Agrobacterium counteracts host-induced degradation of its effector F-box protein.

The SCF (Skp1-Cul1-F-box protein) ubiquitin ligase complex plays a pivotal role in various biological processes, including host-pathogen interactions. Many pathogens exploit the host SCF machinery to promote efficient infection by translocating pathogen-encoded F-box proteins into the host cell. How pathogens ensure sufficient amounts of the F-box effectors in the host cell despite the intrinsically unstable nature of F-box proteins, however, remains unclear. We found that the Agrobacterium F-box protein VirF, an important virulence factor, undergoes rapid degradation through the host proteasome pathway. This destabilization of VirF was counteracted by VirD5, another bacterial effector that physically associated with VirF. These observations reveal a previously unknown counterdefense strategy used by pathogens against potential host antimicrobial responses.