Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/25/2004
Publication Date: 1/1/2005
Citation: Luo, M., Dang, P., Guo, B. Z., He, G., Holbrook, C. C., Bausher, M. G., Lee, R. D. 2005. Generation of expressed sequence tags (ESTs) for gene discovery and marker development in cultivated peanut. Crop Science. 45:346-353. Interpretive Summary: The genome size of peanut is about 2800 Mb in comparison with the genome size 128 Mb and 425 Mb of Arabidopsis thaliana and rice, respectively, which have been completely sequenced. EST (expressed sequence tag) technology is the most cost-effective tool for studying cultivated peanut genome and studying the complicated problem of host resistance to foliar diseases and preharvest aflatoxin contamination. EST libraries for cultivated peanut were developed from two cDNA libraries constructed from leaves of peanut line C34-24 (resistant to leaf spots and TSWV) and immature pod of A13 (tolerant to drought stress and pre-harvest aflatoxin contamination). Randomly selected cDNA clones were partially sequenced to generate a total of 1825 ESTs, 769 from C34-24 cDNA library and 1056 from A13 cDNA library. There are 536 and 769 unique EST sequences, respectively. The results show that 52.8% and 78.6% have homology to known function genes from these libraries. These ESTs were sorted according to putative function into 15 categories. This is the first report on cultivated peanut ESTs and these ESTs could contribute considerable information to peanut functional genomics in novel gene discovery, marker development, and genetic map. We have identified some interesting genes related to drought tolerance and disease resistance. Further characterization of these genes would be interesting in unraveling the resistant mechanisms in these two peanut lines.
Technical Abstract: Expressed sequence tag (EST) libraries for cultivated peanut (Arachis hypogaea L.) were developed from two cDNA libraries constructed using mRNA prepared from leaves of peanut line C34-24 (resistant to leaf spots and tomato spotted wilt virus) and immature pods of peanut line A13 (tolerant to drought stress and preharvest aflatoxin contamination). Randomly selected cDNA clones were partially sequenced to generate a total of 1825 ESTs, 769 from the C34-24 cDNA library and 1056 from the A13 cDNA library, in which 536 and 769 unique ESTs were identified, respectively. Results of BLASTx search showed that 52.8% of the ESTs from leaf tissue and 78.6% of the ESTs from the pod tissue have homology to genes of known function. Approximately 27.3% and 22.1% of ESTs matching homologous sequences in dbEST of GenBank based on BLASTn algorithm have unknown functions. The ESTs were queried against MIPS functional catalogue criteria and sorted according to putative function into 15 categories. A total of 1345 ESTs have been released to GenBank. Four hundred unigenes have been selected from these ESTs and arrayed on glass slides for gene expression analysis, and 44 EST-derived SSR markers have been characterized for cultivated peanut, in which over 20% of the SSRs produced polymorphic markers among 24 cultivated peanut genotypes. This is the first report of ESTs in cultivated peanut, and further characterization of resistance and stress genes may explain mechanisms functioning in these two peanut lines.