Proteomic and metabolic analysis reveals novel sweet cherry fruit development regulatory points influenced by girdling

Comparative analysis of the difference in flavonoid metabolic pathway during coloring between red-yellow and red sweet cherry (Prunus avium L.)

The color of a fruit is an important contributor to the perception of its nutritional value. It is widely acknowledged that the color of sweet cherry changes obviously during ripening. Variations in anthocyanins and flavonoids account for the heterogeneous color of sweet cherries. In this study, we showed that anthocyanins but not carotenoids determine the color of sweet cherry fruits. The difference between red-yellow and red sweet cherry may be attributed to seven anthocyanins, including Cyanidin-3-O-arabinoside, Cyanidin-3,5-O-diglucoside, Cyanidin 3-xyloside, Peonidin-3-O-glucoside, Peonidin-3-O-rutinoside, Cyanidin-3-O-galactoside, Cyanidin-3-O-glucoside (Kuromanin), Peonidin-3-O-rutinoside-5-O-glucoside, Pelargonidin-3-O-glucoside and Pelargonidin-3-O-rutinoside. The content of 85 flavonols differed between red and red-yellow sweet cherries. The transcriptional analysis identified 15 key structural genes involved in the flavonoid metabolic pathway and four R2R3-MYB transcription factors. The expression level of Pac4CL, PacPAL, PacCHS1, PacCHS2, PacCHI, PacF3H1, PacF3H2, PacF3'H, PacDFR, PacANS1, PacANS2, PacBZ1 and four R2R3-MYB were positively correlated with anthocyanin content (ps < 0.05). PacFLS1, PacFLS2 and PacFLS3 expression was negatively correlated with anthocyanin content but positively correlated with flavonols content (ps < 0.05). Overall, our findings suggests that the heterogeneous expression of structural genes in the flavonoid metabolic pathway accounts for the variation in levels of final metabolites, leading to differences between red 'Red-Light' and red-yellow 'Bright Pearl'.

Study of Mineral Composition and Quality of Fruit Using Vascular Restrictions in Branches of Sweet Cherry

Calcium (Ca) and carbohydrate (CHO) supply in sweet cherry have been associated with fruit quality at harvest and during storage. There is little published information integrating CHO and Ca availability and distribution in sweet cherry and their effects on fruit quality. Accordingly, in the 2019-20 season, vascular restrictions were imposed on the phloem (girdling, G, stopping phloem flow) and xylem (transverse incision, S, cutting 50% of xylem cross-section area) of individual vertical branches of the sweet cherry combination 'Lapins'/Colt trained as Kym Green Bush system to modify mineral and CHO composition in fruit and associate such changes with quality at harvest and storage. The girdling to the phloem was used to induce changes in CHO distribution. The transverse incision to the xylem was a tool to modify Ca distribution. Five treatments (TR) were implemented: TR1-CTL = Control (without vascular restriction), TR2-G, at its base, TR3-G + G: at its base, and G further up at the change of year between the second and the third years of growth TR4--S and TR5-S + G. The vegetative (i.e., shoot and leaf growth), reproductive (i.e., fruit set and yield) development and stomatal conductance were monitored. Each branch was divided into the upper (1-and 2-year-old wood) and the lower (3-and 4-year-old wood) segments of the restriction applied. The quality and mineral composition (Ca, Mg, K, and N) of fruit borne on each segment were measured at harvest. The upper segment of TR3-G + G branches were harvested 10 d before the lower segment. The fruit from the upper segment of TR3-G + G was the largest, the sweetest, and had the higher titratable acidity concentration. However, fruits of this segment were the softest, had the lowest Ca concentrations, and had the highest ratios of N:Ca and K:Ca, compared with the other TRs. TR3-G + G branches developed the highest number of lateral current season shoots including shoots below the second girdling in the lower segment of the branch. This vegetative flow of growth would explain the mineral unbalance produced in the fruit from the upper segment of the branch. TR2-G did not register changes in fruit quality and mineral concentration compared with TR1-CTL. Surprisingly, the fruit from the branches with xylem restriction did not show changes in Ca concentration, suggesting that the xylem stream was enough to supply the fruit in branches without lateral shoot development. Fruit firmness was positively related to fruit Ca concentration and negatively related to the ratios of K:Ca and N:Ca.

Molecular and physiologic mechanisms of advanced ripening by trunk girdling at early veraison of 'Summer Black' grape

Although the effects of girdling on grape berry development have been widely studied, the underlying mechanisms are poorly understood, especially at the molecular level. This study investigated the effect of trunk girdling on grape (Vitis L.) berry maturation. Girdling was performed on 5-year-old 'Summer Black' grapevines at early veraison, and transcriptional and physiologic analyses were performed. Trunk girdling promoted sugar accumulation and color development in berries and accelerated berry ripening by 25 days. Genes related to sucrose cleavage and polysaccharide degradation were upregulated at the transcriptional level, which was associated with increased monosaccharide accumulation and berry softening. Anthocyanin biosynthesis and accumulation were also enhanced by trunk girdling through the upregulation of anthocyanin biosynthesis genes including phenylalanine ammonia-lyase and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT). The increased expression of two VvUFGT genes was accompanied by the upregulation of VvMYBA2 under girdling. The upregulation of genes involved in ethylene biosynthesis and hormone (abscisic acid and brassinosteroid) responses and downregulation of genes involved in indoleacetic acid biosynthesis and response may have also promoted berry ripening in the girdling group. A total of 120 differentially expressed transcription factor genes from 29 gene families including MYB, ERF, and MYB-related were identified in the girdling group, which may participate in the regulation of berry development and ripening. These results provide molecular-level insight into the positive effects of trunk girdling on berry development in grapes.

Role of plant growth-promoting rhizobacteria in boosting the phytoremediation of stressed soils: Opportunities, challenges, and prospects

Soil is considered as a vital natural resource equivalent to air and water which supports growth of the plants and provides habitats to microorganisms. Changes in soil properties, productivity, and, inevitably contamination/stress are the result of urbanisation, industrialization, and long-term use of synthetic fertiliser. Therefore, in the recent scenario, reclamation of contaminated/stressed soils has become a potential challenge. Several customized, such as, physical, chemical, and biological technologies have been deployed so far to restore contaminated land. Among them, microbial-assisted phytoremediation is considered as an economical and greener approach. In recent decades, soil microbes have successfully been used to improve plants' ability to tolerate biotic and abiotic stress and strengthen their phytoremediation capacity. Therefore, in this context, the current review work critically explored the microbial assisted phytoremediation mechanisms to restore different types of stressed soil. The role of plant growth-promoting rhizobacteria (PGPR) and their potential mechanisms that foster plants' growth and also enhance phytoremediation capacity are focussed. Finally, this review has emphasized on the application of advanced tools and techniques to effectively characterize potent soil microbial communities and their significance in boosting the phytoremediation process of stressed soils along with prospects for future research.

Application of quantitative proteomics to investigate fruit ripening and eating quality

The consumption of fruit and vegetables play an important role in human nutrition, dietary diversity and health. Fruit and vegetable industries impart significant impact on our society, economy, and environment, contributing towards sustainable development in both developing and developed countries. The eating quality of fruit is determined by its appearance, color, firmness, flavor, nutritional components, and the absence of defects from physiological disorders. However, all of these components are affected by many pre- and postharvest factors that influence fruit ripening and senescence. Significant efforts have been made to maintain and improve fruit eating quality by expanding our knowledge of fruit ripening and senescence, as well as by controlling and reducing losses. Innovative approaches are required to gain better understanding of the management of eating quality. With completion of the genome sequence for many horticultural products in recent years and development of the proteomic research technique, quantitative proteomic research on fruit is changing rapidly and represents a complementary research platform to address how genetics and environment influence the quality attributes of various produce. Quantiative proteomic research on fruit is advancing from protein abundance and protein quantitation to gene-protein interactions and post-translational modifications of proteins that occur during fruit development, ripening and in response to environmental influences. All of these techniques help to provide a comprehensive understanding of eating quality. This review focuses on current developments in the field as well as limitations and challenges, both in broad term and with specific examples. These examples include our own research experience in applying quantitative proteomic techniques to identify and quantify the protein changes in association with fruit ripening, quality and development of disorders, as well as possible control mechanisms.

Research Progress and Trends in Metabolomics of Fruit Trees

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

Differential Phenolic Compounds and Hormone Accumulation Patterns between Early- and Mid-Maturing Sweet Cherry (Prunus avium L.) Cultivars during Fruit Development and Ripening

Color acquisition is one of the most distinctive features of fruit development and ripening processes. The color red is closely related to the accumulation of polyphenolic compounds, mainly anthocyanins, during sweet cherry fruit maturity. In non-climacteric fruit species like sweet cherry, the maturity process is mainly controlled by the phytohormone abscisic acid (ABA), though other hormones may also play a role. However, the coordinated stage-specific production of polyphenolic compounds and their relation with hormone content variations have not been studied in depth in sweet cherry fruits. To further understand the accumulation dynamics of these compounds (hormones and metabolites) during fruit development, two sweet cherry cultivars ("Lapins" and "Glenred") with contrasting maturity timing phenotypes were analyzed using targeted metabolic analysis. The ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) approach revealed that phenolic acids, flavonols, and flavan-3-ols accumulated mainly until the straw-yellow stage in the early-maturing cultivar, while accumulation was mainly at the green stage in the mid-maturing cultivar, suggesting a cultivar-dependent stage-specific production of secondary metabolites. In the mid-maturing cultivar, anthocyanins were detected only from the red stage onward, whereas detection began at the pink stage in the early-maturing cultivar. ABA negatively correlated (p-value < 0.05) with the flavonols and flavan-3-ols in both cultivars. ABA and anthocyanin content increased at the same time in the early-season cultivar. In contrast, anthocyanins accumulated and the pink color initiation started several days after the ABA increase in the mid-maturing cultivar. Differential accumulation patterns of GA₄, a ripening antagonizing hormone, between the cultivars could explain this difference. These results showed that both red-colored cultivars presented different accumulation dynamics of phenolic compounds and plant hormones during fruit development, suggesting underlying differences in the sweet cherry fruit color evolution.

Pre- and Post-harvest Melatonin Application Boosted Phenolic Compounds Accumulation and Altered Respiratory Characters in Sweet Cherry Fruit

The aim of the present study was to investigate the impact of exogenous melatonin (0. 5 mM) application through pre-harvest foliar spray and postharvest immersion, alone or in combination, on ripening parameters of sweet cherry (cv. Ferrovia) fruit and their relationship with bioactive compounds and gene expression at harvest as well after cold storage (0°C) for 12 days and subsequent room temperature (20°C) exposure for 8 h. Although several ripening traits were not influenced by melatonin, the combining pre- and post-harvest treatments delayed fruit softening at post-cold period. Preharvest spray with melatonin depressed fruit respiration at time of harvest while all applied treatments induced respiratory activity following cold, indicating that this anti-ripening action of melatonin is reversed by cold. Several genes related to the tricarboxylic acid cycle, such as PaFUM, PaOGDH, PaIDH, and PaPDHA1 were upregulated in fruit exposed to melatonin, particularly following combined pre- and post-harvest application. The accumulation of phenolic compounds, such as neochlorogenic acid, chlorogenic acid, epicatechin, procyanidin B1, procyanidin B2+B4, cyanidin-3-O-galactoside, and cyanidin-3-O-rutinoside along with the expression of several genes involved in phenols biosynthesis, such as PaSK, PaPAL, Pa4CL, PaC4H, and PaFNR were at higher levels in melatonin-treated cherries at harvest and after cold exposure, the highest effects being observed in fruits subjected to both pre- and post-harvest treatments. This study provides a comprehensive understanding of melatonin-responsive ripening framework at different melatonin application conditions and sweet cherry stages, thereby helps to understand the action of this molecule in fruit physiology.

Novel insights into the calcium action in cherry fruit development revealed by high-throughput mapping

This work provides the first system-wide datasets concerning metabolic changes in calcium-treated fruits, which reveal that exogenously applied calcium may specifically reprogram sweet cherry development and ripening physiognomy. Calcium modulates a wide range of plant developmental processes; however, the regulation of fruit ripening by calcium remains largely uncharacterized. In this study, transcriptome, proteome and metabolome profiling was used to document the responses of sweet cherry fruit to external calcium application (0.5% CaCl₂) at 15, 27 and 37 days after full blossom. Endogenous calcium loading in fruit across development following external calcium feeding was accompanied by a reduction in respiration rate. Calcium treatment strongly impaired water-induced fruit cracking tested by two different assays, and this effect depended on the fruit size, water temperature and light/dark conditions. Substantial changes in the levels of numerous polar/non-polar primary and secondary metabolites, including malic acid, glucose, cysteine, epicatechin and neochlorogenic acid were noticed in fruits exposed to calcium. At the onset of ripening, we identified various calcium-affected genes, including those involved in ubiquitin and cysteine signaling, that had not been associated previously with calcium function in fruit biology. Calcium specifically increased the abundance of a significant number of proteins that classified as oxidoreductases, transferases, hydrolases, lyases, and ligases. The overview of temporal changes in gene expression and corresponding protein abundance provided by interlinked analysis revealed that oxidative phosphorylation, hypersensitive response, DNA repair, stomata closure, biosynthesis of secondary metabolites, and proton-pump activity were mainly affected by calcium. This report provides the fullest characterization of expression patterns in calcium-responsive genes, proteins and metabolites currently available in fruit ripening and will serve as a blueprint for future biological endeavors.

Early metabolic priming under differing carbon sufficiency conditions influences peach fruit quality development

Crop load management is an important preharvest factor to balance yield, quality, and maturation in peach. However, few studies have addressed how preharvest factors impact metabolism on fruit of equal maturity. An experiment was conducted to understand how carbon competition impacts fruit internal quality and metabolism in 'Cresthaven' peach trees by imposing distinct thinning severities. Fruit quality was evaluated at three developmental stages (S2, S3, S4), while controlling for equal maturity using non-destructive visual to near-infrared spectroscopy. Non-targeted metabolite profiling was used to characterize fruit at each developmental stage from trees that were unthinned (carbon starvation) or thinned (carbon sufficiency). Carbon sufficiency resulted in significantly higher fruit dry matter content and soluble solids concentration at harvest when compared to the carbon starved, underscoring the true impact of carbon manipulation on fruit quality. Significant differences in the fruit metabolome between treatments were observed at S2 when phenotypes were similar, while less differences were observed at S4 when the carbon sufficient fruit exhibited a superior phenotype. This suggests a potential metabolic priming effect on fruit quality when carbon is sufficiently supplied during early fruit growth and development. In particular, elevated levels of catechin may suggest a link between secondary/primary metabolism and fruit quality development.