Dynamic changes of enzymes involved in sugar and organic acid level modification during blueberry fruit maturation

Comprehensive analysis of volatile flavor components in pear fruit spanning the entire development stages

The intricate pattern of flavor changes throughout the various stages of fruit development remains poorly understood. Here, we investigated the material dynamics underlying flavor formation, focusing on volatile and metabolite production across 8 fruit developmental and ripening stages of 'Yuluxiang' pear. A total of 154 volatile compounds were characterized by HS-GC-IMS combined with HS-SPME-GC-MS technology, mainly including aldehydes, ketones, and ester compounds in the young fruit and enlarging periods, and the ester compounds increase in the mature period. Notably, the expression of alcohol acetyltransferase gene in the fatty acid metabolism pathway significantly increased with ripening, thereby facilitating ester synthesis. Hexyl acetate was identified as a crucial marker for pear ripeness. Our findings provide a robust theoretical basis for regulating the synthesis and accumulation of these vital flavor compounds during the later stages of fruit development.

Sucrose synthase 3 improves fruit quality in grape

Sucrose synthase (SS) is one of the key functional enzymes involved in sugar metabolism in plants, and its activity can directly affect sugar accumulation, thereby influencing fruit quality. Our previous research found an interaction between VvSS3 and VvSnRK1β. In this study, we discovered that SS enzyme activity was mainly oriented towards decomposition, with the highest activity occurring before the veraison stage, and the overall trend of SS enzyme activity changes was positively correlated with exogenous ABA concentration. Site-directed mutagenesis revealed that VvSS3S176 and VvSS3S381 were crucial sites for the interaction between VvSS3 and VvSnRK1β. Subcellular localization results showed that VvSS3S176 and VvSS3S381, as well as VvSS3, were located on the cell membrane. VvSS3 was sensitive to ABA, promoting the accumulation of soluble sugars and anthocyanins in transgenic callus, increasing endogenous ABA content, and reducing organic acid components. VvSS3S176 and VvSS3S381 only altered the activity of SS in the synthesis direction, while the transcription level of VvSnRK1β in transgenic callus significantly decreased. After exogenous ABA treatment, Ser176 and Ser381 reduced the inhibition of VvSS3 on VvSnRK1β expression. Mutation of the binding sites of VvSS3 prevented the formation of complexes VvSnRK1β-VvSS3, thus interfering with downstream metabolism. This suggests that VvSnRK1β may form a protein complex by interacting with VvSS3, participating in the accumulation of soluble sugars in grape fruits mediated by ABA response.

Antioxidant metabolism insights into ripening and senescence delay of green pepper fruit through the salicylic acid preharvest treatment

Introduction

The systematic investigation of the biochemical and molecular bases of salicylic acid (SA) in the postharvest physiological process of green pepper fruit remains unclear.

Methods

Accordingly, this study aims to analyze the effects of 0.5 mM-SA preharvest treatments, applied by foliar spraying or irrigation, on the ripening and senescence of green pepper fruit for 28 days of storage at 7 °C.

Results

The study revealed that the preharvest application of SA, either by foliar spraying or irrigation, significantly delayed losses of weight, firmness and color during postharvest. Additionally, both treatments increased the total soluble solids and total acidity content, which lead to a significantly reduced ripening index after storage. These results were evidenced by a slowing down of the ripening and senescence processes, accompanied by the stimulation of the antioxidant enzymes in those SA-treated green pepper fruits. Furthermore, a significant increase in chlorophylls, phenolics, ascorbic acid and dehydroascorbic acid content was observed. The SA treatments also enhanced the total antioxidant activity, in both hydrophilic and lipophilic phases. These positive effects were mediated by the upregulation of the relative response of the CaAPX, CaPOD, CaPAL, CaDHAR2 genes at harvest.

Discussion

These findings reinforce the existing knowledge gap regarding the impact of foliar spraying or irrigation SA on the intricate interplay between metabolites and genes related to the antioxidant system in regulating the bell pepper fruit ripening and senescence. The impact of both applications exhibited comparable results; however, the irrigation was identified as the most advantageous due to its ease applicability and cost effectiveness in comparison.

Comparative Transcriptome Analysis Reveals Potential Molecular Regulation of Organic Acid Metabolism During Fruit Development in Late-Maturing Hybrid Citrus Varieties

Late-maturing hybrid citrus is a significant fruit that combines the best traits of both parents and is highly prized for its unique flavor. Not only can organic acids alter the flavor of citrus pulp, but they are also essential for cellular metabolism, energy conversion, and maintaining the acidbase balance in plant tissues. Although organic acids play a key role in the quality formation of citrus fruits, there is still insufficient research on the metabolic processes of organic acids in late-maturing hybrid citrus varieties. In this study, three late-maturing citrus varieties with different acidity levels, namely 'Huangjinjia' (HJ), 'Kiyomi' (QJ), and 'Harumi' (CJ), were selected to systematically investigate the metabolic regulation mechanism of organic acids in late-maturing citrus through transcriptome sequencing technology, combined with physiological and biochemical analyses. This study revealed gene expression differences related to organic acid synthesis and degradation. Through gene expression profiling, several genes closely associated with organic acid metabolism were identified, and a preliminary gene network related to the regulation of organic acid metabolism was constructed. The results showed that there were significant differences in the organic acid metabolic pathways between different varieties and growth stages of the fruit. Specifically, HJ had a higher TA content than QJ and CJ, primarily due to the significantly higher citric acid and malic acid contents in HJ compared to the other two varieties. Further analysis revealed that four gene modules showed a high correlation with the levels of major organic acids in the fruits. The genes involved in these modules are closely related to organic acid synthesis, degradation, and transport. Additionally, we also identified several key genes (AS1, BZP44, COL4, TCP4, IDD10, YAB2, and GAIPB) that might be involved in the regulation of organic acid metabolism. The functions of these genes could have a significant impact on the expression levels changes of enzymes related to organic acid metabolism. This study provides a foundation for exploring the intrinsic mechanisms regulating the organic acid content in late-maturing hybrid citrus fruits and contributes to the functional research of organic acids in late-maturing hybrid citrus and the molecular design of high-quality varieties.

Unraveling the genetic architecture of blueberry fruit quality traits: major loci control organic acid content while more complex genetic mechanisms control texture and sugar content

BACKGROUND

Fruit quality traits, including taste, flavor, texture, and shelf-life, have emerged as important breeding priorities in blueberry (Vaccinium corymbosum). Organic acids and sugars play crucial roles in the perception of blueberry taste/flavor, where low and high consumer liking are correlated with high organic acids and high sugars, respectively. Blueberry texture and appearance are also critical for shelf-life quality and consumers' willingness-to-pay. As the genetic mechanisms that determine these fruit quality traits remain largely unknown, in this study, an F1 mapping population was used to perform quantitative trait loci (QTL) mapping for pH, titratable acidity (TA), organic acids, total soluble solids (TSS), sugars, fruit size, and texture at harvest and/or post-storage and weight loss.

RESULTS

Twenty-eight QTLs were detected for acidity-related parameters (pH, TA, and organic acid content). Six QTLs for pH, TA, and citric acid, two for quinic acid, and two for shikimic acid with major effects were consistently detected across two years on the same genomic regions on chromosomes 3, 4, and 5, respectively. Putative candidate genes for these QTLs were also identified using comparative transcriptomic analysis. No QTL was detected for malic acid content, TSS, or individual sugar content. A total of 146 QTLs with minor effects were identified for texture- and size-related parameters. With a few exceptions, these QTLs were generally inconsistent over years and post-storage, indicating a highly quantitative nature.

CONCLUSIONS

Our findings enhance the understanding of the genetic basis underlying fruit quality traits in blueberry and guide future work to exploit DNA-informed selection strategies in blueberry breeding programs. The major-effect QTLs identified for acidity-related fruit characteristics could be potential targets to develop DNA markers for marker-assisted selection (MAS). On the other hand, genomic selection may be a more suitable approach than MAS when targeting fruit texture, sugars, or size.

A Comprehensive Evaluation of Nutritional Quality and Antioxidant Capacity of Different Chinese Eggplant Varieties Based on Multivariate Statistical Analysis

Free amino acids, polyphenols, and anthocyanins were quantified in 30 Chinese eggplant varieties. Moreover, antioxidant capacity characterizations including 2, 2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric-reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were performed. The total amino acid content of the 30 eggplant varieties ranged from 15,267.19 to 26,827.4 mg kg-1 DW. The most abundant amino acids were glutamic acid, arginine, and aspartic acid. The coefficients of variation (CV) for the 20 amino acids ranged from 5.85 to 106.14%, of which 18 free amino acids had CVs > 20%. Total polyphenol and anthocyanin contents ranged from 17,097.41 to 39,474.98 µg g-1 DW and 5.28 to 978.32 µg g-1 DW, respectively. The variability of both polyphenol and anthocyanin components was >20%, with a range of 21.25-102.89%. Chlorogenic acid was the most abundant polyphenol. The total anthocyanin content of purple eggplant varieties was significantly higher than green varieties. Of the purple eggplant varieties, V28 ('E150725'), V30 ('1952'), and V16 ('Weichangqie101') had significantly higher total anthocyanins than the other eggplant varieties. DPPH, ABTS, and FRAP assays showed peaks at V3 ('Zhengqie924'). Pearson's correlation analysis revealed that polyphenols and anthocyanins were the main contributors to the antioxidant capacity of eggplants. A classification model with principal component analysis classified 30 Chinese eggplant varieties into two categories: high and low antioxidant capacities. The top five Chinese eggplant varieties ranked for amino acids, antioxidants, and antioxidant capacity were V29 ('Zhengqie903'), V24 ('Zhengqie78'), V1 ('1871'), V3 ('Zhengqie924'), and V28 ('E150725'). These findings provide theoretical basis for high-quality breeding and producer/consumer selection of eggplants.

Regulatory network analysis reveals gene-metabolite relationships in pear fruit treated with methyl jasmonate

The economic value of pear is determined by its intrinsic qualities, which are influenced by metabolites produced during the ripening process. Methyl jasmonate (MeJA), a hormone, plays an important role in plant metabolism. To date, few studies have investigated the molecular mechanism underlying the changes in metabolic pathways related to the internal quality of pear fruit after MeJA treatment. In this study, ultrahigh-performance liquid chromatography‒Q Exactive Orbitrap mass spectrometry (UHPLC‒QE‒MS) was used to determine the changes in metabolite contents in pear after MeJA treatment. MeJA treatment primarily activated carbohydrate metabolism and amino acid metabolism pathways. Through combined analysis of UHPLC‒QE‒MS data and whole-transcriptome data, the abovementioned pathways and each metabolite were analysed separately, and competitive endogenous RNA (ceRNA) and microRNA-transcription factor-target (miRNA-TF-target) regulatory networks were constructed. The core nodes of three genes (PEA, Pbr022732.1; GAA, Pbr035655.1; and miR8033-x) and two genes (SDS, Pbr031708.1; and novel-m6796-3p) were associated with the carbohydrate metabolism and amino acid metabolism pathways, respectively. The core mRNA nodes TCONS_00048038 and Pbr019584.1, the core miRNA node miR4993-x, the core lncRNA node TCONS_0004356, the core circRNA node novel_circ_001967 and the core transcription factor node TSO1 (Pbr025407.1) were identified via separate metabolite analyses. These findings elucidate the changes in metabolites related to fruit quality in 'Nanguo' pear and the relationships between the metabolites and genes, reveal the molecular mechanism underlying the response of MeJA treatment in pear fruit, and provide a theoretical basis for improving the internal quality of 'Nanguo' pear.

Sustained carbon import supports sugar accumulation and anthocyanin biosynthesis during fruit development and ripening in blueberry (Vaccinium ashei)

Fruit ripening is a highly coordinated process involving molecular and biochemical changes that collectively determine fruit quality. The underlying metabolic programs and their transitions leading to fruit ripening remain largely under-characterized in blueberry (Vaccinium sp.), which exhibits atypical climacteric behavior. In this study, we focused on sugar, acid and anthocyanin metabolism in two rabbiteye blueberry cultivars, Premier and Powderblue, during fruit development and ripening. Concentrations of the three major sugars, sucrose (Suc), glucose (Glc), and fructose (Fru) increased steadily during fruit development leading up to ripening, and increased dramatically by around 2-fold in 'Premier' and 2- to 3-fold in 'Powderblue' during the final stage of fruit ripening. Starch concentration was very low throughout fruit development in both cultivars indicating that it does not serve the role of a major transitory carbon (C) storage form in blueberry fruit. Together, these patterns indicate continued import of C, likely in the form of Suc, throughout blueberry fruit development. Concentrations of the predominant acids, malate and quinate, decreased during ripening, and may contribute to increased shikimate biosynthesis which, in-turn, allows for downstream phenylpropanoid metabolism leading to anthocyanin synthesis. Consistently, anthocyanin concentrations were highest in fully ripened blue fruit. Weighted gene co-expression network analysis (WGCNA) was performed using a 'Powderblue' fruit ripening transcriptome and targeted fruit metabolite concentration data. A 'dark turquoise' module positively correlated with sugars and anthocyanins, and negatively correlated with acids (malate, quinate), was identified. Gene Ontology (GO) enrichment analysis of this module identified transcripts related to sugar, acid, and phenylpropanoid metabolism pathways. Among these, increased transcript abundance of a VACUOLAR INVERTASE during ripening was consistent with sugar storage in the vacuole. In general, transcript abundance of the glycolysis pathway genes was upregulated during ripening. The transcript abundance of PHOSPHOENOLPYRUVATE (PEP) CARBOXYKINASE increased during fruit ripening and was negatively correlated with malate concentration, suggesting increased malate conversion to PEP, which supports anthocyanin production during fruit ripening. This was further supported by the co-upregulation of several anthocyanin biosynthesis-related genes. Together, this study provides insights into important metabolic programs, and their underlying gene expression patterns during fruit development and ripening in blueberry.

Maintenance of postharvest quality of 'Palmer' mango coated with biodegradable coatings based on cassava starch and emulsion of lemongrass essential oil

This study aimed to evaluate the effect of applying oxidized cassava starch-based edible coatings with addition of lemongrass essential oil emulsion on 'Palmer' mangoes stored under refrigeration. A completely randomized design was used, arranged in a 5 × 3 factorial scheme, with five types of coatings and three evaluation times. The evaluated postharvest quality parameters consisted of weight loss, pulp and peel firmness, biochemical transformations related to pigments, and pulp and peel coloration of mango. The application of edible coatings with a 0.9 % EO concentration resulted in delayed fruit ripening, evidenced mainly by a 7.25 % reduction in weight loss, a 29.23 % increase in soluble solids content, and a 24.15 % decrease in total chlorophyll, when compared to uncoated fruits, which showed 19.8 %, 48.66 %, and 82.00 %, respectively, over the storage period. This effect was also evident in the angle Hue (°h) measurement, with uncoated fruits showing a decrease of 32.2 %. The antimicrobial effect and absence of anthracnose symptoms were observed in the fruits in which the coating with 0.9 % EO was applied. Therefore, biodegradable coating with the addition of 0.9 % emulsion EO, can be used as postharvest treatments for maintenance quality of 'Palmer' mangoes during refrigerated storage.

Biodiversity in nutrients and biological activities of 14 highbush blueberry (Vaccinium corymbosum L.) cultivars

The present study aimed to identify nutrients (UPLC-PDA-ESI-MS/MS, HPLC-RI method) and biological activities (antioxidant activity to reduce Fe3+ and ABTS·+, pancreatic lipase inhibitory effect, α-amylase, and α-glucosidase, anti-bacterial) of 14 highbush blueberries (Vaccinium corymbosum L.) cultivars (Northern type) as well as a principal component analysis (PCA) to assess the variation of these properties in the context of biodiversity. Most of the cultivars in this research have been first presented in this paper. Phytochemical profiling of the tested highbush blueberry fruit revealed 75 bioactive compounds, including 5 macroelements, 7 microelements, 7 monophosphate nucleotides, 15 anthocyanins, 1 phenolic acid, 14 flavonols, 11 essential amino acids, 8 non-essential amino acids, 2 sugars, 7 organic acids. The PCA showed that the profile and contents of the analyzed compounds as well as their anti-bacterial, antioxidant, anti-diabetic, and anti-obesity potentials depended significantly on the tested cultivars. Thus, the study provides comprehensive data on cultivar-specific biodiversity and correlations that can be used to design novel extracts rich in polyphenolic, amino acids, and/or minerals extracts from the selected cultivars of highbush blueberry as natural and alternative sources to fulfill the growing industry demand for supplements, pharmaceuticals, and nutraceutical products.

Urinary Biomarkers of Strawberry and Blueberry Intake

Introduction There is increasing interest in food biomarkers to address the shortcomings of self-reported dietary assessments. Berries are regarded as important fruits worldwide; however, there are no well-validated biomarkers of berry intake. Thus, the objective of this study is to identify urinary biomarkers of berry intake. Methods For the discovery study, participants consumed 192 g strawberries with 150 g blueberries, and urine samples were collected at 2, 4, 6, and 24 h post-consumption. A dose-response study was performed, whereby participants consumed three portions (78 g, 278 g, and 428 g) of mixed strawberries and blueberries. The urine samples were profiled by an untargeted LC-MS metabolomics approach in the positive and negative modes. Results Statistical analysis of the data revealed that 39 features in the negative mode and 15 in the positive mode significantly increased between fasting and 4 h following mixed berry intake. Following the analysis of the dose-response data, 21 biomarkers showed overall significance across the portions of berry intake. Identification of the biomarkers was performed using fragmentation matches in the METLIN, HMDB, and MoNA databases and in published papers, confirmed where possible with authentic standards. Conclusions The ability of the panel of biomarkers to assess intake was examined, and the predictability was good, laying the foundations for the development of biomarker panels.

Hydrogen sulfide alleviates pericarp browning in lichi fruit by modulating energy and sugar metabolisms

Postharvest litchi is susceptible to browning that limits the development of litchi industry. Hydrogen sulfide (H2S) is an important bioactive molecule that can regulate many physiological processes. This study examined the effects of exogenous H2S on pericarp browning and related physiological mechanisms in postharvest litchi. The results exhibited that exogenous H2S treatment delayed the browning of litchi pericarp and reduced the damage to cell membrane integrity during storage. This treatment inhibited the energy losses of litchi fruit by increasing the activities of H+-ATPase, Ca2+- ATPase, cytochrome C oxidase (CCO) and succinate dehydrogenase (SDH) and regulating the expression of energy metabolism-related genes, including LcAtpB, LcSnRK2, LcAAC1, LcAOX1 and LcUCP1. In addition, H2S treatment increased the levels of fructose, glucose, sucrose, inositol, galactose and sorbose in litchi fruit, and promoted sucrose synthesis by regulating the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS), acid invertase (AI) and neutral invertase (NI). Based on the current findings, we suggest that exogenous H2S enhances the energy supply and antioxidant activity of litchi by modulating energy and sugar metabolism, thereby inhibiting fruit browning and senescence. These results indicated that H2S treatment is an effective approach to maintaining the quality of litchi fruit and extending its shelf life.

Chemical Constituents and Antioxidant Potential of Red Guava (Psidium cattleianum Sabine) from Southern Brazil in Different Edible Ripening Stages

Ripening and growing location are important factors that can impact fruit quality characteristics. In this study, the influence of these factors on physicochemical characteristics, carbohydrates, aliphatic organic acids, phenolic compounds, and antioxidant capacity of red guava (Psidium cattleianum Sabine) was evaluated. Fruit ripening increased fructose and glucose (up to 22.83 and 16.42 g 100 g- 1 dry matter (DM), respectively), and decreased citric acid, the major organic acid (up to 135.35 mg g- 1 DM). Ripening and growing location also influenced the concentration of phenolic compounds and antioxidant capacity of red guava, in which a dependency between both factors was observed in most cases. Apigenin, galangin, isoquercitrin, among other phenolic compounds were quantified for the first time in red guava, in which isoquercitrin was the major (up to 13409.81 mg kg- 1 DM). The antioxidant potential of red guava was also confirmed by ferric reducing antioxidant power assay (up to 82.63 µmol Fe+ 2 g- 1 DM), Folin-Ciocalteu reducing capacity assay (up to 17.79 mg gallic acid equivalent g- 1 DM), and DPPH free radical scavenging assay (up to 25.36 mg ascorbic acid equivalent g- 1 DM). These results especially demonstrated the bioactive potential of red guava and provided knowledge regarding the influence of ripening and growing location on chemical and bioactive components encouraging its industrial exploitation.

Comparative physiological, metabolomic and transcriptomic analyses reveal the mechanisms of differences in pear fruit quality between distinct training systems

BACKGROUND

Canopy architecture is critical in determining the fruit-zone microclimate and, ultimately, in determining an orchard's success in terms of the quality and quantity of the fruit produced. However, few studies have addressed how the canopy environment leads to metabolomic and transcriptomic alterations in fruits. Designing strategies for improving the quality of pear nutritional components relies on uncovering the related regulatory mechanisms.

RESULTS

We performed an in-depth investigation of the impact of canopy architecture from physiological, metabolomic and transcriptomic perspectives by comparing pear fruits grown in a traditional freestanding system (SP) or a flat-type trellis system (DP). Physiological studies revealed relatively greater fruit sizes, soluble solid contents and titratable acidities in pear fruits from DP systems with open canopies. Nontargeted metabolite profiling was used to characterize fruits at the initial ripening stage. Significant differences in fruit metabolites, including carbohydrates, nucleic acids, alkaloids, glycerophospholipids, sterol lipids, and prenol lipids, were observed between the two groups. Transcriptomic analysis indicated that a series of organic substance catabolic processes (e.g., the glycerol-3-phosphate catabolic process, pectin catabolic process and glucan catabolic process) were overrepresented in fruits of the DP system. Moreover, integrative analysis of the metabolome and transcriptome at the pathway level showed that DP pear fruits may respond to the canopy microenvironment by upregulating phenylpropanoid biosynthesis pathway genes such as PpPOD. Transient assays revealed that the contents of malic acid and citric acid were lower in the pear flesh of PpPOD RNAi plants, which was associated with regulating the expression of organic acid metabolism-related genes.

CONCLUSIONS

Our results provide fundamental evidence that at the physiological and molecular levels, open-canopy architecture contributes to improving pear fruit quality and is correlated with increased levels of carbohydrates and lipid-like molecules. This study may lead to the development of rational culture practices for enhancing the nutritional traits of pear fruits.

Transcriptomic and Metabolomic Profiling Reveals the Variations in Carbohydrate Metabolism between Two Blueberry Cultivars

Blueberry is a high-quality fruit tree with significant nutritional and economic value, but the intricate mechanism of sugar accumulation in its fruit remains unclear. In this study, the ripe fruits of blueberry cultivars 'Anna' and 'Misty' were utilized as experimental materials, and physiological and multi-omics methodologies were applied to analyze the regulatory mechanisms of the difference in sugar content between them. The results demonstrated that the 'Anna' fruit was smaller and had less hardness than the 'Misty' fruit, as well as higher sugar content, antioxidant capability, and lower active substance content. A total of 7067 differentially expressed genes (DEGs) (3674 up-regulated and 3393 down-regulated) and 140 differentially abundant metabolites (DAMs) (82 up-regulated and 58 down-regulated) were identified between the fruits of the two cultivars. According to KEGG analysis, DEGs were primarily abundant in phenylpropanoid synthesis and hormone signal transduction pathways, whereas DAMs were primarily enriched in ascorbate and aldarate metabolism, phenylpropanoid biosynthesis, and the pentose phosphate pathway. A combined multi-omics study showed that 116 DEGs and 3 DAMs in starch and sucrose metabolism (48 DEGs and 1 DAM), glycolysis and gluconeogenesis (54 DEGs and 1 DAM), and the pentose phosphate pathway (14 DEGs and 1 DAM) were significantly enriched. These findings suggest that blueberries predominantly increase sugar accumulation by activating carbon metabolism network pathways. Moreover, we identified critical transcription factors linked to the sugar response. This study presents new understandings regarding the molecular mechanisms underlying blueberry sugar accumulation and will be helpful in improving blueberry fruit quality through breeding.

Comparative Analysis of Metabolic Variation in Eggplant Fruit of Different Varieties Reveals Metabolites Important for Quality Traits

Eggplant is one of the most important vegetable crops worldwide and has been considered to have great antioxidant activity. However, little information is available about the primary metabolic composition of the nutritional values of eggplant. Using a widely targeted metabolome approach, the current study investigated primary metabolic variation in 13 eggplant varieties with different morphologies. A total of 503 primary metabolites (amino acids, lipids, nucleotides, organic acids, vitamin, saccharides, and alcohols) and 170 phenolic acids were detected, among which 211 metabolites were differently accumulated. Metabolic pathway analysis of the differential metabolites revealed the significant enrichment of phenylpropanoid biosynthesis, arginine biosynthesis, alpha-linolenic acid metabolism, and linoleic acid metabolism. The higher levels of amino acids and lipids were related to the umami, soft, and waxy taste of eggplant fruit. The present work substantially contributes to the knowledge of primary metabolite compositions regarding fruit-eating quality and provides useful information for the future breeding of eggplant.

Metabolomics analysis of the metabolic effects of citric acid on Issatchenkia terricola WJL-G4

In current research, yeast species Issatchenkia terricola WJL-G4 was shown to be capable of degrading citric acid, especially in the processing of fruit juice and wine. I. terricola WJL-G4 was able to use citric acid as a carbon source, but the metabolic effects of citric acid on yeast remained unclear. In this study, the metabolic effects of citric acid on I. terricola WJL-G4 were studied using liquid chromatography-mass spectrometry metabolomics technology, with glucose treatment as the control. Results showed that organic acid contents related to the extracellular tricarboxylic acid cycle (TCA) varied greatly. The metabolomics results indicated that I. terricola WJL-G4 might metabolize citric acid through the TCA pathway, and the glycolysis pathway might be inhibited; however, gluconeogenesis proceeded normally during citric acid treatment. Some fatty acids and phospholipids, along with the metabolic pathways of amino acids, vitamins, purines and nicotinamide in I. terricola WJL-G4 were also affected by the citric acid treatment. This work provided a theoretical basis for further study of the mechanism of yeast metabolism of citric acid.

The telomere-to-telomere gap-free reference genome of wild blueberry (Vaccinium duclouxii) provides its high soluble sugar and anthocyanin accumulation

Vaccinium duclouxii, endemic to southwestern China, is a berry-producing shrub or small tree belonging to the Ericaceae family, with high nutritive, medicinal, and ornamental value, abundant germplasm resources, and good edible properties. In addition, V. duclouxii exhibits strong tolerance to adverse environmental conditions, making it a promising candidate for research and offering wide-ranging possibilities for utilization. However, the lack of V. duclouxii genome sequence has hampered its development and utilization. Here, a high-quality telomere-to-telomere genome sequence of V. duclouxii was de novo assembled and annotated. All of 12 chromosomes were assembled into gap-free single contigs, providing the highest integrity and quality assembly reported so far for blueberry. The V. duclouxii genome is 573.67 Mb, which encodes 41 953 protein-coding genes. Combining transcriptomics and metabolomics analyses, we have uncovered the molecular mechanisms involved in sugar and acid accumulation and anthocyanin biosynthesis in V. duclouxii. This provides essential molecular information for further research on the quality of V. duclouxii. Moreover, the high-quality telomere-to-telomere assembly of the V. duclouxii genome will provide insights into the genomic evolution of Vaccinium and support advancements in blueberry genetics and molecular breeding.

Rain Cover and Netting Materials Differentially Affect Fruit Yield and Quality Traits in Two Highbush Blueberry Cultivars via Changes in Sunlight and Temperature Conditions

The use of covers to protect blueberry orchards from adverse weather events has increased due to the variability in climate patterns, but the effects of rain covers and netting materials on yield and fruit quality have not been studied yet. This research evaluated the simultaneous effect of an LDPE plastic cover, a woven cover, and netting material on environmental components (UV light, PAR, NIR, and growing degree days (GDDs)), plant performance (light interception, leaf area index, LAI, yield, and flower development), and fruit quality traits (firmness, total soluble solids, and acidity) in two blueberry cultivars. On average, UV transmission under the netting was 11% and 43% higher compared to that under woven and LDPE plastic covers, while NIR transmission was 8-13% higher with both types of rain covers, with an increase in fruit air temperature and GDDs. Yield was 27% higher under the woven cover with respect to netting, but fruit firmness values under the netting were 12% higher than those of the LDPE plastic cover. Light interception, LAI, and flower development explained 64% (p = 0.0052) of the yield variation due to the cover material's effect. The obtained results suggest that the type of cover differentially affects yield and fruit quality in blueberries due to the specific light and temperature conditions generated under these materials.

Evaluation of the Effect of Preharvest Melatonin Spraying on Fruit Quality of 'Yuluxiang' Pear Based on Principal Component Analysis

Melatonin (MT), an indoleamine compound, has a pleiotropic effect on plant growth and development and can regulate the quality of tree fruit. Systematic research on the effect of preharvest MT spraying on pear fruit quality and technical solutions for MT application to regulate pear fruit quality are still lacking. Thus, here we aimed to evaluate the effects of different spraying times, concentrations, and exogenous MT application times on 'Yuluxiang' pear fruit quality. Our results showed that the single fruit weight and vertical and horizontal diameters of pear fruit sprayed with MT twice at 30 and 90 d after full bloom were the largest, and the red and green values of the treatment were the highest. MT-treated pears had higher contents of total soluble solids, soluble sugar, sucrose, sorbitol, fructose, and glucose and lower contents of titratable acid, malic acid, and citric acid. Moreover, exogenous MT treatment increased the pear peel strength. Based on the principal component analysis of 10 fruit quality indices, the suitable periods for MT spraying on 'Yuluxiang' pears were 30 and 90 d after full bloom, the suitable concentration was 100 μmol/L, and the suitable number of times was two. This study provides a theoretical reference for optimizing MT application and improving pear fruit quality.

Fruit Quality and Metabolomic Analyses of Fresh Food Accessions Provide Insights into the Key Carbohydrate Metabolism in Blueberry

Blueberry is a nutrient-rich berry, and its taste and flavor directly determine the consumer preference. Until now, few studies have focused on the comparison of fresh food quality and the key metabolites in superior fresh-eating blueberry cultivars. Herein, fruit quality indicators of 10 highbush blueberry cultivars were evaluated using 'Bluerain' as the control. Appearance quality analysis of fruits showed that 'Brigitta' had a larger fruit size and 'Anna' was the smallest. 'Anna' fruits, followed by 'O'Neal', had the highest ratio of soluble solids to acidity because of their lowest titratable acidity content. Despite the high soluble sugar content, the antioxidants in 'Anna' fruits such as total flavonoids, anthocyanins and vitamin C were lowest among all cultivars, while 'Duke' seemed to have opposite patterns. Furthermore, a total of 553 and 557 metabolites were identified by non-targeted metabolomics liquid chromatography-tandem mass spectrometry (LC-MS/MS) in positive and negative ion mode, respectively. Particularly, the numbers of differentially accumulated metabolites (DAMs) were the most between the 'O'Neal' vs. 'Bluerain' group. The DAMs involved in the metabolic pathways, sesquiterpenoid and triterpenoid biosynthesis, monoterpenoid biosynthesis, galactose metabolism, starch and sucrose metabolism, may be mainly related to the synthesis of flavor and carbohydrate substances. Moreover, the expression patterns of genes involved in sugar metabolism were verified by quantitative real-time PCR (qRT-PCR) analysis in different cultivars. Therefore, the systematical comparison of the quality characteristics, metabolites and expression profiles of related genes in highbush blueberries with good flavor could provide some basis for further research on fresh fruit breeding of blueberries.

Identification of CmACL genes in melon and analysis of their potential functions in fruit sugar and acid accumulation

Citric acid is the most important organic acid in melon and has a great influence on fruit flavor quality. ATP-citrate (pro-S) lyase (ACL) is a key regulator in the acetyl-CoA pathway and plays an important role in citric acid metabolism. In this study we analyzed the structure and phylogenetics of CmACL genes and their functions in sugar and acid accumulation in melon. A total of four CmACL genes were identified in the melon genome, and phylogenetic analysis assigned these genes into the α subfamily (CmACLα1 and CmACLα2) and the β subfamily (CmACLβ1 and CmACLβ2). Conserved motif and gene structure analyses showed that members of the same subfamily shared identical conserved motifs and gene structures, and probably have similar biological functions. Analysis of cis-acting elements revealed that CmACL promoter sequences contained regulatory elements related to light, stress, phytohormones, and growth and development, indicating that CmACL genes may be involved in melon growth and stress responses. The prediction of protein interaction network showed that CmACL proteins were closely related to the proteins belonging to tricarboxylic acid cycle, glyoxylic acid cycle and glycolytic pathway, suggesting that CmACL proteins may play an important role in sugar and acid metabolism. The expression of CmACLβ1 was significantly and positively correlated with sucrose content, and CmACLβ2 expression was significantly positively correlated with citric acid content, suggesting that CmACLβ1 and CmACLβ2 have important roles in sugar and acid accumulation in melon. Our results offer novel insights and avenues for the regulation of sugar and acid levels in melon and provide a theoretical foundation for breeding high-quality melon cultivars.

Physiological and biochemical changes during fruit maturation and ripening in highbush blueberry (Vaccinium corymbosum L.)

The sweetness of blueberry fruit increases over time, as acids are converted to sugars, and full flavor development is formed by harvest. We comprehensively analyzed the changes and correlation in physiological and biochemical characteristics of blueberries at different maturity stages, including texture, quality, taste and energy change. Our analysis revealed that total anthocyanin content increased and firmness decreased as fruit ripened. Percent moisture, titratable acid (TA), chlorophyll and carotenoid content also decreased, while total soluble solids (TSS), pH, TSS/TA ratio, vitamin C, soluble proteins, and ethylene production all increased. Antioxidant enzyme activity gradually increased during ripening but energy-related metabolites decreased. The flavor attributes of sweetness, bitterness, and sourness were readily perceived using an electronic tongue and a total of 76 volatile compounds were detected by GC-MS. In summary, the maturation of blueberries was correlated with increases of anthocyanins, nutrients, antioxidant activity, taste and aroma, but negatively correlated with energy metabolism.

Metabolomic and transcriptomic analyses of the flavonoid biosynthetic pathway in blueberry (Vaccinium spp.)

As a highly economic small fruit crop, blueberry is enjoyed by most people in terms of color, taste, and rich nutrition. To better understand its coloring mechanism on the process of ripening, an integrative analysis of the metabolome and transcriptome profiles was performed in three blueberry varieties at three developmental stages. In this study, 41 flavonoid metabolites closely related to the coloring in blueberry samples were analyzed. It turned out that the most differential metabolites in the ripening processes were delphinidin-3-O-arabinoside (dpara), peonidin-3-O-glucoside (pnglu), and delphinidin-3-O-galactoside (dpgal), while the most differential metabolites among different varieties were flavonols. Furthermore, to obtain more accurate and comprehensive transcripts of blueberry during the developmental stages, PacBio and Illumina sequencing technology were combined to obtain the transcriptome of the blueberry variety Misty, for the very first time. Finally, by applying the gene coexpression network analysis, the darkviolet and bisque4 modules related to flavonoid synthesis were determined, and the key genes related to two flavonoid 3', 5'-hydroxylase (F3'5'H) genes in the darkviolet module and one bHLH transcription factor in the bisque4 module were predicted. It is believed that our findings could provide valuable information for the future study on the molecular mechanism of flavonoid metabolites and flavonoid synthesis pathways in blueberries.

Targeted multi-platform metabolome analysis and enzyme activity analysis of kiwifruit during postharvest ripening

Kiwifruit is a climacteric fruit, in which the accumulation of flavor substances mainly occurs at the postharvest ripening stage. However, the dynamic changes in metabolite composition remain poorly understood. Here, targeted multi-platform metabolome analysis based on GC-MS and UPLC-MS/MS and enzyme activity analysis were performed at different postharvest ripening stages of kiwifruit. A total of 12 soluble sugars and 31 organic acids were identified. The main soluble sugars are sucrose, glucose and fructose, which exhibited similar variation tendencies along with the extension of ripening. The main organic acids are citric acid, quinic acid and malic acid, which showed different variation patterns. A total of 48 energy metabolites were identified, which were classified into two groups based on the content variation. The content of substances related to the respiratory metabolic pathway decreased gradually along with postharvest ripening, and there was obvious accumulation of downstream products such as amino acids at the late ripening stage. A total of 35 endogenous hormones were identified, among which seven cytokinins were highly accumulated at the later stage of softening. We further investigated the dynamic changes in the activities of 28 ripening-related enzymes. As a result, the activities of 13 enzymes were highly correlated with changes in starch, total pectin, and soluble sugars, and those of seven enzymes were closely associated with the change in firmness. In conclusion, this study comprehensively describes the dynamic changes in soluble sugars, organic acids, hormones, energy substances, and ripening-related enzyme activities during kiwifruit postharvest ripening, and provides a theoretical basis for the postharvest quality improvement of kiwifruit.

Organic Acid Accumulation and Associated Dynamic Changes in Enzyme Activity and Gene Expression during Fruit Development and Ripening of Common Loquat and Its Interspecific Hybrid

Loquats have gained increasing attention from consumers and growers for their essential nutrients and unusual phenology, which could help plug a gap period at market in early spring. Fruit acid is a critical contributor to fruit quality. The dynamic changes in organic acid (OA) during fruit development and ripening of common loquat (Dawuxing, DWX) and its interspecific hybrid (Chunhua, CH) were compared, as well as the corresponding enzyme activity and gene expression. At harvest, titratable acid was significantly lower (p ≤ 0.01) in CH (0.11%) than in DWX loquats (0.35%). As the predominant OA compound, malic acid accounted for 77.55% and 48.59% of the total acid of DWX and CH loquats at harvest, followed by succinic acid and tartaric acid, respectively. PEPC and NAD-MDH are key enzymes that participate in malic acid metabolism in loquat. The OA differences in DWX loquat and its interspecific hybrid could be attributed to the coordinated regulation of multiple genes and enzymes associated with OA biosynthesis, degradation, and transport. The data obtained in this work will serve as a fundamental and important basis for future loquat breeding programs and even for improvements in loquat cultural practices.

Effects of Hydrogen Sulfide on Sugar, Organic Acid, Carotenoid, and Polyphenol Level in Tomato Fruit

Hydrogen sulfide (H₂S) is known to have a positive effect on the postharvest storage of vegetables and fruits, but limited results are available on its influence in fruit flavor quality. Here, we presented the effect of H₂S on the flavor quality of tomato fruit during postharvest. H₂S decreased the content of fructose, glucose, carotene and lycopene but increased that of soluble protein, organic acid, malic acid and citric acid. These differences were directly associated with the expression of their metabolism-related genes. Moreover, H₂S treatment raised the contents of total phenolics, total flavonoids and most phenolic compounds, and up-regulated the expression level of their metabolism-related genes (PAL5, 4CL, CHS1, CHS2, F3H and FLS). However, the effects of the H₂S scavenger hypotaurine on the above flavor quality parameters were opposite to that of H₂S, thus confirming the role of H₂S in tomato flavor quality. Thus, these results provide insight into the significant roles of H₂S in tomato fruit quality regulation and implicate the potential application of H₂S in reducing the flavor loss of tomato fruit during postharvest.

Metabolic Profiling and Potential Taste Biomarkers of Two Rambutans during Maturation

The metabolite-caused taste variation during rambutan maturation is unknown due to a lack of systematic investigation of all components. In this study, three growing stages, including unripe (S1), half-ripe (S2), and full-ripe (S3) BY2 and BY7 rambutans were compared and profiled by UPLC-MS/MS-based widely targeted metabolomics analysis. We demonstrated that the sugar-acid ratios of two rambutans were greatly improved between the S2 and S3 stages. A total of 821 metabolites were identified, including 232, 205, 204, and 12 differential metabolites (DMs) in BY2-S1 vs. BY2-S2, BY2-S2 vs. BY2-S3, BY7-S1 vs. BY7-S2, and BY7-S2 vs. BY7-S3, respectively. A correlation analysis showed that gamma-aminobutyric acid (GABA) could be the sugar-acid ratio biomarker of BY2 rambutan. Methionine (Met), alanine (Ala), and S-methyl-L-cysteine (SMC) could be total amino acid biomarkers of BY2 and BY7 rambutans. In addition, UPLC-MS/MS-based quantitative verification of the above biomarkers exhibited the same variations as metabolomics analysis. This study not only provides useful nutritive information on rambutans but also valuable metabolic data for rambutan breeding strategies.

Integrated untargeted metabolome, full-length sequencing, and transcriptome analyses reveal insights into the fruit quality at different harvest times of Chaenomeles speciosa

Chaenomeles speciosa fruit is a homologous medicine and food plant with a long history of multiple uses. It could be harvested near maturity and last for a long time. However, the optimal harvest strategy of Chaenomeles speciosa for various uses is currently unavailable. Here, untargeted metabolome at different harvest times during maturation was investigated for the first time, and 896 metabolites, including sugars, organic acids, amino acids, and phenylpropanoids, were identified. Optimal harvesting methods were proposed for different purposes. During the early maturation stages (before 105 days after full bloom), Ch. speciosa fruit could be harvested as Chinesemedicine. Whereas as snacks and food, Ch. speciosa fruit might be harvested at late maturity (after 120 days after full bloom). In addition, the overall network was revealed by integrating full-length Iso-seq and transcriptomics (RNA-seq) to investigate the association between quality-associated metabolites and Chaenomeles speciosa fruit gene expression during maturation. A few putative genes were captured via screening, dissecting and correlation analysis with the quality-associated metabolites (including d-glucose, catechin, gallocatechin, and succinic acid). Overall, in addition to providing a harvesting strategy for food and medicine, we also investigated the metabolism and gene expression pattern of Chaenomeles speciosa fruit during maturation. This comprehensive data and analyses laid the foundation for further investigating potential regulatory mechanisms during harvest and provided a new possibility for its development and utilization.

Integrated Physiological and Metabolomic Analyses Reveal the Differences in the Fruit Quality of the Blueberry Cultivated in Three Soilless Substrates

With improving living standards, traditional blueberry planting modes cannot meet commercial demands, and blueberry cultivation with soilless substrate has become a popular solution in the blueberry industry. In this study, different soilless substrate treatments were found to markedly influence fruit appearance and intrinsic quality. The fruit in the 50:50 peat/pine bark (v/v) (FPB) treatment group had the maximum single fruit weight, largest vertical diameter, and brightest color, as well as the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) value, solid-acid ratio and anthocyanin content. The fruit in the 50:50 pine bark/rice husk (v/v) (FBR) treatment group had the highest total phenol and flavonoid levels, largest drip loss value, and lowest total pectin content and firmness value. Metabolomic analysis showed that flavonoid, carbohydrate, and carbohydrate conjugate, and amino acid, peptide, and analog levels were significantly different between groups. Fruit in the FPB group had the highest sucrose, D-fructose 1,6-bisphosphate, salidroside, tectorigenin, naringenin chalcone, trifolirhizin, and galangin contents. The increase in the relative expression of phenylalanine (Phe) promoted the synthesis of fruit polyphenols in the FBR group. Our results provide new insights into the effects of different substrates on the quality of blueberries and a reference for the soilless substrate cultivation of blueberries.

Evolution of polyphenolic, anthocyanin, and organic acid components during coinoculation fermentation (simultaneous inoculation of LAB and yeast) and sequential fermentation of blueberry wine

This research aims to investigate the effects of both sequential fermentation and coinoculation fermentation with yeast and lactic acid bacterial (LAB) on the dynamics of changes in basic quality parameters and organic acid, anthocyanin, and phenolic components as well as antioxidant activity during the fermentation of blueberry. The coculture-fermented blueberry wine showed significant decreases in total phenolics, flavonoids, and anthocyanins,by 23.9%, 15.9%, and 13.7%, respectively, as compared with those before fermentation Fermentation changed the contents of organic acids in each group, with a more than 7-fold increase in lactic acid contents as well as a more than 4-fold reduction in quinic acid and malic acid contents. The content of all investigated anthocyanins first increased and then decreased. Moreover, different fermentation strategies exerted a profound influence on the dynamic change in phenolic components during fermentation; specifically, most of the phenolic acids showed a trend of increasing first, then decreasing, and finally increasing. Gallic acid, p-coumaric acid, quercetin, and myricetin were increased by 116.9%, 130.1%, 127.2% and 177.6%, respectively, while syringic acid, ferulic acid, cinnamic acid, and vanillic acid were decreased by 49.5%, 68.5%, and 37.1% in sequentially fermented blueberry wine. Coinoculation fermentation with yeast and LAB produces faster dynamic variations and higher organic acid, anthocyanin, and phenolic profiles than sequential inoculation fermentation. PRACTICAL APPLICATION: In this work, brewing technology of sequential fermentation and coinoculation fermentation with yeast and LAB (Lactobacillus plantarum SGJ-24 and Oenococcus oeni SD-2a) was adopted to ferment blueberry wine. This is an innovative technology of fruit wine brewing technology to produce wine products. Compared with traditional sequential brewing, simultaneous inoculation brewing can significantly accelerate the brewing process of fruit wine and slightly improve the quality of fruit wine in terms of active ingredients.

Exogenous salicylic acid regulates organic acids metabolism in postharvest blueberry fruit

Fruit acidity is an essential factor affecting blueberry organoleptic quality. The organic acid content in blueberry fruit mainly contributes to fruit acidity. This study aims to evaluate the effect of exogenous salicylic acid (SA), the principal metabolite of aspirin, on the organoleptic quality and organic acid metabolism in rabbiteye blueberry (Vaccinium virgatum Ait, 'Powderblue') during cold storage (4 °C). Results showed that SA-treated fruit reduced fruit decay and weight loss delayed fruit softening, and decline of total soluble solids (TSS). TA and total organic acid amounts stayed the same during the late storage period in SA-treated fruit. Four kinds of organic acid components, malic acid, quinic acid, citric acid, and succinic acid, were at higher levels in fruit treated by SA as compared to control. SA enhanced the activities of PEPC, NAD-MDH, and CS to promote the synthesis of malic acid and citric acid. Meanwhile, the activities of NADP-ME, ACL, and ACO, which participated in the degradation of malic acid and citric acid, were inhibited by SA. qPCR results also showed that the expression of VcPEPC, VcNAD-MDH, and VcCS genes were upregulated. In contrast, SA downregulated the expression of VcNADP-ME, VcACL, and VcACO genes. In conclusion, SA could regulate the key genes and enzymes that participated in organic acids metabolism to maintain the freshness of blueberry during cold storage, therefore minimizing the economic loss.

Metabolite Profiles Provide Insights into Underlying Mechanism in Bupleurum (Apiaceae) in Response to Three Levels of Phosphorus Fertilization

Phosphorus (P) deficiency affects plant yield and quality, yet at the same time, excessive phosphorus application does not necessarily promote the growth of plants. How to maintain a balance between biomass accumulation and phosphorus application is a problem. Therefore, the purpose of this research was to explore the relationship between yield and quality of Bupleurum and phosphorus fertilization, based on three phosphorus fertilization levels (20 kg∙ha^-1; 10 kg∙ha^-1; and 0 kg∙ha^-1). We adopted gas chromatography-mass spectrometry to assess the response of primary metabolites of different plant tissues (flowers, main shoots, lateral shoots and roots) to phosphorus fertilization. At the same time, high-performance liquid chromatography was used to quantify saikosaponin A and saikosaponin D, the main active ingredients of Bupleurum. Our research showed that low phosphorus level application has a positive impact on the yield and quality of Bupleurum, especially the above-ground parts increasing the fresh weight of flowers and lateral shoots and the length of main shoots, and moreover, increasing the saikosaponins content in all above-ground parts while decreasing the content in roots which show no significance increase in fresh weight and length. However, high phosphorus level showed a negative impact as it decreases the saikosaponins content significantly in flowers and roots. Furthermore, phosphorus application changed the proportion of saikosaponins, promoting the content of saikosaponin A and inhibiting the content of saikosaponin D in most organs of Bupleurum. Therefore, we can say that high phosphorus application is not preferable to the yield and quality of Bupleurum. To identify the metabolic pathways and special key metabolites, a total of 73 metabolites were discovered, and four differential metabolites-ether, glycerol, chlorogenic and L-rhamnose-were considered to be the key metabolites of Bupleurum's response to phosphorus fertilization. Furthermore, Bupleurum's response to phosphorus fertilization was mainly related to metabolic pathways, such as starch and sucrose metabolism and galactose metabolism. Under the phosphorus level, the content of sugars, organic acids and their derivatives, polyols and their derivatives and alkyl were upregulated in flowers. Furthermore, the contents of compounds in the main shoot and lateral shoots showed the same upward trend, except glycosides and polyols and their derivatives.

Fruit Quality and Yield of Three Highbush Blueberry (Vaccinium corymbosum L.) Cultivars Grown in Two Planting Systems under Different Protected Environments

Due to the increasing interest in highbush blueberry (Vaccinium corymbosum L.) among consumers, together with the problems of climate change and specific substrate requirements, a novel approach to intensive blueberry production is required. Here, ‘Duke’, ‘Aurora’, and ‘Brigitta’ blueberry cultivars were planted under the protective environments of a high tunnel and black hail net, each using ridge and pot planting systems. The high tunnel increased the maximal air temperature on average by 7.2 °C compared to the hail net. For all three cultivars, harvest began 6 to 18 days earlier under the high tunnel than under the hail net; however, lower yields and individual phenolics contents were obtained for the fruit. In ‘Aurora’ and ‘Brigitta’, environmental conditions under the high tunnel also reduced plant volume and fruit sugar/organic acid ratio. Growing blueberry plants in 60 L pots had no negative effects on plant volume and fruit ripening time, yield, firmness, color, and chemical composition. This study represents the first to compare highbush blueberry grown under the high tunnel and hail net protective environments using ridge and pot planting systems across three different cultivars. Here, we can conclude that optimal highbush blueberry production of ‘Duke’, ‘Aurora’, and ‘Brigitta’ under the climate conditions of the study provides earlier ripening times under the high tunnel. However, according to fruit yield and quality, all three cultivars benefit from the hail net over the high tunnel, while ‘Duke’ and ‘Brigitta’ also benefit in particular from the hail net combined with growth in pots.

Transcriptome analysis and identification of genes associated with floral transition and fruit development in rabbiteye blueberry (Vaccinium ashei)

Flowering and fruit set are important traits affecting fruit quality and yield in rabbiteye blueberry (Vaccinium ashei). Intense efforts have been made to elucidate the influence of vernalization and phytohormones on flowering, but the molecular mechanisms of flowering and fruit set remain unclear. To unravel these mechanisms, we performed transcriptome analysis to explore blueberry transcripts from flowering to early fruit stage. We divided flowering and fruit set into flower bud (S2), initial flower (S3), bloom flower (S4), pad fruit (S5), and cup fruit (S6) based on phenotype and identified 1,344, 69, 658, and 189 unique differentially expressed genes (DEGs) in comparisons of S3/S2, S4/S3, S5/S4, and S6/S5, respectively. There were obviously more DEGs in S3/S2 and S5/S4 than in S4/S3, and S6/S5, suggesting that S3/S2 and S5/S4 represent major transitions from buds to fruit in blueberry. GO and KEGG enrichment analysis indicated these DEGs were mostly enriched in phytohormone biosynthesis and signaling, transporter proteins, photosynthesis, anthocyanins biosynthesis, disease resistance protein and transcription factor categories, in addition, transcript levels of phytohormones and transporters changed greatly throughout the flowering and fruit set process. Gibberellic acid and jasmonic acid mainly acted on the early stage of flowering development like expression of the florigen gene FT, while the expression of auxin response factor genes increased almost throughout the process from bud to fruit development. Transporter proteins were mainly associated with minerals during the early flowering development stage and sugars during the early fruit stage. At the early fruit stage, anthocyanins started to accumulate, and the fruit was susceptible to diseases such as fungal infection. Expression of the transcription factor MYB86 was up-regulated during initial fruit development, which may promote anthocyanin accumulation. These results will aid future studies exploring the molecular mechanism underlying flowering and fruit set of rabbiteye blueberry.

Transcriptome Analysis Reveals the Molecular Mechanism of GABA Accumulation during Quinoa (Chenopodium quinoa Willd.) Germination

Quinoa (Chenopodium quinoa Willd.) with a history of 5000 years as food is extremely rich in nutrients and bioactive compounds, including γ-aminobutyric acid (GABA), a natural four-carbon non-protein amino acid with great benefits to human health. In quinoa, GABA generally increases with the germination time, but the underlying molecular mechanism is unclear. Here, we found that the GABA content in quinoa varied significantly among 25 varieties using an automatic amino acid analyzer. Next, six varieties (three low-GABA and three high-GABA varieties) were used for further analyses. The content of GABA in six varieties all showed an increasing trend after germination. In addition, Pearson's correlation analysis showed that the changes in GABA content were closely related to the transcript level or enzyme activity of three key enzymes including glutamate decarboxylase (GAD), GABA transaminase (GABA-T), and succinate-semialdehyde dehydrogenase (SSADH) in the GABA shunt, especially GAD. Based on RNA-sequencing analysis, eight GAD genes, two GABA-T genes, one SSADH gene, nine polyamine oxidase (PAO) genes, five diamine oxidase (DAO) genes, four 4-aminobutyraldehyde dehydrogenase (BADH) genes, and three thermospermine synthase ACAULIS5 (ACL5) genes were identified. Among these, CqGAD8 and CqGABA-T2 may make a greater contribution to GABA accumulation during quinoa germination.

Development of fruit color in Rubus chingii Hu (Chinese raspberry): A story about novel offshoots of anthocyanin and carotenoid biosynthesis

Rubus chingii, is widely distributed in many Asian countries and well known for its medicinal and dietary properties. Diversity of fruit color in raspberry has been attributed to the presence of either anthocyanins or carotenoids. In this study, we investigated anthocyanins and carotenoids, and their biosynthesis by LC-MS/MS. Six anthocyanins mainly consisted of flavanol-anthocyanins while five carotenoids mainly consisted of β-citraurin esters. Flavanol-anthocyanins were produced from an offshoot of the anthocyanin biosynthesis, which started with biosynthesis of flavanols and anthocyanidin by leucoanthocyanidin reductase (LAR)/anthocyanidin reductase (ANR) and anthocyanidin synthase (ANS/LDOX) respectively. β-citraurin esters were produced from cleavage of zeaxanthin and esterification by organic acid, which was an offshoot of the carotenoid biosynthesis. The offshoot started with biosynthesis of zeaxanthin and β-citraurin by carotene β-hydroxylase (CHYB/LUT5) and carotenoid cleavage dioxygenase (CCD) respectively. During fruit ripening, biosynthesis of flavanols and anthocyanins was down-regulated by genes/proteins involved in phenylpropanoid and flavonoid biosynthesis, while biosynthesis of β-citraurin esters was up-regulated by imbalanced expression of genes/proteins involved in β,β-ring and β, ε-ring hydroxylation. Thus, β-citraurin esters, instead of anthocyanins imparted reddish color to the ripe fruit. These pigments and their biosynthesis in R. chingii are totally different from what occurs in other raspberry species.

Transcriptomic, Proteomic and Metabolomic Analysis of Flavonoid Biosynthesis During Fruit Maturation in Rubus chingii Hu

Rubus chingii HU, is a medicinal and nutritious fruit, which is very rich in flavonoids. However, the biosynthesis of its flavonoids is poorly understood. This study examined flavonoids and the genes/proteins at four fruit ripening phases using LC-MS/MS and qPCR. Six major kinds of anthocyanins, primarily consisted of flavanol-anthocyanins, which differed in form or concentration from other Rubus species. In contrast to other known raspberries species, R. chingii had a decline in flavonoids during fruit ripening, which was due to down-regulation of genes and proteins involved in phenylpropanoid and flavonoid biosynthesis. Unexpectedly, anthocyanin also continuously decreased during fruit maturation. This suggests that anthocyanins are not responsible for the fruit's reddish coloration. Flavanol-anthocyanins were derived from the proanthocyanidin pathway, which consumed two flavonoid units both produced through the same upstream pathway. Their presence indicates a reduction in the potential biosynthesis of anthocyanin production. Also, the constantly low expression of RchANS gene resulted in low levels of anthocyanin biosynthesis. The lack of RchF3'5'H gene/protein hindered the production of delphinidin glycosides. Flavonoids primarily comprising of quercetin/kaempferol-glycosides were predominately located at fruit epidermal-hair and placentae. The proportion of receptacle/drupelets changes with the maturity of the fruit and may be related to a decrease in the content of flavonoids per unit mass as the fruit matures. The profile and biosynthesis of R. chingii flavonoids are unique to Rubus. The unique flavonol pathways of R. chingii could be used to broaden the genetic diversity of raspberry cultivars and to improve their fruit quality.

Metabolite profile and genes/proteins expression in β-citraturin biosynthesis during fruit ripening in Chinese raspberry (Rubus chingii Hu)

Carotenoids are one of the most abundant pigments in raspberries. Rubus chingii Hu, indigenous to China, is traditionally consumed for health benefits. However, the carotenoid composition and pathways of R. chingii have not yet been studied. In this study, the components of carotenoids and genes/proteins involved in their biosynthesis were investigated during four fruit ripening phases via LC-MS/MS. Zeaxanthin, β-citraurin and its esters, first identified in Rubus, gradually accumulated during fruit maturation. These compounds, rather than anthocyanins, were responsible for the ripe fruit coloration. In carotenoid metabolism, upstream synthesis genes of RcPSY2 (CL1406.Contig2), RcPDS1 (CL7625.Contig2), RcZDS1 (CL590.Contig6) and RcCRTISO1 (CL6919.Contig2) were up-regulated in gene/protein expression to accelerate carotene biosynthesis. Downstream genes of RcLUT5CHYB/CYP97A (CL8884.Contig3) and RcCHYB/BCH (CL7966.Contig1) were up-regulated in gene/protein expression, while RcCHYE/CYP97C (CL9380.Contig1/2) were maintained at low levels. RcLCYE (Unigene19570) was down-regulated while RcLCYB (CL7586.Contig1) was up-regulated and then down-regulated. These differential gene/protein expressions between LCYB and LCYE, and between CHYE and CHYB led to zeaxanthin accumulation by elevating its biosynthetic enzymes and lowering enzymes for lutein biosynthesis. In apocarotenoid biosynthesis, RcCCD (CL1310.Contig3) was up-regulated in gene/protein expression, which raised the content of β-citraurin and its esters. Additionally, these genes/proteins diverged into different subgroups with distinct pattens of expression, suggesting their difference in function. For example, RcPSY1/3, RcZDS2, and RcCRTISO2/3 genes were expressed at very low levels, suggesting that they may be active in other tissues rather than in fruit. The mechanism of zeaxanthin and β-citraurin biosynthesis is responsible for fruit coloration, which is completely novel to Rubus.

Reflective mulch increases fruit yield of highbush blueberry (Vaccinium corymbosum L. cv. Darrow) grown in a northern maritime environment while maintaining key fruit quality traits

BACKGROUND

In maritime growing environments, blueberry yield often exhibits excessive season-to-season variation, associated with poorly adapted photosynthetic responses to low light conditions. It is therefore necessary to develop methods that stabilise yield while maintaining or improving fruit quality. Here, we placed reflective mulch alongside plants at the early green fruit stage, to test the hypothesis that increasing the available seasonal light integral could enhance blueberry yield. We further determined several quality characteristics to ensure fruit marketability.

RESULTS

Placement of mulch alongside plants reflected up to five times more light compared with bare ground, enhancing the amount of light reaching the canopy. This led to an adaptive increase of light saturated maximal photosynthetic rate of mulch-treated plants, resulting in a twofold increase in yield compared with control plants. Analysis of fruit quality characteristics showed that total soluble solids, sugars and organic acids were similar between treatments. Likewise, antioxidant capacity, total anthocyanin content and the content of individual anthocyanins did not change in response to reflective mulch treatment.

CONCLUSIONS

The use of reflective mulch should be explored by industry as a cost-effective method for enhancing blueberry yield while maintaining fruit quality in maritime environments. © 2020 Society of Chemical Industry.

Regulatory Mechanisms of L-Lactic Acid and Taste Substances in Chinese Acid Rice Soup (Rice-Acid) Fermented With a Lacticaseibacillus paracasei and Kluyveromyces marxianus

Rice-acid has abundant taste substances and health protection function due to the various bioactive compounds it contains, including organic acids. L-lactic acid is the most abundant organic acid in rice-acid, but the regulatory mechanisms of L-lactic acid accumulation in rice-acid are obscure. In this study, we analyzed the dynamic changes in organic acids and taste substances in rice-acid in various fermentation phases and different inoculation methods. We identified the key genes involved in taste substance biosynthesis by RNA-Seq analysis and compared the data of four experimental groups. We found that the interaction of the differences in key functional genes (L-lactate dehydrogenase and D-lactate dehydrogenase) and key metabolism pathways (glycolysis, pyruvate metabolism, TCA cycle, amino acid biosynthesis, and metabolism) might interpret the accumulation of L-lactic acid, other organic acids, and taste substances in rice-acid fermented with Lacticaseibacillus paracasei. The experimental data provided the basis for exploring regulatory mechanisms of taste substance accumulation in rice-acid.

Biochemical differences in the skin of two blueberries (Vaccinium corymbosum) varieties with contrasting firmness: Implication of ions, metabolites and cell wall related proteins in two developmental stages

The pursuit of firmer and better-quality blueberries is a continuous task that aims at a more profitable production. To this end it is essential to understand the biological processes linked to fruit firmness, which may diverge among tissues. By contrasting varieties with opposing firmness, we were able to elucidate events that, taking place at immature stage, lay the foundation to produce a firmer ripe fruit. A deep analysis of blueberry skin was carried out, involving diverse comparative approaches including proteomics and metabolomics coupled to immunolocalization assays. In'O'Neal' (low firmness) enhanced levels of aquaporins, expansins and pectin esterases at the green stage were found to be critical in distinguishing it from 'Emerald' (high firmness). The latter featured higher levels of ABA, low methyl esterified pectins in tricellular junctions and high levels of catechin at this stage. Meanwhile, in 'Emerald' 's ripe fruit epicarp, several mechanisms of cell wall reinforcement such as calcium and probably boron bridges, appear to be more prominent than in 'O'Neal'. This study highlights the importance of cell wall reorganization and structure, abundance of specific metabolites, water status, and hormonal signalling in connection to fruit firmness. These findings result particularly valuable in order to improve the fertilization procedures or in the search of molecular markers related with firmness.

Effects of phosphorus on fruit soluble sugar and citric acid accumulations in citrus

Phosphorus (P) is one of the essential macro-elements for plants. Sugar and organic acid are important factors affecting sensory characteristics of citrus fruit quality. The aim of this study was to investigate how P fertilizer affects quality improvement particularly sucrose (Suc), fructose (Fru), glucose (Glu) and citric acid (CA) accumulations in Cara Cara navel. P fertilizer improved fruit quality of Cara Cara navel, as supported by decreasing titratable acid (TA), CA and increasing soluble solid (TSS), sugars and the ratio of TSS and TA. At the early stage of fruit development, P fertilizer had greater roles in degrading Suc into Fru and Glu due to the increased activities of Suc-degrading enzymes including acid invertase, neutral invertase and Suc synthase-cleavage activity. Coversely, at the mid and late stages of fruit development, P fertilizer had greater roles in re-synthesizing Suc due to the increased activities of Suc-synthesizing enzymes including Suc phosphate synthase and Suc synthase-synthetic activity. These results indicated that application of P fertilizer increased soluble sugars concentrations by improving Suc metabolism and sink strength in fruit conferred by the upregulations of the activities of Suc-degrading and Suc-synthesizing enzymes. P fertilizer decreased CA accumulations at least partially by inhibiting synthesis of CA due to the decreased activities of CA-synthesizing enzymes including citrate synthetase and phosphoenolpyruvate carboxylase. This study suggested that P fertilizer, particularly fertilized with 0.40 kg/plant, increased soluble sugars but decreased CA accumulations in citrus fruit.

Assessment of Physicochemical Quality, Antioxidant Content and Activity, and Inhibition of Cholinesterase between Unripe and Ripe Blueberry Fruit

Five Korean blueberries (''Nelson'', ''Duke '', ''Bluejay '', ''Toro'', and ''Elliot '') were harvested at two maturity stages (unripe and ripe) to evaluate fruit quality and antioxidant activities. The Hunter L, a, and b color of ripe blueberries was lower than that of unripe fruit. Soluble solid concentration (SSC) and pH increased, and titratable acidity (TA) and firmness decreased as the blueberries matured. The ripe blueberry fruits showed a higher SSC/TA ratio than the unripe fruits. Although total anthocyanin, flavonoids, phenolics content, and antioxidant activity were higher in ripe blueberries than in unripe fruit, the unripe fruit had higher acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition activities than ripe fruit in all cultivars. Total antioxidant activity was highly correlated with total flavonoids and phenolics. The relationships between the total antioxidant activity and the AChE or BChE inhibitory activity are negative. There were several physicochemical quality and antioxidant activity differences in blueberries, depending on the cultivar and the maturity at harvest. Unripe fruits also contain potential health-promoting bioactive compounds as functional food ingredients.