Synthesis of dual-modified Fe-doped and carbon-coated Li4Ti5O12 anode based on industrial H2TiO3 for Li-ion batteries.

Spinel Li4Ti5O12 (LTO) is a promising candidate for lithium-ion battery anodes because of its exceptional stability and safety. However, its extensive application is limited by a high comprehensive cost, poor electronic conductivity, and other inherent defects. This work presents a novel synthesis procedure to synthesize carbon-coated Fe-doped LTO composites through carbon reduction, in the presence of Fe-containing industrial H2TiO3 as the titanium source, and glucose as the carbon source. The presence of the Fe-dopant is confirmed through XRD, with Rietveld refinement and EDS experiments. Results show that Fe2+ replaces a portion of Ti4+ after doping, leading to an increase in the LTO cell parameters and the corresponding cell volume. FLTO/C, presents a capacity of 153.79 mAh g-1 at 10 C, and the capacity decay per cycle is only 0.0074% after 1000 cycles at 5 C. Moreover, EIS experiments indicate that the incorporation of Fe and carbon lowers the charge transfer resistance and improves the diffusion and migration of Li+. Notably, since this preparation process requires no additional Fe source as a raw material, it is simple, cost-effective, and suitable for large-scale production and further application.

Corrigendum: Research progress and trends in metabolomics of fruit trees.

[This corrects the article DOI: 10.3389/fpls.2022.881856.].

Research Progress and Trends in Metabolomics of Fruit Trees.

Metabolomics is an indispensable part of modern systems biotechnology, applied in the diseases' diagnosis, pharmacological mechanism, and quality monitoring of crops, vegetables, fruits, etc. Metabolomics of fruit trees has developed rapidly in recent years, and many important research results have been achieved in combination with transcriptomics, genomics, proteomics, quantitative trait locus (QTL), and genome-wide association study (GWAS). These research results mainly focus on the mechanism of fruit quality formation, metabolite markers of special quality or physiological period, the mechanism of fruit tree's response to biotic/abiotic stress and environment, and the genetics mechanism of fruit trait. According to different experimental purposes, different metabolomic strategies could be selected, such as targeted metabolomics, non-targeted metabolomics, pseudo-targeted metabolomics, and widely targeted metabolomics. This article presents metabolomics strategies, key techniques in metabolomics, main applications in fruit trees, and prospects for the future. With the improvement of instruments, analysis platforms, and metabolite databases and decrease in the cost of the experiment, metabolomics will prompt the fruit tree research to achieve more breakthrough results.

Exogenous gibberellin treatment improves fruit quality in self-pollinated apple.

Although a few apple (Malus × ×domestica) varieties are self-compatible, little is known about the differences in fruit quality between self- and cross-pollinated apple. In our current study, we compared the fruit quality of self-pollinated apple plants (cultivar 'Hanfu') in self-pollination or cross-pollinated by another cultivar 'Qinguan'. Analysis of fruit quality revealed substantial differences in the external qualities between self- and cross-pollinated apple fruit, but not in the internal qualities. Fruits harvested from self-pollinated 'Hanfu' were smaller and more asymmetrical than those harvested from the cross-pollinated plants. We developed a mathematical model describing how seed number and distribution affect fruit growth. According to this model, the fewer the seeds, the greater the force released from the seeds and the more asymmetrical the fruit. Detection of endogenous hormone and the associated gene expression revealed that gibberellin (GA) levels and GA transporter gene expression on the seedless side were significantly lower than those on the seeded side. Analysis of fruit pectin methylesterase activity and demethylated pectin levels indicated that the lack of GA limits fruit cell wall extension. Additionally, spraying the self-pollinating plants with gibberellic acid increased the fruit weight and lowered the proportion of asymmetrical fruit, recovering the exterior fruit quality to that of the cross-pollinated fruit. Furthermore, exogenous GA treatment increased the wax layer thickness and reduced the fruit water loss rate, leading to a dramatic improvement in fruit storage capacity. Therefore, exogenous GA treatment could be used to ensure regular fruit production of self-pollinated 'Hanfu'.

The apple MdPTI1L kinase is phosphorylated by MdOXI1 during S-RNase-induced reactive oxygen species signaling in pollen tubes.

Apple (Malus domestica) exhibits classic S-RNase-mediated gametophytic self-incompatibility. Previous studies have shown that the S-RNase secreted from style cells could trigger signal transduction and defense responses mediated by Ca2+ and reactive oxygen species (ROS) after entering into the pollen tube. In this study, we investigated the downstream genes activated by ROS during S-RNase-mediated gametophytic self-incompatibility in pollen tubes. A substantial increase in ROS, as well as up-regulated expression of a serine-threonine protein kinase gene, OXIDATIVE SIGNAL-INDUCIBLE1 (MdOXI1), was detected in apple pollen tubes treated with self-S-RNase. A kinase assay-linked phosphoproteomics (KALIP) analysis suggested that MdOXI1 could bind and phosphorylate the downstream protein kinase Pto-interacting protein 1-like (MdPTI1L). The phosphorylation level of MdPTI1L was significantly reduced after silencing MdOXI1 with antisense oligonucleotides in the pollen tube. Silencing of either MdOXI1 or MdPTI1L alleviated the inhibitory effect of self-S-RNase on pollen tube growth. Our results thus indicate that MdPTI1L is phosphorylated by MdOXI1 in the pollen tube and participates in the ROS signaling pathway triggered by S-RNase.

Ubiquitination of S4-RNase by S-LOCUS F-BOX LIKE2 Contributes to Self-Compatibility of Sweet Cherry 'Lapins'.

Recent studies have shown that loss of pollen-S function in S4' pollen from sweet cherry (Prunus avium) is associated with a mutation in an S haplotype-specific F-box4 (SFB4) gene. However, how this mutation leads to self-compatibility is unclear. Here, we examined this mechanism by analyzing several self-compatible sweet cherry varieties. We determined that mutated SFB4 (SFB4') in S4' pollen (pollen harboring the SFB4' gene) is approximately 6 kD shorter than wild-type SFB4 due to a premature termination caused by a four-nucleotide deletion. SFB4' did not interact with S-RNase. However, a protein in S4' pollen ubiquitinated S-RNase, resulting in its degradation via the 26S proteasome pathway, indicating that factors in S4' pollen other than SFB4 participate in S-RNase recognition and degradation. To identify these factors, we used S4-RNase as a bait to screen S4' pollen proteins. Our screen identified the protein encoded by S 4 -SLFL2, a low-polymorphic gene that is closely linked to the S-locus. Further investigations indicate that SLFL2 ubiquitinates S-RNase, leading to its degradation. Subcellular localization analysis showed that SFB4 is primarily localized to the pollen tube tip, whereas SLFL2 is not. When S 4 -SLFL2 expression was suppressed by antisense oligonucleotide treatment in wild-type pollen tubes, pollen still had the capacity to ubiquitinate S-RNase; however, this ubiquitin-labeled S-RNase was not degraded via the 26S proteasome pathway, suggesting that SFB4 does not participate in the degradation of S-RNase. When SFB4 loses its function, S4-SLFL2 might mediate the ubiquitination and degradation of S-RNase, which is consistent with the self-compatibility of S4' pollen.

A mutation near the active site of S-RNase causes self-compatibility in S-RNase-based self-incompatible plants.

KEY MESSAGE: The structurally simplest amino acid glycine could make contribution to nuclease activity of S-RNase and self-incompatibility in S-RNase-based plants. S-RNase is regarded as inhibitor of self-pollen tube in S-RNase-based self-incompatibility plants. Certain residues like histidine are necessary for RNase activity and self-incompatibility; however, it is unknown whether any other residues contribute to this. Previously, we identified an association between the self-compatible Chinese pear (Pyrus × bretschneideri) cultivar 'Yanzhuang' (YZ) and a mutation causing a residue shift (glycine-to-valine) in the 2nd conserved region (C2) of S21-RNase; however, it was unclear how this nonpolar aliphatic amino acid substitution caused self-compatibility. In this study, we observed that 'YZ' offspring were self-compatible when S21-RNases were all mutated. In vitro pollen tube (S21S21) growth was not completely arrested by the mutated S21-RNase. Residue frequency analysis showed that the glycine residue is highly conserved in diverse S-RNases across many plant species. We therefore generated a mutated petunia SV'-RNase (glycine to valine) and transformed it into S3LS3L petunia. The transformed pistil could not inhibit SV pollen tubes. Three-dimensional protein prediction suggested that the glycine-to-valine mutation alters the spatial structure near the active site, and RNase activity of mutated S-RNase was reducing. Thus, the glycine residue in the C2 is essential for RNase activity, substitution of this residue leads to a failure of self-incompatibility.

Functional identification of lncRNAs in sweet cherry (Prunus avium) pollen tubes via transcriptome analysis using single-molecule long-read sequencing.

Sweet cherry (Prunus avium) is a popular fruit with high nutritional value and excellent flavor. Although pollen plays an important role in the double fertilization and subsequent fruit production of this species, little is known about its pollen tube transcriptome. In this study, we identified 16,409 transcripts using single-molecule sequencing. After filtering 292 transposable elements, we conducted further analyses including mRNA classification, gene function prediction, alternative splicing (AS) analysis, and long noncoding RNA (lncRNA) identification to gain insight into the pollen transcriptome. The filtered transcripts could be matched with 3,438 coding region sequences from the sweet cherry genome. GO and KEGG analyses revealed complex biological processes during pollen tube elongation. A total of 2043 AS events were predicted, 7 of which were identified in different organs, such as the leaf, pistil and pollen tube. Using BLASTnt and the Coding-Potential Assessment Tool (CPAT), we distinguished a total of 284 lncRNAs, among which 154 qualified as natural antisense transcripts (NATs). As the NATs could be the reverse complements of coding mRNA sequences, they might bind to coding sequences. Antisense transfection assays showed that the NATs could regulate the expression levels of their complementary sequences and even affect the growth conditions of pollen tubes. In summary, this research characterizes the transcripts of P. avium pollen and lays the foundation for elucidating the physiological and biochemical mechanisms underlying sexual reproduction in the male gametes of this species.

Atomic Simulations of Grain Structures and Deformation Behaviors in Nanocrystalline CoCrFeNiMn High-Entropy Alloy.

Using the molecular dynamics method, the melting character, mechanical properties, microstructures, and strain deformation mechanisms of nanocrystalline CoCrFeNiMn high-entropy alloy are systematically investigated in the present work. The simulation results suggest that the melting point in CoCrFeNiMn high-entropy alloy decreases with the grain size, decreasing from 3.6 to 2.0 nm. The grain size has a significant effect on shear and Young's modulus compared to bulk modulus. The stress-strain simulation demonstrates that the ultimate tensile strength decreases with the decrease of the grain size, while the plastic deformation increases with the decrease in grain size. While the average grain size decreases to 2.0 nm, the amorphization induced by small grain size reduces plastic deformation. The common neighbor analysis shows that the face-centered cubic (FCC) composition of CoCrFeNiMn decreases gradually with decreasing grain size. For the sample with a grain size of 2.0 nm, the FCC composition is about 19% at a strain of 20%, accompanied by severe amorphization. The inverse Hall-Petch effect is observed for nanocrystalline CoCrFeNiMn high-entropy alloy in the present simulations. The atomic snapshot of CoCrFeNiMn with a grain size of 2.0 nm under the uniaxial strain confirms that the grain shape change, stacking fault formation, and amorphization are important mechanisms of plastic deformation in nanocrystalline high-entropy CoCrFeNiMn.

Proton-Driven Intercalation and Ion Substitution Utilizing Solid-State Electrochemical Reaction.

The development of an unconventional synthesis method has a large potential to drastically advance materials science. In this research, a new synthesis method based on a solid-state electrochemical reaction was demonstrated, which can be made available for intercalation and ion substitution. It was referred to as proton-driven ion introduction (PDII). The protons generated by the electrolytic dissociation of hydrogen drive other monovalent cations along a high electric field in the solid state. Utilizing this mechanism, Li+, Na+, K+, Cu+, and Ag+ were intercalated into a layered TaS2 single crystal while maintaining high crystallinity. This liquid-free process of ion introduction allows the application of high voltage around several kilovolts to the sample. Such a high electric field strongly accelerates ion substitution. Actually, compared to conventional solid-state reaction, PDII introduced 15 times the amount of K into Na super ionic conductor (NASICON)-structured Na3-xKxV2(PO4)3. The obtained materials exhibited a thermodynamically metastable phase, which has not been reported so far. This concept and idea for ion introduction is expected to form new functional compounds and/or phases.

Md-miR156ab and Md-miR395 Target WRKY Transcription Factors to Influence Apple Resistance to Leaf Spot Disease.

MicroRNAs (miRNAs) are key regulators of gene expression that post-transcriptionally regulate transcription factors involved in plant physiological activities. Little is known about the effects of miRNAs in disease resistance in apple (Malus×domestica). We globally profiled miRNAs in the apple cultivar Golden Delicious (GD) infected or not with the apple leaf spot fungus Alternaria alternaria f. sp. mali (ALT1), and identified 58 miRNAs that exhibited more than a 2-fold upregulation upon ALT1 infection. We identified a pair of miRNAs that target protein-coding genes involved in the defense response against fungal pathogens; Md-miR156ab targets a novel WRKY transcription factor, MdWRKYN1, which harbors a TIR and a WRKY domain. Md-miR395 targets another transcription factor, MdWRKY26, which contains two WRKY domains. Real-time PCR analysis showed that Md-miR156ab and Md-miR395 levels increased, while MdWRKYN1 and MdWRKY26 expression decreased in ALT1-inoculated GD leaves; furthermore, the overexpression of Md-miR156ab and Md-miR395 resulted in a significant reduction in MdWRKYN1 and MdWRKY26 expression. To investigate whether these miRNAs and their targets play a crucial role in plant defense, we overexpressed MdWRKYN1 or knocked down Md-miR156ab activity, which in both cases enhanced the disease resistance of the plants by upregulating the expression of the WRKY-regulated pathogenesis-related (PR) protein-encoding genes MdPR3-1, MdPR3-2, MdPR4, MdPR5, MdPR10-1, and MdPR10-2. In a similar analysis, we overexpressed MdWRKY26 or suppressed Md-miR395 activity, and found that many PR protein-encoding genes were also regulated by MdWRKY26. In GD, ALT-induced Md-miR156ab and Md-miR395 suppress MdWRKYN1 and MdWRKY26 expression, thereby decreasing the expression of some PR genes, and resulting in susceptibility to ALT1.

Malus domestica ADF1 severs actin filaments in growing pollen tubes.

A dynamic actin cytoskeleton is essential for pollen tube growth and germination. However, the molecular mechanism that determines the organisation of the actin cytoskeleton in pollen remains poorly understood. ADF modulates the structure and dynamics of actin filaments and influences the higher-order organisation of the actin cytoskeleton in eukaryotic cells. Members of the ADF family have been shown to have important functions in pollen tube growth. However, the role of this gene family remains largely unknown in apple (Malus domestica Borkh.). In this study, we identified seven ADFs in the apple genome. Phylogenetic analysis showed that MdADF1 clusters with Arabidopsis thaliana (L.) Heynh. AtADF7, ADF8, ADF10 and AtADF11. We performed sequence alignments and analysed the domain structures of the seven MdADF proteins and identified the chromosome locations of the encoding genes. We cloned the gene encoding MdADF1 from 'Ralls Janet' apple and found that it was strongly expressed in pollen. Biochemical assays revealed that MdADF1 directly bound to and severed F-actin under low Ca2+ conditions. We demonstrated that knockdown of MdADF1 inhibited pollen tube growth and reduced the pollen germination rate, but rendered the pollen insensitive to treatment with Latrunculin B, an actin depolymerising agent. Taken together, our results provide insight into the function of MdADF1 and serve as a reference for studies of ADF in other plants.

Molecular and genetic characterization of a self-compatible apple cultivar, 'CAU-1'.

In this study, we characterized a naturally occurring self-compatible apple cultivar, 'CAU-1' (S1S9), and studied the underlying mechanism that causes its compatibility. Analyses of both fruit set rate and seed number after self-pollination or cross-pollination with 'Fuji' (S1S9), and of pollen tube growth, demonstrated that 'CAU-1' is self-compatible. Genetic analysis by S-RNase PCR-typing of selfed progeny of 'CAU-1' revealed the presence of all progeny classes (S1S1, S1S9, and S9S9). Moreover, no evidence of S-allele duplication was found. These findings support the hypothesis that loss of function of an S-locus unlinked pollen-part mutation (PPM) expressed in pollen, rather than a natural mutation in the pollen-S gene (S1- and S9- haplotype), leads to SI breakdown in 'CAU-1'. In addition, there were no significant differences in pollen morphology or fertility between 'Fuji' and 'CAU-1'. However, we found that the effect of S1- and S9-RNase on the SI behavior of pollen could not be addressed better in 'CAU-1' than in 'Fuji'. Furthermore, we found that a pollen-expressed hexose transporter, MdHT1, interacted with S-RNases and showed significantly less expression in 'CAU-1' than in 'Fuji' pollen tubes. These findings support the hypothesis that MdHT1 may participate in S-RNase internalization during the SI process, and decrease of MdHT1 expression in 'CAU-1' hindered the release of self S-RNase into the cytoplasm of pollen tubes, thereby protecting pollen from the cytotoxicity of S-RNase, finally probably resulting in self-compatibility. Together, these findings indicate that S-locus external factors are required for gametophytic SI in the Rosaceae subtribe Pyrinae.