Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/24/2001
Publication Date: 7/1/2002
Citation: GRAHAM, M.A., MAREK, L.F., SHOEMAKER, R.C. PCR SAMPLING OF DISEASE RESISTANCE-LIKE SEQUENCES FROM A DISEASE RESISTANCE GENE CLUSTER IN SOYBEAN. JOURNAL OF THEORETICAL AND APPLIED GENETICS. 2002. v. 105. p. 50-57. Interpretive Summary: Plants are constantly attacked by insects and by pathogens. They respond through defenses initiated by resistance genes (R-genes). The evolution of R-genes is critical to the plants ability to respond to new diseases or to new forms of old diseases. R-genes generally are clustered together and look highly alike. This makes it hard to use standard DNA decoding methods to gain information on their structure and evolution. In this paper the authors developed a rapid method by which specific regions of R-genes can be sampled to evaluate the mechanisms by which they evolve. They found that the R-genes studied here evolve by a combination of illegitimate recombination and mutation in specific regions of the genes. This research will allow scientists to evaluate large numbers of R-genes without the time and expense associated with standard gene sequencing procedures. The information derived from these studies may help to understand how plants defend from insect and pathogen attack.
Technical Abstract: Many plant disease resistance genes contain conserved structural domains which are required for protein function. Using degenerate primers for these domains it has been possible to amplify resistance gene analogs (RGA's) from a variety of plant species. In many cases, the RGAs are clustered within the genome and correlate with disease resistance loci. However, identifying the R-gene of interest from a cluster of homologs remains difficult. In many plant species, such as soybean, a map-based cloning approach remains the most viable option for cloning a disease resistance gene. The large number of homologs within a cluster make sequencing of disease resistance loci difficult. We have developed a PCR-based genomic sampling technique to obtain sequence information from a cluster of RGAs on soybean linkage group J. By comparing the sequences of two cDNAs corresponding to the linkage group J cluster, we have designed a series of oligonucleotide primer pairs spanning the length of the cDNAs. These primers were used to amplify overlapping R-gene segments from a core BAC within the linkage group J cluster. Using this technique we were able to obtain sequence information from individual genes with a cluster. Analysis of these gene sequences allows us to examine the evolutionary forces acting on these genes.