EXPRESSION AND GENOMIC ARRANGEMENT OF RESISTANCE GENE ANALOGS FROM A SOYBEAN BAC CONTIG

¹ G304 Agronomy, Agronomy Department, Iowa State University, Ames, IA 50011-1010 USA

² Interdepartmental Plant Physiology Major, Agronomy Department, Iowa State University, Ames, IA 50011-1010 USA

³ USDA-ARS/Agronomy Department, Iowa State University, Ames, IA 50011-1010 USA

Using the conserved nucleotide binding domain from several cloned plant disease resistance genes, we identified analogous sequences, Resistance Gene Analogs (RGAs), from soybean (Kanazin et al. 1996). The RGAs were organized into eleven different classes. They mapped singly and in clusters throughout the genome. One cluster of class 1 RGAs mapped to a cluster of genetically mapped resistance genes on linkage group J. Class 1-specific oligionucleotide primers were used to identify BAC clones in the USDA/ISU 'Williams 82' BAC library. Based on fingerprint analysis, a subset of the class 1 BACs were arranged into a contig which has now been expanded to cover more than 700 kb. Markers developed from BAC ends and BAC subclones map within the resistance gene cluster on linkage group J. Screening of two cDNA libraries (root and epicotyl) identified several differentially expressed clones, two of which mapped to the linkage group J BAC contig. Sequence analysis of the clones confirmed a complete plant disease resistance gene signature and placed the clones in the Toll/Interleukin-1 receptor/nucleotide binding domain/leucine rich repeat family of disease resistance genes. Primers designed from the length of one of the cDNA clones were used to amplify sequence from a BAC from the linkage group J contig containing multiple RGAs. Comparison of over 50 kb of genomic subclone sequence with the non-redundant GenBank database shows high sequence similarity primarily with resistance gene homologs or with retrotransposon homologs. Analysis of PCR derived sequence and the BAC subclone genomic sequence has allowed us to determine the genomic arrangement and structure of the RGAs and to infer mechanisms of evolution of the RGAs within the BAC cluster. Kanazin, V., Marek, L.F., and Shoemaker, R. (1996) Proc. Natl. Acad. Sci. USA 93:11746-11750.