Stem rust caused by Puccinia graminis tritici (Pgt) is one of the most serious diseases in wheat and is combated mainly through the use of resistant varieties. Because the fungus evolves virulence towards previously resistant varieties, continuous breeding and identification of new sources of resistance are necessary to combat the threat of rust epidemics. Our work on the flax rust model system has provided insights into how the plant immune system recognises and responds to rust pathogens. We have been extending this work to wheat stem rust by targeted cloning of resistance (R) genes in wheat and corresponding Avr genes in Pgt. Plant R genes encode immune receptors that recognise and respond to pathogen effector proteins delivered into host cells from haustoria. We recently isolated the Sr33 and Sr50 resistance genes from wheat and have begun functional analyses to determine how they trigger defense responses. We are also targeting effectors from Pgt that are recognised by wheat R genes. We used genome and transcriptome sequencing to predict ~400 candidate effector genes from Australian Pgt race 21- 0. To screen for recognition of these proteins by wheat R genes, we developed a bacterial Type III Secretion System delivery assay using Pseudomonas fluorescens to inject the effector candidates into wheat leaf cells. We are screening candidate effectors on a set of 18 wheat cultivars carrying 22 different R genes and have so far identified one effector that induces a cell death response specifically on a wheat genotype carrying Sr22. Understanding the nature of wheat R genes and the Avr proteins that they recognize will allow better prediction of R gene durability and enable the possibility of rational design of novel R genes. We are also developing techniques for stacking R genes in cassettes for deployment of multiple genes at a single locus in wheat.
Displaying 1 - 8 of 8
Aegilops tauschii Coss., the D genome donor of hexaploid wheat, Triticum aestivum L., has been used extensively for the transfer of agronomically important traits to wheat, including stem rust resistance genes Sr33, Sr45, and Sr46. To identify potentially new stem rust resistance genes in A. tauschii germplasm, we evaluated 456 nonduplicated accessions deposited in the USDA National Small Grains Collection (Aberdeen, ID) and the Wheat Genetic and Genomic Resources Center collection (Kansas State University, Manhattan, KS), with races TTKSK (Ug99), TRTTF, TTTTF, TPMKC, RKQQC, and QTHJC of Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn. Ninety-eight accessions (22%) were identified as resistant to race TTKSK. A broad range of resistant infection types (; to 2+) were found in reaction to race TTKSK. Resistance was significantly associated among most of the races in pairwise comparisons. However, resistance was largely race specific. Only 12 of the accessions resistant to race TTKSK were also resistant to the other five races. Results from this germplasm screening will facilitate further studies on the genetic characterization of accessions with potentially novel sources of resistance to race TTKSK.
Stem rust caused by Puccinia graminis f. sp. tritici (Pgt) has been and still remains a major threat for wheat production worldwide. Following “Green Revolution”, the disease was brought under control by the use of stem rust resistant semi dwarf spring wheats and least attention was given to stem rust improvement for several decades. Recently, evolution of a new Pgt pathotype, Ug99, in Africa has threatened the global wheat industry. This pathotype was initially detected in Uganda during 1999 and later spread to neighbouring countries like Kenya and Ethiopia and now has reached Iran. This pathotype is virulent on many of the current stem rust resistance genes used in different wheat growing regions. Some of the effective stem rust resistance are derived from the wild relatives of wheat. The genes Sr33 and Sr45, derived from Aegilops tauschii, were among the genes effective against Ug99. The present study was planned to identify molecular markers closely linked with stem rust resistance genes Sr33 and Sr45.
Stem rust, caused by Puccinia graminis f. sp. tritici, historically was one of the most destructive diseases of wheat and barley. The disease has been under effective control worldwide through the widespread use of host resistance. A number of stem rust resistance genes in wheat have been characterized for their reactions to specific races of P. graminis f. sp. tritici. Adult plant responses to race TTKS (also known as Ug99) of monogenic lines for Sr genes, a direct measurement of the effectiveness for a given gene, have not been investigated to any extent. This report summarizes adult plant infection responses and seedling infection types for monogenic lines of designated Sr genes challenged with race TTKS. High infection types at the seedling stage and susceptible infection responses in adult plants were observed on monogenic lines carrying Sr5, 6, 7a, 7b, 8a, 8b, 9a, 9b, 9d, 9g, 10, 11, 12, 15, 16, 17, 18, 19, 20, 23, 30, 31, 34, 38, and Wld-1. Monogenic lines of resistance genes Sr13, 22, 24, 25, 26, 27, 28, 32, 33, 35, 36, 37, 39, 40, 44, Tmp, and Tt-3 were effective against TTKS both at the seedling and adult plant stages. The low infection types to race TTKS observed for these resistance genes corresponded to the expected low infections of these genes to other incompatible races of P. graminis f. sp. tritici. The level of resistance conferred by these genes at the adult plant stage varied between highly resistant to moderately susceptible. The results from this study were inconclusive for determining the effectiveness of resistance genes Sr9e, 14, 21, and 29 against race TTKS. The understanding of the effectiveness of individual Sr genes against race TTKS will facilitate the utilization of these genes in breeding for stem rust resistance in wheat.
A stem rust resistance gene, originally derived from Triticum tauschii accession RL5289 and present in the germplasm line 87M66-2-1, is here designated Sr45. Sr45 was found to be closely linked to Sr33 (9 ± 1.9 map units) and the centromere (21 ± 3.4 map units) on chromosome arm 1DS. Sr45 is believed to be the same gene as SrX. The Russian wheat aphid resistance gene, Dn5, was loosely linked (32 ± 5 map units) to Ep-D1b, which occurs on a translocation derived from T. ventricosum, and to the cn?D1 locus (37 ± 6.3 map units) on chromosome arm 7DL. Dn5 derives from T. aestivum accession Pl294994 which was found to express two novel Ep-1 alleles (proposed designations Ep-A1d and Ep-D1e). A gene (here designated Dn7) for Russian wheat aphid resistance that was derived from the rye accession, Turkey 77', mapped 14.5 ± 3.9 map units from Lr26 on the 1BL.1RS translocation.
Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici, afflicts bread wheat (Triticum aestivum). New virulent races collectively referred to as “Ug99” have emerged, which threaten global wheat production. The wheat gene Sr33, introgressed from the wild relative Aegilops tauschii into bread wheat, confers resistance to diverse stem rust races, including the Ug99 race group. We cloned Sr33, which encodes a coiled-coil, nucleotide-binding, leucine-rich repeat protein. Sr33 is orthologous to the barley (Hordeum vulgare) Mla mildew resistance genes that confer resistance to Blumeria graminis f. sp. hordei. The wheat Sr33 gene functions independently of RAR1, SGT1, and HSP90 chaperones. Haplotype analysis from diverse collections of Ae. tauschii placed the origin of Sr33 resistance near the southern coast of the Caspian Sea.
Chromosome 1D homozygous recombinant substitution lines derived from Triticum aestivum 'Chinese Spring' (cross 1) or 'Chinese Spring' double-ditelosomic ID (cross 2) hybridized with a disomic substitution line of Triticum tauschii chromosome 1D in 'Chinese Spring' were used to investigate the linkage relationships among Glu-D1, encoding subunits of high molecular weight glutenin storage proteins; Gli-D1, encoding gliadin storage proteins; Sr33, conferring stem rust resistance; and the centromere. Based on analysis of 88 and 91 recombinant substitution lines of crosses 1 and 2, respectively, Sr33 is tightly linked to Gli-D1 on chromosome arm IDS (5.6 and 7.6% recombination) and less tightly to the centromere (29.6%, cross 2) and to Glu-D1 (40.9 and 39.5%). The order of the loci is Glu-D1 - centromere - Sr33 - Gli-D1.