Molecular mechanisms of the Agrobacterium Type VI DNase effector secretion and antibacterial activity during plant colonization
E. LAI (1) (1) Institute of Plant and Microbial Biology, Academia Sinica, Taiwan

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.


Abstract Number: S5-1
Session Type: Special Session