantly enhances successful integration events.