Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/3/2002
Publication Date: 10/1/2003
Citation: Tan, H., Callahan, F.E., Zhang, X.D., Karaca, M., Saha, S., Jenkins, J.N., Creech, R.G., Ma, D.P. 2003. Identification of resistance gene analogs in cotton (Gossypium hirsutum L.) Euphytica. 134:1-7. Interpretive Summary: There is an impetus to identify molecular markers in cotton to aid breeding programs in selection for host plant resistance to diseases, insects and nematodes. However, identification of useful molecular markers in cotton has been hampered by the lack of an efficient way to generate markers that link to the resistance traits. This is especially true in intraspecific cotton species where obtaining polymorphic markers is difficult. Here we report a PCR approach to generate resistance gene analogs that potentially cluster to resistance loci of the cotton genome. PCR primer design was based on conserved domains of other plant resistance genes that have been previously cloned and characterized. These PCR-derived gene analogs contained conserved motifs and amino acid sequence similarities with the known disease resistance genes from other plants. These resistance gene analogs can serve as molecular probes to aid in the introgression of desirable resistance genes in cotton cultivar improvement programs.
Technical Abstract: Sequence analyses of numerous plant disease resistance genes have revealed the presence of conserved motifs common to this class of gene, namely a nucleotide binding site (NBS) and leucine rich repeat (LRR) region. In this study, thirty-three resistance gene analogs (RGAs) were cloned and sequenced from cotton (Gossypium hirsutum) following PCR with degenerate primers designed from the conserved NBS motif of plant resistance (R) genes. Phylogenetic analysis using the predicted amino acid sequences grouped the RGAs into four distinct classes from which several subgroups were delineated based on nucleic acid sequences. BLAST searches with the consensus protein sequences of each of the four classes and respective subgroups of cotton RGAs revealed their conserved NBS domains and homology to RGAs and known resistance genes from a variety of plant genera. Given the complete lack of knowledge regarding molecular organization of R genes in cotton, the cloned RGAs described here may be useful as probes to map, characterize and manipulate R genes of the cotton genome.