Alexandra Weisberg (Jeff Chang lab) is lead author on a new paper published in Science

Agrobacterium is one of the most important pathogens of plants. These bacteria have the remarkable ability to transfer a portion of its DNA and genetically alter plants to cause crown gall or hairy root diseases. These are economically important disease for nurseries, one of the top agricultural commodities in the state of Oregon. In addition, Agrobacterium strains have been modified into tools and are foundational in plant research and plant biotechnology.

In this study led by Dr. Weisberg, a team of researchers developed a new strategy to study DNA elements, called plasmids, that give Agrobacterium the capacity to cause disease. Whole genome sequences from hundreds of strains collected over nearly one century and across the world were generated and analyzed. The strategy separated plasmid sequences from chromosomal sequences and inferred the evolutionary histories for the two. One of the more surprising findings was that the plasmids, which have a tendency to exchange genes and adopt structural variants, are more closely related to each other than originally assumed. The research team used this information to trace with high accuracy, the global spread of disease. Many different epidemiological patterns were uncovered and revealed how both shipping infected plants across the world and Agrobacterium exchanging plasmids contribute to accelerate disease spread. This understanding can be used to guide strategies to mitigate disease risks.

Michael Belcher was an undergraduate in the lab and is currently pursuing a PhD in plant biology at the University of California, Berkeley.

This study had many key contributions from many collaborators in the department, at USDA-ARS, and from Academia Sinica, an academic institution in Taiwan. Many of the strains that were sequenced were originally collected by Dr. Larry Moore, who retired from the department in 1999.