Agrobacterium tumefaciens is a soil phytopathogen that naturally infects plant wound sites and causes crown gall disease via delivery of T-DNA from bacterial cells into host plant cells through a bacterial type IV secretion system (T4SS). My laboratory studies the mechanistic and biological functions of the T4SS and recently discovered type VI secretion system (T6SS) in A. tumefaciens. Functional and structural studies have revealed that T6SS resembles bacteriophage tail structure and is capable to target toxin effectors to both eukaryotic and prokaryotic cells to increase their fitness. We discover that T6SS is regulated by multiple plant signals at transcriptional and post-translational levels. We found that A. tumefaciens is able to deploy a family of T6SS DNase toxins for competitive survival in planta. We also developed a highly efficient and robust Agrobacterium-mediated transient expression system, named AGROBEST (Agrobacterium-mediated enhanced seedling transformation), which achieves versatile analysis of diverse gene functions in intact Arabidopsis seedlings. This method allows us to uncover a role of the T4SS-associated T-pilus in plant transformation process. In summary, our studies suggests that A. tumefaciens is able to coordinate and deploy T4SS and T6SS for successful transformation and survival during plant infection process.
Host: Mary Beth Mudgett