Phot1 and phot2 mediate blue light regulation of stomatal opening.

The stomatal pores of higher plants allow for gaseous exchange into and out of leaves. Situated in the epidermis, they are surrounded by a pair of guard cells which control their opening in response to many environmental stimuli, including blue light. Opening of the pores is mediated by K(+) accumulation in guard cells through a K(+) channel and driven by an inside-negative electrical potential. Blue light causes phosphorylation and activation of the plasma membrane H(+)-ATPase that creates this potential. Thus far, no blue light receptor mediating stomatal opening has been identified, although the carotenoid, zeaxanthin, has been proposed. Arabidopsis mutants deficient in specific blue-light-mediated responses have identified four blue light receptors, cryptochrome 1 (cry1), cryptochrome 2 (cry2), phot1 and phot2. Here we show that in a double mutant of phot1 and phot2 stomata do not respond to blue light although single mutants are phenotypically normal. These results demonstrate that phot1 and phot2 act redundantly as blue light receptors mediating stomatal opening.     

Gridlock signalling pathway fashions the first embryonic artery.

Arteries and veins are morphologically, functionally and molecularly very different, but how this distinction is established during vasculogenesis is unknown. Here we show, by lineage tracking in zebrafish embryos, that angioblast precursors for the trunk artery and vein are spatially mixed in the lateral posterior mesoderm. Progeny of each angioblast, however, are restricted to one of the vessels. This arterial-venous decision is guided by gridlock (grl), an artery-restricted gene that is expressed in the lateral posterior mesoderm. Graded reduction of grl expression, by mutation or morpholino antisense, progressively ablates regions of the artery, and expands contiguous regions of the vein, preceded by an increase in expression of the venous marker EphB4 receptor (ephb4) and diminution of expression of the arterial marker ephrin-B2 (efnb2). grl is downstream of notch, and interference with notch signalling, by blocking Su(H), similarly reduces the artery and increases the vein. Thus, a notch-grl pathway controls assembly of the first embryonic artery, apparently by adjudicating an arterial versus venous cell fate decision.     

Mechanism of ubiquitin activation revealed by the structure of a bacterial MoeB-MoaD complex.

The activation of ubiquitin and related protein modifiers is catalysed by members of the E1 enzyme family that use ATP for the covalent self-attachment of the modifiers to a conserved cysteine. The Escherichia coli proteins MoeB and MoaD are involved in molybdenum cofactor (Moco) biosynthesis, an evolutionarily conserved pathway. The MoeB- and E1-catalysed reactions are mechanistically similar, and despite a lack of sequence similarity, MoaD and ubiquitin display the same fold including a conserved carboxy-terminal Gly-Gly motif. Similar to the E1 enzymes, MoeB activates the C terminus of MoaD to form an acyl-adenylate. Subsequently, a sulphurtransferase converts the MoaD acyl-adenylate to a thiocarboxylate that acts as the sulphur donor during Moco biosynthesis. These findings suggest that ubiquitin and E1 are derived from two ancestral genes closely related to moaD and moeB. Here we present the crystal structures of the MoeB-MoaD complex in its apo, ATP-bound, and MoaD-adenylate forms, and highlight the functional similarities between the MoeB- and E1-substrate complexes. These structures provide a molecular framework for understanding the activation of ubiquitin, Rub, SUMO and the sulphur incorporation step during Moco and thiamine biosynthesis.     

Horses damp the spring in their step.

The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle-tendon units.These make the legs act like a child's pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle. Despite being apparently redundant for such a mechanism, the muscle fibres in the digital flexors are well developed. Here we show that the mechanical arrangement of the elastic leg permits it to vibrate at a higher frequency of 30-40 Hz that could cause fatigue damage to tendon and bone. Furthermore, we show that the digital flexor muscles have minimal ability to contribute to or regulate significantly the 2.5-Hz cycle of movement, but are ideally arranged to damp these high-frequency oscillations in the limb.     

Magma storage beneath Axial volcano on the Juan de Fuca mid-ocean ridge.

Axial volcano, which is located near the intersection of the Juan de Fuca ridge and the Cobb-Eickelberg seamount chain beneath the northeast Pacific Ocean, is a locus of volcanic activity thought to be associated with the Cobb hotspot. The volcano rises 700 metres above the ridge, has substantial rift zones extending about 50 kilometres to the north and south, and has erupted as recently as 1998 (ref. 2). Here we present seismological data that constrain the three-dimensional velocity structure beneath the volcano. We image a large low-velocity zone in the crust, consisting of a shallow magma chamber and a more diffuse reservoir in the lower crust, and estimate the total magma volume in the system to be between 5 and 21 km3. This volume is two orders of magnitude larger than the amount of melt emplaced during the most recent eruption (0.1-0.2 km3). We therefore infer that such volcanic events remove only a small portion of the reservoir that they tap, which must accordingly be long-lived compared to the eruption cycle. On the basis of magma flux estimates, we estimate the crustal residence time of melt in the volcanic system to be a few hundred to a few thousand years.     

A Unified Framework for Multilingual Text-to-Speech Synthesis with SSML Specification as Interface

This paper describes the design of a unified framework for a multilingual text-to-speech (TTS) synthesis engine – Crystal. The unified framework defines the common TTS modules for different languages and/or dialects. The interfaces between consecutive modules conform to the speech synthesis markup language (SSML) specification for standardization, interoperability, multilinguality, and extensibility. Detailed module divisions and implementation technologies for the unified framework are introduced, together with possible extensions for the algorithm research and evaluation of the TTS synthesis. Implementation of a mixed-language TTS system for Chinese Putonghua, Chinese Cantonese, and English demonstrates the feasibility of the proposed unified framework.     

Mars' volatile and climate history.

There is substantial evidence that the martian volatile inventory and climate have changed markedly throughout the planet's history. Clues come from areas as disparate as the history and properties of the deep interior, the composition of the crust and regolith, the morphology of the surface, composition of the present-day atmosphere, and the nature of the interactions between the upper atmosphere and the solar wind. We piece together the relevant observations into a coherent view of the evolution of the martian climate, focusing in particular on the observations that provide the strongest constraints.     

A massive cloud of cold atomic hydrogen in the outer Galaxy.

A large fraction of the mass of the interstellar medium in our Galaxy is in the form of warm (103-104 K) and cool (50-100 K) atomic hydrogen (H i) gas. Cold (10-30 K) regions are thought to be dominated by dense clouds of molecular hydrogen. Cold H i is difficult to observe, and therefore our knowledge of its abundance and distribution in the interstellar medium is poor. The few known clouds of cold H i are much smaller in size and mass than typical molecular clouds. Here we report the discovery that the H i supershell GSH139-03-69 is very cold (10 K). It is about 2 kiloparsecs in size and as massive as the largest molecular complexes. The existence of such an immense structure composed of cold atomic hydrogen in the interstellar medium runs counter to the prevailing view that cold gas resides almost exclusively in clouds dominated by molecular hydrogen.