The virB operon is the largest operon within the virulence regulon, consisting of 11 genes, virB1 to virB11, and is responsible for transferring T-DNA and effector proteins from the bacterium into the plant cell during infection. VirB1 encodes a lytic transglycosylase that degrades the bacterial peptidoglycan cell wall, facilitating insertion and assembly of T4SS. virB2 encodes the major pilin subunit, which is processed and polymerized to form the T-pilus, which is essential for DNA transfer to the plant cell. VirB3 encodes an inner membrane protein necessary for T-DNA secretion and it interacts with virb4 to facilitate formation of the T-pilus. virB4 and VirB11 encode ATPases that generates energy necessary for T-DNA transport across the membrane. VirB5 forms the minor pilin subunit of the T-pilus. virB6 encodes an inner mermbrane protein involved in the transport of virulence factors through the T4SS and also stabilizes virB5 and virB3 and virB7 formation. virB7 encodes an outer membrane lipoprotein, which together with virB9 anchor the T4SS to the bacterial outer membrane. VirB8 encodes a membrane protein that serves as a scaffold for T4SS assembly. virB9 encodes an outer membrane-associated protein that is part of the T4SS channel and lastly, virB10 encodes a transmembrane protein that forms part of the channel through which T-DNA as well as virB2 and virB5 factors are translocated.

Virulence (virB operon activation) References