无融合生殖悬铃叶苎麻（Boehmeria tricuspis）多倍性发生的染色体行为研究

摘要：对无融合生殖悬铃叶苎麻（2n=42）和有性生殖悬铃叶苎麻(2n=28)花粉母细胞（PMC）减数分裂行为进行比较研究,从而推断两者之间的进化关系;探索无融合生殖悬铃叶苎麻（B.tricuspis）发生的细胞遗传学基础,为无融合生殖发生的遗传学研究提供理论依据。在无融合生殖类型经诱导所产生的PMC的减数分裂过程中,发现有丰富的三价体形成,属典型的同源三倍体减数分裂行为特征;而有性生殖类型 PMC的减数分裂行为绝大多数正常,但也存在少量异常现象。其中有些异常行为,可能与未减数配子（2n）的形成紧密相关。因而推断,在有性生殖类型的生殖过程中,可能发生了未减数配子（2n）与减数配子（n）的融合,产生了同源三倍体合子。这应该是无融合生殖悬铃叶苎麻发生的重要的细胞遗传学基础。     

无融合生殖油菜AMR—1花托离体培养的研究

报道了不同激素浓度对无融合生殖没菜花托器官分化效果的研究,结果显示：（１）以ＭＳ为基本培养基,以带有子房和花柄的花托为外植体离体培养,花托、花柄切口部位直接芽诱导的最佳激素配比为４．０ｍｇ／Ｌ６－ＢＡ＋０．０１ｍｇ／Ｌ ＮＡＡ,频率为５８．８２％,花托、花柄部位先形成愈伤组织,继而分化出丛生芽的最佳激素配比为５．０ｍｇ／Ｌ ６－ＢＡ＋０．５ｍｇ／Ｌ ＮＡＡ,频率为８４．００％;（２）腋芽增殖的最佳     

The epigenetic footprint of poleward range‐expanding plants in apomictic dandelions

Epigenetic modifications, such as DNA methylation variation, can generate heritable phenotypic variation independent of the underlying genetic code. However, epigenetic variation in natural plant populations is poorly documented and little understood. Here, we test whether northward range expansion of obligate apomicts of the common dandelion (Taraxacum officinale) is associated with DNA methylation variation. We characterized and compared patterns of genetic and DNA methylation variation in greenhouse‐reared offspring of T. officinale that were collected along a latitudinal transect of northward range expansion in Europe. Genetic AFLP and epigenetic MS‐AFLP markers revealed high levels of local diversity and modest but significant heritable differentiation between sampling locations and between the southern, central and northern regions of the transect. Patterns of genetic and epigenetic variation were significantly correlated, reflecting the genetic control over epigenetic variation and/or the accumulation of lineage‐specific spontaneous epimutations, which may be selectively neutral. In addition, we identified a small component of DNA methylation differentiation along the transect that is independent of genetic variation. This epigenetic differentiation might reflect environment‐specific induction or, in case the DNA methylation variation affects relevant traits and fitness, selection of heritable DNA methylation variants. Such generated epigenetic variants might contribute to the adaptive capacity of individual asexual lineages under changing environments. Our results highlight the potential of heritable DNA methylation variation to contribute to population differentiation along ecological gradients. Further studies are needed using higher resolution methods to understand the functional significance of such natural occurring epigenetic differentiation.     

甜菜无融合生殖单体附加系M14雌配子体的发生与发育

利用常规石蜡制片法,对甜菜单体附加系M14(Beta vulgarisL.VV 1C、2n=18 1)雌配子体的发生与发育进行了研究,结果表明:二倍体孢子生殖雌配子体为韭型(Allium odorum-type)和蝶须型(Antennaria-type),有性生殖雌配子体为蓼型(Polygonum-type)。韭型和蝶须型的大孢子母细胞发育成为二倍体雌配子体,蓼型大孢子母细胞形成单倍体的雌配子体。在二倍体孢子生殖雌配子体发育过程中,出现发育迟缓,胚囊败育等情况,正常发育的雌配子体只有25%。讨论了二倍体孢子生殖雌配子体发生与发育特点。     

2n雄配子的无融合生殖披碱草（Elymus rectisetus）减数分裂行为研究

用能自然产生2n雄配子的无融合生殖六倍体披碱草为材料,研究了无融合生殖披碱草的减数分裂行为。结果表明：2n雄配子的无融合生殖披碱草减数分裂行为较为异常。在间期细胞内经常有微核存在;在前期I,有倒位环、多介染色体等异常现象;在中期I,染色体有不等分裂的倾向;在后期I和末期I,有染色体的单极分裂（63.9%）、染色走向一极的倾向（21.7%）和多极分裂（3.3%）等现象,单极分裂的结果是不减数配子的产生。在减数分裂Ⅱ中,有高比例的二分子孢子（55.7%）和三分子孢子（23.7%）的形成,二分子孢子在发育后期也直接导致了2n配子的产生。因此,染色体的单极分裂、二分体和三分体形成这3种方式是披碱草2n雄配子的形成的主要途径。     

利用mRNA差异显示技术分离甜菜M14品系特异表达基因的cDNA片段

二倍体栽培甜菜与白花甜菜杂交、进一步回交而获得的单体附加系M14,其染色体组成中除了含有18条栽培甜菜染色体外,还附加有一条野生白花甜菜第9号染色体,该附加染色体通过母本的传递率为96.5%;单体附加系传递率如此高的原因是因为M14中有无融合生殖基因的存在。本实验采用mRNA差异展示技术对甜菜无融合生殖品系M14和正常有性生殖的二倍体栽培甜菜A2Y花蕾减数分裂时期的基因表达进行了差异分析。采用GT15A,GT15G,GT15C3种锚定引物,共筛选了20个随机引物,通过RT-PCR检测,获得了6个阳性差异表达的cDNA片段,应用NCBI的BLASTx软件对测序结果进行同源序列、相似序列检索,为进一步克隆无融合生殖基因提供侯选cDNA片段。     

Mitochondrial DNA diversity and geographical distribution of sexual and asexual strains of the braconid parasitoid Meteorus pulchricornis

Asexuality is an important tool with regard to the use of parasitoid wasps as biocontrol agents. Asexual (apomictic thelytokous) strains of Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae), a polyphagous endoparasitoid of lepidopteran larvae, are sympatric with sexual (arrhenotokous) strains in Japan. The results of phylogenetic analyses of mitochondrial cytochrome c oxidase subunit I (COI) sequences indicated two major haplotype groups on the Japanese islands. The northern group I predominantly contained sexual strains, whereas the southern group II contained both sexual and asexual strains. Most asexual strains were likely derived within group II. An asexual strain recently established in New Zealand has the identical haplotype to a strain in Japan and was proven to have originated from East Asia. Three hypotheses on the evolution of asexuality are discussed for this parasitoid wasp: recessive gene, hybridization, and cytoplasmic element.     

RAPD Evidence for Apomixis and Clonal Populations in Eriotheca (Bombacaceae)

Abstract: Two woody species of Eriotheca (Bombacaceae) of the Central Brazilian Cerrados were submitted to RAPD analyses. Both species are bee pollinated and have a similar flower structure, but E. pubescens presents adventitious embryony and apomixis, while E. gracilipes is self-incompatible. The RAPD screening reflects these differences in breeding systems, with very low genetic variation in the apomictic species, while the sexual species presented much higher variability with no similar genotypes among the sampled trees. The results suggest that adventitious embryony in E. pubescens effectively results in clonal populations or population mosaics of clonal individuals. Since recent studies have indicated poly-embryony and possibly apomixis in a number of Cerrado woody species otherwise considered obligatorily allogamous, the RAPD results presented here indicate the technique will be a useful tool to detect clonal populations of apomictic origin among Cerrado woody species with mixed mating systems and will help to assess the importance of apomixis as a breeding system for the Cerrado flora.     

Detecting small-scale genotype-environment interactions in apomictic dandelion (Taraxacum officinale) populations

Studies of genotype × environment interactions (G × E) and local adaptation provide critical tests of natural selection’s ability to counter opposing forces such as gene flow. Such studies may be greatly facilitated in asexual species, given the possibility for experimental replication at the level of true genotypes (rather than populations) and the possibility of using molecular markers to assess genotype–environment associations in the field (neither of which is possible for most sexual species). Here, we tested for G × E in asexual dandelions (Taraxacum officinale) by subjecting six genotypes to experimental drought, mown and benign (control) conditions and subsequently using microsatellites to assess genotype–environment associations in the field. We found strong G × E, with genotypes that performed poorly under benign conditions showing the highest performance under stressful conditions (drought or mown). Our six focal genotypes comprise > 80% of plants in local populations. The most common genotype in the field showed its highest relative performance under mown conditions (the most common habitat in our study area), and almost all plants of this genotype in the field were found growing in mowed lawns. Genotypes performing best under benign experimental conditions were found most frequently in unmown conditions in the field. These results are strongly indicative of local adaptation at a very small scale, with unmown microsites of only a few square metres typically embedded within larger mown lawns. By studying an asexual species, we were able to map genotypes with known ecological characteristics to environments with high spatial precision.