桃endoPG基因簇控制果肉溶质和离核性状遗传的分子机制研究

Peach is an important fruit tree in China. China ranks first in peach production worldwide. Based on melting flesh and freestone, peach can be classified into three types: freestone melting flesh, clingstone melting flesh and clingstone non-melting flesh. The characteristics of melting flesh and freestone are regulated by endoPG genes located on chromosome 4. The F-M locus contains four different endoPG genes, but it is not clear how they are involved in the regulation of flesh melting and freestone. Thus, the purpose of this project is to gain an understanding in how gene cluster encoding endopolygalacturonase regulates both flesh melting and freestone. PpendoPG genes specifically responsible for melting flesh or freestone will be identified using regional association mapping and transcriptomics analysis. This project consists of primary research including: screening of germplasms to explore haplotype of gene cluster encoding endopolygalacturonase, survey of expression profiles of different PpendoPG genes during fruit development, and the relationship between allelic variances in PpendoPG genes and their corresponding phenotypes such as melting flesh and freestone. Moreover, molecular markers tagging melting flesh and freestone can be developed to serve as molecular tools for genetic improvement of peach fruit quality.

桃是我国重要的经济果树，栽培面积和产量均居世界首位。依据果肉溶质和离核特性，桃可分为离核溶质、粘核溶质和粘核非溶质3种主要类型。桃果肉溶质和离核性状主要受第4号染色体F-M位点endoPG基因簇控制，该基因簇包含4个endoPG同源基因，关于这些同源基因如何控制果肉溶质和离核性状的遗传机制至今尚不清楚。为此，本项目拟采用区间关联分析和转录组学相结合的研究手段，通过对PpendoPG基因簇单元型、PpendoPG同源基因在果实发育过程中表达谱的研究，明确控制果肉溶质和离核性状形成的PpendoPG基因，揭示PpendoPG基因的时空表达特性，阐明PpendoPG基因的等位变异类型及其与果肉溶质和离核性状之间的关联性，获得果肉溶质和离核性状的功能分子标签，为果实品质遗传改良提供分子元件和理论依据。

桃果实溶质和离核特性主要受第4号染色体F-M位点endoPG基因簇控制，该基因簇含有4个不同的endoPG同源基因，但这些同源基因控制果肉溶质和离核性状的遗传机制至今尚不清楚。本研究首先构建了武汉植物园95份可结果桃品种果肉的溶质和离核性状数据库，发现其只存在3中表现类型，离核溶质、粘核溶质和粘核非溶质。其次，分别采集了离核溶质桃-南山甜桃、黏核溶质桃-朝晖和黏核不溶质桃-明星的4个果实发育时期，高质量提取了这些样本的总RNA，并进行RNA-Seq测试。依据三个桃品种果实发育过程及成熟果实的表型性状，从RNA-Seq数据库中分离出了品种内不同发育时期和品种间成熟果实的差异表达基因，初步获得了控制桃果实离核性状的候选基因608个，控制桃果实软化性状的候选基因720个。结合前人对桃果实离核和溶质性状的定位结果，发现仅有5个控制桃果实离核性状和7个控制桃果实软化的候选基因位于4号染色体F-M位点。最终，采用遗传学研究手段，确认了F-M位点的两个endoPG基因分别控制桃果实的离核和溶质性状。在此基础上，采用染色体步移和TAIL-PCR相结合的方法，鉴定出F-M位点endoPG基因簇的三种不同结构特征，H1、H2和H3，它们分别含有该基因簇4个、3个和1个endoPG基因。再次采用遗传学方法，鉴定了95份桃资源品种endoPG基因簇三种结构特征的组合方式，明确了H1H1、H1H2和H1H3基因型桃品种的果实均表现出离核溶质表型特征，H2H2和H2H3基因型桃品种的果实均表现出黏核溶质表型特征，H3H3基因型桃品种的果实表现出黏核不溶质表型特征。本研究不仅明确了控制桃果实离核和溶质性状的关键基因及其分子遗传机制，开发的分子标记为桃育种的苗期性状选择提供了可靠的分子工具。