Plant Physiology Preview Published on November 21, 2002; 10.1104/pp.014951
Received September 19, 2002
Returned for revision September 30, 2002
Accepted October 8, 2002
Comparative Sequence Analysis of the Sorghum Rph Region and the Maize Rp1 Resistance Gene Complex
Wusirika Ramakrishna , John Emberton , Phillip SanMiguel , Matthew Ogden , Victor Llaca , Joachim Messing , and Jeffrey L. Bennetzen *
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907 (W.R., J.E., M.O., J.L.B.); Purdue University Genomics Core, Purdue University, West Lafayette, Indiana 47907 (P.S.M.); and Waksman Institute, Rutgers University, Piscataway, New Jersey 08854 (V.L., J.M.)
* Corresponding author; email: maize{at}bilbo.bio.purdue.edu.
A 268-kb chromosomal segment containing sorghum (Sorghum bicolor) genes that are orthologous to the maize (Zea mays) Rp1 disease resistance (R) gene complex was sequenced. A region of approximately 27 kb in sorghum was found to contain five Rp1 homologs, but most have structures indicating that they are not functional. In contrast, maize inbred B73 has 15 Rp1 homologs in two nearby clusters of 250 and 300 kb. As at maize Rp1, the cluster of R gene homologs is interrupted by the presence of several genes that appear to have no resistance role, but these genes were different from the ones found within the maize Rp1 complex. More than 200 kb of DNA downstream from the sorghum Rp1-orthologous R gene cluster was sequenced and found to contain many duplicated and/or truncated genes. None of the duplications currently exist as simple tandem events, suggesting that numerous rearrangements were required to generate the current genomic structure. Four truncated genes were observed, including one gene that appears to have both 5' and 3' deletions. The maize Rp1 region is also unusually enriched in truncated genes. Hence, the orthologous maize and sorghum regions share numerous structural features, but all involve events that occurred independently in each species. The data suggest that complex R gene clusters are unusually prone to frequent internal and adjacent chromosomal rearrangements of several types.
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