Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/7/2005
Publication Date: 4/20/2005
Citation: Bhattacharyya, M.K., Narayanan, N.N., Gao, H., Salimath, S.S., Santra, D.K., Kasuga, T., Liu, Y., Espinosa, B., Ellison, L., Marek, L., Shoemaker, R.C., Gijzen, M., Buzzell, R.I. 2005. Identification of a large cluster of coiled coil-nucleotide binding site-leucine rich repeat-type genes from the Rps1 region containing phytophthora resistance genes in soybean. Journal of Theoretical and Applied Genetics. 111:75-86. Interpretive Summary: Fungal diseases contribute to millions of dollars of lost soybean production each year. Understanding how disease resistance genes function is an important step to controlling these diseases. Here, the authors used molecular techniques to identify and isolate a gene thought to confer resistance to a soybean fungal root and stem rot disease. They determined that the gene resembled other resistance genes found in other plants. They also concluded that rearrangements within the gene and around the gene probably resulted in a duplication of the gene sequence, thus creating two genes with similar functions. These findings add to our knowledge of disease resistance gene birth and death processes. These findings will be important to geneticists attempting to understand how plant chromosomes change over time and how disease resistance genes acquire new functions.
Technical Abstract: Fourteen Rps genes confer resistance against the oomycete pathogen Phytophthora sojae that causes the root and stem rot disease in soybean. We have isolated a disease resistance gene-like sequence from the genomic region containing Rps1-k. Four classes of cDNAs of the sequence were isolated from etiolated hypocotyl tissues that express the Rps1-k-encoded Phytophthora resistance. Sequence analyses of a cDNA clone showed that the sequence is a member of the coiled coil-nucleotide binding site-leucine rich repeat (CC-NBS-LRR)-type of disease resistance genes. It showed 36% identity to the recently cloned soybean resistance gene Rpg1-b that confers resistance against Pseudomonas syringae pv. glycinea and 56% and 38% sequence identity to putative resistance gene sequences from lotus and Medicago truncatula, respectively. The soybean genome contains about 38 copies of the sequence. Most of these copies are clustered in approximately 600 kb of contiguous DNA that includes Rps1-k. We have identified a recombinant that carries both rps1-k- and Rps1-k-haplotype-specific allelomorphs of two Rps1-k-linked molecular markers. An unequal crossover event presumably led to duplication of alleles for these two physically linked molecular markers. We hypothesize that the unequal crossover was one of the mechanisms involved in tandem duplication of CC-NBS-LRR sequences in the Rps1-k region.