AUTHOR=Raman Harsh , Raman Rosy , Qiu Yu , Zhang Yuanyuan , Batley Jacqueline , Liu Shengyi 

TITLE=The Rlm13 Gene, a New Player of Brassica napus–Leptosphaeria maculans Interaction Maps on Chromosome C03 in Canola

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.654604

DOI=10.3389/fpls.2021.654604

ISSN=1664-462X

ABSTRACT=<p>Canola exhibits an extensive genetic variation for resistance to blackleg disease, caused by the fungal pathogen <italic>Leptosphaeria maculans</italic>. Despite the identification of several <italic>Avr</italic> effectors and <italic>R</italic> (race-specific) genes, specific interactions between <italic>Avr-R</italic> genes are not yet fully understood in the <italic>Brassica napus–L. maculans</italic> pathosystem. In this study, we investigated the genetic basis of resistance in an F<sub>2</sub><sub>:</sub><sub>3</sub> population derived from Australian canola varieties CB-Telfer (<italic>Rlm4</italic>)/ATR-Cobbler (<italic>Rlm4</italic>) using a single-spore isolate of <italic>L. maculans</italic>, PHW1223. A genetic linkage map of the CB-Telfer/ATR-Cobbler population was constructed using 7,932 genotyping-by-sequencing-based DArTseq markers and subsequently utilized for linkage and haplotype analyses. Genetic linkage between DArTseq markers and resistance to PHW1223 isolate was also validated using the <italic>B. napus</italic> 60K Illumina Infinium array. Our results revealed that a major locus for resistance, designated as <italic>Rlm13</italic>, maps on chromosome C03. To date, no <italic>R</italic> gene for resistance to blackleg has been reported on the C subgenome in <italic>B. napus</italic>. Twenty-four candidate <italic>R</italic> genes were predicted to reside within the quantitative trait locus (QTL) region. We further resequenced both the parental lines of the mapping population (CB-Telfer and ATR-Cobbler, &gt; 80 × coverage) and identified several structural sequence variants in the form of single-nucleotide polymorphisms (SNPs), insertions/deletions (InDels), and presence/absence variations (PAVs) near <italic>Rlm13</italic>. Comparative mapping revealed that <italic>Rlm13</italic> is located within the homoeologous A03/C03 region in ancestral karyotype block “R” of <italic>Brassicaceae</italic>. Our results provide a “target” for further understanding the <italic>Avr–Rlm13</italic> gene interaction as well as a valuable tool for increasing resistance to blackleg in canola germplasm.</p>