miRNAs are present in both plant and animal kingdoms. An evolutionarily conserved mechanism involving a protein, known as Dicer in animals and CAF in Arabidopsis, operates in miRNA metabolism. HEN1 is a new player in miRNA accumulation in Arabidopsis, and HEN1 homologs in metazoans may have a similar function. The developmental defects associated with caf-1 and hen1-1 mutations and the patterns of miRNA accumulation suggest that miRNAs play fundamental roles in plant development.

We reported that atomically dispersed Pd on graphene can be fabricated using the atomic layer deposition technique. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy both confirmed that isolated Pd single atoms dominantly existed on the graphene support. In selective hydrogenation of 1,3-butadiene, the single-atom Pd1/graphene catalyst showed about 100% butenes selectivity at 95% conversion at a mild reaction condition of about 50 °C, which is likely due to the changes of 1,3-butadiene adsorption mode and enhanced steric effect on the isolated Pd atoms. More importantly, excellent durability against deactivation via either aggregation of metal atoms or carbonaceous deposits during a total 100 h of reaction time on stream was achieved. Therefore, the single-atom catalysts may open up more opportunities to optimize the activity, selectivity, and durability in selective hydrogenation reactions.

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Small RNAs of 21-25 nucleotides (nt), including small interfering RNAs (siRNAs) and microRNAs (miRNAs), act as guide RNAs to silence target-gene expression in a sequence-specific manner. In addition to a Dicer homolog, DCL1, the biogenesis of miRNAs in Arabidopsis requires another protein, HEN1. miRNAs are reduced in abundance and increased in size in hen1 mutants. We found that HEN1 is a miRNA methyltransferase that adds a methyl group to the 3'-most nucleotide of miRNAs, but the role of miRNA methylation was unknown. Here, we show that siRNAs from sense transgenes, hairpin transgenes, and transposons or repeat sequences, as well as a new class of siRNAs known as trans-acting siRNAs, are also methylated in vivo by HEN1. In addition, we show that the size increase of small RNAs in the hen1-1 mutant is due to the addition of one to five U residues to the 3' ends of the small RNAs. Therefore, a novel uridylation activity targets the 3' ends of unmethylated miRNAs and siRNAs in hen1 mutants. We conclude that 3'-end methylation is a common step in miRNA and siRNA metabolism and likely protects the 3' ends of the small RNAs from the uridylation activity.

A porous MoO2 nanosheet as an active and stable bifunctional electrocatalyst for overall water splitting, is presented. It needs a cell voltage of only about 1.53 V to achieve a current density of 10 mA cm(-2) and maintains its activity for at least 24 h in a two-electrode configuration.

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Developing an active and stable metal single-atom catalyst (SAC) is challenging due to the high surface free energy of metal atoms. In this work, we report that tailoring of the 5d state of Pt1 single atoms on Co3O4 through strong electronic metal–support interactions (EMSIs) boosts the activity up to 68-fold higher than those on other supports in dehydrogenation of ammonia borane for room-temperature hydrogen generation. More importantly, this catalyst also exhibits excellent stability against sintering and leaching, in sharp contrast to the rapid deactivation observed on other Pt single-atom and nanoparticle catalysts. Detailed spectroscopic characterization and theoretical calculations revealed that the EMSI tailors the unoccupied 5d state of Pt1 single atoms, which modulates the adsorption of ammonia borane and facilities hydrogen desorption, thus leading to the high activity. Such extraordinary electronic promotion was further demonstrated on Pd1/Co3O4 and in hydrogenation reactions, providing a new promising way to design advanced SACs with high activity and stability.

Supported metal clusters containing only a few atoms are of great interest. Progress has been made in synthesis of metal single-atom catalysts. However, precise synthesis of metal dimers on high-surface area support remains a grand challenge. Here, we show that Pt2 dimers can be fabricated with a bottom–up approach on graphene using atomic layer deposition, through proper nucleation sites creation, Pt1 single-atom deposition and attaching a secondary Pt atom selectively on the preliminary one. Scanning transmission electron microscopy, x-ray absorption spectroscopy, and theoretical calculations suggest that the Pt2 dimers are likely in the oxidized form of Pt2Ox. In hydrolytic dehydrogenation of ammonia borane, Pt2 dimers exhibit a high specific rate of 2800 molH2 molPt −1 min−1 at room temperature, ~17- and 45-fold higher than graphene supported Pt single atoms and nanoparticles, respectively. These findings open an avenue to bottom–up fabrication of supported atomically precise ultrafine metal clusters for practical applications.