Fruit Softening: Revisiting the Role of Pectin

Nitric oxide delays tomato fruit softening by inhibiting SlNAP2 (NAC-like, activated by apetala3/pistillata2) transcription factor-activated transcription of soften-related genes

Fruit softening is a critical physiological process that occurs during fruit ripening and senescence. Nitric oxide (NO) and NAM-ATAF1/2-CUC2 (NAC) transcription factors (TFs) have been implicated in regulating fruit softening. However, the functions of NO and NAC-like, activated by apetala3/pistillata (NAP) TFs and their interaction in fruit softening are not well understood. Here, we found that NO might suppress cell wall-related enzyme [polygalacturonase (PG), pectin methyl esterase (PME)] activity, thereby effectively postponing tomato fruit softening. Transcriptome and reverse transcription quantitative PCR (RT-qPCR) analyses revealed SlNAP2 in tomato fruit was repressed by NO. Meanwhile, SlNAP2 promoted tomato fruit softening by increasing PG, PME and cellulase activity and reducing cellulose content. Importantly, NO was not effective in delaying tomato fruit softening in the slnap2 mutant. Furthermore, SlNAP2 enhanced fruit soften-related genes SlPL8, SlPG2a and SlCCEL2 transcription by binding to their promoters. However, NO suppressed the activation of SlNAP2 on these genes. Taken together, NO might delay fruit softening by inhibiting the transcriptional activation of SlNAP2 on SlCCEL2, SlPG2a, and SlPL8 to decrease cellulase, PG and PME activity. Thus, this study provides compelling evidence and new insights into the roles of SlNAP2 in NO-regulated tomato fruit softening.

Ethylene-Activated E3 Ubiquitin Ligase MdEAEL1 Promotes Apple Fruit Softening by Facilitating the Dissociation of Transcriptional Repressor Complexes

Fruit of most apple varieties soften after harvest, and although the hormone ethylene is known to induce softening, the associated pathway is not well resolved. In this study, it is determined that MdEAEL1 (Ethylene-activated E3 ubiquitin Like 1) is specifically expressed during apple fruit postharvest storage, activated by ethylene, and interacts with the transcription factor MdZFP3 (zinc finger protein3). MdZFP3 is found to rely on an EAR (ethylene-responsive element binding factor-associated amphiphilic repression) motif to form a transcriptional repression complex with MdTPL4 (TOPLESS4)-MdHDA19 (histone deacetylase19), thereby downregulating the histone acetylation levels of the promoters of a range of cell wall degradation-related genes and inhibiting their transcription. MdEAEL1 ubiquitinates and degrades MdZFP3, leading to the disassembly of the MdZFP3-MdTPL4-MdHDA19 transcriptional repression complex. This process promotes the transcription of cell wall degradation-related genes, resulting in fruit softening during storage. Furthermore, the disassembly of the MdZFP3-MdTPL4-MdHDA19 transcriptional repression complex, mediated by MdEAEL1, upregulates the transcription of MdEAEL1 itself, creating a feedback loop that further promotes softening. This study elucidates the interplay between post-translational modifications of a transcription factor and its epigenetic modification to regulate fruit softening, and highlights the complexity of ethylene-induced softening.

Enrichment of two important metabolites D-galacturonic acid and D-glucuronic acid inhibits MdHb1-mediated fruit softening in apple

In apples, fruit firmness is a crucial quality trait influencing fruit storability, transportability, shelf life and consumer preference. However, the genetic network underlying this trait remains unclear. Therefore, the present study investigated the changes in apple fruit at different stages of postharvest storage using a combination of transcriptomic and metabolomic analyses. With prolonged storage, we detected a significant increase in two metabolites, D-galacturonic acid (D-GalUA) and D-glucuronic acid (D-GlcA), which are associated with a key class 1 non-symbiotic haemoglobin (MdHb1). We innovatively found that MdHb1 regulates fruit softening by catalysing the conversion from protopectin to water-soluble pectin. Biochemical analysis demonstrated that MdMYB2/MdNAC14/MdNTL9 transcription factors directly bind to the MdHb1 promoter to activate its transcriptional expression and promote fruit softening. Further injection experiments in apple fruit and histological as well as transmission electron microscopy analyses of the fruit samples revealed that D-GalUA and D-GlcA reduce the transcription of MdHb1, or through the MdMYB2/MdNAC14/MdNTL9-MdHb1 regulatory module, thereby delaying fruit softening. Our study provides novel insights into the role of two important metabolites, D-GalUA and D-GlcA, in the regulation of MdHb1-mediated fruit softening in apples.

Monosaccharide composition and degree of acetylation of non-cellulosic cell wall polysaccharides and their relationship to apple firmness

The firmness of the two apple varieties: Idared and Pinova was similar during ripening, while it decreased significantly during 3-month storage only for Idared. Pectin-rich fractions were isolated from apple flesh tissue: water-soluble pectin (WSP), imidazole-soluble pectin (ISP), and hemicellulose-rich fractions: natively acetylated hemicelluloses (LiCl-DMSO), deacetylated hemicelluloses (KOH). It was shown that the degree of acetylation (DAc) of the hemicelluloses fraction (LiCl-DMSO) increased during apple ripening and storage, with higher values for Idared. Furthermore, the DAc of the hemicellulose fraction (LiCl-DMSO) was shown to be negatively correlated with apple firmness, and thus, among other factors, the effect of the degree of acetylation of hemicelluloses on fruit softening during storage. In the WSP and ISP, galacturonic acid content increased during ripening and storage of apples, which also showed a correlation with firmness. A higher content of linear pectin was recorded for Idared, while the contribution of rhamnogalacturonans was higher for Pinova.

Cell Wall-Based Machine Learning Models to Predict Plant Growth Using Onion Epidermis

The plant cell wall (CW) is a physical barrier that plays a dual role in plant physiology, providing structural support for growth and development. Understanding the dynamics of CW growth is crucial for optimizing crop yields. In this study, we employed onion (Allium cepa L.) epidermis as a model system, leveraging its layered organization to investigate growth stages. Microscopic analysis revealed proportional variations in cell size in different epidermal layers, offering insights into growth dynamics and CW structural adaptations. Fourier transform infrared spectroscopy (FTIR) identified 11 distinct spectral intervals associated with CW components, highlighting structural modifications that influence wall elasticity and rigidity. Biochemical assays across developmental layers demonstrated variations in cellulose, soluble sugars, and antioxidant content, reflecting biochemical shifts during growth. The differential expression of ten cell wall enzyme (CWE) genes, analyzed via RT-qPCR, revealed significant correlations between gene expression patterns and CW composition changes across developmental layers. Notably, the gene expression levels of the pectin methylesterase and fucosidase enzymes were associated with the contents in cellulose, soluble sugar, and antioxidants. To complement these findings, machine learning models, including Support Vector Machines (SVM), k-Nearest Neighbors (kNN), and Neural Networks, were employed to integrate FTIR data, biochemical parameters, and CWE gene expression profiles. Our models achieved high accuracy in predicting growth stages. This underscores the intricate interplay among CW composition, CW enzymatic activity, and growth dynamics, providing a predictive framework with applications in enhancing crop productivity and sustainability.

Study on the Quality Change and Regulation Mechanism of 'Shannongsu' Pear Under Low-Temperature Storage

'Shannongsu' pear is a new high-quality cultivar. To ascertain the storage characteristics of 'Shannongsu' pears at low temperatures (0 ± 0.5 °C), the following parameters were determined: fruit firmness, ethylene, aromatic compounds, sugar content, acidity, ascorbic acid, and the expression levels of ethylene-related genes and texture-softening genes. The firmness of 'Shannongsu' pears changed less than that of the control, decreasing by only 18.8% after 170 days of storage. Low temperatures suppressed the expression of key genes associated with PbACS1a and PbACO1. Moreover, the expression of key genes related to fruit softening (PbPG1, PbXET, PbPME, and Pbα-L-Af) was suppressed during storage at low temperatures and remained at low levels. Therefore, the low levels of ethylene biosynthesis and the expression of key genes involved in fruit softening might play a major role in the excellent storage characteristics of the 'Shannongsu' cultivar. After 170 days of storage, 'Shannongsu' pears did not show significant changes in key quality dimensions such as firmness, sugar, acid, sugar-acid ratio, and ascorbic acid content. Therefore, low temperatures could help maintain the freshness, flavor, and nutritional quality of the 'Shannongsu' pear. Our findings reveal for the first time the low-temperature storage characteristics of 'Shannongsu' pears, providing a new scientific theoretical basis for pear production and marketing.

Volatile profile of postharvest hardy kiwifruits treated with chitosan-silica nanocomposite coatings

Chitosan (CTS) is a natural polysaccharide derived from the deacetylation of chitin. Chitosan-based coatings are widely used for the preservation of hardy kiwifruits. However, the effect of chitosan-based coating on fruit flavor during ripening is rarely reported. In this study, the postharvest qualities of hardy kiwifruits were investigated using chitosan coating and chitosan-silica nanoparticle coating (CTS-SiNPs) during storage at 25°C and 4°C. Physicochemical analyses showed that chitosan coating extended the shelf-life by delaying ripening and maintaining higher quality than uncoated fruits, and CTS-SiNPs treatment showed a superior preservation effect compared to CTS treatment. Untargeted metabolomics analysis based on HS-SPME-GC-MS was used to comprehensively evaluate the volatile profiles of hardy kiwifruits during postharvest storage. The metabolomics analysis showed that two chitosan coating treatments greatly delayed the accumulation of most volatiles while delaying the ripening process, and the differential volatiles were mostly involved in the terpenoids biosynthesis pathway. Notably, most green leaf volatiles (C6/C9 aldehydes, esters and alcohols) and methyl salicylate were up-regulated in the CTS-SiNPs coating groups. In addition, odor activity value (OAV) was used to characterize the key aroma-active compounds and odor profiles. A total of 32 compounds were identified as key aroma-active compounds (OAV ≥ 1) in hardy kiwifruits. The odor profile evaluation showed that the CTS-SiNPs coating treatment enhanced the intensity of the "herbal" odor, while reducing the intensity of "sweet" and "floral" odors in hardy kiwifruits at the eating-ripe stage.

Engineering tomato disease resistance by manipulating susceptibility genes

Various pathogens severely threaten tomato yield and quality. Advances in understanding plant-pathogen interactions have revealed the intricate roles of resistance (R) and susceptibility (S) genes in determining plant immunity. While R genes provide targeted pathogen resistance, they are often vulnerable to pathogen evolution. Conversely, S genes offer a promising avenue for developing broad-spectrum and durable resistance through targeted gene editing. Recent breakthroughs in CRISPR/Cas-based technologies have revolutionized the manipulation of plant genomes, enabling precise modification of S genes to enhance disease resistance in tomato without compromising growth or quality. However, the utilization of the full potential of this technique is challenging due to the complex plant-pathogen interactions and current technological limitations. This review highlights key advances in using gene editing tools to dissect and engineer tomato S genes for improved immunity. We discuss how S genes influence pathogen entry, immune suppression, and nutrient acquisition, and how their targeted editing has conferred resistance to bacterial, fungal, and viral pathogens. Furthermore, we address the challenges associated with growth-defense trade-offs and propose strategies, such as hormonal pathway modulation and precise regulatory edits, to overcome these limitations. This review underscores the potential of CRISPR-based approaches to transform tomato breeding, paving the way for sustainable production of disease-resistant cultivars amidst escalating global food security challenges.

H2O2-mediated cell wall remodeling and pectin demethylesterification are involved in maintaining postharvest texture of table grape by sulfur dioxide

Berry texture affects consumer acceptance and postharvest shelf life of table grapes. This study elucidates how sulfur dioxide (SO2) treatment maintains grape texture quality, focusing on the role of hydrogen peroxide (H2O2)-mediated cell wall modifications. SO2 treatment exhibited effects similar to those of H2O2 treatment, resulting in firmer berries with more intact cell wall structures, higher contents of chelate-soluble pectin, sodium carbonate-soluble pectin, hemicellulose, and cellulose, with lower levels of water-soluble pectin compared to untreated fruit. Moreover, it delays pectin nanostructure disassembly and reduces degree of pectin methylesterification, which facilitates the formation of calcium bridges between demethylesterified pectin and increased calcium ions, thereby strengthening the cell wall and weakening enzymatic pectin degradation. Conversely, combining ROS generation inhibitors with SO2 mitigated these effects. Overall, these findings highlight the role of H2O2-mediated cell wall modification in maintaining grape postharvest texture through SO2 treatment, providing new insights for managing grape postharvest softening.

Compositional analysis of baru (Dipteryx alata Vogel) pulp highlighting its industrial potential

Baru (Dipteryx alata Vogel), a fruit native to the Brazilian Cerrado, has gained scientific interest due to its nutritional potential and commercial value. Its edible seed, of high commercial value, represents around 5 % of the fruit. On the other hand, its pulp, a byproduct of the baru processing industry, is normally discarded, generating a huge volume of waste with reported antioxidant properties. This study investigates the composition and bioactive properties of baru pulp, aiming to identify the antioxidant components in this byproduct. Our analysis revealed that baru pulp is rich in sugars (41.86 %), fiber (29.12 %), and essential minerals, along with commercially valuable bioactive compounds such as trigonelline (139.10 mg 100 g-1), tannins (429.16 mg tannin equivalent 100 g-1), vitamin C (109.57 mg 100 g-1), and phenolic compounds such as trans-cinnamic acid (5.91 mg 100 g-1), chlorogenic acid, and gallic acid (1.07 mg 100 g-1). Industrially relevant sesquiterpenes, such as α-copaene and bicyclogermacrene, account for 42.75 % of the volatile profile, alongside germacrene D (11.69 %), aromadendrene (9.05 %), α-cubebene (6.84 %), β-elemene (5.90 %), and ledene (5.82 %), which are commonly used in essential oil production from other food matrices. While further studies are required to optimize extraction methods, these findings highlight baru pulp as a promising and low-cost alternative to traditional sources of bioactive compounds, with potential applications in functional food formulations and sustainable industrial processes. Specifically, the use of in natura pulp or its flour for food enrichment is recommended, supporting sustainability through the valorization of agro-industrial waste.

Fruit-specific effects of tryptophan and melatonin as active components to extend the functionality of red fruits during post-harvest processing

Preserving quality attributes in the distribution chain is a challenging task, particularly in fruits with a brief shelf life. The application of melatonin in cherries, raspberries, strawberries and blueberries stored at room temperature was evaluated, as well as the effects of its precursor (tryptophan) to determine their specificity and interchangeable feasibility for post-harvest applications. The results demonstrated that melatonin is effective in all tested fruits, reducing deterioration rate and its severity, preserving fruit firmness and reducing darkening and weight loss. Furthermore, tryptophan applications incremented melatonin contents in strawberries and blueberries and delayed decay in both fruits. Melatonin reduced postharvest losses in all studied fruits related to its antisenescent properties, while the beneficial impact of tryptophan in extending shelf life was fruit-specific and appeared to be partly mediated by melatonin. Melatonin and tryptophan must be considered as active components of new formulations for extending the shelf life of red fruits during post-harvest processing.

Exopolygalacturonase Production from the Novel Strain Lichtheimia sp. UV-16 and Enzyme Hydrolysis Properties

A pectinase-producing strain, Lichtheimia sp. X-8, was isolated from the soil for the first time. Subsequently, Lichtheimia sp. UV-16, with a 1.23-fold increase in pectinase activity, was obtained via UV mutagenesis, and optimization of its liquid fermentation process boosted pectinase activity from 455.6 ± 12.7 to 3202.0 ± 82.1 U/mL. The crude enzyme was purified by salting out and anion exchange resin, with a purification ratio of 2.28-fold and a yield of 36.5%. The optimal reaction temperature for the pure enzyme was 60 °C with an optimal pH of 5.5. Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) confirmed that the enzyme was an exopolygalacturonase, achieving over 99% efficiency in pectin hydrolysis. Furthermore, incorporating pure enzymes into juice pulps can substantially enhance the juice yield, which makes this polygalacturonase a promising application in the beverage industry.

Natural variation in MdNAC5 contributes to fruit firmness and ripening divergence in apple

Fruit firmness is an important trait for characterizing the quality and value of apple. It also serves as an indicator of fruit maturity, as it is a complex trait regulated by multiple genes. Resequencing techniques can be employed to elucidate variations in such complex fruit traits. Here, the whole genomes of 294 F 1 hybrids of 'Fuji' and 'Cripp's Pink' were resequenced, and a high-density binmap was constructed using 5014 bin markers with a total map distance of 2213.23 cM and an average map distance of 0.44 cM. Quantitative trait loci (QTLs) of traits related to fruit were mapped, and an A-T allele variant identified in the coding region of MdNAC5 was found to potentially regulate fruit firmness and ripening. The overexpression of MdNAC5 A resulted in higher production of methionine and 1-aminocyclopropanecarboxylic acid compared to MdNAC5 T , leading to reduced fruit firmness and accelerated ripening in apples and tomatoes. Furthermore, the activities of MdNAC5 A and MdNAC5 T were enhanced through their differential binding to the promoter regions of MdACS1 and MdERF3. Spatial variations in MdNAC5 A and MdNAC5 T caused changes in MdACS1 expression following their interaction with MdERF3. Ultimately, utilizing different MdNAC5 alleles offers a strategy to manipulate fruit firmness in apple breeding.

Sustainable active packaging developed using starch-based foam incorporating 1-Methylcyclopropene@α-Cyclodextrin

The preservation of fruit freshness during long-distance transportation frequently faces significant challenges, especially a high risk of spoilage. 1-Methylcyclopropene (1-MCP), an effective ethylene inhibitor, is widely used to slow down fruit ripening and maintain freshness. However, achieving a controllable release of 1-MCP is challenging, and traditional carrier materials such as paper, chitosan films, and microcapsules have proven unsatisfactory. Here, we introduced an innovative sustainable packaging featuring a "sandwich" structure based on starch-based foam sheets. The hydrophilic properties and porous structure of the foam ensure the controllable and slow release of 1-MCP. Additionally, its mechanical durability provides a cushioning role to minimize physical damage to fruits during transport process. This method achieves a significant reduction in ethylene production and respiration rates by up to 60.49 % and 57.50 % respectively, leading to an extension of the shelf life of climacteric fruits by 5-10 days. The novel active packaging not only effectively prolongs the shelf life and improves the quality of fruit but is also economical and environmentally friendly due to its biodegradable starch-based composition.

The soil application of a plant-derived protein hydrolysate speeds up selectively the ripening-specific processes in table grape

Plant-derived biostimulants have gained attention in agricultural practices for their potential to enhance crop quality and resilience. In this study, we investigated the effects of applying a maize gluten-derived protein hydrolysate at the soil level in vineyards on berry quality in a table grape variety, the Black Magic early table grapevine, during veraison. Our results demonstrate significant improvements in various parameters 14 days after application, including increased anthocyanin levels, enhanced sugar accumulation, and larger berry diameter while maintaining berry firmness. Transcriptomic analysis revealed mechanisms underlying these effects, highlighting the biostimulant's ability to expedite ripening processes while selectively modulating genes associated with cell wall metabolism, thus explaining the observed preservation of berry firmness. Furthermore, the treatment with a gluten-derived protein hydrolysate enhanced the grapevine's resilience to abiotic and biotic stresses, and several related genes were affected. This study sheds light on the potential of plant-derived biostimulants in grapevine cultivation, emphasizing the need for further research to elucidate their mechanisms and optimize agricultural practices.

The MaNAP1-MaMADS1 transcription factor module mediates ethylene-regulated peel softening and ripening in banana

The banana (Musa spp.) peel undergoes rapid softening during ripening, leading to finger drop and a shortened shelf life. The regulatory mechanism behind this process remains to be elucidated. In this study, we confirmed the role of peel softening in banana finger drop and uncovered the underlying transcriptional regulatory network. Cell wall-related (CWR) genes were substantially upregulated in both the peel and finger drop zone during ethylene-induced ripening. Transcriptome analysis and genome-wide profiling of chromatin accessibility and transcription factor (TF) binding revealed that two key regulators of fruit ripening, Musa acuminata NAC-like, Activated by apetala3/Pistillata1 (MaNAP1) and MaMADS1, regulate CWR genes by directly binding to their promoters or by targeting other ripening-related TFs to form a hierarchical regulatory network. Notably, MaNAP1 and MaMADS1 were directly targeted by ETHYLENE INSENSITIVE3 (MaEIN3), and MaNAP1 and MaMADS1 associated with tissue-specific histone modifications, enabling them to integrate MaEIN3-mediated ethylene signaling and undergo epigenetic regulation. Overexpression of MaNAP1, MaMADS1, or other identified regulatory TFs upregulated CWR genes and promoted peel softening. Our findings unveil a MaNAP1-MaMADS1-centered regulatory cascade governing banana peel softening and finger drop, offering potential targets for enhancing banana texture and shelf life.

Genome-Wide Association Study of Grape Texture Based on Puncture

Grapes are grown extensively around the world and play a crucial role in overall fruit production globally. The quality of the grape is largely determined by the texture of the flesh, making it a key focus for grape breeders. Our study was conducted on 437 grape accessions using a puncture method to analyze berry texture characteristics. The results reveal strong correlations among the five texture parameters of grape accessions. Following the GWAS analysis using 2,124,668 population SNPs, 369 significant SNP locations linked to the grape berry texture were discovered. Through the process of gene annotation and expression analysis in the localization regions, several genes potentially linked to berry texture were identified, including E13A, FIS1A, CML35, AGL2, and AGL62. E13A, FIS1A, and CML35 were identified as potentially more relevant to grape berry texture based on gene expression analysis. Further investigation through transient transformation demonstrated that overexpressing E13A and CML35 resulted in notable changes in grape pulp texture. During this study, the berry textures of 437 grape accessions were comprehensively evaluated, and several important candidate genes were screened based on GWAS and analysis of gene function. This discovery paves the way for future research and breeding initiatives related to grape berry texture.

Effect of Short-Term High-CO2 Treatments on the Quality of Highbush and Rabbiteye Blueberries During Cold Storage

The global demand for blueberries has increased due to their health benefits, but postharvest losses, particularly firmness loss and decay, present significant challenges. This study evaluated the effects of high CO2 concentrations (15% and 20%) applied for 3 d at 1.0 °C on highbush (cv. 'Duke') and rabbiteye (cv. 'Ochlockonee') blueberries, with a focus on quality maintenance during cold storage. The quality parameters evaluated included titratable acidity, pH, total soluble solids, weight loss, and decay. The effect of gaseous treatments on firmness was analyzed using mechanical parameters and the expression of genes related to cell wall integrity (XTH23, PL8, PG, PM3, EXP4, and VcGH5). Treatment efficacy varied between species. High CO2 levels reduced decay in both cultivars, but only the highbush cultivar ('Duke') showed improvements in firmness. In 'Duke', CO2 treatments affected the expression of XTH23, PL8, and GH5, while the role of PG and PME in maintaining firmness was minimal, with no significant differences between treatments. In 'Ochlockonee', CO2 effectively reduced weight loss but did not improve firmness. In conclusion, these results highlight the need for tailored postharvest strategies for different blueberry cultivars and suggest that short-term high CO2 treatments may effectively prolong the postharvest life of highbush blueberries.

MdWRKY31-MdNAC7 regulatory network: orchestrating fruit softening by modulating cell wall-modifying enzyme MdXTH2 in response to ethylene signalling

Softening in fruit adversely impacts their edible quality and commercial value, leading to substantial economic losses during fruit ripening, long-term storage, long-distance transportation, and marketing. As the apple fruit demonstrates climacteric respiration, its firmness decreases with increasing ethylene release rate during fruit ripening and postharvest storage. However, the molecular mechanisms underlying ethylene-mediated regulation of fruit softening in apple remain poorly understood. In this study, we identified a WRKY transcription factor (TF) MdWRKY31, which is repressed by ethylene treatment. Using transgenic approaches, we found that overexpression of MdWRKY31 delays softening by negatively regulating xyloglucan endotransglucosylase/hydrolases 2 (MdXTH2) expression. Yeast one-hybrid (Y1H), electrophoretic mobility shift (EMSA), and dual-luciferase assays further suggested that MdWRKY31 directly binds to the MdXTH2 promoter via a W-box element and represses its transcription. Transient overexpression of ethylene-induced MdNAC7, a NAC TF, in apple fruit promoted softening by decreasing cellulose content and increasing water-soluble pectin content in fruit. MdNAC7 interacted with MdWRKY31 to form a protein complex, and their interaction decreased the transcriptional repression of MdWRKY31 on MdXTH2. Furthermore, MdNAC7 does not directly regulate MdXTH2 expression, but the protein complex formed with MdWRKY31 hinders MdWRKY31 from binding to the promoter of MdXTH2. Our findings underscore the significance of the regulatory complex NAC7-WRKY31 in ethylene-responsive signalling, connecting the ethylene signal to XTH2 expression to promote fruit softening. This sheds light on the intricate mechanisms governing apple fruit firmness and opens avenues for enhancing fruit quality and reducing economic losses associated with softening.

Influence of ripening stage on the microwave-assisted pectin extraction from banana peels: A feasibility study targeting both the Homogalacturonan and Rhamnogalacturonan-I region

This work investigated a sustainable and efficient approach of pectin extraction for banana peel waste valorisation and studied the influence of banana ripening stages (RS at 2,5 and 7). Although pectin content in banana peel raw material decreased during ripening, pectin extraction was favoured. The highest alcohol-insoluble solids (AIS) yield (12.5%) was achieved at 70 °C, 15 mins from RS 7 peel. All extracts were homogalacturan-rich with some rhamnogalacturonan-I content (showing HGA/RG-I ratio > 2) with varied degree of methylation (DM). The highest HGA content (837.2 mg/g AIS) and HGA/RG-I ratio (9.9) were achieved at 110 °C, 0 mins from RS 7, suggesting its promising application as gelling agent. The highest RG-I content (111.1 mg/g AIS) were obtained at 110 °C, 5 mins from RS 7, which was comparable with the pectin with reported prebiotic ability isolated from the literature, suggesting its potential application in novel products.

In-situ electrospinning PVB/Camellia oil/ZnO-TiO2 nanofibrous membranes with synergistic antibacterial and degradation of ethylene applied in fruit preservation

This work utilizes a handheld electrospinning device to prepare a novel nanofibrous composite membrane in situ for packaging freshness. It can realize pick-and-pack and is easy to operate. The nanofibrous membrane is based on PVB as the matrix material, adding Camellia oil (CO) and ZnO-TiO2 composite nanoparticles (ZT) as the active material. The antimicrobial property of the CO and the photocatalytic activity of the nanoparticles give the material good antimicrobial and ethylene degradation functions. Meanwhile, this nanofibrous membrane has good mechanical properties, suitable moisture permeability and good optical properties. The nanofibrous membrane are suitable for both climacteric and non- climacteric fruits. Its use as a cling film extends the shelf life of strawberries by 4 days and significantly slows the ripening of small tomatoes. Therefore, this nanofibrous membrane has great potential for application in the field of fruit preservation.

Transcriptome and metabolome analyses provide insights into the fruit softening disorder of papaya fruit under postharvest heat stress

Heat stress in summer causes softening disorder in papaya but the molecular mechanism is not clear. In this study, papaya fruit stored at 35 °C showed a softening disorder termed rubbery texture. Analysis of the transcriptome and metabolome identified numerous differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) between the fruit stored at 25 °C and 35 °C. The DEGs and DAMs related to lignin biosynthesis were upregulated, while those related to ethylene biosynthesis, sucrose metabolism, and cell wall degradation were downregulated under heat stress. Co-expression network analysis highlighted the correlation between the DEGs and metabolites associated with lignin biosynthesis, ethylene biosynthesis, and cell wall degradation under heat stress. Finally, the correlation analysis identified the key factors regulating softening disorder under heat stress. The study's findings reveal that heat stress inhibited papaya cell wall degradation and ethylene production, delaying fruit ripening and softening and ultimately resulting in a rubbery texture.

Structural characteristics of cell wall pectic polysaccharides from wampee and their decreased binding with pectinase by wampee polyphenol

To investigate the structural characteristics of cell wall pectic polysaccharides from wampee, water soluble pectin (WSP), chelator-soluble pectin (CSP) and sodium carbonate-soluble pectin (SSP) were purified. And the inhibitory effects of wampee polyphenol (WPP) on pectinase when these cell wall pectic polysaccharides were used as substrates were also explored. Purified WSP (namely PWSP) had the lowest molecular weight (8.47 × 105 Da) and the highest GalA content (33.43%). While purified CSP (called PCSP) and SSP contained more abundant rhamnogalacturonan I side chains. All of them were low-methoxy pectin (DE < 50%). Enzyme activity and kinetics analysis showed that the inhibition of pectinase by wampee polyphenol was reversible and mixed type. When SSP was used as the substrate, WPP had the strongest inhibition (IC50 = 1.96 ± 0.06 mg/mL) on pectinase. Fluorescence quenching results indicated that WPP inhibited enzyme activity by interacting with substrates and enzymes. Therefore, WPP has the application potential in controlling softening of fruits and vegetables.

Effects of 1-Methylcyclopropene Treatment on Postharvest Quality and Metabolism of Different Kiwifruit Varieties

The kiwifruit (Actinidia) is an important nutritional and economic fruit crop. However, the short edible window period of kiwifruit has seriously affected its market value. 1-Methylcyclopropene (1-MCP), as a novel ethylene inhibitor, is widely applied to delay fruit ripening and senescence. To our knowledge, there are limited studies on the effects of 1-MCP on fruit quality and metabolism of different kiwifruit varieties. Three kiwifruit cultivars (i.e., 'Xuxiang', 'Huayou', and 'Hayward') widely cultivated in China were chosen as our research objects. The variations of storage quality and metabolic characteristics of kiwifruits treated with various 1-MCP concentration (0 μL/L, 0.5 μL/L, and 1.0 μL/L) were systematically investigated. The results showed that 1-MCP treatment significantly improved the quality of kiwifruit during storage. Among them, for 'Xuxiang' and 'Hayward' varieties, 1.0 μL/L 1-MCP treatment could delay the decrease in fruit firmness, the increase in maturity index and cellulase activity, and inhibit the decrease in ascorbic acid (AsA) level. However, the 0.5 μL/L 1-MCP had a great influence on the chlorophyll content and maturity index of the 'Huayou' cultivar, and the preservation effect was satisfactory. In addition, gas chromatography-mass spectrometry (GC-MS) based metabolomics studies revealed that 1-MCP treatment affected carbohydrates metabolism, fatty acids metabolism, and amino acids metabolism in different kiwifruit varieties. Correlation analysis indicated that sugars metabolism has the closest relationship with postharvest physiological quality. This research indicated that the effectiveness of 1-MCP treatments was dependent on fruit variety and treatment concentration. Furthermore, these findings provide a theoretical foundation for extending the shelf life of different kiwifruit varieties.

Ethylene and its crosstalk with hormonal pathways in fruit ripening: mechanisms, modulation, and commercial exploitation

Ethylene is an important phytohormone that orchestrates a multitude of physiological and biochemical processes regulating fruit ripening, from early maturation to post-harvest. This review offers a comprehensive analysis of ethylene's multifaceted roles in climacteric fruit ripening, characterized by a pronounced increase in ethylene production and respiration rates. It explores potential genetic and molecular mechanisms underlying ethylene's action, focusing on key transcription factors, biosynthetic pathway genes, and signal transduction elements crucial for the expression of ripening-related genes. The varied sensitivity and dependency of ripening traits on ethylene are elucidated through studies employing genetic mutations and ethylene inhibitors such as AVG and 1-MCP. Additionally, the modulation of ripening traits by ethylene is influenced by its interaction with other phytohormones, including auxins, abscisic acid, gibberellins, jasmonates, brassinosteroids, and salicylic acid. Pre-harvest fruit drop is intricately linked to ethylene, which triggers enzyme activity in the abscission zone, leading to cell wall degradation and fruit detachment. This review also highlights the potential for applying ethylene-related knowledge in commercial contexts to enhance fruit quality, control pre-harvest drop, and extend shelf life. Future research directions are proposed, advocating for the integration of physiological, genetic, biochemical, and transcriptional insights to further elucidate ethylene's role in fruit ripening and its interaction with other hormonal pathways.

Upregulation of PECTATE LYASE5 by a NAC transcription factor promotes fruit softening in apple

Flesh firmness is a critical breeding trait that determines consumer selection, shelf life, and transportation. The genetic basis controlling firmness in apple (Malus × domestica Borkh.) remains to be fully elucidated. We aimed to decipher genetic variance for firmness at harvest and develop potential molecular markers for marker-assisted breeding. Maturity firmness for 439 F1 hybrids from a cross of "Cripps Pink" and "Fuji" was determined in 2016 and 2017. The phenotype segregated extensively, with a Gaussian distribution. In a combined bulked segregant analysis (BSA) and RNA-sequencing analysis, 84 differentially expressed genes were screened from the 10 quantitative trait loci regions. Interestingly, next-generation re-sequencing analysis revealed a Harbinger-like transposon element insertion upstream of the candidate gene PECTATE LYASE5 (MdPL5); the genotype was associated with flesh firmness at harvest. The presence of this transposon repressed MdPL5 expression and was closely linked to the extra-hard phenotype. MdPL5 was demonstrated to promote softening in apples and tomatoes. Subsequently, using the MdPL5 promoter as bait, MdNAC1-L was identified as a transcription activator that positively regulates ripening and softening in the developing fruit. We also demonstrated that MdNAC1-L could induce the up-regulation of MdPL5, MdPG1, and the ethylene-related genes MdACS1 and MdACO1. Our findings provide insight into TE-related genetic variation and the PL-mediated regulatory network for the firmness of apple fruit.

Effect of histone modifications on fruit ripening

Histone modifications are canonical epigenetic modifications mediating plant growth and development. Specially, histone modifications play important regulatory roles in plant fruit ripening, directly affecting fruit color changes, soluble sugar accumulation, and fruit softening. In this review, we focus on the effects of histone acetylation and methylation during fruit ripening. In particular, histone acetylation at H3 and H4 accelerates fruit ripening, whereas removal of histone acetylation via histone deacetylases (HDACs) inhibits or delays ripening by regulating the expression of carotenoid and anthocyanin production, glycometabolism, cell wall degradation, ethylene synthesis and signalling, and cell expansin-related genes. In addition, histone methylation is also involved in fruit ripening, in which the emergence of H3K27me3 modifications represses fruit ripening and H3K4me3 modifications promote fruit ripening by affecting multiple ripening-related pathways. However, the relationship between other histone modifications and fruit ripening is currently unclear. Here, we point out that accurate and comprehensive studies concerning the regulatory mechanism of histone modifications in fruit ripening are needed to facilitate the design of high-quality and high-yield fruit.

Elucidation of pineapple softening based on cell wall polysaccharides degradation during storage

The degradation of cell wall polysaccharides in pineapple fruit during softening was investigated in the present study. Two pectin fractions and two hemicellulose fractions were extracted from the cell wall materials of 'Comte de Paris' pineapple fruit at five softening stages, and their compositional changes were subsequently analyzed. The process of softening of the fruit corresponded to an increase in the water-soluble pectin (WSP) and 1 M KOH-soluble hemicellulose (HC1) fractions, and a decrease in the acid-soluble pectin (ASP) fraction, which suggested the solubilization and conversion of cellular wall components. However, the content of 4 M KOH-soluble hemicellulose (HC2) decreased and then returned to the initial level. Furthermore, WSP, ASP, and HC1 showed an increment in the content of low molecular weight polymers while a decline in the high molecular weight polymers throughout softening, and not significant change in the contents of different molecular polymers of HC2 was observed. Moreover, the galacturonic acid (GalA) content in the main chain of WSP was maintained at a relatively constant level, but the major branch monosaccharide galactose (Gal) in WSP decreased. Different from WSP, the molar percentages of Gal and GalA in ASP decreased. The Gal or Arabinose (Ara) in HC1 exhibited a gradual decline while the molar percentages of xylose (Xyl) and glucose (Glu) in the main chain increased. These suggested that the main chain of ASP degraded while the branched chains of ASP, WSP and HC1 depolymerized during pineapple softening. Overall, fruit softening of 'Comte de Paris' pineapple was found to be the result of differential modification of pectin and hemicellulose.

Identification of Candidate Genes Associated with Flesh Firmness by Combining QTL Mapping and Transcriptome Profiling in Pyrus pyrifolia

Flesh firmness is an important quality of pear fruits. Breeding cultivars with suitably low flesh firmness is one of the popular pear breeding goals. At present, SNP markers related to pear flesh firmness and genes affecting flesh firmness are still uncertain. In this study, a QTL analysis was performed, and the result showed that the position of 139.857 cM in lineage group 14 (LG14) had the highest average logarithm of odds (3.41) over two years. This newly discovered locus was identified as a flesh firmness-related QTL (qFirmness-LG14). The 'C/T' SNP was found in corresponding Marker1512129. The 'C' genotype is the high-firmness genotype, which is a dominant trait. The average firmness of fruits with genotype C is 21.4% higher than genotype without the C genotype. Transcriptome profiling was obtained between 'Zaoshengxinshui' and 'Qiushui' at five time points. Three candidate genes in the interval of qFirmness-LG14 might affect firmness. A gene of xyloglucan endotransglucosylase 1 (PpXTH1) was upregulated in 'Qiushui' at all five time points. Two transcription factors (PpHY5 and PpERF113) were upregulated in 'Zaoshengxinshui', which might be negative regulatory genes for high flesh firmness. The transcriptome results also isolated a large number of cell wall-related genes (e.g., Pectate lyase, Pectin acetylesterase, Pectin methylesterase, and 4-coumarate-CoA ligase) and transcription factors (e.g., ERF, WRKY). These genes are all potential upstream and downstream genes related to flesh firmness. In conclusion, this study provides valuable insights into the QTLs and molecular mechanisms associated with fruit firmness in Pyrus pyrifolia.

Alleviation of the degradation of cell wall pectin contributes to the maintenance of integrity of papaya (Carica papaya L.) fruit tissue during abnormal chilling injury behavior

Papaya (Carica papaya L.) is highly susceptible to chilling injury (CI), which primarily causes surface pitting, black scald, susceptibility to fungal infection, and the breakdown of tissue. It developed rapidly at 6 °C but was significantly suppressed at 1 °C, which indicated that the papaya tissue was more solid at a lower temperature. This rare phenomenon is considered to be abnormal CI behavior. The maintenance of fruit tissue integrity during abnormal CI behavior may be related to modifications of the cell wall pectin. The modifications of cell wall pectin were studied during storage at 1 and 6 °C. Storage at 1 °C alleviated the progression of CI and inhibited the degradation of pectin components and cell wall structure of papaya fruit. The increase in water-soluble pectin and the solubilization of cyclohexanediamine tetraacetic acid- (CDTA-) and sodium carbonate (Na2CO3)-soluble pectin was limited at 1 °C. Storage at this temperature limited the detachment of linear backbone chains and minimized the degradation of branching and reticular structure in the pectin molecules. Storage at this temperature also delayed the decrease in the size of pectin backbone and helped to prevent the loss of neutral sugars from the pectin side chains. Thus, alleviation of the degradation of cell wall pectin contributes to the structural integrity of the cell wall and thus helps the maintenance of the tissue integrity of papaya at 1 °C.

Inference of the genetic basis of fruit texture in highbush blueberries using genome-wide association analyses

The global production and consumption of blueberry (Vaccinium spp.), a specialty crop known for its abundant bioactive and antioxidant compounds, has more than doubled over the last decade. To hold this momentum, plant breeders have begun to use quantitative genetics and molecular breeding to guide their decisions and select new cultivars that are improved for fruit quality. In this study, we leveraged our inferences on the genetic basis of fruit texture and chemical components by surveying large breeding populations from northern highbush blueberries (NHBs) and southern highbush blueberries (SHBs), the two dominant cultivated blueberries. After evaluating 1065 NHB genotypes planted at the Oregon State University, and 992 SHB genotypes maintained at the University of Florida for 17 texture-related traits, evaluated over multiple years, our contributions consist of the following: (i) we drew attention to differences between NHB and SHB materials and showed that both blueberry types can be differentiated using texture traits; (ii) we computed genetic parameters and shed light on the genetic architecture of important texture attributes, indicating that most traits had a complex nature with low to moderate heritability; (iii) using molecular breeding, we emphasized that prediction could be performed across populations; and finally (iv) the genomic association analyses pinpointed some genomic regions harboring potential candidate genes for texture that could be used for further validation studies. Altogether, the methods and approaches used here can guide future breeding efforts focused on maximizing texture improvements in blueberries.

Combining transcriptomics and HPLC to uncover variations in quality formation between 'Benihoppe' and 'Fenyu No.1' strawberries

'Benihoppe' and 'Fenyu No.1' are representative varieties of red and pink strawberries in China, possess distinct hue and flavor profiles. This study analyzed the underlying biochemical and molecular differences of two varieties utilizing transcriptomics and high-performance liquid chromatography (HPLC). Ripening 'Benihoppe' fruits accumulated more sucrose and pelargonin-3-glucoside (P3G) with a little cyanidin and higher firmness. Whereas ripening 'Fenyu No.1' fruits contained more fructose, glucose, malic acid and ascorbic acid (AsA), but less P3G and citric acid. Moreover, genotype significantly influenced phenolic compounds contents in strawberries. Transcriptome analysis revealed that pectin degradation (PL, PG, PE), sucrose synthesis (CWINV, SUS, TPS) and citric acid metabolism (α-OGDH, ICDH, GAD, GS, GDH, PEPCK, AST) were weakened in 'Benihoppe' fruit. In contrast, the synthesis of sucrose (CWINH, SPS), citric acid (CS, PEPC), anthocyanin (F3H, F3'H, F3'5'H, DFR, UFGT and ANS), and citric acid transport (V-ATPase) was enhanced. In 'Fenyu No.1' fruit, the degradation of sucrose, citric acid, and pectin was enhanced, along with the synthesis of malic acid (ME) and ascorbic acid (PMM, MDHAR and GaLUR). However, anthocyanins synthesis, glucose metabolism (HK, G6PI, PFK, G6PDH, PGK, PGM, ENO, PK), fructose metabolism (FK), citric acid synthesis and transport, and AsA degradation (AO, APX) were relatively weak. RT-qPCR results corroborated the transcriptome data. In conclusion, this study revealed the distinctions and characteristics of strawberries with different fruit colors regarding texture, flavor and color formation processes. These findings offer valuable insights for regulating metabolic pathways and identifying key candidate genes to improve strawberry quality.

Towards Characterization of Hass Avocado Peel and Pulp Proteome during Postharvest Shelf Life

In recent years, avocados have gained worldwide popularity as a nutritive food. This trend is causing a rise in the production of this fruit, which is accompanied by several problems associated with monocultural practices. Despite massive economic gains, limited molecular and structural information has been generated about avocado ripening. In fact, limited studies have attempted to unravel the proteome complexity dynamics of avocado fruit. We therefore conducted a comparative proteomics study on avocado peel and pulp during the postharvest shelf life using tandem mass tag synchronous precursor selection triple-stage mass spectrometry. We identified 3161 and 1128 proteins in the peel and pulp, respectively. Peels exhibited major over-accumulation of proteins associated with water deprivation and oxidative stress, along with abscisic acid biosynthesis. Ethylene, jasmonic acid, phenylpropanoid, and flavonoid biosynthesis pathways were activated. Structurally, we observed the accumulation of lignin and a reduction in cuticular thickness, which coincides with the reduction in the levels of long-chain acyl-coenzyme A synthetase and a marginal increase in 10,16-dihydroxyhexadecanoic acid. Our study sheds light on the association of proteome modulation with the structural features of Hass avocado. Its detailed characterization will provide an alternative for better preservation during the postharvest period.

Ripening and rot: How ripening processes influence disease susceptibility in fleshy fruits

Fleshy fruits become more susceptible to pathogen infection when they ripen; for example, changes in cell wall properties related to softening make it easier for pathogens to infect fruits. The need for high-quality fruit has driven extensive research on improving pathogen resistance in important fruit crops such as tomato (Solanum lycopersicum). In this review, we summarize current progress in understanding how changes in fruit properties during ripening affect infection by pathogens. These changes affect physical barriers that limit pathogen entry, such as the fruit epidermis and its cuticle, along with other defenses that limit pathogen growth, such as preformed and induced defense compounds. The plant immune system also protects ripening fruit by recognizing pathogens and initiating defense responses involving reactive oxygen species production, mitogen-activated protein kinase signaling cascades, and jasmonic acid, salicylic acid, ethylene, and abscisic acid signaling. These phytohormones regulate an intricate web of transcription factors (TFs) that activate resistance mechanisms, including the expression of pathogenesis-related genes. In tomato, ripening regulators, such as RIPENING INHIBITOR and NON_RIPENING, not only regulate ripening but also influence fruit defenses against pathogens. Moreover, members of the ETHYLENE RESPONSE FACTOR (ERF) family play pivotal and distinct roles in ripening and defense, with different members being regulated by different phytohormones. We also discuss the interaction of ripening-related and defense-related TFs with the Mediator transcription complex. As the ripening processes in climacteric and non-climacteric fruits share many similarities, these processes have broad applications across fruiting crops. Further research on the individual contributions of ERFs and other TFs will inform efforts to diminish disease susceptibility in ripe fruit, satisfy the growing demand for high-quality fruit and decrease food waste and related economic losses.

Foliar spraying of boron prolongs preservation period of strawberry fruits by altering boron form and boron distribution in cell

Boron (B), an essential micronutrient for fruit development, also plays a crucial role in maintaining the shelf life of strawberries (Fragaria ananassa Duch.) by affecting cell wall structure and components. We investigated the distribution pattern of B within cells and cell walls in strawberry fruits under different B levels and revealed the relationship between the B distribution in cell walls and fruit firmness after harvesting. Foliar spraying of 0.1% H3BO3 promoted the growth of strawberry seedlings and improved fruit yield and flesh firmness by 45.7% and 25.6%. During the fruit softening and decay process, the content of bound B and cell wall-B decreased while more B was allocated to the protoplast and apoplast. The changes in B distribution in cells were attributed to cell damage during fruit decay, and B extended the freshness period of the fruits by alleviating the decrease of B distribution in cell walls. After leaving the fruits at room temperature for 10 h, the B content in different cell wall components significantly decreased, while foliar spraying of B alleviated the reduction of B content in covalently bound pectin (CBP), cellulose, and hemicellulose. Meanwhile, B spraying on fruit decreased the activity of cell wall degradation enzymes, including polygalacturonase (PG) and pectin lyase (PL), by 20.2% and 38.1%, while enhancing the demethylation of pectin by increasing pectin methylesterase (PME) activity from 21.6 U/g to 25.7 U/g. Thus, foliar spraying of 0.1% H3BO3 enhances the cross-linking of B with cell wall components and maintains cell wall structure, thereby prolonging the shelf life of strawberry fruits.

Quantitative Proteomics Analysis of ABA- and GA3-Treated Malbec Berries Reveals Insights into H2O2 Scavenging and Anthocyanin Dynamics

Abscisic acid (ABA) and gibberellic acid (GA3) are regulators of fruit color and sugar levels, and the application of these hormones is a common practice in commercial vineyards dedicated to the production of table grapes. However, the effects of exogenous ABA and GA3 on wine cultivars remain unclear. We investigated the impact of ABA and GA3 application on Malbec grapevine berries across three developmental stages. We found similar patterns of berry total anthocyanin accumulation induced by both treatments, closely associated with berry H2O2 levels. Quantitative proteomics from berry skins revealed that ABA and GA3 positively modulated antioxidant defense proteins, mitigating H2O2. Consequently, proteins involved in phenylpropanoid biosynthesis were downregulated, leading to decreased anthocyanin content at the almost ripe stage, particularly petunidin-3-G and peonidin-3-G. Additionally, we noted increased levels of the non-anthocyanins E-viniferin and quercetin in the treated berries, which may enhance H2O2 scavenging at the almost ripe stage. Using a linear mixed-effects model, we found statistical significance for fixed effects including the berry H2O2 and sugar contents, demonstrating their roles in anthocyanin accumulation. In conclusion, our findings suggest a common molecular mechanism by which ABA and GA3 influence berry H2O2 content, ultimately impacting anthocyanin dynamics during ripening.

Transcription-Associated Metabolomic Analysis Reveals the Mechanism of Fruit Ripening during the Development of Chinese Bayberry

The ripening process of Chinese bayberries (Myrica rubra) is intricate, involving a multitude of molecular interactions. Here, we integrated transcriptomic and metabolomic analysis across three developmental stages of the Myrica rubra (M. rubra) to elucidate these processes. A differential gene expression analysis categorized the genes into four distinct groups based on their expression patterns. Gene ontology and pathway analyses highlighted processes such as cellular and metabolic processes, including protein and sucrose metabolism. A metabolomic analysis revealed significant variations in metabolite profiles, underscoring the dynamic interplay between genes and metabolites during ripening. Flavonoid biosynthesis and starch and sucrose metabolism were identified as key pathways, with specific genes and metabolites playing crucial roles. Our findings provide insights into the molecular mechanisms governing fruit ripening in M. rubra and offer potential targets for breeding strategies aimed at enhancing fruit quality.

A review of history, properties, classification, applications and challenges of natural and synthetic dyes

Natural dyes have been used for centuries for coloring textiles, food, and other materials. Synthetic dyes are particularly popular due to their ease of use, wide range of available colors, and fastness. However, their usage comes with significant environmental and health challenges. In recent years, there has been a renewed interest in natural dyes due to their eco-friendliness, ready availability, affordability, non-toxicity, and sustainability. Hence, natural dyes are fast gaining popularity as better alternatives to synthetic dyes. Nature is blessed with a rich diversity of plant species with varying colors and properties which can be harnessed in textile, printing, cosmetics, and food industries. This paper presents a comprehensive review on natural and synthetic dyes with particular focus on their history, properties, classification, extraction methods, applications, and health challenges. Although many plants have been suggested as potential sources of natural dyes, there is insufficient information on their exploration and application. Additionally, chemical analyses of these dyes have not been extensively done. Overall, the results of studies conducted so far identified a number of promising taxa for further investigation as plant-based dyes with many indigenous plants as potential sources of natural dyes.

Genome-Wide Analysis of Polygalacturonase Gene Family Reveals Its Role in Strawberry Softening

Fruit softening is a prominent attribute governing both longevity on shelves and commercial worth. Polygalacturonase (PG) plays a major role in strawberry fruit softening. However, the PG gene family in strawberry has not been comprehensively analyzed. In this study, 75 FaPG genes were identified in the octoploid strawberry genome, which were classified into three groups according to phylogenetic analysis. Subcellular localization prediction indicated that FaPGs are mostly localized to the plasma membrane, cytoplasm, and chloroplasts. Moreover, the expression of FaPGs during strawberry development and ripening of 'Benihoppe' and its softer mutant was estimated. The results showed that among all 75 FaPGs, most genes exhibited low expression across developmental stages, while two group c members (FxaC_21g15770 and FxaC_20g05360) and one group b member, FxaC_19g05040, displayed relatively higher and gradual increases in their expression trends during strawberry ripening and softening. FxaC_21g15770 was selected for subsequent silencing to validate its role in strawberry softening due to the fact that it exhibited the highest and most changed expression level across different developmental stages in 'Benihoppe' and its mutant. Silencing FxaC_21g15770 could significantly improve strawberry fruit firmness without affecting fruit color, soluble solids, cellulose, and hemicellulose. Conversely, silencing FxaC_21g15770 could significantly suppress the expression of other genes related to pectin degradation such as FaPG-like, FaPL, FaPME, FaCX, FaCel, FaGlu, FaXET, and FaEG. These findings provide basic information on the FaPG gene family for further functional research and indicate that FxaC_21g15770 plays a vital role in strawberry fruit softening.

Identification and Characterization of Pectate Lyase as a Novel Allergen in Artemisia sieversiana Pollen

INTRODUCTION

Artemisia species are widely spread in north hemisphere. Artemisia sieversiana pollen is one of the common pollen allergens in the north of China. At present, seven allergens were identified and had been listed officially from A. sieversiana pollen, but the remaining allergens are still insufficiently studied, which need to be found.

METHODS

Pectate lyase was purified from the extracts of A. sieversiana pollen by anion exchange, size exclusion, and HPLC-hydrophobic interaction chromatography. The gene of A. sieversiana pectate lyase (Art si pectate lyase) was cloned and expressed in Escherichia coli. The enzyme activity and circular dichroism (CD) spectrum of natural and recombinant proteins were analyzed. The allergenicity of Art si pectate lyase was characterized by enzyme-linked immunosorbent assay (ELISA), Western blot, inhibition ELISA, and basophil activation test. The allergen's physicochemical properties, three-dimensional structure, sequence profiles with homologous allergens and phylogenetic tree were analyzed by in silico methods.

RESULTS

Natural Art si pectate lyase (nArt si pectate lyase) was purified from A. sieversiana pollen extracts by three chromatographic strategies. The cDNA sequence of Art si pectate lyase had a 1191-bp open reading frame encoding 396 amino acids. Both natural and recombinant pectate lyase (rArt si pectate lyase) exhibited similar CD spectrum, and nArt si pectate lyase had higher enzymatic activity. Moreover, the specific immunoglobulin E (IgE) binding rate against nArt si pectate lyase and rArt si pectate lyase was determined as 40% (6/15) in patients' serum with Artemisia species pollen allergy by ELISA. The nArt si pectate lyase and rArt si pectate lyase could inhibit 76.11% and 47.26% of IgE binding activities to the pollen extracts, respectively. Art si pectate lyase was also confirmed to activate patients' basophils. Its structure contains a predominant motif of classic parallel helical core, consisting of three parallel β-sheets, and two highly conserved features (vWiDH, RxPxxR) which may contribute to pectate lyase activity. Moreover, Art si pectate lyase shared the highest sequence identity of 73.0% with Art v 6 among currently recognized pectate lyase allergen, both were clustered into the same branch in the phylogenetic tree.

CONCLUSION

In this study, pectate lyase was identified and comprehensively characterized as a novel allergen in A. sieversiana pollen. The findings enriched the allergen information for this pollen and promoted the development of component-resolved diagnosis and molecular therapy of A. sieversiana pollen allergy.

Gene-Based Developments in Improving Quality of Tomato: Focus on Firmness, Shelf Life, and Pre- and Post-Harvest Stress Adaptations

Tomato (Solanum lycopersicum) is a widely consumed vegetable crop with significant economic and nutritional importance. This review paper discusses the recent advancements in gene-based approaches to enhance the quality of tomatoes, particularly focusing on firmness, shelf life, and adaptations to pre- and post-harvest stresses. Utilizing genetic engineering techniques, such as Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated proteins 9 (CRISPR/Cas9) and Transcription Activator-like Effector Nucleases (TALENs), researchers have made remarkable progress in developing tomatoes with improved traits that address key challenges faced during cultivation, storage, and transportation. We further highlighted the potential of genetic modifications in enhancing tomato firmness, thereby reducing post-harvest losses and improving consumer satisfaction. Furthermore, strategies to extend tomato shelf life through genetic interventions are discussed, emphasizing the importance of maintaining quality and freshness for sustainable food supply chains. Furthermore, the review delves into the ways in which gene-based adaptations can bolster tomatoes against environmental stresses, pests, and diseases, thereby enhancing crop resilience and ensuring stable yields. Emphasizing these crucial facets, this review highlights the essential contribution of genetic advancements in transforming tomato production, elevating quality standards, and promoting the sustainability of tomato cultivation practices.

Effect of modified atmosphere package on attributes of sweet bamboo shoots after harvest

Tender bamboo shoots undergo rapid senescence that influences their quality and commercial value after harvest. In this study, the tender sweet bamboo shoots ('Wensun') were packed by a passive modified atmosphere packaging (PMAP) to inhibit the senescence process, taking polyethylene package as control. The increase in CO2 and the decrease in O2 gas concentrations in the headspace atmosphere of the packages were remarkably modified by PMAP treatments. The modified gas atmosphere packaging inhibited the changes in firmness, as well as the content of cellulose, total pectin, and lignin in the cell walls of bamboo shoots. The enzymatic activities of cellulase, pectinase, and polygalacturonase that act on cell wall polysaccharides, and phenylalanine ammonia lyase, cinnamyl alcohol dehydrogenase, peroxidase, and laccase regulating the lignin biosynthesis were modified by PMAP treatment different from control during storage. The expression levels of the lignin biosynthesis genes PePAL3/4, PeCAD, Pe4CL5, PeC4H, PeCCOAOMT, PeCOMT, cellulose synthase PeCESA1, and related transcription factors PeSND2, PeKNAT7, PeMYB20, PeMYB63, and PeMYB85 were clearly regulated. These results suggest that PMAP efficiently retards the changes in lignin and cell wall polysaccharides, thus delaying the senescence of tender sweet bamboo shoots during storage.

A 5.2-kb insertion in the coding sequence of PavSCPL, a serine carboxypeptidase-like enhances fruit firmness in Prunus avium

Fruit firmness is an important trait in sweet cherry breeding because it directly positively influences fruit transportability, storage and shelf life. However, the underlying genes responsible and the molecular mechanisms that control fruit firmness remain unknown. In this study, we identified a candidate gene, PavSCPL, encoding a serine carboxypeptidase-like protein with natural allelic variation, that controls fruit firmness in sweet cherry using map-based cloning and functionally characterized PavSCPL during sweet cherry fruit softening. Genetic analysis revealed that fruit firmness in the 'Rainier' × 'Summit' F1 population was controlled by a single dominant gene. Bulked segregant analysis combined with fine mapping narrowed the candidate gene to a 473-kb region (7418778-7 891 914 bp) on chromosome 6 which included 72 genes. The candidate gene PavSCPL, and a null allele harbouring a 5244-bp insertion in the second exon that completely inactivated PavSCPL expression and resulted in the extra-hard-flesh phenotype, were identified by RNA-sequencing analysis and gene cloning. Quantitative RT-PCR analysis revealed that the PavSCPL expression level was increased with fruit softening. Virus-induced gene silencing of PavSCPL enhanced fruit firmness and suppressed the activities of certain pectin-degrading enzymes in the fruit. In addition, we developed functional molecular markers for PavSCPL and the Pavscpl5.2-k allele that co-segregated with the fruit firmness trait. Overall, this research identified a crucial functional gene for fruit firmness. The results provide insights into the genetic control and molecular mechanism of the fruit firmness trait and present useful molecular markers for molecular-assisted breeding for fruit firmness in sweet cherry.

Exogenous Methyl Jasmonate (MeJA) Improves 'Ruixue' Apple Fruit Quality by Regulating Cell Wall Metabolism

'Ruixue' apples were used as the test material to study the effect of 10 μM methyl jasmonate (MeJA) on the quality and cell wall metabolism of apples after 18 d of storage. The results showed that MeJA significantly decreased the respiratory rate, reduced the titratable acid content and maintained a high soluble solids content. MeJA has been shown to suppress the activities and gene expressions of WSP, CSP, ISP, and cellulose in contrast to the control group, thereby maintaining a lower cell permeability and higher exocarp firmness. MeJA significantly decreased the expression of MdACS, MdACO, MdPL, Mdgal, and MdPG genes in the apple exocarp when compared to the control group. In addition, the overexpression of MdPL18 increased the content of cell wall polysaccharides such as WSP and CSP, enhanced cell wall-degrading enzyme activities, and accelerated fruit ripening and softening, whereas silencing MdPL18 did the opposite. Together, these results demonstrate that exogenous MeJA maintains the Ruixue apple fruit quality by regulating the metabolism of cell wall substances.

Bifunctional transcription factors SlERF.H5 and H7 activate cell wall and repress gibberellin biosynthesis genes in tomato via a conserved motif

The plant cell wall is a dynamic structure that plays an essential role in development, but the mechanism regulating cell wall formation remains poorly understood. We demonstrate that two transcription factors, SlERF.H5 and SlERF.H7, control cell wall formation and tomato fruit firmness in an additive manner. Knockout of SlERF.H5, SlERF.H7, or both genes decreased cell wall thickness, firmness, and cellulose contents in fruits during early development, especially in double-knockout lines. Overexpressing either gene resulted in thicker cell walls and greater fruit firmness with elevated cellulose levels in fruits but severely dwarf plants with lower gibberellin contents. We further identified that SlERF.H5 and SlERF.H7 activate the cellulose biosynthesis gene SlCESA3 but repress the gibberellin biosynthesis gene GA20ox1. Moreover, we identified a conserved LPL motif in these ERFs responsible for their activities as transcriptional activators and repressors, providing insight into how bifunctional transcription factors modulate distinct developmental processes.

Fruit softening: evidence for rhamnogalacturonan lyase action in vivo in ripe fruit cell walls

BACKGROUND AND AIMS

The softening of ripening fruit involves partial depolymerization of cell-wall pectin by three types of reaction: enzymic hydrolysis, enzymic elimination (lyase-catalysed) and non-enzymic oxidative scission. Two known lyase activities are pectate lyase and rhamnogalacturonan lyase (RGL), potentially causing mid-chain cleavage of homogalacturonan and rhamnogalacturonan-I (RG-I) domains of pectin respectively. However, the important biological question of whether RGL exhibits action in vivo had not been tested.

METHODS

We developed a method for specifically and sensitively detecting in-vivo RGL products, based on Driselase digestion of cell walls and detection of a characteristic unsaturated 'fingerprint' product (tetrasaccharide) of RGL action.

KEY RESULTS

In model experiments, potato RG-I that had been partially cleaved in vitro by commercial RGL was digested by Driselase, releasing an unsaturated tetrasaccharide ('ΔUA-Rha-GalA-Rha'), taken as diagnostic of RGL action. This highly acidic fingerprint compound was separated from monosaccharides (galacturonate, galactose, rhamnose, etc.) by electrophoresis at pH 2, then separated from ΔUA-GalA (the fingerprint of pectate lyase action) by thin-layer chromatography. The 'ΔUA-Rha-GalA-Rha' was confirmed as 4-deoxy-β-l-threo-hex-4-enopyranuronosyl-(1→2)-l-rhamnosyl-(1→4)-d-galacturonosyl-(1→2)-l-rhamnose by mass spectrometry and acid hydrolysis. Driselase digestion of cell walls from diverse ripe fruits [date, sea buckthorn, cranberry, yew (arils), mango, plum, blackberry, apple, pear and strawberry] yielded the same fingerprint compound, demonstrating that RGL had been acting in vivo in these fruits prior to harvest. The 'fingerprint' : (galacturonate + rhamnose) ratio in digests from ripe dates was approximately 1 : 72 (mol/mol), indicating that ~1.4 % of the backbone Rha→GalA bonds in endogenous RG-I had been cleaved by in-vivo RGL action.

CONCLUSIONS

The results provide the first demonstration that RGL, previously known from studies of fruit gene expression, proteomic studies and in-vitro enzyme activity, exhibits enzyme action in the walls of soft fruits and may thus be proposed to contribute to fruit softening.

Extensive Analysis of Mulberry (Morus rubra L.) Polysaccharides with Different Maturities by Using Two-Step Extraction and LC/QqQ-MS

A primary challenge of polysaccharide analysis is the need for comprehensive extraction and characterization methods. In this study, mulberry polysaccharides at different maturities were fully extracted through a two-step process involving ethylenediaminetetraacetic acid (EDTA) and sodium hydroxide (NaOH), and their structures were determined by a combination analysis of monosaccharides and glycosidic linkages based on liquid chromatography triple quadrupole mass spectrometry (LC/QqQ-MS). The results indicate mulberry polysaccharides mainly contain highly branched pectic polysaccharides, (1,3,6)-linked glucan, xylan, and xyloglucan, but the content of different portions varies at different maturity stages. HG decreases from 19.12 and 19.14% (green mulberry) to 9.80 and 6.08% (red mulberry) but increases to 17.83 and 11.83% as mulberry transitioned from red to black. In contrast, the contents of glucan showed opposite trends. When mulberry turns red to black, the RG-I arabinan chains decrease from 47.75 and 28.86% to 13.16 and 12.72%, while the galactan side chains increase from 1.18 and 1.91 to 8.3 and 6.49%, xylan and xyloglucan show an increase in content. Overall, the two-step extraction combined with LC/QqQ-MS provides a new strategy for extensive analysis of complex plant polysaccharides.

WALL-ASSOCIATED KINASE Like 14 regulates vascular tissue development in Arabidopsis and tomato

Initiation of plant vascular tissue is regulated by transcriptional networks during development and in response to environmental stimuli. The WALL-ASSOCIATED KINASES (WAKs) and WAK-likes (WAKLs) are cell surface receptors involved in cell expansion and defence in cells with primary walls, yet their roles in regulation of vascular tissue development that contain secondary walls remains unclear. In this study, we showed tomato (Solanum lycopersicum) SlWAKL2 and the orthologous gene in Arabidopsis thaliana, AtWAKL14, were specifically expressed in vascular tissues. SlWAKL2-RNAi tomato plants displayed smaller fruit size with fewer seeds and vascular bundles compared to wild-type (WT) and over-expression (OE) lines. RNA-seq data showed that SlWAKL2-RNAi fruits down-regulated transcript levels of genes related to vascular tissue development compared to WT. Histological analysis showed T-DNA insertion mutant wakl14-1 had reduced plant stem length with fewer number of xylem vessels and interfascicular fibres compared to WT, with no significant differences in cellulose and lignin content. Mutant wakl14-1 also showed reduced number of vascular bundles in fruit. A proWAKL14::mCherry-WAKL14 fusion protein was able to complement wakl14-1 phenotypes and showed mCherry-WAKL14 associated with the plasma membrane. In vitro binding assays showed both SlWAKL2 and AtWAKL14 can interact with pectin and oligogalacturonides. Our results reveal novel roles of WAKLs in regulating vascular tissue development.

Does harvesting age matter? Changes in structure and rheology of a shear-thickening polysaccharide from Cyathea medullaris as a function of age

A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of -4)-β-D-GlcpA-(1 → 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.