Physical and Genetic Mapping of Wheat Kinase Analogs and NBS-LRR Resistance Gene Analogs

Therefore, RGAs and RGLs have the potential to serve as closely linked markers for marker-assisted breeding Conserved motifs within resistance genes have been utilized in strategies, or they could be candidate R-genes thempolymerase chain reaction (PCR)-based strategies to isolate resistance gene analogs (RGAs) and resistance gene-like (RGLs) sequences from selves. many plant species. RGAs have the potential to serve as closely linked Common or bread wheat is an allohexaploid (2n markers for marker-assisted breeding or even as resistance gene candi6x 42, AABBDD), with a haploid genome size of dates. The objectives of this study were to clone, sequence, and map 1.6 1010 base pairs. Triticum aestivum arose from a RGAs and kinase analogs (KA). Three motifs in nucleotide binding hybridization event between the tetraploid wheat T. site-leucine-rich repeat (NBS-LRR) resistance genes and two conturgidum L. (2n 4x 28, AABB) and the diploid served motifs within R-gene kinases were used to design degenerate wheat Aegilops tauschii Coss. (2n 2x 14, DD) about primers and amplify RGAs and KAs from wheat (Triticum aestivum 8000 yr ago (McFadden and Sears, 1946). Genetic mapL.). Eight NBS-LRR and 26 KAs were isolated. The clones were ping in wheat can be difficult because of polyploidy and physically mapped to chromosomes by means of wheat nulli-tetlow levels of polymorphism because of its recent origin rasomic lines. The probes detected 137 fragments that could be assigned to 20 of the 21 chromosomes; nearly half of the fragments from a few hybridization events. However, because of mapped in the B genome. None of the fragments mapped to chromopolyploid buffering, bread wheat can tolerate deficiensome 4D. Genetic mapping of clones showed simple and complex loci cies of whole chromosomes, chromosome arms, and subindicating both single and multigene families. The RGAs and KAs arm regions, allowing the development of a vast array will be useful as markers for mapping resistance gene loci. of cytogenetic stocks (Sears 1954, 1966; Endo and Gill, 1996). Use of these aneuploid stocks for interand intrachromosomal mapping in wheat is a powerful approach D resistance genes (R-genes) have been and has been used to develop cytogenetic physical maps cloned from a number of plant species and can be of the 21 chromosomes of wheat (Delaney et al., 1995a, categorized into four classes on the basis of the conb; Gill et al., 1993, 1996a,b; Hohmann et al., 1994; Mickserved amino acid sequences of their protein products. elson-Young et al., 1995). The classes include the NBS-LRR genes, which contain Four RGL sequences have been described in wheat a nucleotide-binding site (NBS) and a leucine-rich rethat map in regions known to contain R-genes. The peat (LRR) motif, extracellular LRR genes, protein kiCre3, Yr10, and Lr21 loci contain sequences with motifs nase genes, and receptor kinase genes (Bent, 1996; Dangl, similar to NBS-LRR class genes (Lagudah et al., 1997; 1995; Hammond-Kosack and Jones, 1997). In recent Spielmeyer et al., 2000; Huang and Gill, 2001). The Lr10 studies, conserved amino acid sequences have been exlocus contains both an NBS-LRR and a receptor kinase ploited for the design of oligonucleotide primers that gene that is membrane spanning (Feuillet et al., 1997; are used in a PCR-based technique to isolate resistance Wicker et al., 2001). Even though these genes cosegreggene analogs (RGAs) and resistance gene-like (RGL) ate with the R-gene locus, none has been demonstrated sequences. This technique has been used in soybean to be the R-gene. In comparison with dicotyledonous [Glycine max (L.) Merr.], rice (Oryza sativa L.), and maize species, only a few RGAs have been isolated and (Zea mays L.) (Collins et al., 1998; Kanazin et al., 1996; mapped in wheat. Spielmeyer et al. (1998) used degenerMago et al., 1999). RGAs contain sequences that are ate and nested primers to isolate RGAs that mapped similar to known R-gene sequences and often map to all homeologous groups of wheat. Their study only within specific regions of the genome that are known evaluated NBS-LRR type genes and the nested PCR to contain R-genes. To demonstrate further the potenapproach limited the type of genes isolated. Seah et al. tial of RGAs, Dodds et al. (2001) proved that an RGA (1998) used a similar approach to isolate five distinct cosegregating with the flax N locus was the N gene. NBS RGAs from wheat and barley (Hordeum vulgare L.), of which two were mapped to wheat chromosomes L. Maleki and B.S. Gill, Dep. of Plant Pathology, 4024 Throckmorton 2A and 2B. Chen et al. (1998) did not clone any RGAs Hall, Kansas State University, Manhattan, KS 66506-5502; J.D. Faris, or KAs, but used the conserved motifs to design primers USDA-ARS Cereal Crops Research Unit, Northern Crop Science and identified polymorphisms associated with resistant Laboratory, Fargo, ND 58105-5677; J.P. Fellers and R.L. Bowden, USDA-ARS Plant Science and Entomology Research Unit, Manhatwheat, rice and barley lines. tan, KS 66506-5502. Joint contribution of the USDA-Agricultural Several R-genes have been cloned that contain kinase Research Service and the Kansas Agric. Exp. Stn. Journal no. 02-281domains. Pto from tomato (Lycopersicon esculentum J. Mention of a trademark of a proprietary product does not constitute a guarantee of warranty of the product by the United States Department of Agriculture, and does not imply its approval to the exclusion Abbreviations: KA, kinase analogs; ITMI, International Triticeae of other products that may also be suitable. Received 30 Jan. 2002. Mapping Initiative; NT, nullisomic-tetrasomic line; PCR, polymerase *Corresponding author ([email protected]). chain reaction; R-gene, resistance gene; RGA, resistance gene analog; RGL, resistance gene-like. Published in Crop Sci. 43:660–670 (2003).