Q.57 With reference to Agrobacterium tumefaciens
mediated plant transformation, match the virulence factors in
Group 1 with their protein types in Group 2.

1. P–i, Q–ii, R–iv, S–iii
2. P–iii, Q–i, R–ii, S–iv
3. P–i, Q–iv, R–i, S–iii
4. P–iii, Q–i, R–iv, S–ii

Correct matching is: P–iii, Q–i, R–iv, S–ii, so the right option is (D).​

Virulence factors and their protein types

• VirG → Transcriptional activator (P–iii)

  • VirG is the response‑regulator of the VirA/VirG two‑component system in Agrobacterium tumefaciens.​

  • When phosphorylated by VirA, VirG binds vir gene promoters and activates transcription, hence it is a transcriptional activator.​

• VirA → Kinase (Q–i)

  • VirA is a membrane‑bound histidine sensor kinase that autophosphorylates on a conserved histidine residue.​

  • It then transfers the phosphate to VirG, so VirA is correctly classified as a kinase.​

• VirE → Single‑strand binding protein (R–iv)

  • The virE locus encodes VirE2, a large single‑stranded DNA‑binding protein that coats the T‑strand during transfer to the plant cell.​

  • This coating protects ssT‑DNA from nucleases and aids its transport, so VirE corresponds to a single strand binding protein.​

• VirC → Helicase (S–ii)

  • The VirC operon encodes proteins associated with T‑DNA processing, including a DNA‑dependent ATPase/topoisomerase‑like component that acts in unwinding and nicking at the overdrive sequence.​

  • Functionally this complex behaves as a helicase‑type activity facilitating T‑strand generation, so VirC matches helicase in the given list.​

Why each option is right or wrong

• Option (A): P–i, Q–ii, R–iv, S–iii – Incorrect

  • Assigns VirG as a kinase and VirA as a helicase, but VirG is a transcriptional activator and VirA is a histidine kinase.​

  • VirC is labeled transcriptional activator here, which is wrong because it participates in T‑DNA processing, not global vir gene transcription.​

• Option (B): P–iii, Q–i, R–ii, S–iv – Incorrect

  • Correctly identifies VirG as transcriptional activator and VirA as kinase.​

  • However, it incorrectly classifies VirE as helicase and VirC as single‑strand binding protein, which contradicts the known ssDNA‑binding role of VirE2 and processing role of VirC.​

• Option (C): P–ii, Q–iv, R–i, S–iii – Incorrect

  • Swaps almost all functions, giving VirG a helicase role, VirA a single‑strand binding role, and VirE a kinase role, none of which are supported by experimental data.​

  • Only VirC as transcriptional activator might superficially seem regulatory, but VirC is not the main transcription factor; VirG performs that role.​

• Option (D): P–iii, Q–i, R–iv, S–ii – Correct

  • Matches VirG with transcriptional activator, VirA with kinase, VirE with single‑strand binding protein, and VirC with helicase‑type activity in T‑DNA processing; this fits the established molecular biology of Agrobacterium tumefaciens virulence.​

Introduction

Agrobacterium tumefaciens virulence factors are central to plant genetic transformation and frequently appear in competitive exams like GATE and CSIR NET. Understanding how to correctly match VirG, VirA, VirE and VirC with their protein types helps students master Ti‑plasmid biology and solve assertion‑reason or matching‑type questions with confidence.​

VirA and VirG: two‑component regulators

• VirA is a membrane‑bound histidine kinase that senses plant wound signals such as phenolic compounds and low pH.​

• Phosphorylated VirA transfers the phosphate to VirG, converting VirG into an active transcriptional regulator of multiple vir operons.​

VirE and VirC: T‑DNA processing helpers

• The VirE operon encodes VirE2, a single‑stranded DNA‑binding protein that coats the T‑strand and protects it during transfer into the plant cell.​

• VirC proteins participate in processing at the overdrive region and exhibit helicase‑like DNA unwinding and ATPase activities needed for efficient T‑strand production.​

Exam‑oriented takeaway

• Remember the pair “VirA kinase – VirG activator” as a classic two‑component system in Agrobacterium tumefaciens virulence.​

• Link “VirE ssDNA‑binding – VirC helicase‑like” with T‑DNA formation and protection to quickly choose option (D): P–iii, Q–i, R–iv, S–ii in similar matching questions.​