Increased DNA methylation contributes to the early ripening of pear fruits during domestication and improvement.

BACKGROUND: DNA methylation is an essential epigenetic modification. However, its contribution to trait changes and diversity in the domestication of perennial fruit trees remains unknown. RESULTS: Here, we investigate the variation in DNA methylation during pear domestication and improvement using whole-genome bisulfite sequencing in 41 pear accessions. Contrary to the significant decrease during rice domestication, we detect a global increase in DNA methylation during pear domestication and improvement. We find this specific increase in pear is significantly correlated with the downregulation of Demeter-like1 (DML1, encoding DNA demethylase) due to human selection. We identify a total of 5591 differentially methylated regions (DMRs). Methylation in the CG and CHG contexts undergoes co-evolution during pear domestication and improvement. DMRs have higher genetic diversity than selection sweep regions, especially in the introns. Approximately 97% of DMRs are not associated with any SNPs, and these DMRs are associated with starch and sucrose metabolism and phenylpropanoid biosynthesis. We also perform correlation analysis between DNA methylation and gene expression. We find genes close to the hypermethylated DMRs that are significantly associated with fruit ripening. We further verify the function of a hyper-DMR-associated gene, CAMTA2, and demonstrate that overexpression of CAMTA2 in tomato and pear callus inhibits fruit ripening. CONCLUSIONS: Our study describes a specific pattern of DNA methylation in the domestication and improvement of a perennial pear tree and suggests that increased DNA methylation plays an essential role in the early ripening of pear fruits.

Sulfur-Doped rGO Aerogel Enables the Anchoring of 1T/2H MoS2 for Durable Oxygen Reduction Reaction Catalyst Support.

Durability is crucial for the long-term application of cathode oxygen reduction reaction (ORR) catalysts in fuel cells. In this work, sulfur was successfully doped into reduced graphene oxide (rGO) aerogels to achieve the formation of 1T/2H hybrid phase MoS2 , obtaining MoS2 @S-rGO-300 composite ORR catalyst support. After loading ultrafine Pt nanoparticles, Pt/MoS2 @S-rGO-300 showed not only an enhanced ORR activity, but also a significantly improved stability after 10000 cycles. The mass activity retention for Pt/MoS2 @S-rGO-300 after cycles reached 89.94 %, while that of Pt/rGO was only 37.44 %. Density functional theory calculations revealed that the enlarged binding energy between Pt atoms and MoS2 @S-rGO-300 led to the prevention of Pt agglomeration as well as Ostwald ripening.

Probing Atomic-Scale Fracture of Grain Boundaries in Low-symmetry 2D Materials.

Grain boundaries (GBs) play a central role in the fracture of polycrystals. However, the complexity of GBs and the difficulty in monitoring the atomic structure evolution during fracture greatly limit the understanding of the GB mechanics. Here, in situ aberration-corrected scanning transmission electron microscopy and density functional theory calculations are combined to investigate the fracture mechanics in low-symmetry, polycrystalline, 2D rhenium disulfide (ReS2 ), unveiling the distinctive crack behaviors at different GBs with atomic resolution. Brittle intergranular fracture prefers to rip through the GBs that are parallel to the Re chains of at least one side of the GBs. In contrast, those GBs, which do not align with Re chains on either side of the GBs, are highly resistant to fracture, impeding or deflecting the crack propagation. These results disclose the GB type-dependent mechanical failure of anisotropic 2D polycrystals, providing new ideas for material reinforcement and controllable cutting via GB engineering.

Anhydrous proton conductivity of electrospun phosphoric acid-doped PVP-PVDF nanofibers and composite membranes containing MOF fillers.

A high-temperature proton exchange membrane was fabricated based on polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) blend polymer nanofibers. Using electrospinning method, abundant small ionic clusters can be formed and agglomerated on membrane surface, which would facilitate the proton conductivity. To further enhance the conductivity, phosphoric acid (PA) retention as well as mechanical strength, sulfamic acid (SA)-doped metal-organic framework MIL-101 was incorporated into PVP-PVDF blend nanofiber membranes. As a result, the anhydrous proton conductivity of the composite SA/MIL101@PVP-PVDF membrane reached 0.237 S cm-1 at 160 °C at a moderate acid doping level (ADL) of 12.7. The construction of long-range conducting network by electrospinning method combined with hot-pressing and the synergistic effect between PVP-PVDF, SA/MIL-101 and PA all contribute to the proton conducting behaviors of this composite membrane.

Stretchable Fiber Supercapacitors with High Volumetric Performance Based on Buckled MnO2 /Oxidized Carbon Nanotube Fiber Electrodes.

A stretchable fiber supercapacitor (SC) based on buckled MnO2 /oxidized carbon nanotube (CNT) fiber electrode is fabricated by a simple prestraining-then-buckling method. The prepared stretchable fiber SC has a specific volumetric capacitance up to 409.4 F cm-3 , which is 33 times that of the pristine CNT fiber based SC, and shows the outstanding stability and repeatability in performance as a stretchable SC.

Electrochemical synthesis of palladium nanostructures with controllable morphology.

Pd nanostructures have been synthesized by electrochemical deposition in a highly diluted solution. The morphology of the as-synthesized Pd nanostructures can be solely controlled by depositing potentials because the driving force for variable crystal nucleation and growth is only correlated with overpotentials. The as-prepared Pd nanostructures deposited at -0.25 V show a 3D feather-like dendritic morphology with a nanoscale structure, which exhibits high electrocatalysis activity towards ethanol electro-oxidation in alkaline media. Moreover, the present electrochemical method can be easily applied to fabricate other noble metal nanostructures.