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Co-localisation of the blackleg resistance genes Rlm2 and LepR3 on Brassica napus chromosome A10.

Larkan NJ, Lydiate DJ, Yu F, Rimmer SR, Borhan MH - BMC Plant Biol. (2014)

Bottom Line: Molecular markers tightly linked to the gene were developed for use in mapping the resistance locus and defining the physical interval in B. napus.Rlm2 was localised to a 5.8 cM interval corresponding to approximately 873 kb of the B. napus chromosome A10.The recently-cloned B. napus R-gene, LepR3, occupies the same region of A10 as Rlm2 and analysis of the putative B. napus and B. rapa genes in the homologous region identified several additional candidate defense-related genes that may control Rlm2 function.

View Article: PubMed Central - PubMed

ABSTRACT

Background: The protection of canola (Brassica napus) crops against blackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is largely mediated by race-specific resistance genes (R-genes). While many R-genes effective against blackleg disease have been identified in Brassica species, information of the precise genomic locations of the genes is limited.

Results: In this study, the Rlm2 gene for resistance to blackleg, located on chromosome A10 of the B. napus cultivar 'Glacier', was targeted for fine mapping. Molecular markers tightly linked to the gene were developed for use in mapping the resistance locus and defining the physical interval in B. napus. Rlm2 was localised to a 5.8 cM interval corresponding to approximately 873 kb of the B. napus chromosome A10.

Conclusion: The recently-cloned B. napus R-gene, LepR3, occupies the same region of A10 as Rlm2 and analysis of the putative B. napus and B. rapa genes in the homologous region identified several additional candidate defense-related genes that may control Rlm2 function.

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Comparison of genetic maps forRlm2andLepR3toB. napuschromosome A10. Position of Rlm2 relative to microsatellite (prefixed ‘sN’ or ‘sR’), Indel (prefixed ‘Ind’) and CAPS markers on ‘Topas’ x ‘Glacier’ A10 (TG.A10) map. Nearest B. napus gene to each marker given in brackets. Unanchored B. napus genes corresponding to syntenic B. rapa A10 homologues are denoted with “*”. LepR3 ‘Topas’ x ‘Surpass 400’ A10 (TS.A10) map updated from Larkan et al., 2013a. Marker intervals given in centiMorgans. Solid horizontal lines denote same marker, dashed horizontal lines denote markers sharing same nearest B. napus homologue. Approximate physical location of defense-related candidate genes by triangles. Gap in B. napus A10 chromosome build represented by dotted lines.
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Fig2: Comparison of genetic maps forRlm2andLepR3toB. napuschromosome A10. Position of Rlm2 relative to microsatellite (prefixed ‘sN’ or ‘sR’), Indel (prefixed ‘Ind’) and CAPS markers on ‘Topas’ x ‘Glacier’ A10 (TG.A10) map. Nearest B. napus gene to each marker given in brackets. Unanchored B. napus genes corresponding to syntenic B. rapa A10 homologues are denoted with “*”. LepR3 ‘Topas’ x ‘Surpass 400’ A10 (TS.A10) map updated from Larkan et al., 2013a. Marker intervals given in centiMorgans. Solid horizontal lines denote same marker, dashed horizontal lines denote markers sharing same nearest B. napus homologue. Approximate physical location of defense-related candidate genes by triangles. Gap in B. napus A10 chromosome build represented by dotted lines.

Mentions: The resulting map of ‘Topas’ x ‘Glacier’ A10 (TG.A10) showed Rlm2 was contained within an interval of 5.8 cM, between sN1982 and sN8474 (Figure 2). This interval corresponded to a collinear span of approximately 926 kb of the B. rapa genome, containing 204 putative genes on chromosome A10 (Bra008819 to Bra009023). The majority of the cross-overs detected in the population (52 of 61) occurred either between sN1982 and the Rlm2 locus (24 cross-overs), or between the Rlm2 locus and sN8474 (28 crossovers). Two additional markers were designed for the Rlm2 interval; one sequence characterised amplified region (SCAR) marker (Ind10-20), targeted to the Bra008930 homologue (previously identified as the LepR3 locus) and one cleaved amplified polymorphic sequence (CAPS) marker (CAPS94), targeted to the Bra008928 homologue. Ind10-20 produced fragments of 142 bp for ‘Topas’ and 138 bp for ‘Glacier’. CAPS94 produces amplicons of approximately 900 bp from both parents. Digestion with BstUI produces fragments of 483 and 410 bp from the ‘Glacier’ A-genome amplicon only. When used to genotype the recombinant subset of the mapping population, both of these markers co-segregated with the Rlm2 phenotype, providing markers tightly-linked to the Rlm2 gene yet failing to reduce the size of the target map interval. An additional nine microsatellite markers positioned within the map interval were tested but also failed to provide additional informative data.Figure 2


Co-localisation of the blackleg resistance genes Rlm2 and LepR3 on Brassica napus chromosome A10.

Larkan NJ, Lydiate DJ, Yu F, Rimmer SR, Borhan MH - BMC Plant Biol. (2014)

Comparison of genetic maps forRlm2andLepR3toB. napuschromosome A10. Position of Rlm2 relative to microsatellite (prefixed ‘sN’ or ‘sR’), Indel (prefixed ‘Ind’) and CAPS markers on ‘Topas’ x ‘Glacier’ A10 (TG.A10) map. Nearest B. napus gene to each marker given in brackets. Unanchored B. napus genes corresponding to syntenic B. rapa A10 homologues are denoted with “*”. LepR3 ‘Topas’ x ‘Surpass 400’ A10 (TS.A10) map updated from Larkan et al., 2013a. Marker intervals given in centiMorgans. Solid horizontal lines denote same marker, dashed horizontal lines denote markers sharing same nearest B. napus homologue. Approximate physical location of defense-related candidate genes by triangles. Gap in B. napus A10 chromosome build represented by dotted lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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Fig2: Comparison of genetic maps forRlm2andLepR3toB. napuschromosome A10. Position of Rlm2 relative to microsatellite (prefixed ‘sN’ or ‘sR’), Indel (prefixed ‘Ind’) and CAPS markers on ‘Topas’ x ‘Glacier’ A10 (TG.A10) map. Nearest B. napus gene to each marker given in brackets. Unanchored B. napus genes corresponding to syntenic B. rapa A10 homologues are denoted with “*”. LepR3 ‘Topas’ x ‘Surpass 400’ A10 (TS.A10) map updated from Larkan et al., 2013a. Marker intervals given in centiMorgans. Solid horizontal lines denote same marker, dashed horizontal lines denote markers sharing same nearest B. napus homologue. Approximate physical location of defense-related candidate genes by triangles. Gap in B. napus A10 chromosome build represented by dotted lines.
Mentions: The resulting map of ‘Topas’ x ‘Glacier’ A10 (TG.A10) showed Rlm2 was contained within an interval of 5.8 cM, between sN1982 and sN8474 (Figure 2). This interval corresponded to a collinear span of approximately 926 kb of the B. rapa genome, containing 204 putative genes on chromosome A10 (Bra008819 to Bra009023). The majority of the cross-overs detected in the population (52 of 61) occurred either between sN1982 and the Rlm2 locus (24 cross-overs), or between the Rlm2 locus and sN8474 (28 crossovers). Two additional markers were designed for the Rlm2 interval; one sequence characterised amplified region (SCAR) marker (Ind10-20), targeted to the Bra008930 homologue (previously identified as the LepR3 locus) and one cleaved amplified polymorphic sequence (CAPS) marker (CAPS94), targeted to the Bra008928 homologue. Ind10-20 produced fragments of 142 bp for ‘Topas’ and 138 bp for ‘Glacier’. CAPS94 produces amplicons of approximately 900 bp from both parents. Digestion with BstUI produces fragments of 483 and 410 bp from the ‘Glacier’ A-genome amplicon only. When used to genotype the recombinant subset of the mapping population, both of these markers co-segregated with the Rlm2 phenotype, providing markers tightly-linked to the Rlm2 gene yet failing to reduce the size of the target map interval. An additional nine microsatellite markers positioned within the map interval were tested but also failed to provide additional informative data.Figure 2

Bottom Line: Molecular markers tightly linked to the gene were developed for use in mapping the resistance locus and defining the physical interval in B. napus.Rlm2 was localised to a 5.8 cM interval corresponding to approximately 873 kb of the B. napus chromosome A10.The recently-cloned B. napus R-gene, LepR3, occupies the same region of A10 as Rlm2 and analysis of the putative B. napus and B. rapa genes in the homologous region identified several additional candidate defense-related genes that may control Rlm2 function.

View Article: PubMed Central - PubMed

ABSTRACT

Background: The protection of canola (Brassica napus) crops against blackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is largely mediated by race-specific resistance genes (R-genes). While many R-genes effective against blackleg disease have been identified in Brassica species, information of the precise genomic locations of the genes is limited.

Results: In this study, the Rlm2 gene for resistance to blackleg, located on chromosome A10 of the B. napus cultivar 'Glacier', was targeted for fine mapping. Molecular markers tightly linked to the gene were developed for use in mapping the resistance locus and defining the physical interval in B. napus. Rlm2 was localised to a 5.8 cM interval corresponding to approximately 873 kb of the B. napus chromosome A10.

Conclusion: The recently-cloned B. napus R-gene, LepR3, occupies the same region of A10 as Rlm2 and analysis of the putative B. napus and B. rapa genes in the homologous region identified several additional candidate defense-related genes that may control Rlm2 function.

Show MeSH
Related in: MedlinePlus