High-resolution mapping of <Emphasis Type="Italic">Rsn1</Emphasis>, a locus controlling sensitivity of rice to a necrosis-inducing phytotoxin from <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG1-IA |
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Authors: | Stefano Costanzo Aaron K Jackson Steven A Brooks |
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Institution: | (1) USDA-ARS, Dale Bumpers National Rice Research Center, 2890 Highway 130 East, Stuttgart, AR 72160, USA; |
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Abstract: | Rhizoctonia solani is a necrotrophic fungal pathogen that causes disease on many crop-plant species. Anastomosis group 1-IA is the causal agent
of sheath blight of rice (Oryza sativa L.), one of the most important rice diseases worldwide. R. solani AG1-IA produces a necrosis-inducing phytotoxin and rice cultivar’s sensitivity to the toxin correlates with disease susceptibility.
Unlike genetic analyses of sheath blight resistance where resistance loci have been reported as quantitative trait loci, phytotoxin
sensitivity is inherited as a Mendelian trait that permits high-resolution mapping of the sensitivity genes. An F2 mapping population derived from parent cultivars ‘Cypress’ (toxin sensitive) and ‘Jasmine 85’ (toxin insensitive) was used
to map Rsn1, the necrosis-inducing locus. Initial mapping based on 176 F2 progeny and 69 simple sequence repeat (SSR) markers located Rsn1 on the long arm of chromosome 7, with tight linkage to SSR marker RM418. A high-resolution genetic map of the region was
subsequently developed using a total of 1,043 F2 progeny, and Rsn1 was mapped to a 0.7 cM interval flanked by markers NM590 and RM418. Analysis of the corresponding 29 Kb genomic sequences
from reference cultivars ‘Nipponbare’ and ‘93-11’ revealed the presence of four putative genes within the interval. Two are
expressed cytokinin-O-glucosyltransferases, which fit an apoptotic pathway model of toxin activity, and are individually being investigated further
as potential candidates for Rsn1. |
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