Effector loading onto the VgrG carrier activates type VI secretion system assembly

• Published in: EMBO reports 2020-01, Vol.21 (1), p.e47961-n/a
• Main Authors: Wu, Chih‐Feng, Lien, Yun‐Wei, Bondage, Devanand, Lin, Jer‐Sheng, Pilhofer, Martin, Shih, Yu‐Ling, Chang, Jeff H, Lai, Erh‐Min
• Format: Article
• Language: English
• Subjects: Agrobacterium tumefaciens; Agrobacterium tumefaciens - genetics; Assembly; Bacteria; Bacterial Proteins - genetics; Cargo; Contractility; Contraction; Deoxyribonuclease; Deoxyribonucleases; effector; Effectors; EMBO23; EMBO40; Host plants; interbacterial competition; Secretion; Sheaths; Social behavior; Spikes; Toxins; type VI secretion system; Type VI Secretion Systems - genetics; VgrG
• ISSN: 1469-221X; 1469-3178
• DOI: 10.15252/embr.201947961

The type VI secretion system (T6SS) is used by many bacteria to engage in social behavior and can affect the health of its host plant or animal. Because activities associated with T6SSs are often costly, T6SSs must be tightly regulated. However, our knowledge regarding how T6SS assembly and contraction are regulated remains limited. Using the plant pathogen Agrobacterium tumefaciens , we show that effectors are not just passengers but also impact on T6SS assembly. The A. tumefaciens strain C58 encodes one T6SS and two Tde DNase toxin effectors used as major weapons for interbacterial competition. Here, we demonstrate that loading of Tde effectors onto their cognate carriers, the VgrG spikes, is required for active T6SS secretion. The assembly of the TssBC contractile sheath occurs only in the presence of Tde effectors. The requirement of effector loading for efficient T6SS secretion was also validated in other A. tumefaciens strains. We propose that such a mechanism is used by bacteria as a strategy for efficacious T6SS firing and to ensure that effectors are loaded onto the T6SS prior to completing its assembly. Synopsis Bacterial effectors impact on the assembly of the type VI secretion machinery. Their attachment to VgrG spikes is required for active secretion, which ensures that cargo is loaded onto the T6SS prior to completing its assembly. The presence of VgrG cargo effectors is required for T6SS sheath assembly and secretion. Effector loading onto the VgrG spike activates firing of the T6SS. Effector loading is a common mechanism for regulating type VI secretion systems. Graphical Abstract Bacterial effectors impact on the assembly of the type VI secretion machinery. Their attachment to VgrG spikes is required for active secretion, which ensures that cargo is loaded onto the T6SS prior to completing its assembly.