The virC operon is part of the broader virulence (vir) regulon that is essential for a bacterium's ability to transfer T-DNA to plant cells, causing crown gall disease. The virulence genes are typically located on the Ti (tumor-inducing) plasmid, and their expression is regulated in response to plant-derived signals. The bicistronic operon is composed of 2 genes - virC1 and virC2 and its primary role is to enhance T-DNA transfer from the bacterial cell to the plant cell. The efficiency of the T-DNA transfer is improved by the virC genes which interact with the T-DNA complex and recognize DNA sequences necessary for a successful transfer. Expression is controlled by virA which encodes for transmembrane histidine protein kinase, virG which encodes a cytoplasmic response regulator and the periplasmic sugar-binding protein ChvE. AS binds to transmembrane histidine protein kinase virA, resulting in phosphorylation of virG which then binds to the vir box (10 to 12bp sequences) in the promoter region and initiates transcription. The operon transcription is repressed by a chromosomal gene known as Ros which encodes for a transcriptional regulator and competes with virG thus countering infection.

Virulence (virC operon activation) References