|Graham, Michelle - IOWA STATE UNIVERSITY|
|Marek, Laura - IOWA STATE UNIVERSITY|
|Lohnes, David - OHIO STATE UNIVERSITY|
Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 1999
Publication Date: N/A
Interpretive Summary: Disease costs producers millions of dollars per year in crop loss. Understanding how resistance genes work is a first step toward engineering better resistance in plants. In this study the authors identified a cluster of genes that have all of the characteristics of resistance genes. The cluster was localized on a single cloned piece of DNA that was shown to ospan a group of genes conferring resistance to fungal pathogens and to a bacteria. A detailed analysis of the genetic code of each of the genes showed that, although each of the genes was similar, specific changes were taking place in the structure of the genes that provided insight as to how plants generate diversity to a wide range of pathogens. This information will be used by researchers to help identify new resistance genes and to identify possible sites within genes that can be modified to affect gene specificity.
Technical Abstract: Sequence analysis of cloned plant disease resistance reveals a number of conserved domains. Researchers have used these domains to amplify analogous sequences, Resistance Gene Analogs (RGAs), from soybean and other crops. To study RGA expression and to determine the extent of their similarity to other plant resistance genes, two cDNA libraries (root and epicotyl) were screened by hybridization with RGA class-specific probes. Differential expression of RGA classes was observed between root and epicotyl tissue. Two types of cDNAs were identified from each library. One was full length and contained several R-gene signatures. The other type contained several deletions within these signatures. Sequence analyses of the cDNA clones placed them in the Toll/Interleukin-1 receptor/nucleotide binding domain/leucine rich repeat family of disease resistance genes. Using clone-specific primers from within the 3' end of the LRRs, we were able to map two differentially expressed cDNA clones (LM and MG13) to a BAC contig that was shown to contain known disease resistance genes. To determine the structure of the gene corresponding to cDNA clone LM6, primers were designed along the length of the clone in overlapping intervals. The primers were used to amplify the genomic sequence of LM6 from BAC 34P7. Comparisons of the sequences amplified from other RGAs located on BAC 34P7 indicated that structural changes occur within the RGAs at precise locations. These additions, deletions, and duplications are consistent with recombination events and provide farther evidence implicating RGAs in plant disease resistance.