《Nature》目录要览：2010-07-29出版

封面故事：解决粮食安全问题的办法到底在哪里？
Cover caption
联合国粮农组织估计，世界粮食产量到2050年需要增加70%。 本期Nature上一系列文章分析了植物科学家和生物技术专家能为实现这一目标所做的贡献。这个问题的严重程度在第546页介绍，其中包括这样一个事实：今天挨饿的10亿多人之所以挨饿，不是因为没有足够多的粮食，而是因为他们太穷、买不起粮食。所以，我们需要更好的治理。但如果对本期封面上所刊登问题的答案为“是”， 那么主要农业生物技术公司可能将不得不对增加粮食产量做出很大贡献。正如Natasha Gilbert所报告的那样（第548页），它将意味着我们的工作重点从关注对杀虫剂和除草剂的抗药性向培育能够应对干旱和营养缺乏的作物的转变。从上个世纪40年代起推进绿色革命的高产作物品种倾向于优化作物在地面之上的性状——比如说在能量投入上要让作物产生更多粮食和更少秸秆。在现在注重减少肥料的使用和其他投入的情况下，很多植物育种工作者和遗传工作者在寻找第二次绿色革命道路的过程中都在往下看，即把目光瞄准植物的根。在本期的第552页，Virginia Gewin介绍了目前正在制定当中的用于改进根系和增加粮食产量的策略。如果我们要实现农业可持续发展，那么我们就需要对各种不同耕作实践的影响了解更多。在“Opinion”栏目中，一组粮食安全专家提出一个全球监测网络，这个网络有可能采集到所缺失的数据（第558页），而 Ingo Potrykus根据他自己在“金稻”(golden rice)项目上的经验（该项目生产一种能够补偿维生素A缺乏的水稻）认为，不必要的法律要求目前使得基因工程作物无法让数以百万计的人口免于营养不良和其他更糟的情况（第561页）。另请阅读社论文章（第531页）和网上相关内容。


太阳系的故事——过去、现在和将来（The Solar System story）
The four hundred years of planetary science since Galileo and Kepler
行星科学是从伽利略关于行星和它们卫星的研究才真正开始的。350年来，我们关于太阳系的观点通过地基望远镜去伪存真、通过理论模型提升改进。太阳系探索时代的到来（“水手2号”1962年掠过金星是第一次成功地对行星金星造访）在过去50年使近距离观测、甚至实验成为现实，改变了我们关于太阳系的知识。在本期的一篇“Review”文章中，Joseph Burns分析了空间时代之前的行星科学的历史，进而讨论了最近一些最有趣的发现，凸显了太阳系天体的多样性以及混沌在太阳系演化中所起作用。他还对我们将要迈出的下一步进行了展望——这一步将是一大飞跃，即能够对太阳系外行星进行详细观测。（Review p. 575）


全球浮游植物生物质长期都在下降（Phytoplankton in retreat）
Global phytoplankton decline over the past century
海洋浮游植物在地球的生物地球化学循环中扮演一个关键角色，构成海洋生态系统的基础。来自卫星遥感的数据（可获得的数据自1979年起）提供的证据表明，浮游植物生物质曾在十年尺度上波动，与气候作用力有关，但几十年时间的数据不足于反映长期趋势。现在，Daniel Boyce及其同事通过估计1899年以来浮游植物生物质的局部、区域和全球趋势，将这些结果置于一个长期背景下来进行观察，他们所依据的是来自一系列渠道的数据，其中包括用被称为“Secchi disk”的一种设备对海洋透明度所做的测量以及各种不同类型的船载分析工作。他们从这些记录发现的一个趋势是，全球浮游植物生物质有一个世纪的时间在下降。本文作者们估计，浮游植物现存量的下降在高纬度地区、在赤道地区、在海洋地区和在最近的年份是最大的。大多数地区的趋势都与海洋变暖的增强以及重要气候指数显著相关联。（Article p. 591; News & Views）


“三光子体”纠缠态的直接生成（Entangled photon triplets）
Direct generation of photon triplets using cascaded photon-pair sources
纠缠的光子是基础科学的一个强大资源，具有推动计算和通信方面新型量子技术发展的潜力。纠缠的光子对可以由激光的自然“参量下转换”来生成，但此前一直没有可能以这种方式来生成“三光子体”。现在，Hübel等人报告了利用一个由光子对光源组成的级联来直接生成“三光子体”的方法。在该方法中，每个“三光子体”都来自仅仅一个泵浦光子，从而导致所有三个光子之间产生量子关联。（Letter p. 601）


“新马德里”地震带再次发生地震的风险（New Madrid seismicity）
Triggering of New Madrid seismicity by late-Pleistocene erosion
位于当今美国中部一个人口稠密地区的“新马德里”地震带，是造成1811–1812年“新马德里”地震（震级为7级或以上）的原因。这个地区目前地震风险的程度存在激烈争论。Eric Calais及其同事提供的证据表明，这个地区从地质上来说属于最近时期的系列大地震是由上个冰期末密西西比河北部河湾的河流快速冲走沉积物触发的。模型研究表明，已经断裂的断层带不大可能很快再次断裂，但由沉积物流失和以前地震所造成的应力变化也许最终将足以使尚未断裂的附近其他断层断裂，这表明地震的风险可能比以前人们所认为的范围要大。（Letter p. 608; News & Views）


性染色体的巨大变化（Dynamic sex chromosomes）
Convergent evolution of chicken Z and human X chromosomes by expansion and gene acquisition
鸟类和哺乳动物有鲜明的性染色体。在鸟类中，雄性个体有一对Z染色体，而雌性个体有一个Z染色体和一个W染色体。在哺乳动物中，雄性个体的染色体是XY，雌性是XX。人们长期假设，性染色体演化涉及性特异性染色体（即W染色体和Y染色体）的巨大改变，但两性都有的Z染色体和X染色体只发生较小的改变。但根据一项新的研究，事实并不是这样的。这项研究报告了鸡的Z染色体的序列，并将其与已完成测序的人X染色体序列进行了比较。Z染色体和X染色体与产生它们的常染色体（非性染色体）相比发生了巨大变化。而且Z染色体和X染色体似乎是遵从收敛的演化轨迹，包括由睾丸所表达的基因家族的获得和放大，尽管它们是从先祖基因组的不同部分独立形成的。（Letter p. 612）


生物节律与糖尿病的关系（Clocking on to diabetes）
Disruption of the clock components CLOCK and BMAL1 leads to hypoinsulinaemia and diabetes
在进食期间，胰岛分泌胰岛素来维持葡萄糖体内平衡，这个有节奏的过程在糖尿病患者体内被扰乱了。现在，用小鼠所做实验表明，胰岛有它们自己的生物钟，在睡眠-清醒周期中来组织和安排胰岛素的分泌。转录因子CLOCK 和 BMAL1对这一过程很关键，携带Clock 和Bmal1基因的缺陷版本的小鼠会患“hypoinsulinaemia”（胰岛素水平过低症）和糖尿病。这项工作证明了一个局部组织的生物时钟能够在胰腺贝塔细胞中将生物节律信号和新陈代谢信号整合起来，它说明生物节律分析是更深入了解代谢表现型以及治疗2-型糖尿病等代谢疾病的关键。（Letter p. 627; News & Views）


微RNA在帕金森氏症中的作用（MicroRNAs in Parkinson’s）
Pathogenic LRRK2 negatively regulates microRNA-mediated translational repression
“富含亮氨酸的重复段激酶-2” (LRRK2)所发生的突变已被与家族性和偶发性帕金森氏症联系在一起，但其生化功能却一直不清楚。现在，LRRK2的一个生化功能已被发现。果蝇和人类的LRRK2都被发现拮抗由微RNA调控的对E2F1 和 DP转录因子的翻译抑制。LRRK2与由RNA诱导的沉寂复合物组分Argonaute发生相互作用，来拮抗其对蛋白翻译的抑制效应。活体遗传研究表明，E2F1/DP上调在调控突变体LRRK2的发病机理中扮演一个关键角色。这些发现表明，受损的、由微RNA调控的沉寂作用与特定微RNA目标的失控表达之间有一个联系，它能造成帕金森氏症的发病；而且这些发现还提出了基于微RNA的可能治疗方法。（Letter p. 637）


一类以前未知的短RNA（Another clutch of small RNAs）
New class of gene-termini-associated human RNAs suggests a novel RNA copying mechanism
利用单分子高通量测序方法对来自人类细胞的短RNA（少于200个核苷酸）所做的一项分析，发现了一类有所不同的、以前未知的短RNA。它们在其5ʹ端都有相同的“尾巴”，由非基因组编码的“polyU”残体的一个序列组成。这一点，再加上关于这些RNA与由已知RNA构成的3ʹ端密切相关的发现，指出了在人类细胞中存在一个新型RNA复制机制。（Letter p. 642）


突破衍射极限观测单分子（Seeing single molecules）
Subnanometre single-molecule localization, registration and distance measurements
利用“电荷耦合装置”(CCD)来跟踪附着在所要探测的生物分子上的荧光探针分子，有可能绕过将一个光学显微镜的分辨率限制在约为入射光波长的一半的衍射极限。这种办法将对单分子或分子内距离成像的极限从由衍射极限决定的200纳米降低到接近20纳米。现在，朱棣文与其同事们利用这种CCD-荧光技术的一种变通形式来在一个传统远场荧光成像系统中以亚纳米精确性来测定距离。他们用一个反馈系统来补偿CCD硅阵列对入射光子的不均匀响应（这可能是芯片制造所产生的人为现象），这种响应如果不消除的话，会使代表彼此间的距离只有几个纳米的点的像素模糊。 这种分辨率应能够对较大的多蛋白生物复合物的构成成分进行定性。该方法还应能启发人们对同样依赖于数码相机的纳米技术或天文测量实施类似的改进。（Letter p. 647）



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NEWS AND VIEWS
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Regenerative medicine: An eye to treating blindness pp567-568
Work on stem cells is one of the hottest research areas in biology. But are such studies of any therapeutic value? Fortunately, yes, as is evident from successes in treating blindness.
Elena Ezhkova and Elaine Fuchs
doi:10.1038/466567a
http://www.nature.com/nature/journal/v466/n7306/full/466567a.html

Earthquakes: Climate and intraplate shocks pp568-569
The heartland of the United States lies within a tectonic plate, certain regions of which have experienced large and geologically recent earthquakes. Explanations for those events are still being sought.
Mark D. Zoback
doi:10.1038/466568a
http://www.nature.com/nature/journal/v466/n7306/full/466568a.html

Oceanography: Century of phytoplankton change pp569-571
Phytoplankton biomass is a crucial measure of the health of ocean ecosystems. An impressive synthesis of the relevant data, stretching back to more than 100 years ago, provides a connection with climate change.
David A. Siegel and Bryan A. Franz
doi:10.1038/466569a
http://www.nature.com/nature/journal/v466/n7306/full/466569a.html

Metabolism: Tick, tock, a [beta]-cell clock pp571-572
The daily light-dark cycle affects many aspects of normal physiology through the activity of circadian clocks. It emerges that the pancreas has a clock of its own, which responds to energy fluctuations.
Katja A. Lamia and Ronald M. Evans
doi:10.1038/466571a
http://www.nature.com/nature/journal/v466/n7306/full/466571a.html

Condensed-matter physics: Bringing the noise pp572-573
Noise is usually viewed as the bane of measurements. But a neat experiment has confirmed a long-standing prediction for an exotic electronic state of matter through the increase of noise in charge transmission.
Chetan Nayak
doi:10.1038/466572a
http://www.nature.com/nature/journal/v466/n7306/full/466572a.html

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REVIEW
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The four hundred years of planetary science since Galileo and Kepler pp575-584
For 350 years after Galileo's discoveries, ground-based telescopes and theoretical modelling furnished everything known about the Sun's planetary retinue. Over the past five decades, data from spacecraft sent to all the planets and some of their satellites have shown the diversity of Solar System bodies. Many planets and satellites have changed substantially since their birth, and violent events punctuate their histories.
Joseph A. Burns
doi:10.1038/nature09215
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09215.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09215.html

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ARTICLES
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Observation of neutral modes in the fractional quantum Hall regime pp585-590
The quantum Hall effect takes place in a two-dimensional electron gas under a strong magnetic field and involves current flow along the edges of the sample. In the fractional regime, counter-propagating modes that carry energy but not charge [mdash] the so-called neutral modes [mdash] have been predicted but never observed. These authors report the first direct observation of these elusive modes.
Aveek Bid et al.
doi:10.1038/nature09277
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09277.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09277.html

Global phytoplankton decline over the past century pp591-596
Using historical data combined with more recent satellite observations, these authors show that global phytoplankton biomass has been declining during the past century.
Daniel G. Boyce, Marlon R. Lewis and Boris Worm
doi:10.1038/nature09268
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09268.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09268.html


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LETTERS
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Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons pp597-600
Fluctuations arising from Heisenberg's uncertainty principle enable quantum systems to exhibit phase transitions even at zero temperature. For example, a superfluid-to-insulator transition has been observed for weakly interacting bosonic atomic gases. Here the authors report a novel type of quantum phase transition in a strongly interacting, one-dimensional quantum gas of bosonic caesium atoms. The results open up the experimental study of ultracold gases in a new regime.
Elmar Haller et al.
doi:10.1038/nature09259
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09259.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09259.html

Direct generation of photon triplets using cascaded photon-pair sources pp601-603
Non-classical states of light, such as entangled photon states, form an essential quantum resource. Entangled photon pairs can be created by spontaneous parametric down-conversion of laser light, but so far it has not been possible to produce photon triplets in this way. These authors report the generation of quantum-correlated photon triplets by cascaded down-conversion of a single pump photon. This should find widespread use in optical quantum technologies.
Hannes Hubel et al.
doi:10.1038/nature09175
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09175.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09175.html

Following a chemical reaction using high-harmonic interferometry pp604-607
New methods are emerging that aim to image chemical reactions as they occur using X-ray diffraction, electron diffraction or laser-induced recollision, but spectral selection cannot be used to monitor the reacting molecules for these methods. These authors show that this apparent limitation offers opportunities for recollision-based high-harmonic spectroscopy, in which unexcited molecules can act as local oscillators against which structural and electronic dynamics is observed on an attosecond timescale.
H. J. Worner et al.
doi:10.1038/nature09185
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09185.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09185.html

Triggering of New Madrid seismicity by late-Pleistocene erosion pp608-611
These authors argue that the concentration of magnitude-7 or larger earthquakes in the New Madrid seismic zone since the end of the last ice age results from the recent, climate-controlled, erosional history of the northern Mississippi embayment. They show that the upward flexure of the lithosphere caused a reduction of normal stresses in the upper crust sufficient to unclamp pre-existing faults close to failure equilibrium.
E. Calais, A. M. Freed, R. Van Arsdale and S. Stein
doi:10.1038/nature09258
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09258.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09258.html

Convergent evolution of chicken Z and human X chromosomes by expansion and gene acquisition pp612-616
Birds and mammals have distinct sex chromosomes: in birds, males are ZZ and females ZW; in mammals, males are XY and females XX. By sequencing the chicken Z chromosome and comparing it with the human X chromosome, these authors overturn the currently held view that these chromosomes have diverged little from their autosomal progenitors. The Z and X chromosomes seem to have followed convergent evolutionary trajectories, despite evolving with opposite systems of heterogamety.
Daniel W. Bellott et al.
doi:10.1038/nature09172
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09172.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09172.html

Sparse coding and high-order correlations in fine-scale cortical networks pp617-621
Sensory cortical neurons are interconnected at different scales, and this could be related to differences in functional interactions. Using maximum entropy models, these authors explore the correlation structure of neurons in primary visual cortex of anaesthetized monkeys recorded using multiple tetrodes. They conclude that distant neurons display pairwise correlations but that local networks can have more complex interactions that may act to sparsify the neural code.
Ifije E. Ohiorhenuan et al.
doi:10.1038/nature09178
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09178.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09178.html

Regulation of parkinsonian motor behaviours by optogenetic control of basal ganglia circuitry pp622-626
It has long been thought that motor control is achieved through the balanced activity of two distinct pathways through the basal ganglia that have opposing effects, but this has never been functionally verified. These authors directly test this hypothesis with optogenetic activation of different populations of mouse striatal neurons, and not only trace functional connectivity but demonstrate opposing effects on motor behaviour in a parkinsonian model.
Alexxai V. Kravitz et al.
doi:10.1038/nature09159
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09159.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09159.html

Disruption of the clock components CLOCK and BMAL1 leads to hypoinsulinaemia and diabetes pp627-631
Circadian rhythms control many physiological functions. During periods of feeding, pancreatic islets secrete insulin to maintain glucose homeostasis [mdash] a rhythmic process that is disturbed in people with diabetes. These authors show that pancreatic islets contain their own clock: they have self-sustained circadian oscillations of CLOCK and BMAL1 genes and proteins, which are vital for the regulation of circadian rhythms. Without this clock, a cascade of cellular failure and pathology initiates the onset of diabetes mellitus.
Biliana Marcheva et al.
doi:10.1038/nature09253
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09253.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09253.html

Cross-species genomics matches driver mutations and cell compartments to model ependymoma pp632-636
Ependymoma is a type of neural tumour that arises throughout the central nervous system. Using comparative transcriptomics in mouse and human tumours, these authors home in on mutations that are specific to individual tumour subgroups. In doing so, they generate the first mouse model of ependymoma and demonstrate the power of interspecific genomic comparisons to interrogate cancer subgroups.
Robert A. Johnson et al.
doi:10.1038/nature09173
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09173.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09173.html

Pathogenic LRRK2 negatively regulates microRNA-mediated translational repression pp637-641
LRRK2 activity is dysregulated in Parkinson's disease, but how it contributes to the pathogenesis is unknown. These authors show that Drosophila LRRK2 interacts with the Argonaute component (dAgo1) of the RNA-induced silencing complex. This is associated with reduced levels of dAgo1, interaction between phospho-4E-BP1 and hAgo2, and impairment of microRNA-mediated repression. This leads to overexpression of the cell cycle genes e2f1 and dp, and consequent degeneration of dopaminergic neurons.
Stephan Gehrke, Yuzuru Imai, Nicholas Sokol and Bingwei Lu
doi:10.1038/nature09191
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09191.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09191.html

New class of gene-termini-associated human RNAs suggests a novel RNA copying mechanism pp642-646
In the course of characterizing short RNAs from human cells using single-molecule high-throughput sequencing, these authors identify a new short RNA species. The presence of non-genomically encoded poly(U) residues at their 5' ends implies the existence of an unknown RNA copying mechanism in human cells.
Philipp Kapranov et al.
doi:10.1038/nature09190
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09190.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09190.html

Subnanometre single-molecule localization, registration and distance measurements pp647-651
These authors have developed a method that enables them to observe single-molecule fluorescent probes with subnanometre precision and accuracy using conventional far-field fluorescence imaging. The improved resolution will enable researchers to characterize single 'molecules' of large, multisubunit biological complexes in biologically relevant environments.
Alexandros Pertsinidis, Yunxiang Zhang and Steven Chu
doi:10.1038/nature09163
Abstract: http://www.nature.com/nature/journal/v466/n7306/abs/nature09163.html
Article: http://www.nature.com/nature/journal/v466/n7306/full/nature09163.html

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CORRIGENDA
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Asymptomatic deer excrete infectious prions in faeces p652
Gultekin Tamguney et al.
doi:10.1038/nature09031
http://www.nature.com/nature/journal/v466/n7306/full/nature09031.html

NLRP3 inflammasomes are required for atherogenesis and activated by cholesterol crystals p652
Peter Duewell et al.
doi:10.1038/nature09316
http://www.nature.com/nature/journal/v466/n7306/full/nature09316.html

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FUTURES
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Auntie Merkel p660
The course of true love.
Deborah Walker
doi:10.1038/466660a
http://www.nature.com/nature/journal/v466/n7306/full/466660a.html

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