Paternal effects in Arabidopsis indicate that offspring can influence their own size

The existence of genetic variation in offspring size in plants and animals is puzzling because offspring size is often strongly associated with fitness and expected to be under stabilizing selection. An explanation for variation in seed size is conflict between parents and between parents and offspring. However, for this hypothesis to be true, it must be shown that the offspring genotype can affect its own size. The existence of paternal effects would support this hypothesis, but these have rarely been shown. Using a diallel cross among four natural accessions of Arabidopsis thaliana we show that maternal, paternal and positional effects jointly influence seed size, number and the frequency of seed abortion. We found that seed abortion (%) depends on the combination of maternal and paternal genotypes, suggesting the existence of mate choice or epistatic incompatibility among accessions of A. thaliana. In addition, since paternal genotype explains approximately 10 per cent of the variation in seed size, we propose that A. thaliana''s offspring must influence the amount of resources allocated to themselves. Identification of paternal effects in Arabidopsis should facilitate dissection of the genetic mechanisms involved in paternal effects.     

RAPD polymorphisms detected among the flax genotrophs

The occurrence of environmentally induced heritable changes in certain flax varieties has been shown to be accompanied by changes in the genomic DNA. A large difference in nuclear DNA contents has been characterized between the extreme types, termed genotrophs. The genomic variation between a series of genotrophs has been studied by the polymerase chain reaction using random arbitrary oligonucleotide primers. A total of 320 primers were used in the reactions and 253 polymorphic bands observed. The polymorphic bands were derived from all parts of the genome, namely the highly repetitive, middle-repetitive and low-copy-number sequences. They were also shown to be distributed thoughout the genome. In one group of genotrophs, all of which were induced by temperature treatment, there was a clustering of the polymorphisms with a high degree of shared polymorphisms. These results are in agreement with earlier studies showing that a dispersed fraction of the genome is susceptible to variation when environmentally induced heritable changes occur.     

Evolution of body size in the genus Damaliscus: a comparison with hartebeest Alcelaphus spp.

In species with low levels of sexual size dimorphism, it may be relatively easy to detect the role of natural selection in the evolution of body size. Habitat primary production (HPP) appears to be a key factor in the divergence of size in the hartebeest clade ( Alcelaphus spp.), such that subspecies in less productive savannahs are smaller than those in richer ones. Here I test whether a similar pattern exists within the genus Damaliscus (topi and their allies). Basal skull length was used as a surrogate of body size and measured in the seven allopatric subspecies of Damaliscus . Means for each subspecies and sex were regressed against climatic factors as surrogates of HPP. Variation in skull length across Damaliscus taxa was less than in hartebeest. Two clusters were present in both sexes and corresponded to the distinction between the species, Damaliscus dorcas and Damaliscus lunatus . This may reflect differences in productivity between edaphic grasslands, occupied by all D. lunatus , and dry grasslands, occupied by D. dorcas . Mean annual rainfall was the best predictor of body size in males and showed a non-significant positive tendency in females. After accounting for phylogenetic effects, these correlations were both non-significant. Edaphic grasslands might be less dependent on precipitation for primary production because the impeded drainage of their soil prolongs water availability after the end of the rains. Furthermore, they are probably more consistent in productivity across African regions than secondary grasslands and savannah woodlands, which rely on rainfall for grass growth. These properties of edaphic grasslands may explain why size in Damaliscus appears to be less sensitive to variation in rainfall and less variable across subspecies than in Alcelaphus .     

Insights into the Effects of Long-Term Artificial Selection on Seed Size in Maize

Grain produced from cereal crops is a primary source of human food and animal feed worldwide. To understand the genetic basis of seed-size variation, a grain yield component, we conducted a genome-wide scan to detect evidence of selection in the maize Krug Yellow Dent long-term divergent seed-size selection experiment. Previous studies have documented significant phenotypic divergence between the populations. Allele frequency estimates for ∼3 million single nucleotide polymorphisms (SNPs) in the base population and selected populations were estimated from pooled whole-genome resequencing of 48 individuals per population. Using F_ST values across sliding windows, 94 divergent regions with a median of six genes per region were identified. Additionally, 2729 SNPs that reached fixation in both selected populations with opposing fixed alleles were identified, many of which clustered in two regions of the genome. Copy-number variation was highly prevalent between the selected populations, with 532 total regions identified on the basis of read-depth variation and comparative genome hybridization. Regions important for seed weight in natural variation were identified in the maize nested association mapping population. However, the number of regions that overlapped with the long-term selection experiment did not exceed that expected by chance, possibly indicating unique sources of variation between the two populations. The results of this study provide insights into the genetic elements underlying seed-size variation in maize and could also have applications for other cereal crops.     

基因组印迹与种子发育

胚乳介导营养物质从母体到胚的转运过程,是开花植物中发生印迹的重要部位。胚乳的发育异常会导致胚的败育。在拟南芥中已鉴定到三个FIS (fertilization-independent seed) 基因,能制止无需受精即形成种子的发育过程,即FIS1/ MEDEA、FIS2和FIS3/FIE。其中MEDEA基因是胚乳发育的主要调控基因,在胚乳中被印迹。FWA基因也在胚乳中被印迹。系统阐述了植物基因组印迹的机理以及MEA和FWA印迹机制的研究进展,并介绍了印迹发生的亲本冲突学说、印迹的方式及其它已报道的印迹基因。     

盐胁迫下羊草种子萌发特性的种内变异及其影响因素

植物性状的种内变异能够客观反映植物的适应性,因此研究不同地理种群的植物表型性状和种子萌发特性在生态学和植物进化学中具有重要意义。羊草(Leymus chinensis)为我国松嫩平原的本土优势种,常形成单一优势群落。然而,现有研究多聚焦于其无性繁殖性状,针对不同种群羊草种子萌发及幼苗生长关键时期的研究相对较少。研究选取松嫩平原西部盐碱草地的14个羊草种群(P01-P14)种子,分析其表型性状,并在不同浓度(0,50,100,200,400 mmol/L)的NaCl胁迫下观察萌发特性及幼苗生长变化,探讨种子表型性状与耐盐性对种源地环境因素的响应。结果表明:随着盐浓度的增加,所有羊草种群种子萌发率和发芽指数呈下降趋势。除P13和P14种群,其他12个种群在高于100 mmol/L NaCl时种子萌发受到显著抑制,9个种群在400 mmol/L NaCl时无种子萌发。幼苗生长方面,苗长呈先上升后下降的趋势,根长对盐胁迫更为敏感,在50 mmol/L时即受到显著抑制,然而根系数量随盐浓度增加而增加,表现出较强的生长可塑性。此外,盐胁迫下未萌发的种子在胁迫解除后可快速萌发,除100 mmol/L和200 mmol/L NaCl之外,总萌发率与对照无显著差异,表明羊草种子具有较强的耐盐性,部分种子在盐胁迫下可再次进入休眠以维持活力。结合种子萌发和幼苗生长指标,不同种群综合耐盐评价排序为:P13>P14>P02>P01>P09>P07>P11>P05>P12>P03>P04>P08>P06> P10。相关性分析与逐步回归结果显示,年均温和年均降水量与种子表面积和颖果长显著相关,综合耐盐评价主要受到种子颖果表面积和采样点土壤pH值的显著影响,种源地土壤pH值较高和较大的羊草种子可以更好的适应盐胁迫。综上,不同羊草种群的种子表型性状及盐胁迫下萌发与幼苗生长特性差异显著,种源地的气候和环境条件可能是造成这种差异的主要因素。盐胁迫能够促使部分种子再次进入休眠,在低盐浓度下已萌发种子的幼苗生长及根系发育得到促进,这是羊草种子适应盐胁迫的重要机制。研究为深入理解羊草种群对盐碱环境的适应策略及其进化机制提供了科学依据。     

Electrophoretic variation of seed proteins among U.S. populations of Tripsacum dactyloides Var. dactyloides

Accessions from across the range of Tripsacum dectyloides in the US. were assayed electrophoretically for interpopulation variation in seed proteins. Clustering of isoelectric focusing patterns for Tris-HCl and water-soluble proteins revealed high levels of homogeneity. Preliminary resultswith alcohol-soluble proteins, in contrast, showed this fraction to be intrinsically much more variable. Divergent functional roles of the protein fractions themselves could account for this observed difference in variation and are discussed in the paper.     

格氏栲天然林林窗植物群落功能性状的变异

林窗是森林更新演替的重要环节, 揭示林窗环境下功能性状变异来源及其相对贡献, 有助于阐明植物对林窗环境的响应。该研究以中亚热带格氏栲(Castanopsis kawakamii)天然林为对象, 设置9个不同大小的林窗样地, 运用方差分解探讨林窗、物种和个体对叶性状变异的相对贡献, 采用线性回归分析不同大小林窗下群落性状变化及种间和种内性状变异的重要性。研究发现: (1)格氏栲天然林林窗植物比叶面积、叶干物质含量、叶厚和叶绿素含量由种间性状变异主导, 叶氮含量由种内性状变异主导, 叶磷含量受林窗大小影响最大。(2)群落叶磷含量与林窗大小具有显著正相关关系, 土壤温度和水解氮含量对群落叶磷含量具有显著正效应, 土壤有效磷含量具有显著负效应。(3)沿林冠开放度的群落叶磷含量变化主要由种内性状变异引起, 优势种扮演着重要角色。结果表明, 格氏栲天然林林窗环境下植物功能性状仍以种间性状变异为主(平均41%), 但沿林窗环境梯度的群落性状变化主要源自种内性状变异, 通过植物表型可塑性响应环境改变, 优势种作用明显。