Originally published as Genetics Published Articles Ahead of Print on May 27, 2009.

Genetics, Vol. 182, 1351-1364, August 2009, Copyright © 2009
doi:10.1534/genetics.109.101022

The Fractionated Orthology of Bs2 and Rx/Gpa2 Supports Shared Synteny of Disease Resistance in the Solanaceae

Michael Mazourek^*, Elizabeth T. Cirulli^*,1, Sarah M. Collier^*,, Laurie G. Landry^*, Byoung-Cheorl Kang^*,, Edmund A. Quirin, James M. Bradeen, Peter Moffett^,2 and Molly M. Jahn^**,3

^* Department of Plant Breeding and Genetics, Cornell University, Ithaca, New York 14853, Boyce Thompson Institute for Plant Research, Ithaca, New York 14853, Department of Plant Sciences, Seoul National University, Seoul 151-921, Korea, Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota 55108 and ^** College of Agriculture and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706

³ Corresponding author: College of Agricultural and Life Sciences, University of Wisconsin, 140 Agricultural Hall, Madison, WI 53706.
E-mail: mjahn{at}cals.wisc.edu

Comparative genomics provides a powerful tool for the identification of genes that encode traits shared between crop plants and model organisms. Pathogen resistance conferred by plant R genes of the nucleotide-binding–leucine-rich-repeat (NB–LRR) class is one such trait with great agricultural importance that occupies a critical position in understanding fundamental processes of pathogen detection and coevolution. The proposed rapid rearrangement of R genes in genome evolution would make comparative approaches tenuous. Here, we test the hypothesis that orthology is predictive of R-gene genomic location in the Solanaceae using the pepper R gene Bs2. Homologs of Bs2 were compared in terms of sequence and gene and protein architecture. Comparative mapping demonstrated that Bs2 shared macrosynteny with R genes that best fit criteria determined to be its orthologs. Analysis of the genomic sequence encompassing solanaceous R genes revealed the magnitude of transposon insertions and local duplications that resulted in the expansion of the Bs2 intron to 27 kb and the frequently detected duplications of the 5'-end of R genes. However, these duplications did not impact protein expression or function in transient assays. Taken together, our results support a conservation of synteny for NB–LRR genes and further show that their distribution in the genome has been consistent with global rearrangements.

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