Pathogenicity determinants in smut fungi revealed by genome comparison

Biotrophic pathogens, such as the related maize pathogenic fungi Ustilago maydis and Sporisorium reilianum, establish an intimate relationship with their hosts by secreting protein effectors. Because secreted effectors interacting with plant proteins should rapidly evolve, we identified variable genomic regions by sequencing the genome of S. reilianum and comparing it with the U. maydis genome. We detected 43 regions of low sequence conservation in otherwise well-conserved syntenic genomes. These regions primarily encode secreted effectors and include previously identified virulence clusters. By deletion analysis in U. maydis, we demonstrate a role in virulence for four previously unknown diversity regions. This highlights the power of comparative genomics of closely related species for identification of virulence determinants.     

Evolution of hormone-receptor complexity by molecular exploitation

According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed of tightly integrated parts seem to challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which it interacts are already present. Here we demonstrate how an integrated molecular system-the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor-evolved by a stepwise Darwinian process. Using ancestral gene resurrection, we show that, long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands. Introducing two amino acid changes into the ancestral sequence recapitulates the evolution of present-day receptor specificity. Our results indicate that tight interactions can evolve by molecular exploitation-recruitment of an older molecule, previously constrained for a different role, into a new functional complex.     

利用SSR标记分析19份山羊草属种D基因组遗传多样性

具有D染色体组的山羊草属种是六倍体普通小麦的二级基因源,蕴藏着丰富的抗性基因和遗传变异丰富,可供现代小麦改良利用。选用24对D染色体组特异性微卫星(SSR)标记引物,将19份山羊草属种的D染色体组与3个普通小麦的D染色体组的遗传多样性进行了比较分析。共检测出679个等位基因,每个SSR位点上能检测到1~44个等位基因,平均28.29个。聚类分析结果表明,同一属种的材料基本上聚为一类,19份山羊草属种的D染色体组与普通小麦的D染色体组之间存在较大的遗传差异,可供小麦远缘杂交以丰富栽培小麦遗传多样性。     

The molecular architecture of axonemes revealed by cryoelectron tomography

Eukaryotic flagella and cilia are built on a 9 + 2 array of microtubules plus >250 accessory proteins, forming a biological machine called the axoneme. Here we describe the three-dimensional structure of rapidly frozen axonemes from Chlamydomonas and sea urchin sperm, using cryoelectron tomography and image processing to focus on the motor enzyme dynein. Our images suggest a model for the way dynein generates force to slide microtubules. They also reveal two dynein linkers that may provide "hard-wiring" to coordinate motor enzyme action, both circumferentially and along the axoneme. Periodic densities were also observed inside doublet microtubules; these may contribute to doublet stability.     

Widespread divergence between incipient Anopheles gambiae species revealed by whole genome sequences

The Afrotropical mosquito Anopheles gambiae sensu stricto, a major vector of malaria, is currently undergoing speciation into the M and S molecular forms. These forms have diverged in larval ecology and reproductive behavior through unknown genetic mechanisms, despite considerable levels of hybridization. Previous genome-wide scans using gene-based microarrays uncovered divergence between M and S that was largely confined to gene-poor pericentromeric regions, prompting a speciation-with-ongoing-gene-flow model that implicated only about 3% of the genome near centromeres in the speciation process. Here, based on the complete M and S genome sequences, we report widespread and heterogeneous genomic divergence inconsistent with appreciable levels of interform gene flow, suggesting a more advanced speciation process and greater challenges to identify genes critical to initiating that process.     

Venus: topography revealed by radar data

Surface height variations over the entire equatorial region on Venus have been estimated from extended series of measurements of interplanetary radar echo delays. Most notable is a mountainous section of about 3-kilometer peak height located at a longitude of 100 degrees (International Astronomical Union coordinate system). The eastern edge has an average inclination of about 0.5 degrees, which is unusually steep for a large-scale slope on Venus. The resolution of the radar measurements along the surface of Venus varied between about 200 and 400 kilometers with a repeatability in altitude determination generally between 200 and 500 meters. The mean equatorial radius was found to be 6050.0+/-0.5 kilometers.     

Nuclear and mitochondrial DNA comparisons reveal extreme rate variation in the molecular clock

The discovery that the rate of evolution of vertebrate mitochondrial DNA is rapid, compared to the rate for vertebrate nuclear DNA, has resulted in its widespread use in evolutionary studies. Comparison of mitochondrial and nuclear DNA divergences among echinoid and vertebrate taxa of similar ages indicates that the rapid rate of vertebrate mitochondrial DNA evolution is, in part, an artifact of a widely divergent rate of nuclear DNA evolution. This disparity in relative rates of mitochondrial and nuclear DNA divergence suggests that the controls and constraints under which the mitochondrial and nuclear genomes operate are evolving independently, and provides evidence that is independent of fossil dating for a robust rejection of a generalized molecular clock hypothesis of DNA evolution.     

Eye marks in vertebrates: AIDS to vision

Lines leading forward from the eye may function as aiming sights in many small vertebrates. The chief evidence is the correlation of distribution and positions of eye-lines in various vertebrate groups with predatory feeding habits. Dark patches around the eye may serve to reduce glare in species in bright environments. Facial patterns often have multiple functions.     

Memory extinction, learning anew, and learning the new: dissociations in the molecular machinery of learning in cortex

The rat insular cortex (IC) subserves the memory of conditioned taste aversion (CTA), in which a taste is associated with malaise. When the conditioned taste is unfamiliar, formation of long-term CTA memory depends on muscarinic and beta-adrenergic receptors, mitogen-activated protein kinase (MAPK), and protein synthesis. We show that extinction of CTA memory is also dependent on protein synthesis and beta-adrenergic receptors in the IC, but independent of muscarinic receptors and MAPK. This resembles the molecular signature of the formation of long-term memory of CTA to a familiar taste. Thus, memory extinction shares molecular mechanisms with learning, but the mechanisms of learning anew differ from those of learning the new.     

Breeding together: kin selection and mutualism in cooperative vertebrates

In cooperatively breeding vertebrates, nonbreeding helpers raise young produced by dominant breeders. Although the evolution of cooperative breeding has often been attributed primarily to kin selection (whereby individuals gain "indirect" benefits to their fitness by assisting collateral relatives), there is increasing evidence that helpers can be unrelated to the young they are raising. Recent studies also suggest that the indirect benefits of cooperative behavior may often have been overestimated while the direct benefits of helping to the helper's own fitness have probably been underestimated. It now seems likely that the evolutionary mechanisms maintaining cooperative breeding are diverse and that, in some species, the direct benefits of helping may be sufficient to maintain cooperative societies. The benefits of cooperation in vertebrate societies may consequently show parallels with those in human societies, where cooperation between unrelated individuals is frequent and social institutions are often maintained by generalized reciprocity.     

Evolution of urea synthesis in vertebrates: the piscine connection

Elasmobranch fishes, the coelacanth, estivating lungfish, amphibians, and mammals synthesize urea by the ornithine-urea cycle; by comparison, urea synthetic activity is generally insignificant in teleostean fishes. It is reported here that isolated liver cells of two teleost toadfishes, Opsanus beta and Opsansus tau, synthesize urea by the ornithine-urea cycle at substantial rates. Because toadfish excrete ammonia, do not use urea as an osmolyte, and have substantial levels of urease in their digestive systems, urea may serve as a transient nitrogen store, forming the basis of a nitrogen conservation shuttle system between liver and gut as in ruminants and hibernators. Toadfish synthesize urea using enzymes and subcellular distributions similar to those of elasmobranchs: glutamine-dependent carbamoyl phosphate synthethase (CPS III) and mitochondrial arginase. In contrast, mammals have CPS I (ammonia-dependent) and cytosolic arginase. Data on CPS and arginases in other fishes, including lungfishes and the coelacanth, support the hypothesis that the ornithine-urea cycle, a monophyletic trait in the vertebrates, underwent two key changes before the evolution of the extant lungfishes: a switch from CPS III to CPS I and replacement of mitochondrial arginase by a cytosolic equivalent.     

基于WITNESS的农场收获机器系统配备应用仿真研究

目前农场在收获作业中,大多以经验法进行收获机器系统的配备,从而导致因运载机械配备不合理而造成的收获作业延误情况.结合农场在收获作业中存在的问题,对收获机及运载机械相关数据进行实地测量,将农场的收获过程视作物流系统,运用系统仿真的原理,应用系统仿真软件对收获过程进行建模,查找实际生产中收获机与运载机械的配备中存在的问题,...     

14份杏种质的ISSR分析

以冀光为试材,研究了PCR反应体系的主要成分及退火温度对杏ISSR扩增结果的影响。同时,从42对ISSR引物中筛选出12对扩增条带清晰、多态性好的引物进行扩增,并运用UPGMA聚类分析法,分析了12份杏种质的亲缘关系及多样性。结果表明:在20μL的反应体系中,模板DNA含量在10~80 ng均能得到较好的扩增;dNTP用量对扩增无明显影响;而引物、Mg2+的最适浓度分别为0.25μmol/L、0.25 mmol/L;Taq酶在0.5~4 U均能得到好的扩增条带;退火温度在50~52.1℃范围内均能得到清晰的条带;并在此基础上建立了杏ISSR反应体系。当相似系数在0.444~0.452之间时,将12份杏材料划分为3类:①普通杏(Amentacavulgaris),西伯利亚杏(A.sibirica),辽杏(A.mandshurica),藏杏(A.holosericea)类型;②仁用杏品种一窝蜂;③紫杏(A.dasycarpa)。     

Galapagos hydrothermal mounds: stratigraphy and chemistry revealed by deep-sea drilling

The Galápagos mounds sea-floor hydrothermal system is at least 300,000 years old and once produced manganese-poor sediments, which nearly blanketed the area of the present mounds field. Present-day mound deposits are limited manganese-rich exposures, suggesting that the system has changed from rock-to water-dominated and has diminished in intensity with time.     

杨树Genomic-SSR与EST-SSR分子标记遗传差异性分析

利用16个杨树无性系对Genomic-SSR和EST-SSR两种SSR标记的遗传差异性进行分析。统计分析结果表明,Genomic-SSR平均检测到的等位基因数为4.1、Shannon指数为1.0646、观测杂合度为0.4427、期望杂合度为0.5523;EST-SSR平均检测到的等位基因数为2.8、Shannon指数为0.6985、观测杂合度为0.2330、期望杂合度为0.4684。聚类分析结果显示,EST-SSR相对Genomic-SSR能更精准地鉴别基因型。研究结果表明,在标记多态性及基因型鉴别等方面EST-SSR与Genomic-SSR均具有显著的遗传差异性。通过对两种分子标记遗传差异的比较分析,可为合理利用SSR标记进行物种遗传多样性等相关研究提供依据。     

Beta-glucuronidase activity in serum increased by coronary-artery atherosclerosis

Increase in activity of beta-glucuronidase in serum has been demonstrated in patients having clinically evident coronary-artery atherosclerosis. This fact, yielded by the new, more specific method of Fishman, could not be elicited by the treditional method.     

The principles of controlling mechanical structures in agricultural machinery by frequency characteristics

We present a methodology that might be used for analysis and synthesis of executive subsystems in agricultural machines with frequency control over their working processes; this methodology is adapted to specific features of seeds, soils, and operating conditions.