龙眼高密度遗传图谱构建及果实香气物质含量QTL定位

Fruit aroma, which has high breeding and economic value, is one of the important indicators for the quality of fresh longan. The further studying on the genetic mechanism of aroma phenotype could provide important guidance for longan quality improvement. We had created F1 population of ‘Shixia’בXiangcui’ with 178 individuals, in which the fruit flavor traits varied widely, and had analyzed the hybrid progenies to identify the validity and genetic diversity by SSR markers. The studying on the changes in aroma components of parents fruit during development and ripening and its inheritance had also completed. Based on these results, we intends to use the ddRAD-seq technology to perform reduced-representation sequencing for this population, detect and screen SNP markers, and build a high-density and high-precision genetic map of parents based on SSR and SNP markers; Aroma components content and its inheritance would be analyzed for 2 years using GC-MS; QTL analysis of characteristic aroma component content would be carried out, molecular markers tightly-linked with aroma trait QTL would be screened, and hot-spot QTL regions controlling aroma trait would be identified.The results will lay foundation for marker assisted selection (MAS) for longan aroma quality improvement and provide potential breeding materials for cultivating new varieties.

果实香气是衡量龙眼鲜食品质的一个重要指标，具有较高的育种及经济价值。深入研究其遗传机制对于指导龙眼品质育种具有重要意义。项目组前期创建了果实香气性状广泛分离的178份‘石硖’ב香脆’F1杂交群体，并完成了杂交后代SSR标记真实性鉴定及遗传多样性分析，开展了亲本品种果实香气物质的动态发育变化及其遗传分析。在此基础上，本项目拟利用双酶切RAD-seq技术对该群体材料进行简化基因组测序，检测和筛选SNP标记，并联合SSR标记构建高密度、高精度遗传图谱；采用GC-MS法连续2年测定杂交群体及亲本果实香气物质的含量并分析其遗传规律，对特征香气物质含量进行QTL定位分析，筛选与香气性状QTL紧密连锁的分子标记，确定控制香气性状的QTL热点区域。研究结果为今后龙眼果实香气的分子辅助选择及品质改良提供材料基础和科学依据。

果实香气是评价龙眼鲜果商品品质的一个重要指标，然而，国内生产上缺乏浓香型龙眼品种。杂交育种是实现龙眼品质遗传改良的有效途径，深入研究果实香气性状的遗传调控机制可为香气品质育种提供理论基础和依据。关于龙眼果实香气性状的遗传解析未见报道。因此，本项目开展了相应研究，主要内容及结果如下：（1）以98份‘石硖’ב香脆’杂交后代及其亲本为试材，基于重测序获得约31万个有效SNP标记，开发出EST-SSR引物4670对。利用Joinmap构建了双亲遗传连锁图，该图谱包含15个连锁群共3516个bin marker，平均图距0.47cM，与龙眼基因组及HiC测序数据集的共线性分析表明图谱质量良好。（2）完成杂交亲本果实发育过程及后代群体成熟期果实的香气物质GC-MS鉴定与遗传规律分析，对山梨酸乙酯、苯甲酸甲酯、巴豆酸乙酯、丁酸乙酯、乙酸乙酯、别罗勒烯、罗勒烯、2-己烯醛、乙醛、乙醇等10个特征香气物质进行QTL定位，获得137个QTLs（区间注释基因209个）；结合‘香脆’和‘石硖’果实6个发育阶段（36个测序文库）的RNA-seq数据，筛选出ERF、bHLH、乙醛脱氢酶等5个重要候选基因。（3）延伸开展了龙眼果实发育过程香气物质合成前提物可溶性糖和游离氨基酸的代谢机制的多组学分析，确定了花后100-120d为XC和LDB品种果实糖积累的关键时期，有79个miRNA的表达量达到显著差异水平；果实膨大期（S2-S4）XC果实的香气由无变浓，同时游离的丙氨酸和亮氨酸含量均极显著高于SX和LDB；DilBCAT1, -6, -9，16的表达差异可能是品种间亮氨酸合成代谢差异的原因。本研究结果有助于深入理解龙眼香气品质形成机制，为建立分子辅助育种体系加速培育浓香型新品种提供科学依据。