Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2011
Publication Date: 3/19/2011
Citation: Costanzo, S., Jackson, A.K., Brooks, S.A. 2011. High-resolution mapping of Rsn1, a locus controlling sensitivity of rice to a necrosis-inducing phytotoxin from Rhizoctonia solani AG1-IA. Theoretical and Applied Genetics. 123(1):33-41.
Interpretive Summary: Sheath blight is an important disease of rice everywhere the crop is grown. The fungal pathogen produces a toxin during the infection process that causes death of rice tissues, enabling the fungus to infect the plant and cause disease. Some plants are insensitive to the toxin, and this trait limits the amount of sheath blight disease caused by the fungus. Using genetic analysis, a rice gene controlling sensitivity to the toxin was mapped and candidate genes identified.
Technical Abstract: Rhizoctonia solani is a necrotrophic fungal pathogen that causes disease on all major crop-plant species. Anastomosis group 1-IA is the causal agent of sheath blight of rice (Oryza sativa), one of the most important rice diseases worldwide. R. solani AG-IA produces a necrosis-inducing phytotoxin and sensitivity to the toxin correlates with disease susceptibility. Unlike genetic analyses of sheath blight resistance where resistance loci have been reported as QTL, 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 1043 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 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.