基于西瓜全基因组信息精细定位果实含糖量QTL及糖积累作用机制初析

Fruit sugar content is the core trait of commercial watermelon production. Based on the high density genetic map, we have identified two QTL intervals (Qbrix2-1 and Qbrix2-2) of sugar content trait on chromosome 2. The QTL loci of total sugar, sucrose and fructose content have proved that the QTL Qbrix2-2 is the major QTL for sugar content trait. The heritability (h2) of the birx trait was relatively high at 97% in different environments and years. This project will construct a Near-Isogenic Line(NIL) population for the Qbrix2-2 interval to fine mapping the sugar content QTL trait based on a large population more than 2000. Transcriptome and real time Q-PCR will used for the gene expression analysis of the fine mapping interval, association study of 500 germplasms will used to detect which gene associate with the sugar content trait in the fine mapping QTL region. We will analysis the relation of sugar determination gene's struction variation and sugar content. Subcellular localization by transient expression of target gene-GFP fusion protein and the yeast hybrid system will used to analyse the mechanism of sugar accumulation.

果实含糖量性状是评价西瓜商品品质的核心指标。基于已有西瓜高密度遗传图谱，本实验室已将西瓜折光糖决定基因定位在2号染色体Qbrix2-1和Qbrix2-2两个主效QTL区间，且总糖、蔗糖和果糖含量三组数据均独立显示Qbrix2-2位点为主效QTL，该位点稳定且遗传力高达97%。在此基础上本项目将进一步根据RILs株系重测序信息，通过单倍型图筛选出Qbrix2-2主效QTL区间的近等基因系，并构建2000株以上BC2F2近等基因系群体，进行含糖量决定基因QTL精细定位；通过转录组测序和荧光定量PCR分析QTL精细定位区间基因确定关键候选基因；对选出的候选基因，有代表性的500份材料进行关联分析，最终确定西瓜含糖量关键决定基因，并克隆获得目标基因全长，解析目标基因结构变异与糖含量关系。通过目标基因亚细胞定位，及酵母单杂交或酵母双杂交确定目标基因的调控基因或互作基因，初析目标基因对糖分积累的机制。

果实含糖量性状是评价西瓜商品品质的核心指标。本项目利用高糖西瓜材料97103和低糖西瓜G35构建的近等基因系群体，完成精细定位工作，并利用自然群体材料完成关联分析,获得了候选基因ClTMT2的关键SNP位点的基因型。最终确定西瓜含糖量关键决定基因ClTMT2，并克隆获得目标基因全长。通过目标基因亚细胞定位，发现ClTMT2位于西瓜果实液泡膜表达，是果实液泡糖分积累基因。解析目标基因结构变异与糖含量关系发现在启动子-1368处存在和表型最相关的SNP。-1368SNP (A/C)是WRKY家族转录因子识别位点，位于糖响应元件上。酵母单杂交确定WRKY家族转录因子SUSIWM1可识别ClTMT2基因W box识别位点，烟草中LUC荧光实验证明在植物活体SUSIWM1可调控ClTMT2表达，初步明确了ClTMT2基因对糖分积累的机制。该课题已发表SCI文章2篇，《Plant Cell》审稿文章1篇，申请国家发明专利1项。