大红甜橙高柠檬酸积累的分子机制解析

Both Citrus sinesis (L.) Osbeck ‘Dahongtiancheng’ and Citrus sinesis (L.) Osbeck ‘Bingtangcheng’ derive from the bud mutation of common sweet orange (Citrus sinesis (L.) Osbeck), but citric acid content in the former is 3.6 fold higher than that in the latter. Previous researching results showed that the main reason was different accumulation pattern of citric acid; however, the specific mechanism of citric acid accumulation between two cultivars is still unclear. . In this project, we will firstly explore the key stage of citric acid accumulation by researching citric acid accumulation regular pattern in both ‘Dahongtiancheng’ and ‘Bingtangcheng’, and then identify the key genes involving that process through related gene expression analysis and transcriptom sequencing analysis. The function of the key genes will thirdly be identified through changing the citric acid content in ‘Dahongtiancheng’ which is achieved by regulating the activity of key genes-encoded enzymes. . Through this research, the formation mechanism of the high citric acid accumulation in ‘Dahongtiancheng’ can be clarified. Results of this research have important significance in improving the mechanism of citric acid metabolism and lay the foundation for regulating fruit quality subsequently.

大红甜橙和冰糖橙均源于普通甜橙芽变，而前者柠檬酸含量为后者的3.6倍。前期研究表明柠檬酸积累模式不同是造成该差异的主要原因，但两品种柠檬酸差异积累的具体机制尚不明确。本项目首先对大红甜橙和冰糖橙柠檬酸积累规律开展研究，明确两品种柠檬酸含量差异形成的关键时期；进而针对两品种柠檬酸差异积累关键时期进行柠檬酸代谢相关基因表达和转录组测序分析，鉴定参与大红甜橙高柠檬酸积累的关键基因，然后通过调节关键基因相应酶活性改变柠檬酸含量的方法进行验证，最终揭示大红甜橙高柠檬酸积累的分子机制。本项目的开展对完善柑橘柠檬酸代谢机制具有重要意义，也为进一步调节果实品质形成奠定基础。

柠檬酸是柑橘果实主要的有机酸类型，其在果实中的代谢直接影响果实风味的形成。大红甜橙和冰糖橙是湖南省地方特色品种，两者同是普通甜橙的芽变但柠檬酸含量差异巨大。本项目以这两个材料开展生理生化和分子生物学研究，揭示大红甜橙高柠檬酸积累的具体机制。研究结果表明，盛花后50-70天是大红甜橙和冰糖橙果实柠檬酸差异积累的关键时期；针对该时期的转录组测序结果表明，光合作用和氨基酸合成途径显著上调、柠檬酸降解途径显著下调是导致大红甜橙高柠檬酸积累的重要原因；CsAco和CsIDH基因家族下调表达在高柠檬酸积累中有重要作用，进一步通过生物信息学分析和酵母单杂交筛选到5个与CsAco1启动子互作的转录因子，深入探讨了调控柑橘果高柠檬酸积累的分子机制。本研究为阐明柑橘果实柠檬酸形成机制和进一步调控果实品质形成提供理论依据。