Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2002
Publication Date: 5/22/2002
Citation: MALEKI,L., FELLERS,J.P., FARIS,J.D., BOWDEN,R.L., GILL,B.S., PHYSICAL AND GENETIC MAPPING OF WHEAT NBS-LRR AND KINASE CLASS RESISTANCE GENE ANALOGS, CROP SCIENCE, 2002. 43:660-670. Interpretive Summary: One of the major difficulties in developing disease resistant varieties is the transfer of resistance genes to adapted germplasm. The development of molecular tags for genes allows breeders to generate new cultivars more efficiently and more timely. The work in this manuscript describes the development of new wheat markers specific for resistance genes. It is also ounique in that the markers were cloned using genetic sequences from other plant species. Resistance genes have a high level of similarity and this has been exploited in the work described in the manuscript. There are now 37 new markers that can be used in mapping resistance genes in wheat.
Technical Abstract: Conserved motifs within resistance genes have been utilized in PCR based strategies to isolate resistance gene analogs (RGAs) from many plant species. RGAs have the potential to serve as closely linked markers for marker-assisted breeding or even as resistance gene candidates. The objectives of this study were to clone, sequence and cytogenetically map RGAs and to analyze their associations with resistance genes. Two conserved motifs within kinase-class and three motifs in nucleotide binding site-leucine rich repeat resistance genes were used to design degenerate primers and amplify RGAs from wheat. Isolated clones were sequenced and physically and genetically mapped. Eight NBS-LRR and 26 kinase class analogs were isolated. Initially the clones were physically mapped to chromosomes using wheat nulli-tetrasomic deletion lines. The probes detected 137 fragments that could be assigned to 20 of the 21 chromosomes; nearly half of the fragments mapped in the B genome. None of the fragments mapped to chromosome 4D. Genetic mapping of RGAs showed simple and complex loci indicating both single and multigene families. Associations between the RGA probes and leaf rust resistance (Lr) genes were drawn using near-isogenic lines (NILs). A correlation could be drawn with the Lr gene in eight polymorphic NILs (Lr14A, Lr15, Lr18, Lr19, Lr21, Lr24, Lr26, Lr35) with a corresponding RGA probe(s) since both mapped to the same chromosome via either the nulli-tetrasomic aneuploids, ITMI mapping population, or both. The RGAs will be useful as markers for mapping resistance gene loci.