水稻印记基因SPK的表观遗传调控及其在胚乳发育中的功能研究

Imprinted genes are referred to a group loci that only expressed one allele of the hybrids, while the other allele is largely silenced, usually due to differential epigenetic regulation, such as DNA methylation or histone modification, between parental alleles. Recent studies indicated that some imprinted genes play important roles in the development of endosperm. More than hundred putative imprinted genes have been identified from rice. However, biological significance of these genes is largely unknown. Previous study found that a calcium-dependent protein kinase gene SPK is important to the endosperm development of rice, through regulating the starch biosynthesis and accumulation. We confirmed that SPK is a maternally expressed imprinted gene and propose unravelling the epigenetic regulation of its imprinting. In addition, we have identified that a Nuclear Factor-Y transcription factor, SIF1 (SPK Interacted Factor 1), physically interacts with SPK in cytoplasm. Similar to the expression profile of SPK, SIF1 is predominantly expressed in the endosperm of rice. Therefore, we hypothesized that SPK and SIF1 are both essential for the development of rice endosperm. In the present study, we propose studying the underlying molecular mechanism of SPK-SIF1 mediated endosperm development of rice. The new findings will broaden our understandings of the biological significance of imprinted genes in plant.

印记基因是一类特殊的基因，由于父、母本等位基因DNA甲基化或者组蛋白修饰的差异，导致只有一个等位基因正常表达，而另一个等位基因被表达沉默。研究表明印记基因可能参与胚乳的发育调控。目前水稻中发现了一些潜在的印记基因，但是关于其生物学功能的研究还鲜有报道。水稻钙依赖激酶基因SPK能够通过调控水稻胚乳中淀粉合成影响胚乳发育。我们前期研究发现SPK是一个只表达母本等位基因的印记基因，本研究拟对SPK印记产生的表观调控机制进行分析。此外，通过酵母双杂交、BiFC等实验我们发现SPK可以与一个NF-YB转录因子家族成员SIF1在细胞质中相互作用。与SPK的表达模式类似，SIF1是一个在胚乳特异表达的基因，我们推测两者可能共同调控水稻胚乳发育。本研究拟通过对SPK和SIF1的功能分析，构建SPK-SIF1调控水稻胚乳发育的分子通路。相关结果将加深我们对印记基因表观调控机制和生物学功能的理解。

印记基因是一类特殊的基因，由于父、母本等位基因DNA甲基化或者组蛋白修饰的差异，导致只有一个等位基因正常表达，而另一个等位基因被表达沉默。研究表明印记基因可能参与胚乳的发育调控。目前水稻中发现了一些潜在的印记基因，但是关于其生物学功能的研究还鲜有报道。水稻钙依赖激酶基因SPK能够通过调控水稻胚乳中淀粉合成影响胚乳发育。我们的研究发现SPK是一个只表达母本等位基因的印记基因，其印记表达模式可能主要受到DNA甲基化的影响，而PRC2介导的组蛋白H3K27me3甲基化对基因印记的影响有限。通过酵母双杂交、BiFC和GST-pulldown等实验我们发现SPK可以与一个NF-YB转录因子家族成员OsNF-YB9在细胞质中相互作用。与SPK的表达模式类似，OsNF-YB9是一个在胚乳特异表达的基因，我们推测两者可能共同调控水稻胚乳发育。通过构建SPK和OsNF-YB9的CRISPR/Cas9靶向敲除突变体，我们发现这两个基因突变都能引起水稻胚乳出现垩白度和垩白粒率增加的表型。当SPK和OsNF-YB9共表达时可以增加OsNF-YB9在细胞核内的分布，因此我们推测SPK可能通过磷酸化OsNF-YB9调控其亚细胞定位，进而影响淀粉等储藏物质在胚乳中的积累。相关结果加深了我们对印记基因表观调控机制和生物学功能的理解。