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.
Supporting information is available online at http://www.genetics.org/cgi/content/full/genetics.109.101022/DC1.
↵1 Present address: Center for Human Genome Variation, Duke University, Durham, NC 27708.
↵2 Present address: Département de Biologie, Université de Sherbrooke, 2500 Blvd. de l'Université, Sherbrooke QC J1K 2R1, Canada.
Communicating editor: V. Sundaresan
- Received January 27, 2009.
- Accepted April 29, 2009.
- Copyright © 2009 by the Genetics Society of America