Genetic control of broad-spectrum resistance to turnip mosaic virus in Brassica rapa (Chinese cabbage)

Abstract

The Brassica rapa line RLR22 was resistant to eight diverse turnip mosaic virus (TuMV) isolates. A B. rapa genetic map based on 213 marker loci segregating in 120 first back-cross (B 1 ) individuals was established and aligned with the B. rapa genome reference map using some of the RFLP probes. B 1 individuals were self-pollinated to produce B 1 S 1 families. The existence of two loci controlling resistance to TuMV isolate CDN 1 was established from contrasting patterns of segregation for resistance and susceptibility in the B 1 S 1 families. The first gene, recessive TuMV resistance 01 (retr01), had a recessive allele for resistance, was located on the upper portion of chromosome R4 and was epistatic to the second gene. The second gene, Conditional TuMV resistance 01 (ConTR01), possessed a dominant allele for resistance and was located on the upper portion of chromosome R8. These genes also controlled resistance to TuMV isolate CZE 1 and might be sufficient to explain the broad-spectrum resistance of RLR22. The dominant resistance gene, ConTR01, was coincident with one of the three eukaryotic initiation factor 4E (eIF4E) loci of B. rapa and possibly one of the loci of eIF(iso)4E. The recessive resistance gene retr01 was apparently coincident with one of the three loci of eIF(iso)4E in the A genome of Brassica napus and therefore, by inference, in the B. rapa genome. This suggested a mode of action for the resistance that is based on denying the viral RNA access to the translation initiation complex of the plant host. The gene retr01 is the first reported example of a recessive resistance gene mapped in a Brassica species. INTRODUCTIONTurnip mosaic virus (TuMV; genus Potyvirus) infects a wide range of cultivated plant species (Edwardson & Christie, 1991) and causes significant economic losses in Brassica crops (Shattuck, 1992). TuMV is a positive-strand RNA virus with a genome comprising 9830-9835 nt (Nicolas & Laliberté, 1992;Ohshima et al., 1996; Jenner et al., 2000) and is the subject of advanced molecular characterization (Revers et al., 1999; Jenner et al., 2000;. Plant genes for resistance to TuMV have been mapped in lettuce (Tu, Robbins et al., 1994), Brassica napus (TuRB01, Walsh et al., 1999; TuRB03, Hughes et al., 2003; TuRB04 and TuRB05, J. A. Walsh & D. J. Lydiate, unpublished) and Brassica rapa (TuRB01b, Rusholme et al., 2007). All are dominant resistance genes (R genes) that control resistance to narrow spectra of TuMV isolates. In the case of TuRB01, TuRB01b and TuRB04, the cytoplasmic inclusion protein has been identified as the viral avirulence determinant (Jenner et al., 2000Walsh et al., 2002). For TuRB03 and TuRB05, the viral avirulence determinant is the P3 protein .Plants possess a range of defence responses against viral pathogens. The best-characterized defence responses lead to a hypersensitive reaction with localized cell death and are often associated with activation of systemic acquired resistance and restriction of the virus to the initial site of infection (Staskawicz et al., ...

Mapping and candidate-gene screening of the novel Turnip mosaic virus resistance gene retr02 in Chinese cabbage (Brassica rapa L.)

“…TuRB04 and TuRB05 (Jenner et al , 2003, TuRB01b (Rusholme 2000), and retr01 and ConTR01 (Rusholme 2000;Rusholme et al 2007). These genes were mapped with RFLP, AFLP, and SSR markers.…”

“…In B. rapa, broad-spectrum resistance appears to be controlled by the combined action of a recessive (retr01) and a dominant (ConTR01) gene (Rusholme 2000;Rusholme et al 2007). The recessive resistance gene, retr01, mapped to the upper portion of chromosome A04 and was probably coincident with an eIF(iso)4E gene.…”

“…Dominant resistance genes (R genes) control resistance to narrow spectra of TuMV isolates. Broad-spectrum resistance has also been identified, and appears to be controlled by the combined action of a recessive (retr01) and a dominant (ConTR01) gene (Rusholme 2000;Rusholme et al 2007). …”

“…Most of the genes mapped in brassicas are specific to certain TuMV isolates, being found in B. napus and B. rapa . Most of them are dominant, such as TuRB01 , TuRB03 (Hughes et al 2003), TuRB04-05 (Jenner et al , 2003, and TuRB01b (Rusholme 2000). TuRB01 is a single dominant resistance gene and was the first TuMV resistance gene described in Brassica.…”

“…Molecular markers have been used to position TuMV resistance genes on genetic linkage maps Rusholme 2000;Hughes et al 2003;Rusholme et al 2007), which provide a powerful tool to facilitate marker-assisted selection for This paper describes molecular markers linked to a resistance gene effective against TuMV-C4 in B. rapa and the genetic and physical mapping of the gene retr02 in Chinese cabbage, using the bulked segregant analysis (BSA) approach of Michelmore et al (1991). The candidate TuMV resistance gene is described and sequences from resistant and susceptible plants provided.…”