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Title: Loss of function of the barley Nad1 gene, encoding a cation/proton exchanging protein, results in necrosis and defense response to stem rust

Author
item ZHANG, L - WASHINGTON STATE UNIV
item LAVERY, L - WASHINGTON STATE UNIV
item GILL, U - WASHINGTON STATE UNIV
item GILL, K - WASHINGTON STATE UNIV
item STEFFENSON, B - UNIV OF MINNESOTA
item YAN, G - WASHINGTON STATE UNIV
item Chen, Xianming
item KLEINHOFS,, A - WASHINGTON STATE UNIV

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2008
Publication Date: 10/28/2008
Citation: Zhang, L., Lavery, L., Gill, U., Gill, K., Steffenson, B., Yan, G.P., Chen, X., Kleinhofs,, A. 2008. Loss of function of the barley Nad1 gene, encoding a cation/proton exchanging protein, results in necrosis and defense response to stem rust. Theor. Appl. Genet. 118:385-397.

Interpretive Summary: To determine if barley lesion mimic necrosis genes contribute to stem rust resistance, we characterized three lesion mimic necrosis and defense mutants, induced by fast neutron treatment of barley cultivar Steptoe. The three mutants are recessive and allelic. When infected with two wheat stem rust races and one rye stem rust isolate, all three mutants exhibited enhanced resistance compared to parent cultivar Steptoe. These results suggested that the lesion mimic mutants carry broad-spectrum resistance to stem rust. Transcript-based cloning identified the gene Nad1 as responsible for the mutant phenotype. Two genes, represented by three probe sets, of which two were the same, were deleted in all three mutants. Consistent with the increased disease resistance, all three mutants constitutively accumulated elevated transcript levels of pathogenesis-related genes. Genetic analysis suggested that the lesion mimic phenotype was due to a mutation in one or both of these genes. Barley stripe mosaic virus (BSMV) has been developed as a virus-induced gene-silencing (VIGS) vector for monocots. We utilized BSMV-VIGS to demonstrate that silencing of one of the genes, but not the other, caused the necrotic lesion mimic phenotype on barley seedling leaves. Therefore, we identified the sequence of the Nad1 gene and its encoded protein. These results help us understand the mechanisms of plant resistance.

Technical Abstract: We characterized three lesion mimic Nad1 (necrosis and defense 1) mutants, induced by fast neutron treatment of barley cultivar Steptoe. The three mutants are recessive and allelic. When infected with Puccinia graminis f. sp. tritici pathotypes MCC and QCC and Puccinia graminis f. sp. secalis isolate 92-MN-90, all three mutants exhibited enhanced resistance compared to parent cultivar Steptoe. These results suggested that the lesion mimic mutants carry broad-spectrum resistance to stem rust. Transcript-based cloning identified the gene Nad1 as responsible for the mutant phenotype. Two genes, represented by three probesets (Contig4211_at and Contig4212_s_at, representing the same gene, and Contig10850_s_at), were deleted in all three mutants. Consistent with the increased disease resistance, all three mutants constitutively accumulated elevated transcript levels of pathogenesis-related (PR) genes. Genetic analysis suggested that the lesion mimic phenotype was due to a mutation in one or both of these genes. Barley stripe mosaic virus (BSMV) has been developed as a virus-induced gene-silencing (VIGS) vector for monocots. We utilized BSMV-VIGS to demonstrate that silencing of Contig4211_at, but not Contig10850_s_at caused the necrotic lesion mimic phenotype on barley seedling leaves. Therefore, Contig4211_at is the Nad1 gene, which encodes a cation/proton exchanging protein (HvCAX1).