蓖麻种子籽粒大小性状形成的遗传机理研究

Seed size is a critical agronomical trait which significantly determines crop yield. Plant endosperm-seeds (using endosperm as storage tissue) are usually important resources. Asiding from Arabidopsis, little is known the molecular basis of seed development in dicots. Dissecting the molecular mechanisms underlying formation of endosperm-seed size would provide new insights in understanding the biological process of seed development and serve the varieties improvement and breeding in practice as well. Castor bean (Ricinus communis L., 2n=20), one of the most important non-edible oilseed crops and a model plant for studying the development of endosperm and seed in dicot, is a great potential biodiesel crop widely cultivated in tropical, sub-tropical and temperate countries for its high economic value. In this proposal, study will focus on 1)constructing RIL population based on the cross of the elite zb107 (with big seed in size) and zb306 (with small seed in size) and performing the high-throughout RNA sequencing techniques and transcriptome analyses; 2) conducting the genome-wide SNP association with seed size and identifying the QTL loci in seed coat and endosperm, respectively; 3) based on results from 1) and 2), conducting functional analyses of key genes identified, which is targeted to control the seed formation in size, by molecular manipulation techniques to discover the underlying molecular mechanisms of regulating the seed formation in size in castor. This study will not only provide new insights to understand the molecular mechanisms underlying seed formation in size in castor bean, but also serve the breeding and genetic improvement of varieties toward increasing seed size in practice.

种子籽粒大小是作物最核心的产量性状之一。双子叶胚乳型种子是一类典型的种子类型，解析其种子籽粒大小形成的遗传机理不仅对理解植物种子生长发育的分子基础具有崭新的理论意义，而且对双子叶胚乳型种子植物的遗传改良与育种具有指导意义。蓖麻是重要的非食用油料作物，也是典型的双子叶胚乳型种子。蓖麻一直被看作是种子生物学研究的模式植物，其种子籽粒大小主要取决于种皮和胚乳的发育调控。本研究以蓖麻为材料，运用遗传学、基因组学、生物信息学和分子操作等综合的方法，通过构建籽粒大小品系（ZB107和ZB306）的重组自交系和籽粒大小在杂交后代的群体分离规律，着重种皮组织高通量转录组GWAS分析和基因定位、胚乳组织功能基因组GWAS关联分析与印迹基因和靶点基因定位与解析、关键靶点基因的功能分析，集中鉴别、解析调控种皮和胚乳组织发育的靶点基因及其功能机制，为旨在提高双子叶胚乳型种子产量的遗传改良实践提供理论依据。

蓖麻是双子叶胚乳型种子的典型代表，解析种子籽粒大小形成不仅对蓖麻的遗传育种及油料作物育种具有重要指导意义。该项目重点开展三个方面的研究：1）利用高通量测序快速基因定位法鉴别控制种皮发育的主效基因位点；2）开展蓖麻种子胚乳组织群体RNA_seq和GWAS分析与基因印迹分析；3）调控蓖麻种子大小靶点基因的功能分析。通过项目的执行，系统、深入解析了双子叶胚乳型种子籽粒大小形成的分子机理。主要的发现包括：1)发现了双子叶胚乳型种子籽粒大小形成主要是控制种皮发育的关键基因和控制胚乳发育的关键基因协同调控的结果，控制种皮发育的关键基因调控了决定了种子体积上的大小；2）鉴别了蓖麻基因组上控制种子籽粒大小的遗传位点16个，通过解析这些位点发现了控制种子籽粒大小的关键候选基因82，这些候选基因的功能主要涉及调控种子发育关键酶基因和种子发育特异性调控因子，特别是发现了控制种皮大小形成的关键调控因子NARS1能够和MYB类转录因子结合通过参与种皮中木质素的生物合成调控，由于种皮木质素的合成直接影响了种皮的发育，进而影响了蓖麻种子籽粒大小的形成；发现了调控种子重量的关键功能基因ARPN直接影响种子胚乳的发育。这些关键候选基因的鉴别为旨在提高蓖麻种子籽粒大小的遗传改良或分子育种提供了重要的基因源；3）系统、全面构建蓖麻种子大小胚乳组织群体转录组基因表达数据库，该数据库对理解蓖麻种子发育、储存物质累积和蓖麻的遗传育种具有重要的指导意义；4）通过鉴别和深入解析杂交胚乳中胚乳和胚基因印迹的发生，阐明了蓖麻基因印迹发生的规律及其调控种子籽粒大小的生物学意义；5）发展了蓖麻种子大小高效SNP分子标记116个，这些SNP分子标记能够高效鉴别蓖麻种子大小的种质或品系，对蓖麻旨在提高种子籽粒大小的遗传育种具有重要的应用价值。这些研究结果崭新地发现双子叶胚乳型油料种子籽粒大小形成的遗传机理。