Effector Onboard Activating Type VI Secretion System Assembly

The type VI secretion system (T6SS) is a molecular nanomachine used by many bacteria for pathogenesis or bacterial competition by injecting effectors into the target cells. Because activities associated with T6SS are often costly, T6SS must be tightly regulated. However, our knowledge regarding how T6SS assembly and contraction are regulated remains limited. Using the plant pathogen Agrobacterium tumefaciens, Erh-Min Lai and colleagues show that effectors are not just passengers but their loading onto the carriers also activate T6SS assembly across the A. tumefaciens group of bacteria. This is potentially a widespread new mechanism, which may be deployed by many T6SS-possessing bacteria as a strategy for efficacious T6SS firing to ensure that effectors are loaded onto T6SS prior to completing its assembly.