SWEET家族基因调控枇杷果实糖分配与积累的功能解析

Loquat is of economic importance around Jiang-Zhe areas, but flat flavor of leading cultivars makes the economic benefit not as good as expected. Fruit flavor mostly depends on sugar and acid contents. Among which sugar is the foundation, both of fruit taste and flavor closely connect with sugar contents, as a little difference from sugar accumulation could cause large difference in fruit quality. Sugar accumulation is affected by external conditions such as cultivation and climate, but more importantly, intrinsic conditions of cultivars are of crucial roles. Therefore, understanding the mechanism of sugar allocation and accumulation is of great importance for quality improving and for breeding as well. Recently, SWEET family has been found to have essential roles on plant sugar allocation and accumulation in model plants. Luckly, twelve members of SWEET family from loquat have been identified according to transcriptome sequencing in our previous study. This project is willing to further investigate the mechanism of SWEET family on sugar allocation and accumulation in loquat fruit. By using of MALDI imaging mass spectrometry, CRISPR and transcriptomic techniques, the different sugar accumulation mechanims between cultivars will be clarifued at histological and molecular level. The molecular network of sugar allocation, accumulation and regulation will be illustrated. The possible results of this project will provide fundamental basis for breeding.

枇杷是江浙等地重要经济树种，但是多地因主栽品种风味偏淡、品质不佳而导致经济效益远低于预期。果实风味主要由糖酸含量决定，糖是品质形成的基础和核心，糖分配和积累水平的差异可以直接导致果实品质的巨大差距。果实糖积累水平受栽培、气候等外界条件影响，但是起决定作用的仍然是其内在因素，阐明糖积累及调控机理是实现品质调控、指导高品质育种的理论基础。近来在模式植物中发现SWEET家族基因对植物体内糖分配及生长发育起重要作用。我们前期通过对两个糖积累水平差异较大的枇杷品种不同发育时期果实转录组测序获得了枇杷SWEET基因家族12个成员，本项目在此基础上开展枇杷SWEET家族基因调控糖分配及积累机理研究，利用MALDI质谱成像、CRISPR和转录组分析技术从组织水平和分子水平寻找品种间糖积累水平差异的原因，解析糖在果实中分配、积累及调控的分子网络，从理论上探索果实品质形成机理，为育种实践提供基础。

枇杷是四川、福建、浙江等地的重要经济树种，在地方农业经济中发挥重要作用。果实品质是发挥其经济价值的核心，而风味品质是果实品质的核心。果实风味主要由糖酸含量决定，糖是品质形成的基础和核心，糖分配和积累水平的差异可以直接导致果实品质的巨大差距。本研究围绕枇杷果实品质按照研究计划展开研究，完成了研究计划中制定的内容，鉴定了枇杷SWEET基因家族7个成员，对其亚细胞定位、保守结构功能域等进行了分析，分析了SWEET基因家族成员表达对不同外源糖处理和盐胁迫的响应。利用转录组测序从照种、白梨、冠玉、茂木、田中、栎叶、宁海白、宝珠、软条白沙等不同枇杷品种中分离到SWEET2、SWEET17等糖运输家族基因，并对不同品种基因表达与果实糖积累水平进行相关性分析，结果显示，糖运输基因表达与糖积累呈显著正相关，SWEET基因表达水平的差异可能是造成不同品种糖积累水平差异的原因之一，研究结果为SWEET基因的糖转运功能提供了依据。通过生物信息学分析筛选了可能参与枇杷糖运输蛋白SWEET基因转录水平调控的三类转录因子，包括25个MYB、27个bHLH、13个DOF，初步分析了枇杷三类转录因子的编码信息、基序结构及进化关系。项目实施期间，课题组结合实际情况对研究工作进行了拓展，比较了几种简易实用保鲜方法对枇杷采后贮藏保鲜的效果，分析了枇杷果实成熟过程中内源激素水平的变化及内源激素与糖的相关性，课题组联合福建省农科院和浙江省农科院研究了高强度光胁迫对枇杷叶片矿质元素和三萜酸含量的影响，开展了枇杷属植物落黄叶片颜色遗传多样性分析。本项目从生理和分子水平探索了果实品质形成机理，为育种实践提供了一定理论基础。