The stem rust resistance Sr33 was first discovered in Aegilops tauschii and transferred to chromosome arm 1DS of wheat. This gene provides an intermediate level a resistance to several Puccinia graminis sp. tritici races including Ug99 related races.
Sambasivam et al. (1) analyzed a population of recombinant inbred lines derived from a cross between Chinese Spring and CS1D5405, a substitution line for chromosome 1D in Chinese Spring carrying Sr33 from Ae. tauschii RL5288. They found Sr33 was flanked by Xbarc152 and Xcfd15 at a distance of 1.8 cM on either side.
More recently, Periyannan et al. (2) cloned the Sr33 gene and determined it encodes a coiled-coil nucleotide-binding, leucine-rich repeat protein, orthologous to barley Mla mildew resistance genes. These authors determined that EST loci BE405778 and BE499711flank a 1 cM region containing Sr33. They also screened sequence variants in 368 accessions of Ae. tauschii with PCR primers specific for the Sr33 locus of RL5288. Of these, 332 yielded no amplification, suggesting they lacked the gene or it was highly divergent. The sequences obtained from the other 36 accessions fell into five groups. The first included sequences identical to that of RL5288 (Genbank accession KF031291), the second group were retrieved from plants showing an Sr33 phenotype (Genbank accession KF031297), the other three sequences were present in susceptible plants. The five genomic sequence types can be retrieved from here. For a description of sequence differences see Ref. 2.
Markers for Sr33
Xbarc152
BARC152-F 5'- CTT CCT AAA ATC GGG CAA CCG CTT GTT G -3'
BARC152-R 5'- GCG TAA TGA TGG GAG TGG CTA TAG GGC AGT T -3'
Annealing tempearature: 50°C
Xcfd15
CFD15-F 5'- CTC CCG TAT TGA GCA GGA AG -3'
CFD15-R 5'- GGC AGG TGT GGT GAT GAT CT -3'
Annealing tempearature: 60°C
References
1. Identification of markers linked with stem rust resistance genes Sr33 and Sr45. Sambasivam PK, Bansal UK, Hayden MJ, Dvorak J, Lagudah ES, Bariana HS. In: The 11th International Wheat Genetics Symposium proceedings. Edited by Rudi Appels Russell Eastwood Evans Lagudah Peter Langridge Michael Mackay Lynne. link
2. The gene Sr33, an ortholog of barley Mla genes, encodes resistance to wheat stem rust race Ug99<. Periyannan S, Moore J, Ayliffe M, Bansal U, Wang X, Huang L, Deal K, Luo M, Kong X, Bariana H, Mago R, McIntosh R, Dodds P, Dvorak J, Lagudah E. In:Science, 2013, 341:786-788. DOI:10.1126/science.1239028