2n Gamete formation in the genus Brachiaria (Poaceae: Paniceae)

Microsporogenesis of several Brachiaria species of the Brazilian collection at Embrapa Beef Cattle has been analyzed in detail. This paper reports abnormal cytokinesis in three accessions of three different species (Brachiaria humidicola, 2n = 4x = 36, Brachiaria decumbens, 2n = 4x = 36, and Brachiaria dura, 2n = 6x = 54). Chromosomes paired in bi-, tri-, and quadrivalents in these accessions, whereas chromosome segregation at meiosis I was characterized by exclusion of laggards as micronuclei. In a high number of meiocytes, the first sign of cytokinesis appeared only in metaphase II and did not divide the meiocyte into a dyad. Total absence of cytokinesis was also detected among meiocytes in the second division. Since in both cases the two metaphase plates were very close, they favored the rejoining of chromosome sets after anaphase II and formed a restitutional nucleus in telophase II. Second cytokinesis occurred after telophase II in most meiocytes. Monads, dyads, and triads with n or 2n nuclei were observed among meiotic products. The 2n gametes observed correspond to the first division restitution (FDR). The number of affected cells in each accession was variable, but the number of microspores with restitutional nucleus, including those scored in tetrads and the released ones, did not exceed 9%. Although polyploidy is common in the genus Brachiaria, its origin is still unclear. Current results suggest that 2n gametes may have contributed to the evolutionary history of the genus.     

植物多倍化过程中小分子RNA调控基因表达机制研究进展

多倍体在植物界中广泛存在,因其往往具有显著超出双亲的生长优势和适应性而成为植物学研究的热点之一。越来越多的研究表明小分子RNA介导的基因激活或沉默及染色质修饰在植物多倍化过程中的基因表达调控方面发挥重要作用。本文结合本实验室在小麦多倍化研究中的观察,着重综述近几年来小分子RNA层面的植物多倍化过程中基因表达调控的机制,以期对多倍体作物的研究和利用提供有益的借鉴。     

鲈鲤(Percocypris pingi)染色体核型及C-带分析

鲈鲤(Percocypris pingi)为长江上游特有鱼类及四川省重点保护鱼类,为验证其倍性及丰富其细胞遗传学内容,采用植物性血凝素(PHA)体内注射肾细胞直接制片法研究鲈鲤的核型,采用改进的BSG法研究其C-带.结果显示,鲈鲤的染色体数目为98条,其核型公式为4n=98=42m+30sm+10st+16t,臂数NF=170.本研究发现,鲈鲤有16条端部着丝粒染色体,未发现小染色体及其他异型性染色体.鲈鲤C-带带纹较丰富,显示着丝粒带、端粒带和染色体居间带3种类型的C-带,部分染色体同时含有多种类型的C-带着色,如m2、st4同时含有以上3种C-带带纹类型.鲈鲤染色体异染色质含量高达(58.824±0.034)％.本研究再次确认鲈鲤为四倍体,同时指出其染色体具有一定的“可塑性”,反应出鲈鲤对于地区特化的生境具有较强的适应性.     

Polyploidization of Miscanthus sinensis and Miscanthus x giganteus by plant colchicine treatment

The purpose of this study was to find a suitable treatment combination that would effectively induce polyploids in the grass species from the genus Miscanthus. In the experiments, the combinations of two concentrations of colchicine, three options of supplementing the colchicine solution with additional substances and three exposure times were tested. The experiments were conducted using diploid and triploid genotypes belonging to M. sinensis and M. x giganteus. Colchicine treatments generated 50 tetraploids in four diploid genotypes and two hexaploids in one out of two triploid genotypes. Induction of polyploids by plant colchicine treatment was highly dependent on genotype. In three out of six genotypes, some tested combinations resulted around 20% of polyploidization effectiveness. Re-examination of obtained material confirmed that 95% of plants are fully solid polyploids. Generated tetraploids were fertile. Polyploidization by ex vitro colchicine treatment of Miscanthus plants can be useful in plant breeding, particularly because its advantages in saving time.     

甘蓝型油菜脯氨酸合成相关同源基因的进化和差异表达分析

以异源四倍体甘蓝型油菜(Brassica napus)及其二倍体祖先白菜(B.rapa)和甘蓝(B.oleracea)为对象,研究了脯氨酸合成途径关键酶基因P5CS和OAT的进化命运以及各自不同祖先来源的同源基因的差异表达情况。序列比对和进化分析表明,甘蓝型油菜中P5CS基因和OAT基因和其二倍体祖先的相对应基因高度同源;进化上,和二倍体亲本相比甘蓝型油菜P5CS2基因发生了1个拷贝的丢失,而OAT基因没有基因丢失现象;半定量RT-PCR结果表明,甘蓝型油菜中来自二倍体亲本白菜和甘蓝的P5CS2和OAT同源基因在所有检测器官中均表达,没有发生基因沉默;但是它们可能发生了亚功能化,不同祖先来源的2个P5CS2同源基因存在较弱的偏向性表达,不同器官的同源基因表达模式稍有不同;而OAT基因明显偏向于表达来自于甘蓝祖先的同源基因,OAT的2个同源基因的不同器官表达模式基本一致;盐胁迫处理后,来自于甘蓝的BnaC.P5CS1.d表达量显著高于来自于白菜的Bna A.P5CS1.a,表明盐处理条件下甘蓝型油菜偏向性表达BnaC.P5CS1.d。甘蓝型油菜的脯氨酸合成基因Bna A.P5CS1.a、BnaC.P5CS1.d及Bna A.P5CS2.a、BnaC.P5CS2.c的盐诱导表达模式均基本保持了亲本来源基因的特征。以上结果表明,与二倍体祖先相比,甘蓝型油菜中脯氨酸合成基因序列和表达模式均存在高度保守性,这可能说明了脯氨酸积累在进化上对植物的有利性。     

人工合成甘蓝型油菜及其亲本的甲基化变异模式分析

甘蓝型油菜作为多倍体起源和发生的历史较短, 遗传背景较为狭窄, 人工合成甘蓝型油菜可作为植物多倍化研究的优选模型, 本文以人工合成的甘蓝型油菜为材料, 通过HPLC分析发现白菜型油菜和甘蓝的甲基化率分别为8.33%和15.88%, 2个杂种株系的全基因组甲基化水平介于双亲之间(分别为10.29%和12.83%)。MSAP分析发现杂种F₁代及其亲本的甲基化水平存在明显差异(白菜型油菜<杂种F₁<甘蓝), 杂种F1代的甲基化变异(23.71%)中来自A、C基因组的变异分别占6.60%和10.16%。MSAP差异性条带的序列分析发现多倍化过程中与甲基化变化相关的基因参与了多种生物学过程, 且差异甲基化基因在人工合成甘蓝型油菜及其亲本间的表达差异与甲基化修饰模式是一致的。本研究为了解甘蓝型油菜多倍化过程中发生的表观变异奠定了基础。     

论栽培植物起源的遗传基础

文章列举了野生植物与栽培植物表型的一些主要区别，着重讨论栽培植物起源的遗传基础，并根据观察和试验，论证了自然界中通过杂交与多倍体化形成新的栽培植物的可能性．