Table_2_The Rlm13 Gene, a New Player of Brassica napus–Leptosphaeria maculans Interaction Maps on Chromosome C03 in Canola.XLSX

Canola exhibits an extensive genetic variation for resistance to blackleg disease, caused by the fungal pathogen Leptosphaeria maculans. Despite the identification of several Avr effectors and R (race-specific) genes, specific interactions between Avr-R genes are not yet fully understood in the Brassica napus–L. maculans pathosystem. In this study, we investigated the genetic basis of resistance in an F2:3 population derived from Australian canola varieties CB-Telfer (Rlm4)/ATR-Cobbler (Rlm4) using a single-spore isolate of L. maculans, 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 B. napus 60K Illumina Infinium array. Our results revealed that a major locus for resistance, designated as Rlm13, maps on chromosome C03. To date, no R gene for resistance to blackleg has been reported on the C subgenome in B. napus. Twenty-four candidate R 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, > 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 Rlm13. Comparative mapping revealed that Rlm13 is located within the homoeologous A03/C03 region in ancestral karyotype block “R” of Brassicaceae. Our results provide a “target” for further understanding the Avr–Rlm13 gene interaction as well as a valuable tool for increasing resistance to blackleg in canola germplasm.

油菜（Canola）对由真菌病原菌黑胫病菌（Leptosphaeria maculans）引发的黑胫病（blackleg disease）具有丰富的遗传变异抗性。尽管已鉴定出多种无毒效应子（Avr effectors）和小种专化性抗病基因（R genes），但在甘蓝型油菜（Brassica napus）-黑胫病菌病害互作系统（pathosystem）中，Avr-R基因间的特异性互作机制仍未完全阐明。本研究以澳大利亚油菜品种CB-Telfer（携带Rlm4）/ATR-Cobbler（携带Rlm4）构建的F2:3分离群体为材料，利用黑胫病菌单孢分离物PHW1223，解析了该群体的抗病遗传基础。本研究利用7932个基于测序分型（genotyping-by-sequencing）的多样性阵列技术测序（DArTseq）标记，构建了CB-Telfer/ATR-Cobbler群体的遗传连锁图谱，并将其用于连锁分析与单倍型分析。本研究还通过甘蓝型油菜60K Illumina Infinium基因芯片（B. napus 60K Illumina Infinium array），验证了DArTseq标记与抗PHW1223分离物性状间的遗传连锁关系。研究结果显示，一个命名为Rlm13的主效抗病位点定位于C03染色体上。截至目前，甘蓝型油菜C亚基因组中尚未见报道与黑胫病抗性相关的R基因。经预测，该数量性状位点（quantitative trait locus, QTL）区域内存在24个候选抗病基因。本研究进一步对作图群体的两个亲本（CB-Telfer和ATR-Cobbler，测序深度>80×）进行了重测序，在Rlm13位点附近鉴定到多种结构序列变异，包括单核苷酸多态性（single-nucleotide polymorphisms, SNPs）、插入/缺失（insertions/deletions, InDels）以及有无变异（presence/absence variations, PAVs）。比较作图分析显示，Rlm13位点位于十字花科（Brassicaceae）祖先核型“R”模块的同源A03/C03区域内。本研究结果为进一步解析Avr–Rlm13基因互作机制提供了研究靶点，同时也为改良油菜种质的黑胫病抗性提供了极具价值的工具。