Abstract
About a third of Gram-negative bacteria encode one or multiple type VI secretion systems (T6SS) that function to inject effectors/toxins into eukaryotic or prokaryotic cells to benefit their survival and fitness. Structural and functional studies revealed that T6SS machine resembles bacteriophage tail-like structure with valine glycine repeat G (VgrG) likely acting as a spike protein to pierce the host cell membrane for effector delivery. We study the secretion mechanisms and effector functions of T6SS in Agrobacterium tumefaciens, a plant pathogenic bacterium causing crown gall disease in a wide range of plants. A. tumefaciens T6SS produces three toxins, namely a peptidoglycan targeting protein Tae and two nucleic acid targeting proteins Tde1 and Tde2, which confer T6SS-dependent interbacterial competitive advantage to A. tumefaciens inside the host plant. Further studies revealed that two VgrG paralogs in A. tumefaciens, namely VgrG1 and VgrG2, specifically control the secretion and in-planta bacterial competition activity of Tde1 and Tde2, respectively. By deletion and domain swapping, we revealed that the variable C-terminal region of VgrGs is responsible for the Tde secretion and/or bacterial competition specificity. The molecular determinants responsible for Tde secretion specificity and underlying mechanisms will be presented and discussed.
Bio
The major research interests in my laboratory are to understand the molecular mechanisms underlying how bacterial pathogens deploy protein secretion systems for survival and successful infection. My laboratory investigates the mechanistic and biological insights of the type IV and type VI secretion systems (T4SS and T6SS) in Agrobacterium tumefaciens, the causal agent of crown gall disease and powerful gene transfer tool. Our recent research findings have uncovered a role of T4SS-associated T-pilus during DNA transformation process and novel T6SS DNase effectors involved in interbacterial competition during plant infection process. We are also interested in developing new tools for dissecting Agrobacterium-plant interactions and applying our knowledge of T4SS and T6SS nanomachines for technology development.