Summary
Anthocyanins have crucial biological functions and affect quality of horticultural produce. Anthocyanins accumulate in ripe peach fruit; differential accumulation is observed in deep coloured ...cultivar ‘Hujingmilu’ and lightly pigmented cultivar ‘Yulu’. The difference was not fully explained by accumulation of total flavonoids and expression of anthocyanin biosynthetic genes. Expression analysis was conducted on a glutathione S‐transferase gene (PpGST1), and it was found that the expression correlated well with anthocyanin accumulation in peach fruit tissues. Functional complementation of the Arabidopsis tt19 mutant indicated that PpGST1 was responsible for transport of anthocyanins but not proanthocyanidins. PpGST1 was localized in nuclei and the tonoplast, including the sites at which anthocyanin vacuolar sequestration occurred. Transient overexpression of PpGST1 together with PpMYB10.1 in tobacco leaves and peach fruit significantly increased anthocyanin accumulation as compared with PpMYB10.1 alone. Furthermore, virus‐induced gene silencing of PpGST1 in a blood‐fleshed peach not only resulted in a reduction in anthocyanin accumulation but also a decline in expression of anthocyanin biosynthetic and regulatory genes. Cis‐element analysis of the PpGST1 promoter revealed the presence of four MYB binding sites (MBSs). Dual‐luciferase assays indicated that PpMYB10.1 bound to the promoter and activated the transcription of PpGST1 by recognizing MBS1, the one closest to the ATG start codon, with this trans‐activation being stronger against the promoter of deep coloured ‘Hujingmilu’ compared with lightly coloured cultivar ‘Yulu’. Altogether, our data provided molecular evidence supporting coordinative regulatory roles of PpGST1 and PpMYB10.1 in anthocyanin accumulation in peach.
• Anthocyanin and proanthocyanidin (PA) accumulation is regulated by both myeloblastosis (MYB) activators and repressors, but little information is available on hierarchical interactions between the ...positive and negative regulators. Here, we report on a R2R3-MYB repressor in peach, designated PpMYB18, which acts as a negative regulator of anthocyanin and PA accumulation.
• PpMYB18 can be activated by both anthocyanin- and PA-related MYB activators, and is expressed both at fruit ripening and juvenile stages when anthocyanins or PAs, respectively, are being synthesized.
• The PpMYB18 protein competes with MYB activators for binding to basic Helix Loop Helixes (bHLHs), which develops a fine-tuning regulatory loop to balance PA and anthocyanin accumulation. In addition, the bHLH binding motif in the R3 domain and the C1 and C2 repression motifs in the C-terminus of PpMYB18 both confer repressive activity of PpMYB18.
• Our study also demonstrates a modifying negative feedback loop, which prevents cells from excess accumulation of anthocyanin and PAs, and serves as a model for balancing secondary metabolite accumulation at the transcriptional level.
Anthocyanin pigmentation is an important consumer trait in peach (Prunus persica). In this study, the genetic basis of the blood‐flesh trait was investigated using the cultivar Dahongpao, which shows ...high levels of cyanidin‐3‐glucoside in the mesocarp. Elevation of anthocyanin levels in the flesh was correlated with the expression of an R2R3 MYB transcription factor, PpMYB10.1. However, PpMYB10.1 did not co‐segregate with the blood‐flesh trait. The blood‐flesh trait was mapped to a 200‐kb interval on peach linkage group (LG) 5. Within this interval, a gene encoding a NAC domain transcription factor (TF) was found to be highly up‐regulated in blood‐fleshed peaches when compared with non‐red‐fleshed peaches. This NAC TF, designated BLOOD (BL), acts as a heterodimer with PpNAC1 which shows high levels of expression in fruit at late developmental stages. We show that the heterodimer of BL and PpNAC1 can activate the transcription of PpMYB10.1, resulting in anthocyanin pigmentation in tobacco. Furthermore, silencing the BL gene reduces anthocyanin pigmentation in blood‐fleshed peaches. The transactivation activity of the BL‐PpNAC1 heterodimer is repressed by a SQUAMOSA promoter‐binding protein‐like TF, PpSPL1. Low levels of PpMYB10.1 expression in fruit at early developmental stages is probably attributable to lower levels of expression of PpNAC1 plus the presence of high levels of repressors such as PpSPL1. We present a mechanism whereby BL is the key gene for the blood‐flesh trait in peach via its activation of PpMYB10.1 in maturing fruit. Partner TFs such as basic helix–loop‐helix proteins and NAC1 are required, as is the removal of transcriptional repressors.
Summary
Anthocyanins are visual cues for pollination and seed dispersal. Fruit containing anthocyanins also appeals to consumers due to its appearance and health benefits. In kiwifruit (Actinidia ...spp.) studies have identified at least two MYB activators of anthocyanin, but their functions in fruit and the mechanisms by which they act are not fully understood.
Here, transcriptome and small RNA high‐throughput sequencing were used to comprehensively identify contributors to anthocyanin accumulation in kiwifruit.
Stable overexpression in vines showed that both 35S::MYB10 and MYB110 can upregulate anthocyanin biosynthesis in Actinidia chinensis fruit, and that MYB10 overexpression resulted in anthocyanin accumulation which was limited to the inner pericarp, suggesting that repressive mechanisms underlie anthocyanin biosynthesis in this species. Furthermore, motifs in the C‐terminal region of MYB10/110 were shown to be responsible for the strength of activation of the anthocyanic response. Transient assays showed that both MYB10 and MYB110 were not directly cleaved by miRNAs, but that miR828 and its phased small RNA AcTAS4‐D4(−) efficiently targeted MYB110. Other miRNAs were identified, which were differentially expressed between the inner and outer pericarp, and cleavage of SPL13, ARF16, SCL6 and F‐box1, all of which are repressors of MYB10, was observed.
We conclude that it is the differential expression and subsequent repression of MYB activators that is responsible for variation in anthocyanin accumulation in kiwifruit species.
Summary
Anthocyanin biosynthesis is induced by low temperatures in a number of plants. However, in peach (cv Zhonghuashoutao), anthocyanin accumulation was observed in fruit stored at 16°C but not at ...or below 12°C. Fruit stored at 16°C showed elevated transcript levels of genes encoding anthocyanin biosynthetic enzymes, the transport protein glutathione S‐transferase and key transcription factors. Higher transcript levels of PpPAL1/2, PpC4H, Pp4CL4/5/8, PpF3H, PpF3’H, PpDFR1/2/3 and PpANS, as well as transcription factor gene PpbHLH3, were associated with lower methylation levels in the promoter of these genes. The DNA methylation level was further highly correlated with the expression of the DNA methyltransferase genes and DNA demethylase genes. The application of DNA methylation inhibitor 5‐azacytidine induced anthocyanin accumulation in peach flesh, further implicating a critical role for DNA demethylation in regulating anthocyanin accumulation in peach flesh. Our data reveal that temperature‐dependent DNA demethylation is a key factor to the post‐harvest temperature‐dependent anthocyanin accumulation in peach flesh.
Significance Statement
Anthocyanin accumulates at 16°C but not below 12°C in an originally white‐fleshed peach cultivar, accompanied by a global increase in transcript levels of anthocyanin biosynthetic and transcription factor genes. Elevated transcript levels are associated with decreases in DNA methylation as a result of regulating expression of DNA methyltransferase and DNA demethylase genes. The involvement of DNA demethylation in induction of anthocyanin accumulation was further confirmed using fruit treated with the DNA methylation inhibitor 5‐azacytidine.
Perovskite photovoltaics are strong potential candidates to drive low‐power off‐grid electronics for indoor applications. Compared with rigid devices, flexible perovskite devices can provide a more ...suitable surface for indoor small electronic devices, enabling them have a broader indoor application prospect. However, the mechanical stability of flexible perovskite photovoltaics is an urgent issue solved. Herein, a kind of 3D crosslinking agent named borax is selected to carry out grain boundary penetration treatment on perovskite film to realize full‐dimensional stress release. This strategy improves the mechanical and phase stabilities of perovskite films subjected to external forces or large temperature changes. The fabricated perovskite photovoltaics deliver a champion power conversion efficiency (PCE) of 21.63% under AM 1.5G illumination, which is the highest one to date. The merit of low trap states under weak light makes the devices present a superior indoor PCE of 31.85% under 1062 lux (LED, 2956 K), which is currently the best flexible perovskite indoor photovoltaic device. This work provides a full‐dimensional grain boundary stress release strategy for highly stable flexible perovskite indoor photovoltaics.
A grain boundary stress release strategy is proposed for high‐stability flexible perovskite indoor photovoltaics by the grain boundary penetration with borax 3D stretchable molecules. The full‐dimensional grain boundary stress release enables the flexible perovskite photovoltaics deliver a champion power conversion efficiency (PCE) of 21.63% under AM 1.5G illumination and an indoor PCE of 31.85% under 1062 lux.
Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution‐processed blue light‐emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability ...responsible for trap‐mediated non‐radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene‐based π‐conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky‐blue and true‐blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π‐conjugated cationic polymers have a great potential to realize efficient blue mixed‐halide perovskite LEDs with stable electroluminescence.
A fluorene‐based π‐conjugated cationic polymer as a multifunctional passivator to suppress non‐radiative processes, improve charge transport properties, and inhibit ion migration for blue mixed‐halide perovskite semiconductors, is reported. As a result, efficient and spectrally stable blue perovskite light‐emitting diodes with emission wavelengths from 485 to 458 nm are achieved.
Aggregation-caused quenching (ACQ) has long been a problem that inhibits the application of organic light-emitting materials in organic light-emitting diodes, especially near-infrared (NIR) ...materials. Figuring out the reasons that induce ACQ is important for the quantum efficiency enhancement of NIR materials. In this paper, an NIR molecule (TPA-QCN) with thermally activated delayed fluorescence (TADF) is studied based on first-principles calculations and excited-state dynamics investigation in both toluene and in the aggregation state. Our calculation indicates that aggregation can induce a smaller energy gap between the first singlet excited state and the first triplet excited state, which is favorable for TADF. Both the decreased fluorescent rate and the increased nonradiative rate will induce emission quenching in the aggregation state. Based on detailed analyses of the reorganization energy and intermolecular interaction, we find that the hydrogen bond will induce enhanced contribution to the reorganization energy from C–H stretching vibration modes and thus a larger nonradiative rate in the aggregation state than in toluene. A new mechanism of ACQ is proposed, and it could help in the design of new types of NIR-TADF molecules with enhanced fluorescence efficiency.
The control of plant anthocyanin accumulation is via transcriptional regulation of the genes encoding the biosynthetic enzymes. A key activator appears to be an R2R3 MYB transcription factor. In ...apple fruit, skin anthocyanin levels are controlled by a gene called MYBA or MYB1, while the gene determining fruit flesh and foliage anthocyanin has been termed MYB10. In order to further understand tissue-specific anthocyanin regulation we have isolated orthologous MYB genes from all the commercially important rosaceous species.
We use gene specific primers to show that the three MYB activators of apple anthocyanin (MYB10/MYB1/MYBA) are likely alleles of each other. MYB transcription factors, with high sequence identity to the apple gene were isolated from across the rosaceous family (e.g. apples, pears, plums, cherries, peaches, raspberries, rose, strawberry). Key identifying amino acid residues were found in both the DNA-binding and C-terminal domains of these MYBs. The expression of these MYB10 genes correlates with fruit and flower anthocyanin levels. Their function was tested in tobacco and strawberry. In tobacco, these MYBs were shown to induce the anthocyanin pathway when co-expressed with bHLHs, while over-expression of strawberry and apple genes in the crop of origin elevates anthocyanins.
This family-wide study of rosaceous R2R3 MYBs provides insight into the evolution of this plant trait. It has implications for the development of new coloured fruit and flowers, as well as aiding the understanding of temporal-spatial colour change.
The generation of photoinduced defects and freely moving halogen ions is dynamically updated in real time. Accordingly, most reported strategies are static and short‐term, which make their ...improvements in photostability very limited. Therefore, seeking new passivation strategies to match the dynamic characteristics of defect generation is very urgent. Without newly generated defects, a passivation molecule should exist in the configuration that would not become the initiation sites for defect generation. With newly generated defects, the passivation molecule should transfer into the other configuration that possesses the passivation sites. Herein, a classical photoisomeric molecule, spiropyran, is adopted, whose pre‐ and post‐isomeric forms meet the requirements for two different configurations, to realize the state transition once the photoinduced defects appear during subsequent operation and dynamic capture for continuous renewal of defects. Consequently, spiropyrans work as light‐triggered and self‐healing sustainable passivation sites to realize continuous defect repair. The target devices retain 93% and 99% of their initial power conversion efficiencies after 456 h aging under ultraviolet illumination and 1200 h aging under full‐spectrum illumination, respectively. This work provides a novel concept of sustainable passivation strategy to realize continuous defect‐passivation and film‐healing in perovskite photovoltaics.
A sustainable dynamic passivation strategy by incorporating a photoisomeric molecule is put forward, which greatly enhances the photostability of perovskite photovoltaics. This dynamic strategy pays attention to and well matches the dynamics of defect generation during operation. The characteristics of the changeable molecular structure enable us to cope with defects updated in operation without introducing excess active sites.
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