Publications

Abstract Thaxtomin A is a phytotoxin produced by Streptomyces scabies and other Streptomyces species, the causative agents of common scab disease in potato and other taproot crops. At nanomolar concentrations, thaxtomin causes dramatic cell swelling, reduced seedling growth, and inhibition of cellulose synthesis in Arabidopsis. We identified a mutant of Arabidopsis, designated txr1, that exhibits increased resistance to thaxtomin as a result of a decrease in the rate of toxin uptake. The TXR1 gene was identified by map-based cloning and found to encode a novel, small protein with no apparent motifs or organelle-targeting signals. The protein, which has homologs in all fully sequenced eukaryotic genomes, is expressed in all tissues and during all developmental stages analyzed. Microarray transcript profiling of some 14,300 genes revealed two stomatin-like genes that were expressed differentially in the txr1 mutant and the wild type. We propose that TXR1 is a regulator of a transport mechanism.

Branched mesoporous silica SBA-15 materials have been prepared in a simple process using non-ionic surfactant in acidic conditions in the presence of metal ions.

The genes for apolipoprotein B and microsomal triglyceride transfer protein are expressed in mouse and human heart tissue. Why the heart would express these "lipoprotein assembly" genes has been unclear. Here we demonstrate that the beating mouse heart actually secretes spherical lipoproteins. Moreover, increased cardiac production of lipoproteins (e.g., in mice that express a human apolipoprotein B transgene) was associated with increased triglyceride secretion from the heart and decreased stores of triglycerides within the heart. Increased cardiac production of lipoproteins also reduced the pathological accumulation of triglycerides that occurs in the hearts of mice lacking long-chain acyl coenzyme A dehydrogenase. In contrast, blocking heart lipoprotein secretion (e.g., in heart-specific microsomal triglyceride transfer protein knockout mice) increased cardiac triglyceride stores. Thus, heart lipoprotein secretion helps regulate cardiac triglyceride stores and may protect the heart from the detrimental effects of surplus lipids.

In this demo, we present Ripcord, a modular platform for rapidly prototyping scale-out data center networks. Ripcord enables researchers to build and evaluate new network features and topologies, using only commercially available hardware and open-source software. The Ripcord demo will show three examples of custom network functions, operating together, on top of a 160-node cluster. The first is a routing engine that isolates classes of traffic. The second is a dynamic network manager than adjusts links and switch power states to reduce energy. The third is a statistics aggregator that supports network health monitoring and automatic alerts. The demo will be interactive, with a visualization of live parameters for each link and switch, such as bandwidth, drops, and power status, as well a control panel to modify the traffic load. We feel that an interactive demo is the best way to introduce the research community to Ripcord and get their feedback.

Carbon monoxide (CO) is an emerging gasotransmitter and reactive carbon species with broad anti-inflammatory, cytoprotective, and neurotransmitter functions along with therapeutic potential for the treatment of cardiovascular diseases. The study of CO chemistry in biology and medicine relative to other prominent gasotransmitters such as NO and H2S remains challenging, in large part due to limitations in available tools for the direct visualization of this transient and freely diffusing small molecule in complex living systems. Here we report a ligand-directed activity-based sensing (ABS) approach to CO detection through palladium-mediated carbonylation chemistry. Specifically, the design and synthesis of a series of ABS probes with systematic alterations in the palladium-ligand environment (e.g., sp3-S, sp3-N, sp2-N) establish structureactivity relationships for palladacycles to confer selective reactivity with CO under physiological conditions. These fundamental studies led to the development of an optimized probe, termed Carbon Monoxide Probe-3 Ester Pyridine (COP3E-Py), which enables imaging of CO release in live cell and brain settings, including monitoring of endogenous CO production that triggers presynaptic dopamine release in fly brains. This work provides a unique tool for studying CO in living systems and establishes the utility of a synthetic methods approach to activity-based sensing using principles of organometallic chemistry

40Ar/39Ar geochronology constraints to aggradational phases and grainsize variations show that the sedimentary filling of the Liri fluvial-lacustrine basin (central Italy) recorded the occurrence of deglaciation events associated with global meltwater pulses. Integrating these data with those from the Tiber River catchment basin, we find a precise match between the ages of gravel deposition and the occurrence of moderate sea-level rise events which anticipate those more marked during the glacial termination V and IV in the Red Sea relative sea level curve. Such correspondence suggests that gravel deposition is facilitated by melting of Apennine mountain range glaciers, which provide the water transport energy and a surplus of clastic input to the rivers draining the mountain regions and flowing into the Tyrrhenian Sea. Therefore, the thick gravel beds intercalated in the sedimentary filling of the catchment basins of the major rivers in central Italy may be regarded as an equivalent proxy of large deglaciation events, similar to the ice-rafted debris in northern Atlantic. Consistent with this hypothesis, we also show the close correspondence between the occurrence of particularly mild (warmer) minima of the mean summer insolation at 65° N and these early aggradational phases, as well as with other anomalous early sea-level rises occurred 750 ka and 540 ka at the onset of glacial termination VIII and VI, and 40 ka at the onset of the so-called Heinrich events.

We have investigated the role of surface roughening on the CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) over Cu. The activity and product selectivity of Cu surfaces roughened by plasma pretreatment in Ar, O<sub>2</sub>, or N<sub>2</sub> were compared with that of electrochemically polished Cu samples. Differences in total and product current densities, the ratio of current densities for HER (the hydrogen evolution reaction) to CO<sub>2</sub>RR, and the ratio of current densities for C<sub>2+</sub> to C<sub>1</sub> products depend on the electrochemically active surface and are nearly independent of plasma composition. Theoretical analysis of an electropolished and roughened Cu surface reveals a higher fraction of undercoordinated Cu sites on the roughened surface, sites that bind CO preferentially. Roughened surfaces also contain square sites similar to those on a Cu(100) surface but with neighboring step sites, which adsorb OC-COH, a precursor to C<sub>2+</sub> products. Here, these findings explain the increases in the formation of oxygenates and hydrocarbons relative to CO and the ratio of oxygenates to hydrocarbons observed with increasing surface roughness.

In the past decade, thousands of synthetic building blocks, intermediates, and drug candidates containing a spirocyclopropane core with at least one nitrogen atom have been investigated for a range of biological activities. These compounds create three-dimensional architectures that maintain the rigidity of their more sp²-rich analogs. Most examples contain simple core structures with unsubstituted cyclopropyl moieties, and only one has been made enantioselectively. Therefore, a straightforward method to produce more complex spirocyclic amines with high stereoselectivity would be of great synthetic utility. Here, we report the stereoselective cyclopropanation of methylene-substituted saturated heterocycles catalyzed by an iridium-containing cytochrome. After just four rounds of mutagenesis, we identified a variant that forms spiroazetidines, spiropyrrolidines, and spiropiperidines with enantioselectivities up to 99%. These results demonstrate an expeditious route to valuable, rigid, sp³-rich amino acid linchpins.

We present a study of the hexagonal-close-packed Ising model for binary alloys within the cluster-variation approximation. Ground states of order stabilized by interactions that span the next-nearest-neighbor (NNN) distance (octahedron and all of its subclusters) were determined with the cluster-configuration polyhedron method. We predict 32 physically realizable ground states with stoichiometries A, AB, ${\mathit{A}}_{2}$B, ${\mathit{A}}_{3}$B, ${\mathit{A}}_{5}$B, and ${\mathit{A}}_{4}$${\mathit{B}}_{3}$. Of these structures, six are stabilized by NN pairs and eight by NNN pairs; the remaining 18 structures require multiplet interactions for their stability. The results in this study are consistent with previous pair-interaction studies. Information concerning ground states and their domains of stability was then used in conjunction with the cluster-variation method (CVM) to calculate the finite-temperature phase equilibria for prototypical binary alloys. We present ordering phase diagrams computed with the CVM that contain all relevant ground states for both isotropic and anisotropic NN pair interactions. The results of the ground-state and CVM calculations are compared with those for ordering on the face-centered-cubic lattice.

We introduce Ego4D, a massive-scale egocentric video dataset and benchmark suite. It offers 3,670 hours of dailylife activity video spanning hundreds of scenarios (household, outdoor, workplace, leisure, etc.) captured by 931 unique camera wearers from 74 worldwide locations and 9 different countries. The approach to collection is designed to uphold rigorous privacy and ethics standards, with consenting participants and robust de-identification procedures where relevant. Ego4D dramatically expands the volume of diverse egocentric video footage publicly available to the research community. Portions of the video are accompanied by audio, 3D meshes of the environment, eye gaze, stereo, and/or synchronized videos from multiple egocentric cameras at the same event. Furthermore, we present a host of new benchmark challenges centered around understanding the first-person visual experience in the past (querying an episodic memory), present (analyzing hand-object manipulation, audio-visual conversation, and social interactions), and future (forecasting activities). By publicly sharing this massive annotated dataset and benchmark suite, we aim to push the frontier of first-person perception.