Harnessing plant immune receptors for resistance to wheat stem rust
P. DODDS (1), S. Cesari (1), R. Mago (1), N. Upadhyaya (2), S. Periyannan (1), A. bentham (3), L. Casey (3), P. Lavrencic (3), J. Chen (4), B. Xu (1), M. Bernoux (1), R. Park (5), J. Ellis (1), M. Ayliffe (1), S. Williams (3), B. Kobe (3), E. Lagudah (1) (1) CSIRO Agriculture, Australia; (2) CSIRO Agirculture, Australia; (3) University of Queensland, Australia; (4) Univeristy of Sydney, Australia; (5) University of Sydney, Australia

Stem rust caused by Puccinia graminis tritici (Pgt) is one of the most serious diseases in wheat and the recent resurgence of this disease caused by new virulent races in Africa poses a threat to food security. The disease is combated mainly through breeding disease resistant varieties. Because the fungus evolves virulence towards previously resistant varieties, continuous breeding and identification of new sources of resistance is necessary to combat the threat of rust epidemics. Plant disease resistance can be triggered by specific recognition of microbial effectors by plant immune receptors that encode nucleotide binding leucine rich repeat (NB-LRR) receptors. Our work on the model system of flax (Linum usitatissium) resistance to the flax rust fungus (Melampsora lini) 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 disease by targeted cloning of Resistance (R) genes in wheat and corresponding Avr genes in Pgt. We have recently isolated the Sr33 and Sr50 resistance genes from wheat. Functional analysis indicates that these proteins signal cell death and rust resistance responses from the cytosol. The minimal signalling domain has been identified as the N terminal 142 amino acids containing the full coiled-coil domain. Dimerisation of the N-terminal domain fragments correlates with signalling ability, suggesting this is an important structural requirement for signalling. We have also isolated stem rust mutants virulent on Sr50 and identified candidate Avr genes through genome sequence analysis. Understanding the nature of wheat R genes and the Avr proteins that they recognize will allow better prediction of R gene durability and choice of the optimal combinations of R genes to deploy in gene stacks.

Abstract Number: S6-1
Session Type: Special Session