梅花垂枝性状的关联分析及遗传机理解析

As an early spring ornamental woody plant native to China, mei (Prunus mume Sieb. et Zucc.) has long represented an unique symbol of the Chinese culture. Weeping mei has particularly a high ornamental value because of its elegant tree form and flowers. However, there are very few weeping cultivars currently available on market, far lagging behind their commercial demands. Because of the unknown genetic mechanisms underlying weeping traits, the selection of superior cultivars by traditional hybridization strategies is highly time consuming and inefficient. This project aims to portray a picture of the genetic architecture of weeping traits through a joint strategy of genome-wide association studies (GWAS) and bulked segregant RNA sequencing (BSR), based on the genetic information available from previous genetic linkage mapping and core variety sequencing. Specific aims are to: (1) detecting significant quantitative trait loci (QTLs) that are associated with the formation of weeping pattern in mei hybrid populations by monitoring the growth process of branch traits and implementing sophisticated functional mapping approaches; (2) obtaining high-resolution mapping of key QTLs for weeping traits by a combined approach of GWAS and population genetic principles based on the results from dynamic QTL detection in aim (1); and (3) mine candidate genes for weeping phenotypes by a joint BSR and transcriptomic analysis of vertical and weep branches. The biological function of these genes will be verified by a transgenic approach. This study will pave a road to shed light on the genetic mechanisms of weeping traits, which facilitate the design of maker-assisted selection breeding and elite cultivar breeding for mei.

梅花是我国特有的早春观赏木本花卉。特别是垂枝型梅花品种因其树姿隽秀，既可赏花又可观姿，自古以来广受人们喜爱。目前，垂枝型梅花品种少，控制该性状遗传机理仍不清晰，新品种培育以人工杂交为主，花费时间长，育种效率低。因此，本研究在已经构建的梅花垂枝性状遗传图谱和核心品种重测序的基础上，通过全基因组关联和集群分离分析相结合的方法解析垂枝性状的遗传机理，具体内容为：（1）通过测定梅花杂交群体中垂枝性状生长过程，利用功能作图方法，获得与该性状动态发育相关联的QTLs。（2）利用全基因组关联分析和群体遗传学原理对梅花重测序品种的垂枝性状进行解析，结合QTL动态分析结果，获得控制该性状高解析度QTLs。（3）利用集群分离分析法对直枝和垂枝子代个体进行转录组测序，挖掘候选基因，通过转基因方法验证其功能。本研究结果旨在解析垂枝性状形成的遗传机理，为开展分子标记辅助育种和新品种培育奠定重要基础。

梅花是我国早春重要的观赏木本花卉，垂枝型梅花品种因其姿态隽秀广受人们喜爱。本项目针对垂枝型梅花品种少，新品种培育以人工杂交为主，花费时间长，育种效率低等问题，在已经构建梅花垂枝性状遗传图谱和核心品种重测序基础上，开展具体内容为：①通过对梅花垂枝遗传作图群体表型性状观察实验发现，梅花垂枝性状独立自主的发生于茎分生组织，不受来自砧木和直枝梅花信号分子交流的影响；生长素 IAA对处理垂枝梅花茎的远轴侧能够显著恢复垂枝梅枝条向上生长；茎伸长区组织学观察发现垂枝梅韧皮部发育异常，缺少韧皮纤维结构。巢式表型分型法获得的7个亚性状呈显著正相关，能够代表垂枝性状表型特征，为开展梅花QTL动态分析奠定基础。②利用GWAS分析、群体遗传学原理和QTL动态分析相结合的方法，开发控制垂枝性状的QTL标记16个，其中 6个主效 QTLs位于 7号连锁群69.25–76.74 cM区间，解释 10.8%–55.3%表型变异；10个微效QTLs位于其它四个连锁群（LG2、LG3、LG4和 LG5） 解释 1.2–5.1%的表型变异，将梅花垂枝性状主效QTL 位点缩小在LG7，区间大小为 0.26 Mb，将其定义为 PmWEEP位点（包含37 个候选基因）；③基于BSR-Seq和转录组测序分析，发现 PmWEEP 区间内的37个候选基因中，仅有PmGT72B1和PmTrx呈现显著特异表达，通过对梅花垂枝相关基因PmGT72B1和PmTrx进行克隆、生物信息学分析、表达水平检测、植物遗传转化等，全面分析垂枝性状相关基因的生物学功能，研究发现在转基因拟南芥中，PmGT72B1转基因拟南芥出现了花序茎开散的现象，PmTrx转基因拟南芥花序茎较细弱，抽茎时间参差不齐。负向地性试验结果表明，PmGT72B1和PmTrx转基因拟南芥的茎对外界刺激更敏感。该结果旨在解析垂枝性状的遗传调控机理，为开展分子标记辅助育种和新品种培育奠定重要基础。