DNA甲基化和非编码小分子RNA对大豆杂种优势综合调控机制研究

Heterosis or hybrid vigor, refers to the phenomenon that offspring of individuals of a species or crosses between species show greater biomass, speed of development, and fertility than both parents. Although heterosis is widely exploited in agriculture, the details of its molecular underpinnings have remained elusive despite extensive investigation. Several genetic models, including dominance, overdominance, and pseudo-overdominance, have been supposed to explain heterosis, but neither each hypothesis nor combination of them could explain all the outcoming of heterosis. Instead, it is likely that heterosis arises in crosses between genetically distinct individuals as a result of a variety of mechanisms. Complementation of allelic variation, as well as complementation of variation in gene expression patterns, potentially contributed to heterosis. Epigenetic variation has the potential to interact in hybrid genotypes via novel mechanisms. Several genomic scaled epigenetics investigation in Arabidopsis, maize and rice revealed that DNA methylation with siRNA involved may play a role in heterosis. Soybean is an important cash crop for high oil and protein contents. Developing the hybrid soybean is crucially important since the local industry is suffering severe threat of imported transgenic soybean in China. To investigate the underlying mechanisms regulating heterosis in soybean, we employ high throughput sequencing to compare DNA methylomes, sRNAomes, and transcriptomes in a pair of parental lines and their reciprocal F1 hybrids that exhibited heterosis. The consequence that epigenetically generated differences in gene activity may contribute to the heterotic phenotype could help us to understand the complicated mechanisms regulating heterosis and apply in hybrid soybean breeding.

杂种优势是指杂交后代的某些表型，如生物量、生长速率、育性等方面超过了其双亲的现象。杂种优势在农业上有非常广泛的应用，但其内部的分子机制仍不清楚。经典遗传学提出显性效应、超显性效应和假超显性效应等模型来解释杂种优势，但任何一种或全部已有的模型都难以解释所有的杂种优势现象。因此，目前的观点认为遗传背景不同的个体间产生的杂种优势是受一系列不同的机制调控的。在拟南芥、玉米和水稻上开展的全基因组范围的表观遗传学调查表明受siRNA调控的DNA甲基化对杂种优势有重要影响。大豆是高油高蛋白的重要的经济作物。为了调查大豆杂种优势的调控机制，拟通过高通量测序手段产生DNA甲基化、sRNA及转录组的数据，比较一组杂交亲本与其存在杂种优势的正反交后代间的表观遗传差异，预期鉴定出一批与杂种优势表型相关的受表观遗传调控的基因/座位。本研究对深入理解杂种优势的复杂调控机制以及在杂交大豆育种中的应用有重要意义。

本研究首先开展了大豆非编码RNA（如miRNA, phasiRNA, eTM和circRNA等）鉴定，为后续杂种优势研究建立基础；二是根据双亲和F1的实验室设计，进行三者的非编码RNA及其甲基化的比较，获得与杂种优势如含油量相关小RNA等位点。经过研究，鉴定大豆miRNA 554个，34个长非编码RNA内源miRNA靶标诱捕（eTM）、49个phasiRNA和几百个circRNA。构建了靶向油脂合成相关非编码RNA基因调控网络。同时进行了非编码RNA及其甲基化在大豆和油菜含油量杂种优势的比较研究，发现非编码小RNA发挥关键杂种优势调控功能。本研究首次大规模和全面鉴定大豆非编码小RNA基因，拓展了油料作物非编码RNA调控网络，深化了对油料作物非编码RNA调控含油量杂种优势分子机制的认识。该研究具有明显创新性。