This project grew out of our work on the RPM1 disease resistance gene of Arabidopsis, which mediates recognition of the AvrB protein of Pseudomonas syringae. To obtain insights into how the specificity of disease resistance genes is determined, and how it co-evolves with pathogens, we sought to isolate a resistance gene from soybean, Rpg1, which also mediates recognition of AvrB. Our original expectation was that Rpg1 and RPM1 would be derived from a common ancestral gene. However, we have recently isolated Rpg1 and determined that although it belongs to the same general class of R genes as RPM1 (i.e. the CC-NBS-LRR class), Rpg1 and RPM1 are independently derived, which indicates that R genes with AvrB specificity have evolved at least twice during flowering plant evolution.

In the course of isolating Rpg1 from soybean we found that it is located amongst a very large cluster of R genes distributed over several hundred kilobases of soybean linkage group F. We also found very little conservation of gene order between soybean and Arabidopsis in this region, which indicates that this chromosomal region may be rearranging at a rapid rate. Because recombination between R genes is believed to contribute to the evolution of new specificities, we decided to take a much more in depth look at this region relative to its genomic structure and how it is evolving. We have recently received funding from the NSF PGRP to sequence and analyze an approximately one megabase region surrounding Rpg1 in soybean, and in several wild relatives of soybean, including both diploid and polyploid species. These analyses will enable us to track genomic rearrangement events over evolutionary time, and to assess the impact of genome duplication events on chromosomal structure. See our dedicated website NSF PROJECT for additional details on this project.