表观遗传变异与作物遗传改良

植物天然群体中存在大量遗传变异,这些变异是随机突变和自然选择的结果,也是物种赖以生存和进化的原料.此外,不同植物种间乃至属间的天然远缘杂交是经常发生的事件,也是新种形成的重要方式,而远缘杂交为高度分歧的物种之间的基因交流提供了机会,因此也是产生新的遗传变异的重要途径.近年来的大量研究表明,植物天然群体中还存在一类不基于DNA序列差异的变异,被称为表观遗传变异(epigeneticvariation).植物发生远缘杂交以及此后的多倍体化过程可以产生大量的表观遗传变异,其遗传行为不能用经典遗传规律解释.表观遗传变异的另外一个重要来源是环境中的各种生物和非生物胁迫.研究较深入的表观遗传变异主要是编码基因和转座子DNA甲基化水平和模式的改变,但可以推测与之相关的组蛋白修饰和染色质结构也可能发生变化.目前对此类表观遗传变异的分子机理尚缺乏深入研究,但不难想像可能与各类non-coding RNA有关.这些表观遗传变异的后果是基因表达的大规模改变并由此产生新表型.作物远缘杂交育种实践表明,这些不能用经典遗传学理论解释的变异中蕴含许多在育种上有重要价值的变异并可能与杂种优势密切相关,对它们的产生机理和遗传规律的深入解析将有助于其在作物改良中的有效利用.     

多倍体植物的遗传和表观遗传现象

人们在人工合成多倍体及基因组研究时发现,在多倍体合成过程中发生了很多遗传和表观遗传现象。了解和弄清这些遗传和表观遗传现象及其背后的机制,将会使我们对植物进化、新种形成以及杂种优势的机制有更深一步的了解。     

異源多倍体与远缘杂交

本文着重谈什么叫多倍体,自然界中植物的多倍体是如何形成的,它与远缘杂交有什么关系,以及它在作物育种工作上的用处。     

沙田柚多倍体基因组AFLP分析

沙田柚性状优良却多核,通过多倍体选育获得无核或少核品种具有很高的价值.本研究运用AFLP技术分析沙田柚多倍体基因组的变化,以期为多倍化选育优良品种提供一定的理论依据.结果表明,多倍体沙田柚基因组存在大量片段的丢失,也有许多新的酶切位点出现,变异率在21 %～29 %之间.其中多个位点同时发生了相同变异,暗示着多倍体基因组的进化并不是一个随机事件,而这些变异与哪些表观遗传变异直接相关,还有待深入研究.     

黄粉虫良种选育与培育(下)

<正>四、杂交育种杂交育种是指两个或两个以上遗传结构不同的品种杂交,利用亲本品种间优良基因重组,创造新的变异,按照育种目标,从中选优去劣,育成具有双亲综合优点的新品种。随着黄粉虫育种工作进展的深入,也可以开展种间杂交,即远缘杂交。远缘杂交可以扩大变异范围,获得性状更为优良的新品种。HH-1即是利用黄粉虫与黑粉虫进行种间杂交、分离选育的结果,以黄粉虫与黑粉虫杂交,产生的杂交一代杂种可以产生正常的子二代F2。杂交品种生命力强、繁殖率高、个体大,但杂交种生长期较长。杂交育种是一项复杂的技术过程,需要在长期的养殖过程中逐步进行与完善。     

原生质体再生植株变异及其在植物育种上的应用

原生质体再生植株发生变异的现象较为普遍，已涉及到很多作物，变异的类型较多，主要有染色体变异、形态和农艺性状变性、抗性变异等，产生变异的机理主要有遗传和生理两方面，此类变异有其优点和不足，但无庸置疑的是原生质体再生植株遗传变异为植物育种提供了大量可供选择和利用的材料。     

中棉(G.arboreum L.)同源四倍体的形态、发育和细胞遗传研究

在自然界只有极少数植物是能够自己繁殖的同源多倍体,马铃薯就是这一类植物的代表。人工诱导的同源多倍体植物很多,有些已在生产中应用,例如三倍体无籽西瓜,三倍体甜菜,四倍体荞麦和四倍体黑麦等。人工诱导的同源多倍体常用来克服远缘杂交不孕性,也用来研究保持杂种优势及某些性状的遗传规律等。同源四倍体无论在理沦上或实践上,都有一定的研究意义。     

偏凸山羊草--硬粒小麦双二倍体自交后代的染色体数变异及其遗传基础

关于六倍体普通小麦的起源,过去通常归结于通过远缘杂交和多倍体的进化。但这种进化模式无法解释每个种内存在的遗传多样性。　　进入八十年代后,Ｇｒａｎｔ（1 981 ）提出了重组型物种形成的理论框架,为小麦的起源研究指出了一个重要的方向。研究表明,在小麦进化过程中,不仅通过染色体组内的转化和染色体组间的互换,而且由于遗传渐渗和杂化基因（节段）染色体组的形成,促使多倍体小麦种的染色体发生了改变。但到目前为止还缺少有关新染色体组形成的报道。　　过去我们已经报道了偏凸山羊草与硬粒小麦双二倍体杂交的遗传不稳定性,指…     

植物2n配子发生机理研究进展

未减数配子是植物多倍化的源动力，也是植物多倍体育种的重要手段和工具。自然界植物多倍体的自发形成主要包括有性多倍化和无性多倍化2条途径，其中有性多倍化途径在植物界占据着绝对统治地位。本文在分析文献的基础上，从性母细胞减数分裂染色体行为、减数分裂微管骨架、细胞质分裂等异常细胞学现象，减数分裂转变调控以及2n配子发生的分子调控等3个方面，对植物2n配子发生机理研究进展进行了综述，并讨论了植物2n配子利用过程中存在的问题。指出综合利用高通量测序、生物信息学和多组学分析技术，发掘2n配子发生的关键基因，并验证其生物学功能，解析植物2n配子发生的分子调控机理，可能是未来植物2n配子发生机理研究领域的热点。提出综合利用生物信息学分析技术和CRISPR-Cas9等现代基因编辑技术，开展精准分子设计育种，可能是从根本上解决单倍性花粉授粉竞争问题、提高三倍体诱导效率的有效方法。     

观赏植物远缘杂交和多倍体育种研究进展

介绍了植物远缘杂交不亲和、远缘杂种不育的原因及克服方法,概括了远缘杂交及多倍化在观赏植物育种中取得的成就,指出远缘杂交和多倍体育种是目前观赏植物商业化育种的两大重要手段。     

Epigenetic reprogramming in plant and animal development

Epigenetic modifications of the genome are generally stable in somatic cells of multicellular organisms. In germ cells and early embryos, however, epigenetic reprogramming occurs on a genome-wide scale, which includes demethylation of DNA and remodeling of histones and their modifications. The mechanisms of genome-wide erasure of DNA methylation, which involve modifications to 5-methylcytosine and DNA repair, are being unraveled. Epigenetic reprogramming has important roles in imprinting, the natural as well as experimental acquisition of totipotency and pluripotency, control of transposons, and epigenetic inheritance across generations. Small RNAs and the inheritance of histone marks may also contribute to epigenetic inheritance and reprogramming. Reprogramming occurs in flowering plants and in mammals, and the similarities and differences illuminate developmental and reproductive strategies.     

Imprinting and the epigenetic asymmetry between parental genomes

Genomic imprinting confers a developmental asymmetry on the parental genomes, through epigenetic modifications in the germ line and embryo. These heritable modifications regulate the monoallelic activity of parental alleles resulting in their functional differences during development. Specific cis-acting regulatory elements associated with imprinted genes carry modifications involving chromatin structural changes and DNA methylation. Some of these modifications are initiated in the germ line. Comparative genomic analysis at imprinted domains is emerging as a powerful tool for the identification of conserved elements amenable to more detailed functional analysis, and for providing insight into the emergence of imprinting during the evolution of mammalian species. Genomic imprinting therefore provides a model system for the analysis of the epigenetic control of genome function.     

Epigenetic reprogramming in mammalian development

DNA methylation is a major epigenetic modification of the genome that regulates crucial aspects of its function. Genomic methylation patterns in somatic differentiated cells are generally stable and heritable. However, in mammals there are at least two developmental periods-in germ cells and in preimplantation embryos-in which methylation patterns are reprogrammed genome wide, generating cells with a broad developmental potential. Epigenetic reprogramming in germ cells is critical for imprinting; reprogramming in early embryos also affects imprinting. Reprogramming is likely to have a crucial role in establishing nuclear totipotency in normal development and in cloned animals, and in the erasure of acquired epigenetic information. A role of reprogramming in stem cell differentiation is also envisaged. DNA methylation is one of the best-studied epigenetic modifications of DNA in all unicellular and multicellular organisms. In mammals and other vertebrates, methylation occurs predominantly at the symmetrical dinucleotide CpG (1-4). Symmetrical methylation and the discovery of a DNA methyltransferase that prefers a hemimethylated substrate, Dnmt1 (4), suggested a mechanism by which specific patterns of methylation in the genome could be maintained. Patterns imposed on the genome at defined developmental time points in precursor cells could be maintained by Dnmt1, and would lead to predetermined programs of gene expression during development in descendants of the precursor cells (5, 6). This provided a means to explain how patterns of differentiation could be maintained by populations of cells. In addition, specific demethylation events in differentiated tissues could then lead to further changes in gene expression as needed. Neat and convincing as this model is, it is still largely unsubstantiated. While effects of methylation on expression of specific genes, particularly imprinted ones (7) and some retrotransposons (8), have been demonstrated in vivo, it is still unclear whether or not methylation is involved in the control of gene expression during normal development (9-13). Although enzymes have been identified that can methylate DNA de novo (Dnmt3a and Dnmt3b) (14), it is unknown how specific patterns of methylation are established in the genome. Mechanisms for active demethylation have been suggested, but no enzymes have been identified that carry out this function in vivo (15-17). Genomewide alterations in methylation-brought about, for example, by knockouts of the methylase genes-result in embryo lethality or developmental defects, but the basis for abnormal development still remains to be discovered (7, 14). What is clear, however, is that in mammals there are developmental periods of genomewide reprogramming of methylation patterns in vivo. Typically, a substantial part of the genome is demethylated, and after some time remethylated, in a cell- or tissue-specific pattern. The developmental dynamics of these reprogramming events, as well as some of the enzymatic mechanisms involved and the biological purposes, are beginning to be understood. Here we look at what is known about reprogramming in mammals and discuss how it might relate to developmental potency and imprinting.     

表观遗传与分子育种

表观遗传变异是一种不涉及DNA序列的改变但可以通过有丝分裂和(或)减数分裂实现代间传递的变异,主要包括组蛋白修饰、DNA甲基化和miRNA。本文分别对这3种变异做了简单综述,同时介绍了表观遗传学在分子育种上的应用进展。     

不同入侵地区黄顶菊DNA表观遗传多样性变化特征

从黄顶菊入侵的四个典型地区——邯郸市永年县(HDY)、沧州市献县(CZX)、衡水市衡水湖(HSH)和天津市静海县(TJJ)采集植物叶片,利用甲基化MSAP技术研究黄顶菊DNA表观遗传和多态性变化特征以及土壤环境因子与黄顶菊整体甲基化水平之间的相关性。结果表明:13对引物共扩增出993条MSAP条带,引物多态性百分比为88.52%。四个地区黄顶菊种群的多态性位点百分比较高,在84.03%~92.31%之间,遗传分化系数(G_(st))为0.07,只有7%的遗传变异存在于不同地区黄顶菊种群间,93%的遗传变异则存在于种群内,基因流(N_m)为3.321(1),表明四个不同入侵地区黄顶菊种群间存在广泛而频繁的基因交流。不同地区黄顶菊种群间遗传分化不显著,但甲基化模式差异显著,推测黄顶菊可能通过改变甲基化水平来维持自身对新环境的适应。MSP与MISP聚类结果表明TJJ与HDY亲缘关系最近,认为可能与两地土壤理化因子和所处地理位置相近有关,但相关性分析后发现黄顶菊甲基化水平与土壤因子之间的相关性并不显著(P0.01),推测地区环境对黄顶菊表观遗传多样性的影响是受多重因素共同作用的结果,而非某个单一因子的作用。     

表观遗传调控骨骼肌发育的研究进展（英文）

动物骨骼肌约占体重的50%左右,因此被认为是机体最大的器官。骨骼肌的发育是一个严格调控的过程。在胚胎发育早期,一部分具有肌肉发育潜能的干细胞在一系列不同基因的精确调控下激活、增殖,经融合后形成有功能的骨骼肌。骨骼肌细胞的增殖、分化等过程是诸多转录因子协同作用的结果,这些因子包括Pax3/Pax7、MyoD、Myf5、Myogenin和MRF4等。表观遗传是指不改变DNA序列的情况下对目的基因表达的调控。近年来的研究表明动物骨骼肌的发育也受到了表观遗产的调控。综述了当前关于表观遗传,包括DNA、组蛋白以及miRNA等水平对骨骼肌发育调控的最新研究进展。