|Scofield, Steven - Steve|
Submitted to: Plant Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2009
Publication Date: 12/6/2009
Citation: Loutre, C., Wicker, T., Travella, S., Galli, P., Scofield, S.R., Fahima, T., Feuillet, C., Keller, B. 2009. Two Genes Encoding Structurally Different CC-NB-LRR Proteins are Required for Lr10-Mediated Leaf Rust Resistance in Wheat of Two Ploidy Levels. Plant Journal. 60:1043-54. Interpretive Summary: Lr10 is a wheat gene that confers resistance to particular races of leaf rust. Lr10 is a member of the largest class of plant disease resistance genes, those containing a nucleotide binding site (NB) and leucine-rich repeat domain (LRR). This work provides two significant new findings about the function and evolution of the Lr10 leaf rust resistance gene of wheat. 1) This study indicates that a second closely linked NB-LRR gene, designated RGA2, is also required for Lr10-mediated resistance. 2) These experiments indicate that regions in the N-terminal Coil-Coil domain of the Lr10 protein have essential functions for pathogen recognition, where as, typically these functions have been found to reside in the C-terminal LRR domain. This information will be significant for scientists working to understand disease resistance pathways as well as breeders working to incorporate disease resistance traits into wheat.
Technical Abstract: The gene pools of crop plant relatives have been proposed as a source of new functional resistance genes to broaden the basis of genetic resistance. Here, we have studied the allelic diversity of the Lr10 leaf rust resistance gene, encoding a CC-NBS-LRR protein originally identified in hexaploid bread wheat, in 20 diploid and tetraploid wheat lines. Besides a gene in the tetraploid wheat ‘Altar’ that is identical to bread wheat Lr10, three new functional resistance alleles were identified in tetraploid wheat lines by virus-induced gene silencing. Sequence analysis revealed that an N-terminal domain of the LR10 protein was under diversifying selection, with highest diversity in the non-hydrophobic residues of a leucine-zipper motif. In contrast, the LRR domain was under strong purifying selection. A second NBS-LRR coding gene at the Lr10 locus, RGA2, is structurally different from Lr10. It was found to be essential for Lr10 function as resistance based on Lr10 was lost after specific virus-induced silencing of the RGA2 gene. Interestingly, RGA2 showed much less sequence diversity if compared to Lr10. These data demonstrate that there is functional, allelic diversity at the Lr10 locus in tetraploid wheat and these new genes can be further tested for agronomic relevance. In addition, Lr10 resistance is highly unusual both in its dependence on two non-homologous CC-NBS-LRR proteins as well as in the N-terminal domain being under diversifying selection. This indicates a new and complex molecular mechanism of pathogen detection and signal transduction. This information will be significant for scientists working to understand disease resistance pathways as well as breeders working to incorporate disease resistance traits into wheat.