Table_3_QTL for induced resistance against leaf rust in barley.xlsx

Leaf rust caused by Puccinia hordei is one of the major diseases of barley (Hordeum vulgare L.) leading to yield losses up to 60%. Even though, resistance genes Rph1 to Rph28 are known, most of these are already overcome. In this context, priming may promote enhanced resistance to P. hordei. Several bacterial communities such as the soil bacterium Ensifer (syn. Sinorhizobium) meliloti are reported to induce resistance by priming. During quorum sensing in populations of gram negative bacteria, they produce N-acyl homoserine-lactones (AHL), which induce resistance in plants in a species- and genotype-specific manner. Therefore, the present study aims to detect genotypic differences in the response of barley to AHL, followed by the identification of genomic regions involved in priming efficiency of barley. A diverse set of 198 spring barley accessions was treated with a repaired E. meliloti natural mutant strain expR+ch producing a substantial amount of AHL and a transformed E. meliloti strain carrying the lactonase gene attM from Agrobacterium tumefaciens. For P. hordei resistance the diseased leaf area and the infection type were scored 12 dpi (days post-inoculation), and the corresponding relative infection and priming efficiency were calculated. Results revealed significant effects (p<0.001) of the bacterial treatment indicating a positive effect of priming on resistance to P. hordei. In a genome‐wide association study (GWAS), based on the observed phenotypic differences and 493,846 filtered SNPs derived from the Illumina 9k iSelect chip, genotyping by sequencing (GBS), and exome capture data, 11 quantitative trait loci (QTL) were identified with a hot spot on the short arm of the barley chromosome 6H, associated to improved resistance to P. hordei after priming with E. meliloti expR+ch. Genes in these QTL regions represent promising candidates for future research on the mechanisms of plant-microbe interactions.

由大麦柄锈菌（Puccinia hordei）引起的叶锈病是栽培大麦（Hordeum vulgare L.）的主要病害之一，可导致最高达60%的产量损失。尽管目前已鉴定出Rph1至Rph28系列抗病基因，但其中绝大多数已被该病原菌克服。在此研究背景下，抗病预激发（priming）可增强大麦对大麦柄锈菌的抗性。已有研究表明，包括苜蓿根瘤菌（Ensifer（异名Sinorhizobium）meliloti）在内的多种细菌类群可通过预激发途径诱导植物抗病性。革兰氏阴性细菌在群体感应（quorum sensing）过程中会产生N-酰基高丝氨酸内酯（N-acyl homoserine-lactones, AHL），这类物质可按照物种和基因型特异性方式诱导植物产生抗病性。因此，本研究旨在探究不同大麦基因型对AHL的响应差异，并鉴定与大麦预激发抗病效率相关的基因组区域。本研究选用198份多样化的春大麦种质资源，分别用修复后的苜蓿根瘤菌天然突变菌株expR+ch（可大量产生AHL）以及携带根癌农杆菌（Agrobacterium tumefaciens）来源的内酯酶基因attM（lactonase gene attM）的转基因苜蓿根瘤菌菌株进行处理。针对大麦柄锈菌的抗性，我们于接种后12天（days post-inoculation, dpi）对病叶面积与侵染类型进行分级统计，并据此计算相对侵染量与预激发抗病效率。研究结果显示，细菌处理组存在极显著差异（p<0.001），表明抗病预激发可正向提升大麦对大麦柄锈菌的抗性。基于观测到的表型差异，以及由Illumina 9k iSelect基因芯片、测序基因分型（genotyping by sequencing, GBS）和外显子组捕获数据获得的493,846个过滤后的单核苷酸多态性（single nucleotide polymorphism, SNPs），本研究开展全基因组关联分析（genome‐wide association study, GWAS），最终鉴定出11个数量性状位点（quantitative trait loci, QTL）；其中大麦6H染色体短臂存在一个热点区域，该区域与苜蓿根瘤菌expR+ch预激发处理后大麦抗大麦柄锈菌能力的提升显著相关。上述QTL区域内的基因，可作为未来解析植物-微生物互作机制的优质候选研究靶点。