Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2003
Publication Date: 9/1/2003
Citation: Ashfield, T., A. Bocian, D. Held, A.D. Henk, L.F. Marek, D. Danesh, S. Penuela, K. Meksem, D.A. Lightfoot, N.D. Young, R.C. Shoemaker and R.W. Innes. 2003. Genetic and physical localization of the soybean Rpg1-b disease resistance gene reveals a complex locus containing several tightly linked families of NBS-LRR genes. Molecular Plant-Microbe Interactions 16:817-826. Interpretive Summary: AThis paper describes the evolution of a gene that confers resistance to a bacterial pathogen of legumes. Similarities and differences of DNA sequences were used to gain insights on evolution within legumes, and the point of divergence between Glycine and Phaseolus.
Technical Abstract: Alleles or tightly linked genes at the soybean (Glycine max L. Merr.) Rpg1 locus confer resistance to strains of Pseudomonas syringae pv. glycinea that express the avirulence genes avrB or avrRpm1. We have previously mapped Rpg1-b (the gene specific for avrB) to a cluster of resistance genes (R genes) with diverse specificities in molecular linkage group F. Here, we describe the high-resolution physical and genetic mapping of Rpg1-b to a 0.16-cM interval encompassed by two overlapping BAC clones spanning approximately 270 kilobases. Rpg1-b is part of a complex locus containing numerous genes related to previously characterized coiled coil-nucleotide binding site-leucine rich repeat (CC-NBS-LRR)- type R genes that are spread throughout this region. Phylogenetic and Southern blot analyses group these genes into four distinct subgroups, some of which are conserved in the common bean, Phaseolus vulgaris, indicating that this R gene cluster may predate the divergence of Phaseolus and Glycine. Members from different subgroups are physically intermixed and display a high level of polymorphism between soybean cultivars, suggesting that this region is rearranging at a high frequency. At least five CC-NBS-LRR-type genes cosegregate with Rpg1-b in our large mapping populations.