The limits of selection during maize domestication

The domestication of all major crop plants occurred during a brief period in human history about 10,000 years ago. During this time, ancient agriculturalists selected seed of preferred forms and culled out seed of undesirable types to produce each subsequent generation. Consequently, favoured alleles at genes controlling traits of interest increased in frequency, ultimately reaching fixation. When selection is strong, domestication has the potential to drastically reduce genetic diversity in a crop. To understand the impact of selection during maize domestication, we examined nucleotide polymorphism in teosinte branched1, a gene involved in maize evolution. Here we show that the effects of selection were limited to the gene's regulatory region and cannot be detected in the protein-coding region. Although selection was apparently strong, high rates of recombination and a prolonged domestication period probably limited its effects. Our results help to explain why maize is such a variable crop. They also suggest that maize domestication required hundreds of years, and confirm previous evidence that maize was domesticated from Balsas teosinte of southwestern Mexico.     

植物激素调控腋生分生组织发育的研究进展

植物分枝的生长是植物发育的一个标志性生长特征,不仅影响着植物株型的多样化,而且也影响着植物的生产力。植物分枝是由腋生分生组织（Axillary Meristems,AMs）实现的,腋生分生组织分布在每个叶基的腋部,并发育成分枝。因此,腋生分生组织发育分化规律的研究,不仅是植物生长发育的基础问题,而且对植物的实践生产也具有重要的指导意义。近年来,随着植物激素合成、信号途径等突变体被分离、鉴定以及相应基因被克隆,人们在植物激素调控腋生分生组织发育方面有了深入的了解。本文对生长素、细胞分裂素、赤霉素和独角金内酯等植物激素在植物腋生分生组织形成与发育过程中的调控机制进行阐述,认为随着新的检测工具和分析技术的发展,未来应加强环境信号介导下植物激素互作对腋生分生组织发育的研究。     

Conserved factors regulate signalling in Arabidopsis thaliana shoot and root stem cell organizers

Throughout the lifespan of a plant, which in some cases can last more than one thousand years, the stem cell niches in the root and shoot apical meristems provide cells for the formation of complete root and shoot systems, respectively. Both niches are superficially different and it has remained unclear whether common regulatory mechanisms exist. Here we address whether root and shoot meristems use related factors for stem cell maintenance. In the root niche the quiescent centre cells, surrounded by the stem cells, express the homeobox gene WOX5 (WUSCHEL-RELATED HOMEOBOX 5), a homologue of the WUSCHEL (WUS) gene that non-cell-autonomously maintains stem cells in the shoot meristem. Loss of WOX5 function in the root meristem stem cell niche causes terminal differentiation in distal stem cells and, redundantly with other regulators, also provokes differentiation of the proximal meristem. Conversely, gain of WOX5 function blocks differentiation of distal stem cell descendents that normally differentiate. Importantly, both WOX5 and WUS maintain stem cells in either a root or shoot context. Together, our data indicate that stem cell maintenance signalling in both meristems employs related regulators.     

玉米耐盐早期筛选体系的初步研究

耐盐性鉴定是植物耐盐分子育种的重要环节,为了建立玉米耐盐性鉴定的早期筛选体系,选用了丹340,Mo17和TL94B 3个自交系,设置了10个NaCl浓度梯度,并通过室内沙培盐胁迫处理实验,对出苗率、6天株高、10天株高、14天株高、地上部和根系鲜重等性状进行了考察.结果表明:丹340和TL94B的耐盐性较强,而Mo17的耐盐性较弱,且对盐胁迫敏感;出苗率与盐浓度无显著相关,不宜作为耐盐性筛选的定量指标;株高、地上部和根系鲜重都与盐浓度高度负相关,达极显著水平,可以作为玉米耐盐性早期筛选的指标.研究还发现:在沙培条件下,20 mmol.L-1左右的NaC l浓度对幼苗的生长有促进作用;进行玉米耐盐性鉴定的NaC l临界下限浓度是100~120 mmol.L-1.     

海南南繁基地玉米茎腐病病原菌的分离及鉴定

为明确海南地区南繁基地玉米茎腐病的病原,从玉米发病组织中分离病原菌,并进行了纯化培养、革兰氏染色、病原菌回接等试验,得到了2株对玉米有较强致病力的菌株,分别命名为JF02与JF04.随后通过PCR反应扩增了所分离的玉米茎腐病病原菌JF02与JF04的16S rRNA序列,并测序,序列分析表明,所分离的玉米茎腐病病原菌序列相同,属同一病原菌,且为狄克氏菌.该病原菌的分离和鉴定为玉米细菌性茎腐病的防治和抗性品种选育提供了一定的理论参考.     

Plant polar growth in tobacco disturbed by γ-tubulin gene silencing

To further understand the functions of γ-tubulin in plant cells, we conducted a study in which the γ-tubulin gene was down-regulated in tobacco plants (obtained by the Agrobacterium-mediated method). This involved transforming the target fragments, in which the sense and antisense partial γ-tubulin cDNA fragments were ligated together, into Nicotiana tabacum var. Samsun NN. The γ-tubulin downregulated transformants developed multiple meristems or branches with trumpet-shaped leaves; their root generation also appeared abnormal, with the taproots undeveloped, whereas lateral roots were developed. In addition, the content of indole-3-acetic acid (IAA) and expression of polarity transportation vector PGP1 were aberrant. These results suggest that γ-tubulin gene silencing disturbed the polar growth of tobacco plants, and that this phenomenon was probably correlated with the IAA content and the polar transportation process.     

Ubi1 intron-mediated enhancement of the expression of Bt cry1Ah gene in transgenic maize (Zea mays L.)

The cry1Ah gene was one of novel insecticidal genes cloned from Bacillus thuringiensis isolate BT8. Two plant expression vectors containing cry1Ah gene were constructed. The first intron of maize ubiqutin1 gene was inserted between the maize Ubiquitin promoter and cry1Ah gene in one of the plant expressing vectors (pUUOAH). The two vectors were introduced into maize immature embryonic calli by microprojectile bombardment, and the reproductively plants were acquired. PCR and Southern blot analysis showed that foreign genes had been integrated into maize genome and inherited to the next generation stably. The ELISA assay to T1 and T2 generation plants showed that the expression of Cry1Ah protein in the construct containing the ubi1 intron (pUUOAH) was 20% higher than that of the intronless construct (pUOAH). Bioassay results showed that the transgenic maize harboring cry1Ah gene had high resistance to the Asian corn borers and the insecticidal activity of the transgenic maize containing the ubi1 intron was higher than that of the intronless construct. These results indicated that the maize ubi1 intron can enhance the expression of the Bt cry1Ah gene in transgenic maize efficiently     

Plant polar growth in tobacco disturbed by y-tubulin gene silencing

To further understand the functions of y-tubulin in plant cells, we conducted a study in which the y-tubulin gene was down-regulated in tobacco plants (obtained by the Agrobacterium-mediated method). This involved transforming the target fragments, in which the sense and antisense partial y-tubulin cDNA fragments were ligated together, into Nicotiana tabacum var. Samsun NN. The y-tubulin down-regulated transformants developed multiple meristems or branches with trumpet-shaped leaves; their root generation also appeared abnormal, with the taproots undeveloped, whereas lateral roots were developed. In addition, the content of indole-3-acetic acid (IAA) and expression of polarity transportation vector PGPI were aberrant. These results suggest that y-tubulin gene silencing disturbed the polar growth of tobacco plants, and that this phenomenon was probably correlated with the IAA content and the polar transpor-tation process.     

墨西哥玉米草组培体系的建立及愈伤组织切片观察

墨西哥玉米草是与玉米最近野生近缘种之一，可多茬刈割，产量高，品质好，被誉为青饲料之王，在畜牧业中扮演着重要角色，因此对墨西哥玉米草的深入研究具有重大的科研价值和经济效益．虽然墨西哥玉米草杂交体系已有较多报道，但墨西哥玉米草组培体系却鲜有研究．组培快速繁殖体系是通过生物技术对墨西哥玉米草进行品质改良的基础，因此建立高效的墨西哥玉米草组培快速繁殖体系具有重要意义．文中以墨西哥玉米草 8493 种子为实验材料，在含有2，4-D和6-BA的MS培养基上可以诱导幼苗基部的膨大节间，其在黑暗条件下两周可以诱导出愈伤组织．石蜡切片观察显示愈伤组织具备胚性愈伤特性．     

HAR1 mediates systemic regulation of symbiotic organ development

Symbiotic root nodules are beneficial to leguminous host plants; however, excessive nodulation damages the host because it interferes with the distribution of nutrients in the plant. To keep a steady balance, the nodulation programme is regulated systemically in leguminous hosts. Leguminous mutants that have lost this ability display a hypernodulating phenotype. Through the use of reciprocal and self-grafting studies using Lotus japonicus hypernodulating mutants, har1 (also known as sym78), we show that the shoot genotype is responsible for the negative regulation of nodule development. A map-based cloning strategy revealed that HAR1 encodes a protein with a relative molecular mass of 108,000, which contains 21 leucine-rich repeats, a single transmembrane domain and serine/threonine kinase domains. The har1 mutant phenotype was rescued by transfection of the HAR1 gene. In a comparison of Arabidopsis receptor-like kinases, HAR1 showed the highest level of similarity with CLAVATA1 (CLV1). CLV1 negatively regulates formation of the shoot and floral meristems through cell-cell communication involving the CLV3 peptide. Identification of hypernodulation genes thus indicates that genes in leguminous plants bearing a close resemblance to CLV1 regulate nodule development systemically, by means of organ-organ communication.     

玉米ELM1基因的序列变异及与株型和穗部相关性状的关联分析

 玉米elm1 突变体使得光敏色素载色体合成受阻并导致光敏色素活性下降,从而使得突变体植株表现出对光的不敏感性.为研究玉米ELM1 基因序列的多态性及其与主要农艺性状之间的关联,本研究对玉米ELM1 基因在80 个自交系中进行了目标序列重测序,并与株高和穗位高2 个株型性状以及穗长、穗粗、轴粗、穗重、行粒数、穗行数和穗粒数7 个穗部性状进行关联分析.ELM1 基因在供试玉米自交系中共有85 个变异,包括73 个SNP 和12 个Indel.尽管该基因的编码区不含Indel,但15 个SNP 变异位点依然可以将编码区划分成7 种单倍型,并编码6 种ELM1 蛋白质.关联分析发现,玉米ELM1 基因中1 个非同义突变位点与穗位高存在显著关联,另有2 个非同义突变位点与行粒数存在显著关联.     

Recruitment of entomopathogenic nematodes by insect-damaged maize roots

Plants under attack by arthropod herbivores often emit volatile compounds from their leaves that attract natural enemies of the herbivores. Here we report the first identification of an insect-induced belowground plant signal, (E)-beta-caryophyllene, which strongly attracts an entomopathogenic nematode. Maize roots release this sesquiterpene in response to feeding by larvae of the beetle Diabrotica virgifera virgifera, a maize pest that is currently invading Europe. Most North American maize lines do not release (E)-beta-caryophyllene, whereas European lines and the wild maize ancestor, teosinte, readily do so in response to D. v. virgifera attack. This difference was consistent with striking differences in the attractiveness of representative lines in the laboratory. Field experiments showed a fivefold higher nematode infection rate of D. v. virgifera larvae on a maize variety that produces the signal than on a variety that does not, whereas spiking the soil near the latter variety with authentic (E)-beta-caryophyllene decreased the emergence of adult D. v. virgifera to less than half. North American maize lines must have lost the signal during the breeding process. Development of new varieties that release the attractant in adequate amounts should help enhance the efficacy of nematodes as biological control agents against root pests like D. v. virgifera.     

Pleiotropy as a mechanism to stabilize cooperation

Most genes affect many traits. This phenomenon, known as pleiotropy, is a major constraint on evolution because adaptive change in one trait may be prevented because it would compromise other traits affected by the same genes. Here we show that pleiotropy can have an unexpected effect and benefit one of the most enigmatic of adaptations--cooperation. A spectacular act of cooperation occurs in the social amoeba Dictyostelium discoideum, in which some cells die to form a stalk that holds the other cells aloft as reproductive spores. We have identified a gene, dimA, in D. discoideum that has two contrasting effects. It is required to receive the signalling molecule DIF-1 that causes differentiation into prestalk cells. Ignoring DIF-1 and not becoming prestalk should allow cells to cheat by avoiding the stalk. However, we find that in aggregations containing the wild-type cells, lack of the dimA gene results in exclusion from spores. This pleiotropic linkage of stalk and spore formation limits the potential for cheating in D. discoideum because defecting on prestalk cell production results in an even greater reduction in spores. We propose that the evolution of pleiotropic links between cheating and personal costs can stabilize cooperative adaptations.     

Gene control of flowering time in higher plants

Flowering involves a transition process from vegetative growth to reproductive development, in which a series of routine changes take place in the shoot apical meristems from metabolic pathway to external phenotype. Expression of the genes related to flowering is the foundation for achieving the transition. Environmental factors (such as vernalization and photoperiod) and the growth status of cell itself induce the expression of the specific genes. A lot of achievements have been made recently in gene control for the determination of flowering time. The article reviews some new advances of such researches related to our work and the interesting field.     

三维网植被护坡技术在广巴高速公路的运用和改良

本文论述了三维网植被技术在广巴高速公路上的运用和改良,针对适用边坡坡度等方面的问题提出见解.该技术适用坡比1:1的土质路堑边坡和坡比不陡于1:1的泥岩及砂泥岩互层路堑边坡;在实施过程中应选择EM4型三维网并充分重视其养护;网下覆盖耕植地表土后挂网种植相关植物;前期以草坪草防护为主、后期再行灌木防护;灌木品种选择适应性强、较耐干旱、瘠薄的物种和当地的土著树种.     

自然的异化:现代建材制造与现代建筑

从材料的微观结构出发,分析比较了木材、天然石材、粘土砖瓦、水泥(混凝土)、玻璃、钢材等主要传统和现代建筑材料的制造过程,探讨了现代建筑材料制造过程同现代主义建筑及其文化的联系.认为现代建材制造的发展过程就是人类对自然的不断异化过程,使用现代建材的现代建筑则在更大尺度上异化了自然,而对自然的异化是现代主义建筑文化问题的根源之一.