苹果果实酸度QTLs区域液泡膜H+-ATPase及相关调节基因的关联分析和功能研究

Apple is an economically important fruit tree in China. Malic acid is the main organic acid in mature apple fruit, and its content is one of the most important determinants of apple fruit quality. Thus, it is of important academic significance and realistic value for apple high-quality breeding programs to study on the mechanism underlying malic acid biosynthesis in fruit. Malic acid is stored in the vacuole and intracellular transport of malate is closely related to fruit acidity. We have identified a series of genes related to malate transport, including vacuolar H+-ATPase and putative regulatory genes in genomic regions harboring QTLs for apple fruit acidity. The main objective of this project is to further investigate DNA sequence variation in these genes and identify candidate genes, rather than Ma genes, responsible for apple fruit acidity using a combined approach of linkage and association mapping. We will analyze the relationship between the expression of the candidate genes and fruit acidity, and the functional analysis of the candidate genes will be carried out as well. We will also develop functional markers of candidate genes and exploit interaction network of genes involved in the transport and accumulation of malate in fruit. Therefore, this project has the potential to contribute to improve our understanding regulation of malate metabolism in fruit, and it will also provide molecular tools to facilitate the development of new varieties with high-quality fruit in apple and other fruit tree crops.

苹果是我国重要经济果树。苹果酸是苹果成熟果实中主要有机酸，其含量是决定苹果品质的一个重要因素，解析苹果酸合成调控机制，对于优质品种的选育具有重要理论意义与应用价值。苹果酸主要贮存于液泡中，液泡中苹果酸转运与果实酸度关系密切。本项目拟在我们前期鉴定的位于苹果果实酸度QTLs区域液泡膜H+-ATPase及相关调节基因的基础上，进一步鉴定这些基因的DNA多态性位点，运用QTL定位与候选基因关联分析相结合的方法，发掘与果实酸度显著关联的DNA变异序列及候选基因，分析候选基因的表达水平与果实酸度性状之间的相关性，开展候选基因参与果实酸度性状形成的功能研究，发掘Ma基因位点之外控制果实酸度的候选基因及其功能标签，同时研究候选基因之间的相互作用，探索果实苹果酸转运与积累过程中的基因互作网络，为苹果等果树果实品质性状的遗传改良提供理论依据和分子工具。

酸度是决定苹果品质的一个重要因素，解析苹果有机酸合成调控机制，对于优质品种的选育具有重要理论意义与应用价值。有机酸主要贮存于液泡中，液泡中苹果酸转运与果实酸度关系密切。本项目开展了苹果果实酸度QTL定位研究并获得了一个位于QTL区间的控制果实酸度的质子泵基因Ma10，候选基因关联分析表明Ma10可解释苹果资源果实酸度表型变异的8%左右，Ma10位于液泡膜，在酵母YAK2突变株和番茄中异位表达可显著提高苹果酸在酵母细胞或番茄果实的积累。同时阐明了苹果果实酸度主效基因Ma1编码框尾端单碱基变化位点影响果实酸度的分子机理，该SNP位点可解释苹果资源果实酸度表型变异方差5%左右，该SNP位点碱基为G时，对应的编码蛋白位于液泡膜，能够将苹果酸转运到液泡，促进果实有机酸积累；但当SNP位点碱基为A时，造成终止密码子提前，编码的不完整蛋白位于细胞质膜上，无法负责将苹果酸向液泡中转运，不利于有机酸积累。此外，开发了Ma10和Ma1基因分子标记，研究结果为苹果等果树果实品质性状的遗传改良提供理论依据和分子工具。

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