生长素响应基因EiSAU23调控枇杷果实细胞膨大的功能解析

Low yield capacity is an important bottleneck restricting the development of loquat industry. The applications of bigger fruit size cultivars and fruit growth promoting techniques are effectual ways help to alleviate the low yield problem and therefore enhance the planting benefit of loquat. For loquat, fruit size is not only one of the most important quality traits, but also the crucial composition of yield. The results of our previous research indicated that cell size contributes more than cell number to loquat fruit size formation. Meanwhile, we discovered a sibling lines (ZP44 and ZP65) from a loquat hybrid population, which set extremely small and extremely large fruits, respectively. A comprehensive study of cellular characteristics and differential expressed genes (RNA-seq) in ZP44 and ZP65, showed that the expression model of EjSAUR23 was significantly correlated to both cell volume and fruit size. And VIGS down regulation of EjSAUR23 in loquat fruit verified its function on cell size and thus fruit size regulation. However, the mechanism how EjSAUR23 regulates cell and fruit size remains to be uncover. In this study, loquat lines ZP44 and ZP65 are selected as main material to confirm the role of EjSAUR23 in cell and fruit size regulation and uncover the molecular pathway of EjSAUR23 by means of biochemical analyses including the dynamic changes of cell size, auxin content, H+-ATPase activity, pH value and molecular and biotechnology strategies including EjSAUR23 expression assays, VIGS and so on. This study would firstly broaden our understanding about the mechanism of fruit and cell size regulation. And hope that the results of this study will provide important references for germplasm evaluation, genetic improvement, and fruit size regulation in loquat.

产量低是限制枇杷产业发展的重要瓶颈问题，培育和推广大果优质品种是提高枇杷单产进而提高种植业效益的有效途径。果实大小是枇杷重要的品质性状，同时又是产量形成的重要基础。本项目组前期研究发现影响果实大小的主要细胞学因子是细胞大小；进一步以枇杷杂交群体中发现的一对果实大小极端差异的姊妹系为材料，进行转录组分析发现生长素响应基因EjSAUR23的表达与二者果实大小差异显著相关；基因本体功能验证初步确定了EjSAUR23参与枇杷果实大小的调控，但EjSAUR23调控枇杷果实膨大的分子通路尚不清楚。本项目拟以果实大小有显著差异的枇杷姊妹株系为主要试材，设计一系列实验，从生理生化和分子生物学角度，明确生长素响应基因EjSAUR23在果实细胞膨大中的作用，并阐明其调控细胞膨大的分子机制。研究结果将为果实大小的定向遗传改良提供靶标，具有重要的理论意义和应用价值。

本项目针对枇杷生产过程中较为严重的产量过低瓶颈问题，开展细胞学比较、指示基因筛选、果实大小关联基因转录组筛选、异源遗传转化、果实基因沉默、群体基因组学、分子标记开发、生长素外源处理、生长素信号因子互作因子筛选、生理生化变化分析等实验。厘清了枇杷驯化过程中果实大小变异的主要细胞学差异归结于细胞大小层面的、建立果实生长的细胞变化模式图、异源转化与基因沉默验证FWL、SAUR23、BZR1等基因调控果实大小的功能；解析枇杷EjBZR1转录因子通过介导CYP90A等油菜素生物合成基因的表达水平，抑制果实油菜素合成，进而限制细胞膨大与果实大小的分子机制；开发了包括在生长素合成相关基因EjTRN1相关位点在内的3个果实大小高度关联分子标记；鉴定了生长素信号转导SAUR家族与并解析了SAUR23通过与质膜H+-ATP酶和PP2C蛋白磷酸酶等蛋白互作，调控果实细胞膜与细胞壁间pH值，进而通过调控胞间酸化促进细胞膨大，最终达到促进枇杷果实生长的功能与分子机制。这些细胞学、遗传学和分子生物学研究结果，为通过农艺措施改良保障果实生长量奠定了理论基础，为环境友好型枇杷果品生产提供新思路。分子机制的解析和分子标记的开发还为为了解枇杷果重的遗传基础提供了丰富且关键的信息，也为从细胞膨大角度调控枇杷果实大小及其他农作物籽粒等产品器官大小、保证作物产量提供分子育种靶标。