Preparation of amphiphilic polyquaternium nanofiber films with antibacterial activity via environmentally friendly microfluidic-blow-spinning for green food packaging applications

Green food packaging plays an important role in environmental protection and sustainable development. Therefore, it is advisable to employ low-energy consumption manufacturing techniques, select environmentally friendly materials, and focus on cost-effectiveness with high production yields during the production process. In this study, an amphiphilic polyquaternium called PBzCl was proposed and synthesized by free radical polymerization of cost-efficient quaternary ammonium salts and methacrylate monomers. Then, biodegradable PCL and PVP were used to rapidly prepare the PBzCl@PCL/PVP nanofiber films via environmentally friendly microfluidic-blow-spinning (MBS). The best antibacterial effect was observed at a PBzCl loading concentration of 13.5%, and the PBzCl@PCL/PVP nanofiber films had 91% and 100% antibacterial rates against Escherichia coli and Staphylococcus aureus, respectively. Besides, the loading of PBzCl improved the water stability of the PCL/PVP nanofiber films, and the films also showed excellent biocompatibility. Overall, PBzCl@PCL/PVP nanofibre films have promising food packaging potential.

Methyl jasmonate-loaded composite biofilm sustainably alleviates chilling lignification of loquat fruit during postharvest storage

In this work, the MeJA-loaded gelatin/pullulan/chitosan composite biofilm was prepared to inhibit the chilling lignification of the loquat fruit during storage at 0 °C. The firmness and lignin content were decreased by 89 % and 81.77 % after MeJA-loaded biofilm treatment. Malondialdehyde (MDA) production was almost completely suppressed and chilling injury of loquat fruit was significantly reduced. Enzyme activity results show that the biofilm alleviated chilling lignification mainly by inhibiting peroxidase (POD) activity in the phenylpropanoid pathway (PCCs = 0.715, with lignin content). Also, the conventional MeJA vapor treatment only alleviated lignification on day 3, but the biofilm treatment had a better and more sustained effect throughout the whole storage due to its sustained release ability. Besides, the biofilm had good mechanical properties, transparency and water vapor transmission rate. This work indicates that loading preservatives into biofilms has a promising application prospect for inhibiting the postharvest quality deterioration of fruit and vegetables.

Fabrication of antimicrobial PCL/EC nanofibrous films containing natamycin and trans-cinnamic acid by microfluidic blow spinning for fruit preservation

Fruit is susceptible to various postharvest pathogens; thus, the development of multifunctional preservation materials that can achieve the broad-spectrum inhibition of different pathogens is a current research hotspot. Here, microfluidic blow spinning was used to create a biodegradable polycaprolactone/ethyl cellulose (PCL/EC) nanofibrous film that incorporated two naturally-sourced compounds, natamycin and trans-cinnamic acid, resulting in multi-microbial inhibition. The PCL/EC-based film had a smooth and even morphology, indicating the favorable integration of PCL and EC. After the incorporation of ingredients, the film exhibited good inhibitory activity against Escherichia coli, Staphylococcus aureus, and Botrytis cinerea, and it had finer fiber diameters, higher permeability, and antioxidant properties. We further demonstrated that strawberries that were padded with the film had good resistance to Botrytis cinerea. Also, the film did not interference with the qualities of the strawberries during storage. The study demonstrates a promising application for multi-antimicrobial and bio-friendly packaging materials in postharvest fruit preservation.

MYB transcription factors encoded by diversified tandem gene clusters cause varied Morella rubra fruit color

Chinese bayberry (Morella rubra) is a fruit tree with a remarkable variation in fruit color, ranging from white to dark red as determined by anthocyanin content. In dark red "Biqi" (BQ), red "Dongkui" (DK), pink "Fenhong" (FH), and white "Shuijing" (SJ), we identified an anthocyanin-related MYB transcription factor-encoding gene cluster of four members, i.e. MrMYB1.1, MrMYB1.2, MrMYB1.3, and MrMYB2. Collinear analysis revealed that the MYB tandem cluster may have occurred in a highly conserved region of many eudicot genomes. Two alleles of MrMYB1.1 were observed; MrMYB1.1-1 (MrMYB1.1n) was a full-length allele and homozygous in "BQ", MrMYB1.1-2 (MrMYB1.1d) was a nonfunctional allele with a single base deletion and homozygous in "SJ", and MrMYB1.1n/MrMYB1.1d were heterozygous in "DK" and "FH". In these four cultivars, expression of MrMYB1.1, MrMYB1.2, and MrMYB2 was enhanced during ripening. Both alleles were equally expressed in MrMYB1.1n/MrMYB1.1d heterozygous cultivars as revealed by a cleaved amplified polymorphic sequence marker. Expression of MrMYB1.3 was restricted to some dark red cultivars only. Functional characterization revealed that MrMYB1.1n and MrMYB1.3 can induce anthocyanin accumulation while MrMYB1.1d, MrMYB1.2, and MrMYB2 cannot. DNA-protein interaction assays indicated that MrMYB1.1n and MrMYB1.3 can directly bind to and activate the promoters of anthocyanin-related genes via interaction with a MYC-like basic helix-loop-helix protein MrbHLH1. We concluded that the specific genotype of MrMYB1.1 alleles, as well as the exclusive expression of MrMYB1.3 in some dark red cultivars, contributes to fruit color variation. The study provides insights into the mechanisms for regulation of plant anthocyanin accumulation by MYB tandem clusters.

A signaling cascade mediating fruit trait development via phosphorylation-modulated nuclear accumulation of JAZ repressor

It is generally accepted that jasmonate-ZIM domain (JAZ) repressors act to mediate jasmonate (JA) signaling via CORONATINE-INSENSITIVE1 (COI1)-mediated degradation. Here, we report a cryptic signaling cascade where a JAZ repressor, FvJAZ12, mediates multiple signaling inputs via phosphorylation-modulated subcellular translocation rather than the COI1-mediated degradation mechanism in strawberry (Fragaria vesca). FvJAZ12 acts to regulate flavor metabolism and defense response, and was found to be the target of FvMPK6, a mitogen-activated protein kinase that is capable of responding to multiple signal stimuli. FvMPK6 phosphorylates FvJAZ12 at the amino acid residues S179 and T183 adjacent to the PY residues, thereby attenuating its nuclear accumulation and relieving its repression for FvMYC2, which acts to control the expression of lipoxygenase 3 (FvLOX3), an important gene involved in JA biosynthesis and a diverse array of cellular metabolisms. Our data reveal a previously unreported mechanism for JA signaling and decipher a signaling cascade that links multiple signaling inputs with fruit trait development.

Transcriptional regulation of flavonol biosynthesis in plants

Flavonols are a class of flavonoids that play a crucial role in regulating plant growth and promoting stress resistance. They are also important dietary components in horticultural crops due to their benefits for human health. In past decades, research on the transcriptional regulation of flavonol biosynthesis in plants has increased rapidly. This review summarizes recent progress in flavonol-specific transcriptional regulation in plants, encompassing characterization of different categories of transcription factors (TFs) and microRNAs as well as elucidation of different transcriptional mechanisms, including direct and cascade transcriptional regulation. Direct transcriptional regulation involves TFs, such as MYB, AP2/ERF, and WRKY, which can directly target the key flavonol synthase gene or other early genes in flavonoid biosynthesis. In addition, different regulation modules in cascade transcriptional regulation involve microRNAs targeting TFs, regulation between activators, interaction between activators and repressors, and degradation of activators or repressors induced by UV-B light or plant hormones. Such sophisticated regulation of the flavonol biosynthetic pathway in response to UV-B radiation or hormones may allow plants to fine-tune flavonol homeostasis, thereby balancing plant growth and stress responses in a timely manner. Based on orchestrated regulation, molecular design strategies will be applied to breed horticultural crops with excellent health-promoting effects and high resistance.

Transcription factor PpNAC1 and DNA demethylase PpDML1 synergistically regulate peach fruit ripening

Fruit ripening is accompanied by dramatic changes in color, texture, and flavor and is regulated by transcription factors (TFs) and epigenetic factors. However, the detailed regulatory mechanism remains unclear. Gene expression patterns suggest that PpNAC1 (NAM/ATAF1/2/CUC) TF plays a major role in peach (Prunus persica) fruit ripening. DNA affinity purification (DAP)-seq combined with transactivation tests demonstrated that PpNAC1 can directly activate the expression of multiple ripening-related genes, including ACC synthase1 (PpACS1) and ACC oxidase1 (PpACO1) involved in ethylene biosynthesis, pectinesterase1 (PpPME1), pectate lyase1 (PpPL1), and polygalacturonase1 (PpPG1) related to cell wall modification, and lipase1 (PpLIP1), fatty acid desaturase (PpFAD3-1), and alcohol acyltransferase1 (PpAAT1) involved in volatiles synthesis. Overexpression of PpNAC1 in the tomato (Solanum lycopersicum) nor (nonripening) mutant restored fruit ripening, and its transient overexpression in peach fruit induced target gene expression, supporting a positive role of PpNAC1 in fruit ripening. The enhanced transcript levels of PpNAC1 and its target genes were associated with decreases in their promoter mCG methylation during ripening. Declining DNA methylation was negatively associated with increased transcripts of DNA demethylase1 (PpDML1), whose promoter is recognized and activated by PpNAC1. We propose that decreased methylation of the promoter region of PpNAC1 leads to a subsequent decrease in DNA methylation levels and enhanced transcription of ripening-related genes. These results indicate that positive feedback between PpNAC1 and PpDML1 plays an important role in directly regulating expression of multiple genes required for peach ripening and quality formation.

Expansin SlExp1 and endoglucanase SlCel2 synergistically promote fruit softening and cell wall disassembly in tomato

Fruit softening, an irreversible process that occurs during fruit ripening, can lead to losses and waste during postharvest transportation and storage. Cell wall disassembly is the main factor leading to loss of fruit firmness, and several ripening-associated cell wall genes have been targeted for genetic modification, particularly pectin modifiers. However, individual knockdown of most cell wall-related genes has had minimal influence on cell wall integrity and fruit firmness, with the notable exception of pectate lyase. Compared to pectin disassembly, studies of the cell wall matrix, the xyloglucan-cellulose framework, and underlying mechanisms during fruit softening are limited. Here, a tomato (Solanum lycopersicum) fruit ripening-associated α-expansin (SlExpansin1/SlExp1) and an endoglucanase (SlCellulase2/SlCel2), which function in the cell wall matrix, were knocked out individually and together using clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing. Simultaneous knockout of SlExp1 and SlCel2 enhanced fruit firmness, reduced depolymerization of homogalacturonan-type pectin and xyloglucan, and increased cell adhesion. In contrast, single knockouts of either SlExp1 or SlCel2 did not substantially change fruit firmness, while simultaneous overexpression of SlExp1 and SlCel2 promoted early fruit softening. Collectively, our results demonstrate that SlExp1 and SlCel2 synergistically regulate cell wall disassembly and fruit softening in tomato.

Carboxymethyl chitosan and polycaprolactone-based rapid in-situ packaging for fruit preservation by solution blow spinning

Nanofiber packaging has not yet gained practical application in fruit preservation because of some limitations, such as low production rate and utilization, and failure due to poor adhesion to the fruit. Herein, to solve this issue, a novel fruit packaging method based on solution blow spinning (SBS), called in-situ packaging, was pioneered. Specifically, carboxymethyl chitosan (CMCH) and polycaprolactone (PCL) were chosen as substrate materials and cherry tomatoes were selected as demonstration subjects. CMCH/PCL nanofibers were deposited directly onto the surface of cherry tomatoes by SBS, forming a tightly adherent and stable fiber coating in 8 min. Also, this in-situ packaging could be easily peeled off by hand. The in-situ packaging was an excellent carrier for active substances and was effective in inhibiting gray mold on cherry tomatoes. The in-situ packaging film formed a barrier on the surface of cherry tomatoes to limit moisture penetration, resulting in reduced respiration of fruits, which led to reduced weight and firmness loss. In addition, metabolomics and color analysis revealed that the in-situ packaging delayed ripening of cherry tomatoes after harvest. Overall, the in-situ packaging method developed in the present work provides a new solution for post-harvest fruit preservation.

Comprehensive analysis of transcriptome and metabolome provides insights into the stress response mechanisms of apple fruit to postharvest impact damage

An integrated analysis of the transcriptome and metabolome was conducted to investigate the underlying mechanisms of apple fruit response to impact damage stress. During the post-damage storage, a total of 124 differentially expressed genes (DEGs) were identified, which were mainly annotated in 13 pathways, including phenylpropanoid biosynthesis. Besides, 175 differentially expressed metabolites (DEMs), including 142 up-regulated and 33 down-regulated metabolites, exhibited significant alteration after impact damage. The DEGs and DEMs were simultaneously annotated in 7 metabolic pathways, including flavonoid biosynthesis. Key genes in the volatile esters and flavonoid biosynthesis pathways were revealed, which may play a crucial role in the coping mechanisms of apple fruit under impact damage stress. Moreover, 13 ABC transporters were significantly upregulated, indicating that ABC transporters may contribute to the transportation of secondary metabolites associated with response to impact damage stress. The results may elucidate the comprehension of metabolic networks and molecular mechanisms in apple fruits that have undergone impact damage.

Mechanisms of the response of apple fruit to postharvest compression damage analyzed by integrated transcriptome and metabolome

Apple fruit is susceptible to compression damage within the postharvest supply chain given its thin peels and brittle texture, which can result in decay and deterioration and have a substantial impact on its marketability and competitiveness. Thorough bioinformatics investigations are lacking on postharvest compression damage stress-induced alterations in genes and metabolic regulatory networks in fruits. In the present study, a comprehensive analysis of both the transcriptome and metabolome was conducted on 'Red Fuji' apples experiencing compression-induced damage. During the storage after damage has occurred, the gene expression of MdOFUT19, MdWRKY48, MdCBP60E, MdCYP450 and MdSM-like of the damaged apples was consistently higher than that of the control group. The damaged apples also had higher contents of some metabolites such as procyanidin A1, Dl-2-Aminooctanoic acid, 5-O-p-Coumaroyl shikimic acid and 5,7-Dihydroxy-3',4',5'-trimethoxyflavone. Analysis of genes and metabolites with distinct expressions on the common annotation pathway suggested that the fruit may respond to compression stress by promoting volatile ester and lignin synthesis. The above results can deepen the comprehension of the response mechanisms in apple fruits undergoing compression-induced damage.

Natamycin-Loaded Ethyl Cellulose/PVP Films Developed by Microfluidic Spinning for Active Packaging

The preparation of active packaging loaded with antimicrobial, antioxidant, and other functional agents has become a hot topic for food preservation in recent years. In this field, active fiber films based on spinning methods have attracted the interest of researchers owing to their high specific surface area, high porosity, high loading capacity, and good controlled release capacity. In the present work, neatly arranged ethyl cellulose (EC)/polyvinyl-pyrrolidone (PVP) fibrous films loaded with natamycin as an antimicrobial agent were prepared by microfluidic spinning. The encapsulation efficiency of natamycin was more than 90% in each group and the loading increased with increasing natamycin content. According to the characterization results of the natamycin-loaded EC/PVP fibrous films, hydrogen bonding was formed between natamycin and EC and PVP in the fibrous films. Meanwhile, the water contact angle of the fibrous films was increased, suggesting the improved hydrophobicity of the films. In the in vitro bacterial inhibition experiments, the active fiber films loaded with natamycin showed good antimicrobial activity, which could significantly inhibit the growth of gray mold. In conclusion, N-EC/PVP fibrous films with antimicrobial activity prepared by microfluidic spinning showed good potential in the field of active packaging.

Sucrose-delaying flower color fading associated with delaying anthocyanin accumulation decrease in cut chrysanthemum

As fresh ornamental crops, vase life and post-harvested quality of cut flowers have attracted much attention. Flower color fading is the prominent defect in red and purple cut flowers, especially in cut chrysanthemum which have a relative long vase life. Here, the effect of sucrose on change in anthocyanin contents during the vase life of 'Dante Purple' cut chrysanthemum was studied. Results showed that 500 mM sucrose as holding solution could significantly delay the decrease in anthocyanin content and maintain the ornamental value for as long as 38 vase days. Moreover, the sucrose also increased the flower diameter, soluble sugar contents and total antioxidant capacity, while decreasing the malondialdehyde contents. Further studies suggested that the transcript levels of anthocyanin biosynthetic genes and transcription factors, CmMYB6 and CmMYB#7, had continuously decreased during the vase life. The changes in these genes expression patterns was retarded by the sucrose treatment, except for CmMYB#7 which is a repressor of anthocyanin biosynthesis gene expression. The decline in relative expression of CmMYB#7 was accelerated by sucrose. These results have supplied clues to study the mechanism whereby sucrose serves as a signal molecule to regulate anthocyanin biosynthesis.

Chilling-induced peach flavor loss is associated with expression and DNA methylation of functional genes

INTRODUCTION

Flavor is a major contributor to consumer preference. Despite being effective at extending the fruit's commercial life, cold storage also results in a significant loss of flavor volatiles. To date, there has been few studies on the metabolic dynamics and the mechanism underlying the regulatory networks that modulate flavor loss during cold storage for fruit.

METHODS

The volatile contents were detected by Gas Chromatography-Mass Spectrometer (GC-MS). Weighted gene co-expression network analysis (WGCNA) was used to identify structure genes and transcription factors (TFs). DNA methylation was analyzed by whole-genome methylation sequencing during cold storage.

RESULTS

We generated a temporal map, over hourly to weekly timescales, for the effects of chilling on flavor volatiles by combining metabolome, transcriptome, and DNA methylome in peach fruit. Based on the big data analysis, we developed a regulatory network for volatile formation and found that a decrease in volatiles during cold storage was significantly correlated with a decrease in the expression of synthesis genes. Moreover, TFs associated with these structure genes were identified. Expression of genes involved in ethylene biosynthesis was reduced while cold tolerance pathway was activated in response to low temperature. Functions of those genes were confirmed through transgenic experiments and across peach cultivars, suggesting our dataset is a useful tool for elucidating regulatory factors that have not yet been clarified in relation to flavor and cold tolerance. Genome wide DNA methylation was induced by chilling and peaked at 7 d followed by a decline during 28 d cold storage. Reduction of gene expression was accompanied by major changes in the methylation status of their promoters, including PpACS1, PpAAT1, PpTPS3 and PpMADS2.

CONCLUSION

Our study revealed the mechanism for chilling-induced flavor loss of peach fruit through time-course transcriptome and DNA methylome analysis.

Application of atomic force microscopy in the characterization of fruits and vegetables and associated substances toward improvement in quality, preservation, and processing: nanoscale structure and mechanics perspectives

Fruits and vegetables are essential horticultural crops for humans. The quality of fruits and vegetables is critical in determining their nutritional value and edibility, which are decisive to their commercial value. Besides, it is also important to understand the changes in key substances involved in the preservation and processing of fruits and vegetables. Atomic force microscopy (AFM), a powerful technique for investigating biological surfaces, has been widely used to characterize the quality of fruits and vegetables and the substances involved in their preservation and processing from the perspective of nanoscale structure and mechanics. This review summarizes the applications of AFM to investigate the texture, appearance, and nutrients of fruits and vegetables based on structural imaging and force measurements. Additionally, the review highlights the application of AFM in characterizing the morphological and mechanical properties of nanomaterials involved in preserving and processing fruits and vegetables, including films and coatings for preservation, bioactive compounds for processing purposes, nanofiltration membrane for concentration, and nanoencapsulation for delivery of bioactive compounds. Furthermore, the strengths and weaknesses of AFM for characterizing the quality of fruits and vegetables and the substances involved in their preservation and processing are examined, followed by a discussion on the prospects of AFM in this field.

DNA methylation mediated by RdDM pathway and demethylation affects furanone accumulation through regulation of QUINONE OXIDOREDUCTASE in strawberry

Recently, increasing evidence suggests that DNA methylation plays a crucial role in fruit ripening. However, the role of DNA methylation in regulating specific traits, such as flavor, remains unclear. Here, we report a role of DNA methylation in affecting furanone biosynthesis in strawberry. Strawberry quinone oxidoreductase (FaQR) is a key enzyme in furanone biosynthesis. There are four FaQR homologs in strawberry cultivar 'Yuexin', and one of them, FaQR3, contributes ~50% of FaQR transcripts, indicating a major role of FaQR3 in furanone biosynthesis. Through characterization of levels of DNA methylation and FaQR3 transcript and furanone contents during fruit ripening and after the application of DNA methylation inhibitor, we found that the DNA methylation level of the FaQR3 promoter was negatively correlated with FaQR3 expression and furanone accumulation, suggesting that DNA methylation may be involved in furanone biosynthesis through adjusting FaQR3 expression, and responded to different temperatures consistently. In addition, transient expression of a gene in the RNA-directed DNA methylation (RdDM) pathway, FaAGO4, and enrichment analysis of the 24-nucleotide siRNAs suggested that DNA methylation in the FaQR3 promoter is mediated by the RdDM pathway. Transient RNA interference (RNAi) of FaDML indicated that the demethylation pathway may be involved in regulating furanone accumulation. These findings provide new insights into the role of DNA methylation and demethylation in affecting flavor quality in strawberry during fruit ripening.

The transcription factor CitZAT5 modifies sugar accumulation and hexose proportion in citrus fruit

Sugars are fundamental to plant developmental processes. For fruits, the accumulation and proportion of sugars play crucial roles in the development of quality and attractiveness. In citrus (Citrus reticulata Blanco.), we found that the difference in sweetness between mature fruits of "Gongchuan" and its bud sport "Youliang" is related to hexose contents. Expression of a SuS (sucrose synthase) gene CitSUS5 and a SWEET (sugars will eventually be exported transporter) gene CitSWEET6, characterized by transcriptome analysis at different developmental stages of these 2 varieties, revealed higher expression levels in "Youliang" fruit. The roles of CitSUS5 and CitSWEET6 were investigated by enzyme activity and transient assays. CitSUS5 promoted the cleavage of sucrose to hexoses, and CitSWEET6 was identified as a fructose transporter. Further investigation identified the transcription factor CitZAT5 (ZINC FINGER OF ARABIDOPSIS THALIANA) that contributes to sucrose metabolism and fructose transportation by positively regulating CitSUS5 and CitSWEET6. The role of CitZAT5 in fruit sugar accumulation and hexose proportion was investigated by homologous transient CitZAT5 overexpression, -VIGS, and -RNAi. CitZAT5 modulates the hexose proportion in citrus by mediating CitSUS5 and CitSWEET6 expression, and the molecular mechanism explained the differences in sugar composition of "Youliang" and "Gongchuan" fruit.

Preparation of covalent organic framework-based nanofibrous films with temperature-responsive release of thymol for active food packaging

Thymol (THY) is commonly used in active food packaging, however because of its high volatility, poor water solubility, and strong aromatic odor, the application of THY is facing challenges. Herein, covalent organic frameworks (COFs) were synthesized in room temperature by asymmetric monomer exchange method for THY encapsulation, and solution blow spinning was used to fabricate the THY@COF/polycaprolactone (PCL) nanofibrous films. The synthesized COFs had a large specific surface area, porous structure, and loading capacity of 30.35% for THY, and THY@COFs possessed good thermal stability. Characterization analysis showed that THY@COFs were successfully incorporated into the PCL films and increased the barrier property of the films. Besides, the films showed good biocompatibility and antibacterial activity. Moreover, THY@COF/PCL films exhibited temperature-responsive THY release profiles, which is important for practical preservation applications, especially for preserving food in warm environments. Overall, THY@COF/PCL films possess promising potential in active food packaging.

The microRNA ppe-miR393 mediates auxin-induced peach fruit softening by promoting ethylene production

Auxin can inhibit or promote fruit ripening, depending on the species. Melting flesh (MF) peach fruit (Prunus persica L. Batsch) cultivars produce high levels of ethylene caused by high concentrations of indole-3-acetic acid (IAA), which leads to rapid fruit softening at the late stage of development. In contrast, due to the low concentrations of IAA, the fruit of stony hard (SH) peach cultivars does not soften and produces little ethylene. Auxin seems necessary to trigger the biosynthesis of ethylene in peach fruit; however, the mechanism is not well understood. In this study, we identified miRNA gene family members ppe-miR393a and ppe-miR393b that are differentially expressed in SH and MF fruits. RNA ligase-mediated 5' rapid amplification of cDNA ends and transient transformation of Nicotiana benthamiana revealed TRANSPORT INHIBITOR RESPONSE 1 (PpTIR1), part of the auxin perception and response system, as a target of ppe-miR393a and b. Yeast 2-hybrid assay and bimolecular fluorescence complementation assay revealed that PpTIR1 physically interacts with an Aux/IAA protein PpIAA13. The results of yeast 1-hybrid assay, electrophoretic mobility shift assay, and dual-luciferase assay indicated that PpIAA13 could directly bind to and trans-activate the promoter of 1-aminocyclopropane-1-carboxylic acid synthase 1 (PpACS1), required for ethylene biosynthesis. Transient overexpression and suppression of ppe-miR393a and PpIAA13 in peach fruit induced and repressed the expression of PpACS1, confirming their regulatory role in ethylene synthesis. Gene expression analysis in developing MF and SH fruits, combined with postharvest α-naphthalene acetic acid (NAA) treatment, supports a role for a ppe-miR393-PpTIR1-PpIAA13-PpACS1 module in regulating auxin-related differences in ethylene production and softening extent in different types of peach.

The preparation, resources, applications, and future trends of nanofibers in active food packaging: a review

Active packaging is a novel strategy for maintaining the shelf life of products and ensuring their safety, freshness, and integrity that has emerged with the consumer demand for safer, healthier, and higher quality food. Nanofibers have received a lot of attention for the application in active food packaging due to their high specific surface area, high porosity, and high loading capacity of active substances. Three common methods (electrospinning, solution blow spinning, and centrifugal spinning) for the preparation of nanofibers in active food packaging and their influencing parameters are presented, and advantages and disadvantages between these methods are compared. The main natural and synthetic polymeric substrate materials for the nanofiber preparation are discussed; and the application of nanofibers in active packaging is elaborated. The current limitations and future trends are also discussed. There have been many studies on the preparation of nanofibers using substrate materials from different sources for active food packaging. However, most of these studies are still in the laboratory research stage. Solving the issues of preparation efficiency and cost of nanofibers is the key to their application in commercial food packaging.

Indirect treatment of plasma-processed air to decrease decay and microbiota of strawberry fruit caused by mechanical damage

Due to the soft texture of strawberry fruit, it is highly susceptible to mechanical damage during postharvest supply chains, resulting in decay and quality deterioration. Urgent investigation is needed on the treatment techniques to mitigate the impact of postharvest mechanical damage of strawberry fruit. In the present study, the effect of indirect plasma-processed air (PPA) pretreatment to decrease decay and microbiota of strawberry fruit caused by mechanical damage was investigated. The results show PPA pretreatment reduced the total counts of indigenous microbiota on the surface of intact and mechanical damaged strawberry fruit by 4.29 and 3.76 log₁₀CFU/g at day 0, respectively, and reduced the counts of S. aureus and E. coli inoculated on strawberry fruit by 3.05-3.16 and 3.55-3.56 log₁₀CFU/g, respectively. The disease incidence of fruit inoculated with Botrytis cinerea was also decreased by 6.67 %-18.89 % during storage. Besides, PPA pretreatment reduced the decay rate of strawberry fruit by 5.56 %-21.11 % during storage and did not significantly affect the firmness, color index of red grapes (CIRG) and total soluble solids (TSS) content of strawberry fruit. DHHP results indicate that the antioxidant activity of the strawberry fruit was increased. After PPA pretreatment, 39 metabolites were differentially accumulated in strawberry fruits, 37 of which were up-regulated, including flavonoids, phenolic acids and organic acid.

A metabolic perspective of selection for fruit quality related to apple domestication and improvement

BACKGROUND

Apple is an economically important fruit crop. Changes in metabolism accompanying human-guided evolution can be revealed using a multiomics approach. We perform genome-wide metabolic analysis of apple fruits collected from 292 wild and cultivated accessions representing various consumption types.

RESULTS

We find decreased amounts of certain metabolites, including tannins, organic acids, phenolic acids, and flavonoids as the wild accessions transition to cultivated apples, while lysolipids increase in the "Golden Delicious" to "Ralls Janet" pedigree, suggesting better storage. We identify a total of 222,877 significant single-nucleotide polymorphisms that are associated with 2205 apple metabolites. Investigation of a region from 2.84 to 5.01 Mb on chromosome 16 containing co-mapping regions for tannins, organic acids, phenolic acids, and flavonoids indicates the importance of these metabolites for fruit quality and nutrition during breeding. The tannin and acidity-related genes Myb9-like and PH4 are mapped closely to fruit weight locus fw1 from 3.41 to 3.76 Mb on chromosome 15, a region under selection during domestication. Lysophosphatidylethanolamine (LPE) 18:1, which is suppressed by fatty acid desaturase-2 (FAD2), is positively correlated to fruit firmness. We find the fruit weight is negatively correlated with salicylic acid and abscisic acid levels. Further functional assays demonstrate regulation of these hormone levels by NAC-like activated by Apetala3/Pistillata (NAP) and ATP binding cassette G25 (ABCG25), respectively.

CONCLUSIONS

This study provides a metabolic perspective for selection on fruit quality during domestication and improvement, which is a valuable resource for investigating mechanisms controlling apple metabolite content and quality.

Synergistic actions of three MYB transcription factors underpins the high accumulation of myricetin in Morella rubra

Flavonols are health-promoting bioactive compounds important for human nutrition, health, and plant defense. The transcriptional regulation of kaempferol and quercetin biosynthesis has been studied extensively, while little is known about the regulatory mechanisms underlying myricetin biosynthesis, which has strong antioxidant, anticancer, antidiabetic, and anti-inflammatory activities. In this study, the flavonol-specific MrMYB12 in Morella rubra preferred activating the promoter of flavonol synthase 2 (MrFLS2) (6.4-fold) rather than MrFLS1 (1.4-fold) and upregulated quercetin biosynthesis. Furthermore, two SG44 R2R3-MYB members, MrMYB5 and MrMYB5L, were identified by yeast one-hybrid library screening using the promoter of flavonoid 3',5'-hydroxylase (MrF3'5'H), and transcript levels of these R2R3-MYBs were correlated with accumulation of myricetin derivatives during leaf development. Dual-luciferase and electrophoretic mobility shift assays demonstrated that both MrMYB5 and MrMYB5L could bind directly to MYB recognition sequence elements in promoters of MrF3'5'H or MrFLS1 and activate their expression. Protein-protein interactions of MrMYB5 or MrMYB5L with MrbHLH2 were confirmed by yeast two-hybrid and bimolecular fluorescence complementation assays. MrMYB5L-MrbHLH2 showed much higher synergistic activation of MrF3'5'H or MrFLS1 promoters than MrMYB5-MrbHLH2. Studies with Arabidopsis thaliana homologs AtMYB5 and AtTT8 indicated that similar synergistic regulatory effects occur with promoters of MrF3'5'H or MrFLS1. Transient overexpression of MrMYB5L-MrbHLH2 in Nicotiana benthamiana induced a higher accumulation of myricetin derivatives (57.70 μg g^-1 FW) than MrMYB5-MrbHLH2 (7.43 μg g^-1 FW) when MrMYB12 was coexpressed with them. This study reveals a novel transcriptional mechanism regulating myricetin biosynthesis with the potential use for future metabolic engineering of health-promoting flavonols.

A transporter of 1-aminocyclopropane-1-carboxylic acid affects thallus growth and fertility in Marchantia polymorpha

In seed plants, 1-aminocyclopropane-1-carboxylic acid (ACC) is the precursor of the plant hormone ethylene but also has ethylene-independent signaling roles. Nonseed plants produce ACC but do not efficiently convert it to ethylene. In Arabidopsis thaliana, ACC is transported by amino acid transporters, LYSINE HISTIDINE TRANSPORTER 1 (LHT1) and LHT2. In nonseed plants, LHT homologs have been uncharacterized. Here, we isolated an ACC-insensitive mutant (Mpain) that is defective in ACC uptake in the liverwort Marchantia polymorpha. Mpain contained a frameshift mutation (1 bp deletion) in the MpLHT1 coding sequence, and was complemented by expression of a wild-type MpLHT1 transgene. Additionally, ACC insensitivity was re-created in CRISPR/Cas9-Mplht1 knockout mutants. We found that MpLHT1 can also transport l-hydroxyproline and l-histidine. We examined the physiological functions of MpLHT1 in vegetative growth and reproduction based on mutant phenotypes. Mpain and Mplht1 plants were smaller and developed fewer gemmae cups compared to wild-type plants. Mplht1 mutants also had reduced fertility, and archegoniophores displayed early senescence. These findings reveal that MpLHT1 serves as an ACC and amino acid transporter in M. polymorpha and has diverse physiological functions. We propose that MpLHT1 contributes to homeostasis of ACC and other amino acids in M. polymorpha growth and reproduction.

Learning Curve for Flow Diversion of Posterior Circulation Aneurysms: A Long-Term International Multicenter Cohort Study

BACKGROUND AND PURPOSE

Flow diversion has gradually become a standard treatment for intracranial aneurysms of the anterior circulation. Recently, the off-label use of the flow diverters to treat posterior circulation aneurysms has also increased despite initial concerns of rupture and the suboptimal results. This study aimed to explore the change in complication rates and treatment outcomes across time for posterior circulation aneurysms treated using flow diversion and to further evaluate the mechanisms and variables that could potentially explain the change and outcomes.

MATERIALS AND METHODS

A retrospective review using a standardized data set at multiple international academic institutions was performed to identify patients with ruptured and unruptured posterior circulation aneurysms treated with flow diversion during a decade spanning January 2011 to January 2020. This period was then categorized into 4 intervals.

RESULTS

A total of 378 procedures were performed during the study period. Across time, there was an increasing tendency to treat more vertebral artery and fewer large vertebrobasilar aneurysms (P = .05). Moreover, interventionalists have been increasingly using fewer overlapping flow diverters per aneurysm (P = .07). There was a trend toward a decrease in the rate of thromboembolic complications from 15.8% in 2011-13 to 8.9% in 2018-19 (P = .34).

CONCLUSIONS

This multicenter experience revealed a trend toward treating fewer basilar aneurysms, smaller aneurysms, and increased usage of a single flow diverter, leading to a decrease in the rate of thromboembolic and hemorrhagic complications.

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage

INTRODUCTION

Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant.

OBJECTIVES

This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness.

METHODS

The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca²⁺ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit.

RESULTS

The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0°C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca²⁺ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals.

CONCLUSION

PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca²⁺ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Genome-wide analysis of UDP-glycosyltransferase gene family and identification of members involved in flavonoid glucosylation in Chinese bayberry (Morella rubra)

Glycosylation was catalyzed by UDP-glycosyltransferase (UGT) and was important for enriching diversity of flavonoids. Chinese bayberry (Morella rubra) has significant nutritional and medical values because of diverse natural flavonoid glycosides. However, information of UGT gene family was quite limited in M. rubra. In the present study, a total of 152 MrUGT genes clustered into 13 groups were identified in M. rubra genome. Among them, 139 MrUGT genes were marked on eight chromosomes and 13 members located on unmapped scaffolds. Gene duplication analysis indicated that expansion of MrUGT gene family was mainly forced by tandem and proximal duplication events. Gene expression patterns in different tissues and under UV-B treatment were analyzed by transcriptome. Cyanidin 3-O-glucoside (C3Glc) and quercetin 3-O-glucoside (Q3Glc) were two main flavonoid glucosides accumulated in M. rubra. UV-B treatment significantly induced C3Glc and Q3Glc accumulation in fruit. Based on comprehensively analysis of transcriptomic data and phylogenetic homology together with flavonoid accumulation patterns, MrUFGT (MrUGT78A26) and MrUGT72B67 were identified as UDP-glucosyltransferases. MrUFGT was mainly involved in C3Glc and Q3Glc accumulation in fruit, while MrUGT72B67 was mainly involved in Q3Glc accumulation in leaves and flowers. Gln375 and Gln391 were identified as important amino acids for glucosyl transfer activity of MrUFGT and MrUGT72B67 by site-directed mutagenesis, respectively. Transient expression in Nicotiana benthamiana tested the function of MrUFGT and MrUGT72B67 as glucosyltransferases. The present study provided valuable source for identification of functional UGTs involved in secondary metabolites biosynthesis in M. rubra.

Facile microfluidic fabrication and characterization of ethyl cellulose/PVP films with neatly arranged fibers

Much attention and endeavor have been paid to developing biocompatible food packaging films. Here, ethyl cellulose (EC) and polyvinylpyrrolidone (PVP) were fabricated into films through a facile method, microfluidic spinning. Morphology observations showed that the fibers were neatly arranged with an average diameter of 1-4 μm. FTIR and X-ray diffraction analysis suggested the existence of good compatibility and interaction between EC and PVP. Thermogravimetric analysis demonstrated that PVP ameliorates the thermal properties; moreover, the tensile properties were improved, with tensile strength (TS) and Young's modulus up to 11.10 ± 1.04 MPa and 350.16 ± 45.46 MPa, respectively. The optimal formula was EC/PVP (2:3), of which the film displayed an enhanced TS of 4.61 ± 1.15 MPa and a modified water contact angle of 61.8 ± 4.4°, showing fine tensile and hydrophilic performance. This study provides a facile and green film fabrication method promising to be used for food wrapping.

The role and interaction between transcription factor NAC-NOR and DNA demethylase SlDML2 in the biosynthesis of tomato fruit flavor volatiles

Flavor-imparting volatile chemicals accumulate as fruits ripen, making major contributions to taste. The NAC transcription factor nonripening (NAC-NOR) and DNA demethylase 2 (SlDML2) are essential for tomato fruit ripening, but details of the potential roles and the relationship between these two regulators in the synthesis of volatiles are lacking. Here, we show substantial reductions in fatty acid and carotenoid-derived volatiles in tomato slnor and sldml2 mutants. An unexpected finding is the redundancy and divergence in volatile profiles, biosynthetic gene expression, and DNA methylation in slnor and sldml2 mutants relative to wild-type tomato fruit. Reduced transcript levels are accompanied by hypermethylation of promoters, including the NAC-NOR target gene lipoxygenase (SlLOXC) that is involved in fatty acid-derived volatile synthesis. Interestingly, NAC-NOR activates SlDML2 expression by directly binding to its promoter both in vitro and in vivo. Meanwhile, reduced NAC-NOR expression in the sldml2 mutant is accompanied by hypermethylation of its promoter. These results reveal a relationship between SlDML2-mediated DNA demethylation and NAC-NOR during tomato fruit ripening. In addition to providing new insights into the metabolic modulation of flavor volatiles, the outcome of our study contributes to understanding the genetics and control of fruit ripening and quality attributes in tomato.

Contrasting Roles of Ethylene Response Factors in Pathogen Response and Ripening in Fleshy Fruit

Fleshy fruits are generally hard and unpalatable when unripe; however, as they mature, their quality is transformed by the complex and dynamic genetic and biochemical process of ripening, which affects all cell compartments. Ripening fruits are enriched with nutrients such as acids, sugars, vitamins, attractive volatiles and pigments and develop a pleasant taste and texture and become attractive to eat. Ripening also increases sensitivity to pathogens, and this presents a crucial problem for fruit postharvest transport and storage: how to enhance pathogen resistance while maintaining ripening quality. Fruit development and ripening involve many changes in gene expression regulated by transcription factors (TFs), some of which respond to hormones such as auxin, abscisic acid (ABA) and ethylene. Ethylene response factor (ERF) TFs regulate both fruit ripening and resistance to pathogen stresses. Different ERFs regulate fruit ripening and/or pathogen responses in both fleshy climacteric and non-climacteric fruits and function cooperatively or independently of other TFs. In this review, we summarize the current status of studies on ERFs that regulate fruit ripening and responses to infection by several fungal pathogens, including a systematic ERF transcriptome analysis of fungal grey mould infection of tomato caused by Botrytis cinerea. This deepening understanding of the function of ERFs in fruit ripening and pathogen responses may identify novel approaches for engineering transcriptional regulation to improve fruit quality and pathogen resistance.

Genome-wide identification and expression analysis of MATE gene family in citrus fruit (Citrus clementina)

Multidrug and toxic compound extrusion (MATE) proteins are a class of secondary active multidrug transporters. In plants, this family has significantly expanded and is involved in numerous plant physiological processes. Although MATE proteins have been identified in an increasing number of species, the understanding about this family in citrus remains unclear. In this study, a total of 69 MATE transporters were identified in the citrus genome (Citrus clementina) and classified into four groups by phylogenetic analysis. Tandem and segmental duplication events were the main causes of the citrus MATE family expansion. RNA-seq and qRT-PCR analyses were performed during citrus fruit development. The results indicated that CitMATE genes showed specific expression profiles in citrus peels and flesh at different developmental stages. Combined with the variations of flavonoids and citrate levels in citrus fruit, we suggested that CitMATE43 and CitMATE66 may be involved in the transport process of flavonoids and citrate in citrus fruit, respectively. In addition, two flavonoids positive regulators, CitERF32 and CitERF33, both directly bind to and activated the CitMATE43 promoter. Our results provide comprehensive information on citrus MATE genes and valuable understanding for the flavonoids and citrate metabolism in citrus fruit.

Unravelling the consecutive glycosylation and methylation of flavonols in peach in response to UV-B irradiation

Flavonol glycosides are bioactive compounds important for plant defence and human nutrition. Glycosylation and methylation play an important role in enriching the diversity of flavonols in response to the environment. Peach flowers and fruit are rich in flavonol diglycosides such as isorhamnetin 3-O-rutinoside (I3Rut), kaempferol 3-O-rutinoside and quercetin 3-O-rutinoside, and flavonol monoglycosides such as I 3-O-glucoside and Q 3-O-galactoside. UV-B irradiation of fruit significantly induced accumulation of all these flavonol glycosides. Candidate biosynthetic genes induced by UV-B were identified by genome homology searches and the in vitro catalytic activities of purified recombinant proteins determined. PpUGT78T3 and PpUGT78A2 were identified as flavonol 3-O-glucosyltransferase and 3-O-galactosyltransferase, respectively. PpUGT91AK6 was identified as flavonol 1,6-rhamnosyl trasferase catalysing the formation of flavonol rutinosides and PpFOMT1 was identified as a flavonol O-methyltransferase that methylated Q at the 3'-OH-OH to form isorhamnetin derivatives. Transient expression in Nicotiana benthamiana confirmed the specificity of PpUGT78T3 as a flavonol 3-O-glucosyltransferase, PpUGT78A2 as a 3-O-galactosyltransferase, PpUGT91AK6 as a 1,6-rhamnosyltrasferase and PpFOMT1 as an O-methyltransferase. This study provides new insights into the mechanisms of glycosylation and methylation of flavonols, especially the formation of flavonol diglycosides such as I3Rut, and will also be useful for future potential metabolic engineering of complex flavonols.

Characterization of glycosylated gelatin/pullulan nanofibers fabricated by multi-fluid mixing solution blow spinning

In this work, multi-fluid mixing solution blow spinning was applied to develop gelatin/pullulan composite nanofibers, and then the nanofibers were glycated to enhance the physical properties. The results show that the grafting degree of the nanofibers increased significantly from 17.5 % to 36.0 % as the glycation time increased, and the morphology results indicated that 72 h of glycation did not destroy the structure of the nanofibers. FTIR results show that the glycation consumed the the-NH₂ groups, cleaved sugar units of polysaccharide, and affected the secondary structure of the protein. The glycation enhanced the thermal stability and improved the rigidity of the nanofibers. Besides, after 120 h of glycation, the water contact angle of nanofibers increased from 0° to 79.1°, and the water vapor transmission rates decreased from 12.49 to 8.97 g mm/m² h kPa, indicating the enhanced hydrophobicity and barrier properties. In addition, the glycation improved the water stability of the nanofibers, which increased the applicability of the gelatin/pullulan nanofibers in food packaging. The present work provides a green and efficient method for improving the physical properties of gelatin/pullulan nanofibers.

Mechanical damages and packaging methods along the fresh fruit supply chain: A review

Mechanical damage of fresh fruit occurs throughout the postharvest supply chain leading to poor consumer acceptance and marketability. In this review, the mechanisms of damage development are discussed first. Mathematical modeling provides advanced ways to describe and predict the deformation of fruit with arbitrary geometry, which is important to understand their mechanical responses to external forces. Also, the effects of damage at the cellular and molecular levels are discussed as this provides insight into fruit physiological responses to damage. Next, direct measurement methods for damage including manual evaluation, optical detection, magnetic resonance imaging, and X-ray computed tomography are examined, as well as indirect methods based on physiochemical indexes. Also, methods to measure fruit susceptibility to mechanical damage based on the bruise threshold and the amount of damage per unit of impact energy are reviewed. Further, commonly used external and interior packaging and their applications in reducing damage are summarized, and a recent biomimetic approach for designing novel lightweight packaging inspired by the fruit pericarp. Finally, future research directions are provided.HIGHLIGHTSMathematical modeling has been increasingly used to calculate damage to fruit.Cell and molecular mechanisms response to fruit damage is an under-explored area.Susceptibility measurement of different mechanical forces has received attention.Customized design of reusable and biodegradable packaging is a hot topic of research.

Two Myricetin-Derived Flavonols from Morella rubra Leaves as Potent α-Glucosidase Inhibitors and Structure-Activity Relationship Study by Computational Chemistry

Diabetes mellitus (DM) is a chronic disease characterized by hyperglycemia, and oxidative stress is an important cause and therapeutic target of DM. Phytochemicals such as flavonols are important natural antioxidants that can be used for prevention and treatment of DM. In the present study, six flavonols were precisely prepared and structurally elucidated from Morella rubra leaves, which were screened based on antioxidant assays and α-glucosidase inhibitory activities of different plant tissues. Myricetin-3-O-(2″-O-galloyl)-α-L-rhamnoside (2) and myricetin-3-O-(4″-O-galloyl)-α-L-rhamnoside (3) showed excellent α-glucosidase inhibitory effects with IC50 values of 1.32 and 1.77 μM, respectively, which were hundredfold higher than those of positive control acarbose. Molecular docking simulation illustrated that the presence of galloyl group altered the binding orientation of flavonols, where it occupied the opening of the cavity pocket of α-glucosidase along with Pi-anion interaction with Glu304 and Pi-Pi stacked with His279. Pi-conjugations generated between galloyl moiety and key residues at the active site of α-glucosidase reinforced the flavonol-enzyme binding, which might explain the greatly increased activity of compounds 2 and 3. In addition, 26 flavonols were evaluated for systematic analysis of structure-activity relationship (SAR) between flavonols and α-glucosidase inhibitory activity. By using their pIC50 (-log IC50) values, three-dimensional quantitative SAR (3D-QSAR) models were developed via comparative molecular field analysis (CoMFA) and comparative similarity index analysis (CoMSIA), both of which were validated to possess high accuracy and predictive power as indicated by the reasonable cross-validated coefficient (q 2) and non-cross-validated coefficient (r 2) values. Through analyzing 3D contour maps of both CoMFA and CoMSIA models, QSAR results were in agreement with in vitro experimental data. Therefore, such results showed that the galloyl group in compounds 2 and 3 is crucial for interacting with key residues of α-glucosidase and the established 3D-QSAR models could provide valuable information for the prediction of flavonols with great antidiabetic potential.

Peach fruit PpNAC1 activates PpFAD3-1 transcription to provide ω-3 fatty acids for the synthesis of short-chain flavor volatiles

Volatile organic compounds (VOCs) derived from fatty acids are major contributors to fruit flavor and affect human preferences. The ω-3 fatty acid linolenic acid 3 (18:3) serves as an important precursor for synthesis of (E)-2-hexenal and (Z)-3-hexenol. These short-chain C6 VOCs provide unique fresh notes in multiple fruit species. Metabolic engineering to improve fruit aroma requires knowledge of the regulation of fatty acid-derived VOCs. Here, we determined that ripe fruit-specific expression of PpFAD3-1 contributes to 18:3 synthesis in peach fruit. However, no significant increases in (E)-2-hexenal and (Z)-3-hexenol were detected after overexpressing PpFAD3-1. Interestingly, overexpressing the PpNAC1 transcription factor increased the content of 18:3 and enhanced the production of its derived volatiles. Moreover, induced expression of genes responsible for downstream VOC synthesis was observed for transgenic tomato fruit overexpressing PpNAC1, but not for transgenic fruit overexpressing PpFAD3-1. Electrophoretic mobility shift and ChIP-Seq assays showed that PpNAC1 activated PpFAD3-1 expression via binding to its promoter. Therefore, PpNAC1 plays an important role in modulating fatty acid flux to produce fruit flavor-related VOCs. In addition to PpNAC1, PpFAD3-1 expression was also associated with epigenetic modifications during peach fruit ripening. Taken together, our results provide new insights into the molecular mechanisms regulating biosynthesis of fatty acid and short-chain VOCs in fruit.

Linalool synthesis related PpTPS1 and PpTPS3 are activated by transcription factor PpERF61 whose expression is associated with DNA methylation during peach fruit ripening

The monoterpene linalool is a major contributor to flavor of multiple fruit species. Although great progress has been made in identifying genes related to linalool formation, transcriptional regulation for the pathway remains largely unknown. As a super transcription factor family, roles of AP2/ERF in regulating linalool production have not been elucidated. Peach linalool is catalyzed by terpene synthases PpTPS1 and PpTPS3. Here, we observed that expression of PpERF61 correlated with these two PpTPSs during fruit ripening by transcriptome co-expression analysis. Dual-luciferase assay and EMSA results indicated that PpERF61 activated the PpTPS1 and PpTPS3 transcription by binding to the DRE/CRT motif in their promoters. Transient overexpressing PpERF61 in peach fruit significantly increased PpTPS1 and PpTPS3 expression and linalool content. Further study revealed significant correlation between PpERF61 transcripts and linalool contents across 30 peach cultivars. Besides transcriptional regulation, accumulated linalool was associated with DNA demethylation of PpERF61 during peach fruit ripening. In addition, interactions between PpERF61 and PpbHLH1 were evaluated, indicating these two transcription factors were associated with linalool production during peach fruit ripening. Overall, our results revealed a new insight into the regulation of linalool synthesis in fruit.

The Interaction Between CitMYB52 and CitbHLH2 Negatively Regulates Citrate Accumulation by Activating CitALMT in Citrus Fruit

Citric acid plays significant roles in numerous physiological processes in plants, including carbon metabolism, signal transduction, and tolerance to environmental stress. For fruits, it has a major effect on fruit organoleptic quality by directly influencing consumer taste. Citric acid in citrus is mainly regulated by the balance between synthesis, degradation, and vacuolar storage. The genetic and molecular regulations of citric acid synthesis and degradation have been comprehensively elucidated. However, the transporters for citric acid in fruits are less well understood. Here, an aluminum-activated malate transporter, CitALMT, was characterized. Transient overexpression and stable transformation of CitALMT significantly reduced citrate concentration in citrus fruits and transgenic callus. Correspondingly, transient RNA interference-induced silencing of CitALMT and increased citrate significantly, indicating that CitALMT plays an important role in regulating citrate concentration in citrus fruits. In addition, dual-luciferase assays indicated that CitMYB52 and CitbHLH2 could trans-activate the promoter of CitALMT. EMSA analysis showed that CitbHLH2 could physically interact with the E-box motif in the CitALMT promoter. Bimolecular fluorescence complementation assays, yeast two-hybrid, coimmunoprecipitation and transient overexpression, and RNAi assay indicated that the interaction between CitMYB52 and CitbHLH2 could synergistically trans-activate CitALMT to negatively regulate citrate accumulation.

An EjbHLH14-EjHB1-EjPRX12 module is involved in methyl jasmonate alleviation of chilling-induced lignin deposition in loquat fruit

Loquat fruit are susceptible to chilling injuries induced by postharvest storage at low temperature. The major symptoms are increased lignin content and flesh firmness, which cause a leathery texture. Pretreatment with methyl jasmonate (MeJA) can alleviate this low-temperature-induced lignification, but the mechanism is not understood. In this study, we characterized a novel class III peroxidase, EjPRX12, and studied its relationship to lignification. Transcript levels of EjPRX12 were attenuated following MeJA pretreatment, consistent with the reduced lignin content in fruit. In vitro enzyme activity assay indicated that EjPRX12 polymerized sinapyl alcohol, and overexpression of EjPRX12 in Arabidopsis promoted lignin accumulation, indicating that it plays a functional role in lignin polymerization. We also identified an HD-ZIP transcription factor, EjHB1, repressed by MeJA pretreatment, which directly bound to and significantly activated the EjPRX12 promoter. Overexpression of EjHB1 in Arabidopsis promoted lignin accumulation with induced expression of lignin-related genes, especially AtPRX64. Furthermore, a JAZ-interacting repressor, EjbHLH14, was characterized, and it is proposed that MeJA pretreatment caused EjbHLH14 to be released to repress the expression of EjHB1. These results identified a novel regulatory pathway involving EjbHLH14-EjHB1-EjPRX12 and revealed the molecular mechanism whereby MeJA alleviated lignification of loquat fruit at low temperature.

Grafting Hollow Covalent Organic Framework Nanoparticles with Thermal-Responsive Polymers for the Controlled Release of Preservatives

Covalent organic frameworks (COFs) hold great potential in various applications because of their well-defined pore structures and morphologies. However, most COF materials demonstrate poor dispersibility in solvents that significantly limits their processing and applications. Herein, we report the synthesis of COF-based hollow nanoparticles (h-NPs) with good water dispersibility, high capacity, and thermal responsiveness to load essential oil molecules for longer-term preservation of fruits. Imine-based COF h-NPs possessing a pore width of 1.3 nm, inner/outer diameters of ∼150/239 nm, and high crystallinity were synthesized and grafted with water-soluble polymers such as polyethylene glycol or poly(N-isopropylacrylamide) (PNIPAM) with molecular weights of 1-3 kDa. The h-NP products with grafting densities of 0.6-2.1 nm-2 can be well dispersed in water at room temperature. PNIPAM-grafted ones are temperature-responsive in that they can precipitate out from the dispersion at 40 °C and redisperse at 25 °C for at least 15 cycles. The h-NPs are used as nanocarriers to load essential oils such as hexanal and trans-2-hexenal with a high capacity of 1.1 g/g for fruit fresh-keeping, and the encapsulated preservatives can be released controllably at 25-40 °C as regulated by the grafted polymers. As a result, the storage time of cherry tomatoes can be prolonged by 4 days compared to the control run. Moreover, these h-NPs can be recycled and reused. Our work highlights the potential of COF nanomaterials grafting with stimuli-responsive polymers for controlled release application in various food preservation.

Hydroxylation decoration patterns of flavonoids in horticultural crops: chemistry, bioactivity and biosynthesis

Flavonoids are the most widespread polyphenolic compounds and are important dietary constituents present in horticultural crops such as fruits, vegetables, and tea. Natural flavonoids are responsible for important quality traits, such as food colors and beneficial dietary antioxidants and numerous investigations have shown that intake of flavonoids can reduce the incidence of various non-communicable diseases (NCDs). Analysis of the thousands of flavonoids reported so far has shown that different hydroxylation modifications affect their chemical properties and nutritional values. These diverse flavonoids can be classified based on different hydroxylation patterns in the B, C, A rings and multiple structure-activity analyses have shown that hydroxylation decoration at specific positions markedly enhances their bioactivities. This review focuses on current knowledge concerning hydroxylation of flavonoids catalyzed by several different types of hydroxylase enzymes. Flavonoid 3'-hydroxylase (F3'H) and flavonoid 3'5'-hydroxylase (F3'5'H) are important enzymes for the hydroxylation of the B ring of flavonoids. Flavanone 3-hydroxylase (F3H) is key for the hydroxylation of the C ring, while flavone 6-hydroxylase (F6H) and flavone 8-hydroxylase (F8H) are key enzymes for hydroxylation of the A ring. These key hydroxylases in the flavonoid biosynthesis pathway are promising targets for the future bioengineering of plants and mass production of flavonoids with designated hydroxylation patterns of high nutritional importance. In addition, hydroxylation in key places on the ring may help render flavonoids ready for degradation, the catabolic turnover of which may open the door for new lines of inquiry.

Identification of UDP-rhamnosyltransferases and UDP-galactosyltransferase involved in flavonol glycosylation in Morella rubra

Flavonol glycosides are health-promoting phytochemicals important for human nutrition and plant defense against environmental stresses. Glycosylation modification greatly enriches the diversity of flavonols. Morella rubra, a member of the Myricaceae, contains high amounts of myricetin 3-O-rhamnoside (M3Rha), quercetin 3-O-rhamnoside (Q3Rha), and quercetin 3-O-galactoside (Q3Gal). In the present study, MrUGT78R1 and MrUGT78R2 were identified as two functional UDP-rhamnosyltransferases, while MrUGT78W1 was identified as a UDP-galactosyltransferase. Site-directed mutagenesis identified Pro143 and Asn386 as important residues for rhamnosyl transfer activity of MrUGT78R1, while the two corresponding positions in MrUGT78W1 (i.e. Ser147 and Asn370) also play important roles in galactosyl transfer activity. Transient expression data for these three MrUGTs in Nicotiana benthamiana tested the function of MrUGT78R1 and MrUGT78R2 as rhamnosyltransferases and MrUGT78W1 as a galactosyltransferase in glycosylation of flavonols. This work enriches knowledge of the diversity of UDP-rhamnosyltransferase in planta and identifies two amino acid positions important for both rhamnosyltransferase and galactosyltransferase.

Transcription Factor CitERF16 Is Involved in Citrus Fruit Sucrose Accumulation by Activating CitSWEET11d

Sugars are the primary products of photosynthesis and play an important role in plant growth and development. They contribute to sweetness and flavor of fleshy fruits and are pivotal to fruit quality, and their translocation and allocation are mainly dependent on sugar transporters. Genome-wide characterization of Satsuma mandarin identified eighteen SWEET family members that encode transporters which facilitate diffusion of sugar across cell membranes. Analysis of the expression profiles in tissues of mandarin fruit at different developmental stages showed that CitSWEET11d transcripts were significantly correlated with sucrose accumulation. Further studies indicated that overexpression of CitSWEET11d in citrus callus and tomato fruit showed a higher sucrose level compared to wild-type, suggesting that CitSWEET11d could enhance sucrose accumulation. In addition, we identified an ERF transcription factor CitERF16 by yeast one-hybrid screening assay which could directly bind to the DRE cis-element on the promoter of CitSWEET11d. Overexpression of CitERF16 in citrus callus significantly induced CitSWEET11d expression and elevated sucrose content, suggesting that CitERF16 acts as a positive regulator to promote sucrose accumulation via trans-activation of CitSWEET11d expression.

Role of the tomato fruit ripening regulator MADS-RIN in resistance to Botrytis cinerea infection

Tomato MADS-RIN (RIN) transcription factor has been shown to be a master activator regulating fruit ripening. Recent studies have revealed that in addition to activating many other cell wall genes, it also represses expression of XTH5, XTH8, and MAN4a, which are positively related to excess flesh softening and cell wall degradation, which might indicate it has a potential role in pathogen resistance of ripening fruit. In this study, both wild-type (WT) and RIN-knockout (RIN-KO) mutant tomato fruit were infected with Botrytis cinerea to investigate the function of RIN in defense against pathogen infection during ripening. The results showed that RIN-KO fruit were much more sensitive to B. cinerea infection with larger lesion sizes. Transcriptome data and qRT-PCR assay indicate genes of phenylalanine ammonialyase (PAL) and chitinase (CHI) in RIN-KO fruit were reduced and their corresponding enzyme activities were decreased. Transcripts of genes encoding pathogenesis-related proteins (PRs), including PR1a, PRSTH2, and APETALA2/Ethylene Response Factor (AP2/ERF) including ERF.A1, Pti5, Pti6, ERF.A4, were reduced in RIN-KO fruit compared to WT fruit. Moreover, in the absence of RIN the expression of genes encoding cell wall-modifying enzymes XTH5, XTH8, MAN4a has been reported to be elevated, which is potentially correlated with cell wall properties. When present, RIN represses transcription of XTH5 by activating ERF.F4, a class II (repressor class) ERF gene family member, and ERF.F5. These results support the conclusion that RIN enhances ripening-related resistance to gray mold infection by upregulating pathogen-resistance genes and defense enzyme activities as well as reducing accumulation of transcripts encoding some cell wall enzymes.

Elucidation of myricetin biosynthesis in Morella rubra of the Myricaceae

Flavonols are health-promoting bioactive compounds important for plant defense and human nutrition. Quercetin (Q) and kaempferol (K) biosynthesis have been studied extensively while little is known about myricetin (M) biosynthesis. The roles of flavonol synthases (FLSs) and flavonoid 3',5'-hydroxylase (F3'5'H) in M biosynthesis in Morella rubra, a member of the Myricaceae rich in M-based flavonols, were investigated. The level of MrFLS transcripts alone did not correlate well with the accumulation of M-based flavonols. However, combined transcript data for MrFLS1 and MrF3'5'H showed a good correlation with the accumulation of M-based flavonols in different tissues of M. rubra. Recombinant MrFLS1 and MrFLS2 proteins showed strong activity with dihydroquercetin (DHQ), dihydrokaempferol (DHK), and dihydromyricetin (DHM) as substrates, while recombinant MrF3'5'H protein preferred converting K to M, amongst a range of substrates. Tobacco (Nicotiana tabacum) overexpressing 35S::MrFLSs produced elevated levels of K-based and Q-based flavonols without affecting M-based flavonol levels, while tobacco overexpressing 35S::MrF3'5'H accumulated significantly higher levels of M-based flavonols. We conclude that M accumulation in M. rubra is affected by gene expression and enzyme specificity of FLS and F3'5'H as well as substrate availability. In the metabolic grid of flavonol biosynthesis, the strong activity of MrF3'5'H with K as substrate additionally promotes metabolic flux towards M in M. rubra.