Dan Pierce's Lab

The pathogen Agrobacterium tumefaciens (also known as Rhizobium radiobacter) causes crown gall tumors in plants. Decades of work in various labs have worked out the molecular players that are necessary for this process, including the discovery that Agrobacterium capitalize on wounding events in plants to initiate pathogenesis. Agrobacterium uses molecules released by these wound sites to 1) undergo chemotaxis towards a healthy plant cell and 2) induce the production of virulence proteins that physically secrete oncogenic DNA into the healthy plant cell. The tumorigenic plant cells then produce opines, which are selectively metabolized by pathogenic Agrobacterium. This system of pathogenesis is the only known instance of interkingdom gene transfer and has been capitalized by plant geneticists around the world to create transgenic plants.

Our current research primarily focuses on how Agrobacterium receives signals from the plant wound site. Two signals, phenols and sugars, are recognized via an intermembrane histidine kinase, VirA. We have developed several mutants of VirA that appear to alter pathogenic strategy of signal recognition and we continue to probe this using mutagenesis. We can then test how these mutants affect tumor formation in a variety of plants. Additionally, we are examining how the function of VirA is determined by its structure. Finally, we have created fluorescent Agrobacterium biosensors that help us determine the signaling landscape around a wound site that allows for bacterial pathogenesis.

Current Projects

  • Characterizing the histidine kinase VirA in its coordination of signals from a host wound site
  • Biochemical and biophysical analysis of the linker region of VirA in phenol recognition
  • Uncovering Agrobacterium pathogenesis using confocal microscopy and assaying plant tumor formation
  • Synthetic development of AgroImmunity, a method of inducing a plant immune response to prevent pathogenesis from virulent Agrobacterium

Current University of Richmond Research Students

Nicole Walker (’20)
Ahkar Phyo (’20)
Ana Shimeall (’20)
Savannah Del Cid (’21)
Majd Aboul Hosn (’21)
Loreto Malinowski (’22)
Chandler Barrett (’22)
Rich Diep (’22)

University of Richmond Graduates (selected list)

Bryan Daunt (Shenandoah University, PA program)
Joe McCahon (Philadelphia College of Osteopathic Medicine)
Silvia Garcia-Moreno (Shenandoah University, PA program)
Zaka Asif (University of Georgia, Life Sciences PhD program)
Aidan Murphy (Boston University, Chemistry PhD program)