Peach Fruit Ripening Research Articles

Identification and expression analysis of abscisic acid signal transduction genes during peach fruit ripening

To characterize transcriptional regulation of the abscisic acid (ABA) signal transduction pathway during peach fruit early development and ripening, genes encoding the core components of the pathway, including 7 PpPYR (ABA receptor), 10 PpPP2C (type 2C protein phosphatase), and 7 PpSnRK2 (subfamily 2 of SNF1-related kinases), were identified from the peach (Prunus persica) reference genome. PpPYRs, PpPP2Cs, and PpSnRK2s from peach were putative homologous to proteins from tomato and Arabidopsis. Phylogenetic analysis showed that PpPYRs and PpSnRK2s were clustered into three subfamilies/subclasses. Transcript profile indicated that PpPYR2, PpPYR6, and PpPYR7 expression decreased sharply while ABA concentration increased during peach fruit ripening. Expression of PpPP2C4, PpPP2C9, and PpPP2C10 increased along with ABA concentration during fruit ripening. Expression of PpSnRK2.4 and PpSnRK2.6 also increased together with ABA concentration during fruit ripening. Furthermore, PpPP2C10 could interact with PpSnRK2.6 was determined by Yeast two-hybrid and BiFC analyses. The results will improve our understanding of ABA signal transduction genes in peach and lay the foundation for further exploring the mechanisms underlying peach fruit ripening.

PpGST1, an anthocyanin-related glutathione S-transferase gene, is essential for fruit coloration in peach.

SummaryAnthocyanins have crucial biological functions and affect quality of horticultural produce. Anthocyanins accumulate in ripe peach fruit; differential accumulation is observed in deep coloured cultivar ‘Hujingmilu’ and lightly pigmented cultivar ‘Yulu’. The difference was not fully explained by accumulation of total flavonoids and expression of anthocyanin biosynthetic genes. Expression analysis was conducted on a glutathione S‐transferase gene (PpGST1), and it was found that the expression correlated well with anthocyanin accumulation in peach fruit tissues. Functional complementation of the Arabidopsis tt19 mutant indicated that PpGST1 was responsible for transport of anthocyanins but not proanthocyanidins. PpGST1 was localized in nuclei and the tonoplast, including the sites at which anthocyanin vacuolar sequestration occurred. Transient overexpression of PpGST1 together with PpMYB10.1 in tobacco leaves and peach fruit significantly increased anthocyanin accumulation as compared with PpMYB10.1 alone. Furthermore, virus‐induced gene silencing of PpGST1 in a blood‐fleshed peach not only resulted in a reduction in anthocyanin accumulation but also a decline in expression of anthocyanin biosynthetic and regulatory genes. Cis‐element analysis of the PpGST1 promoter revealed the presence of four MYB binding sites (MBSs). Dual‐luciferase assays indicated that PpMYB10.1 bound to the promoter and activated the transcription of PpGST1 by recognizing MBS1, the one closest to the ATG start codon, with this trans‐activation being stronger against the promoter of deep coloured ‘Hujingmilu’ compared with lightly coloured cultivar ‘Yulu’. Altogether, our data provided molecular evidence supporting coordinative regulatory roles of PpGST1 and PpMYB10.1 in anthocyanin accumulation in peach.

Characterization and Identification of PpEIN3 during the Modulation of Fruit Ripening Process by Ectopic Expressions in Tomato.

First study of PpEIN3 by transgenic experiments to verify its function in the maturity process PpEIN3 is a positive regulator of ethylene signal transduction pathway to promote fruits ripening Ethylene is one of the most important phytohormone in plants and plays a critical role during growth, development, maturity, and aging. The framework of the ethylene signaling pathway is well reported. Nevertheless, studies on Ethylene Insensitive 3 (EIN3), the downstream regulator of the ethylene signaling pathway, need to be investigated, especially in peach [Prunus persica (L.) Batsch]. In this study, we cloned PpEIN3 from peach and characterized it in tomato (Solanum lycopersicum L.). Our results depicted that the open-reading frame of PpEIN3 was 1875 bp, encoding a protein with 624 amino acid residues that contained a conserved EIN3 domain, a highly conserved N-terminal region, and seven DNA-binding sites. PpEIN3 showed very close association with homologous EIN genes from apple (Malus domestica Borkh.) and grapevine (Vitis vinifera L.). All investigated EIN proteins shared similar domains and structures. The PpEIN3 promoter possessed several motifs related to hormones that affect fruit development and ripening. Spatial-temporal expression analysis revealed that PpEIN3 was expressed at high levels in the late stage of fruit development vs. the early stage. In transgenic tomato, PpEIIN3 showed overexpression and the key ethylene biosynthesis genes SlACO1, SlACS1, and SlSAMS1 were upregulated and promoted early maturation in fruit. By contrast, PpEIIN3 silencing delayed ripening and reduced SlEIN3 expression in tomato. The results confirmed that PpEIN3 is a positive regulator of the ethylene signal transduction pathway, which promoted fruit ripening. Our findings provide valuable insight to the roles in ethylene signal components in the modulation of peach fruit ripening.

Peach fruit ripening: Proteomic comparative analyses of two cultivars with different flesh texture phenotypes at two ripening stages

Firmness is an important textural attribute of peach fruit that directly influences its shelf life and consumer acceptance. To investigate the underlying mechanism that determines the texture of peach flesh, we conducted a proteome study on the fruits of two cultivars: hard melting flesh Xiahui 8 and stony hard Xiacui. Then we compared these at the unripe and ripe stages using the isobaric tags for relative and absolute quantification (iTRAQ) technique. In total, 190 proteins with more than 1.5-fold (P < 0.05) abundance changes were observed, including 57 proteins in Xiacui and 171 proteins in Xiahui 8. The differentially expressed proteins in Xiahui 8 were mainly in classes of proteins involved in cellular activities such as sugar metabolism, membrane structure, and cell-cycle control. Our findings imply that the enzymes polygalacturonase (PG), pectate lyase (PL), calmodulin (CaM), calcineurin B-like protein (CBL), peptidyl-prolyl isomerase (PPIase), and 9-cis-epoxycarotenoid dioxygenase (NCED) play functional roles in controlling fruit development and maintaining textural integrity and fruit quality during ripening. The results shed new light on proteomic differences and protein interactions during the metabolism of ethylene, amino acids, sugars, and carbohydrates; the general defense response in cultivars with varied texture phenotypes; and the underlying mechanisms of peach fruit ripening. They also provide a knowledge base needed for postharvest quality control and breeding strategies for cultivar improvement.

Expression patterns of genes involved in sugar metabolism and accumulation during peach fruit development and ripening

In fleshy fruits, sugars (glucose, fructose, sucrose and sorbitol) are most important for fruit growth and development but also play a central role in fruit quality. In Peach (Prunus persica), we observed the sugars content at six developmental stages through high pressure liquid chromatography (HPLC). There was variation during fruit development and ripening, sucrose first increased then decreased; glucose and fructose first decreased, and then increased while sorbitol always decreased. In past, understanding about the mechanisms which control the sugar metabolism and accumulation in peach remains quite limited. We studied the transcript profiles of total 30 genes encoding key enzymes and transporters, which were involved in sucrose metabolism, resynthesis and transport. 13 putative genes including sucrose phosphatase synthase (PpSPS4 and PpSPS2), Hexokinases (PpHK1 and PpHK3), neutral/natural invertase (PpNINV1and PpNINV2), vacuolar acid invertase (PpVAINV2), sucrose transporter (PpSUT2), vacuolar glucose transporters (PpVGT1, PpVGT2 and PpVGT3) and tonoplast monosaccharides transporters (PpTMT1 and PpTMT2) highly expressed during peach fruit ripening. PpSPS4 had significantly positive correlation with glucose and fructose. Our results suggested that more sucrose accumulated in cytosol because of upregulation of (PpSPS4 and PpSPS2), that sucrose imported into vacuole through upregulation of PpSUT2, PpVGT1, PpVGT2, PpVGT3, PpTMT1 and PpTMT2 transporters, where cleaving of sucrose is done by upregulation of PpVAINV2. Hence, level of sucrose decreased as fruit ripe. As a result, the concentration of glucose and fructose increased at ripening stage (S4 II to S4 III). So, these marker genes can be involved in peach fruit ripening. This study will improve our understanding and lay foundation to explore the function of these genes and improvement of peach fruit quality.

Deciphering the interplay among genotype, maturity stage and low-temperature storage on phytochemical composition and transcript levels of enzymatic antioxidants in Prunus persica fruit

The aim of this study was to understand the antioxidant metabolic changes of peach (cvs. ‘Royal Glory’, ‘Red Haven’ and ‘Sun Cloud’) and nectarine fruits (cv. ‘Big Top’) exposed to different combinations of low-temperature storage (0, 2, 4 weeks storage at 0 °C, 90% R.H.) and additional ripening at room temperature (1, 3 and 5 d, shelf life, 20 °C) with an array of analytical, biochemical and molecular approaches. Initially, harvested fruit of the examined cultivars were segregated non-destructively at advanced and less pronounced maturity stages and qualitative traits, physiological parameters, phytochemical composition and antioxidant capacity were determined. ‘Big Top’ and ‘Royal Glory’ fruits were characterized by slower softening rate and less pronounced ripening-related alterations. The coupling of HPLC fingerprints, consisted of 7 phenolic compounds (chlorogenic, neochlorogenic acid, catechin, epicatechin, rutin, quecetin-3-O-glucoside, procyanidin B1) and spectrophotometric methods disclosed a great impact of genotype on peach bioactive composition, with ‘Sun Cloud’ generally displaying the highest contents. Maturity stage at harvest did not seem to affect fruit phenolic composition and no general guidelines for the impact of cold storage and shelf-life on individual phenolic compounds can be extrapolated. Subsequently, fruit of less pronounced maturity at harvest were used for further molecular analysis. ‘Sun Cloud’ was proven efficient in protecting plasmid pBR322 DNA against ROO attack throughout the experimental period and against HO attack after 2 and 4 weeks of cold storage. Interestingly, a general down-regulation of key genes implicated in the antioxidant apparatus with the prolongation of storage period was recorded; this was more evident for CAT, cAPX, Cu/ZnSOD2, perAPX3 and GPX8 genes. Higher antioxidant capacity of ‘Sun Cloud’ fruit could potentially be linked with compounds other than enzymatic antioxidants that further regulate peach fruit ripening.

Characterization and Transcript Profiling of PME and PMEI Gene Families during Peach Fruit Maturation

Pectins are synthesized and secreted to the cell wall as highly methyl-esterified polymers and demethyl-esterified by pectin methylesterases (PMEs), which are regulated by pectin methylesterase inhibitors (PMEIs). PMEs and PMEIs are involved in pectin degradation during fruit softening; however, the roles of the PME and PMEI gene families during fruit softening remain unclear. Here, 71 PME and 30 PMEI genes were identified in the peach (Prunus persica) genome and shown to be unevenly distributed on all eight chromosomes. The 71 PME genes comprised 36 Type-1 PMEs and 35 Type-2 PMEs. Transcriptome analysis showed that 11 PME and 15 PMEI genes were expressed during fruit ripening in melting flesh (MF) and stony-hard (SH) peaches. Three PME and five PMEI genes were expressed at higher levels in MF than in SH fruit and exhibited softening-associated expression patterns. Upstream regulatory cis elements of these genes related to hormone response, especially naphthaleneacetic acid and ethylene, were investigated. One PME (Prupe.7G192800) and two PMEIs (Prupe.1G114500 and Prupe.2G279800), and their promoters were identified as potential targets for future studies on the biochemical metabolism and regulation of fruit ripening. The comprehensive data generated in this study will improve our understanding of the PME and PMEI gene families in peach. However, further detailed investigation is necessary to elucidate the biochemical function and regulation mechanism of the PME and PMEI genes during peach fruit ripening.

Effect of methyl jasmonic acid on peach fruit ripening progress

In order to investigate the role of jasmonates (JAs) during the ripening of peach fruit, two concentrations of methyl jasmonate (MeJA, 10 and 100mM) were evaluated using field system. Fruit quality parameters, such as the contents of anthocyanin, volatile compounds and cell wall enzymes, and the transcriptional profiles of several ripening-related genes were analyzed. Our results showed that MeJA promoted fruit chlorophyll degradation and anthocyanin accumulation, volatile compounds enhancement, but it would also delay fruit softening through regulation cell wall enzymes activities of PG and cellulase. MeJA increased fruit anti-stress because of the promotion of SOD, POD, CAT, PPO enzyme activities. MeJA reduced fruit endogenous ethylene content, although ethylene accelerated fruit softening and decreased titratable acidity that resulted in fruit ripening. MeJA altered the expression profiles of its biosynthesis pathway genes of PpLOX, PpAOS, and PpOPR3, which resulted the accumulation of JA accumulation in peach fruit. MeJA also increased the expression levels of anthocyanin-associated genes PpMYB, PpPAL, PpCHS, PpCHI, PpF3H, PpDFR, and PpUFGT. MeJA increased chlorophyll degradation gene of PpPAO, as well as decreased its biosynthesis gene of PpPORC, which led to chlorophyll reduction. However, ethylene had a reverse effect on the genes’ expression levels, and it inhibited anthocyanin accumulation. Ultimately, heterologous expression peach PpAOS in strawberry showed that JA promoted fruit anthocyanin accumulation. The present findings suggest that JA promotes peach fruit ripening through regulation anthocyanin accumulation, which is different from the way triggered by ethylene in regulation peach fruit ripening.

Differential expression of iron–sulfur cluster biosynthesis genes during peach fruit development and ripening, and their response to iron compound spraying

Iron (Fe) is required for the iron–sulphur (Fe–S) cluster biosynthesis, which occurs in chloroplasts, mitochondria and cytosol that needs dozens of genes. However, molecular mechanisms of Fe metabolism in fruit trees are largely rare, especially towards fruit development and ripening. In this work, we characterized ‘Xiahui8′ peach development, and analyzed expression profiles of 44 Fe–S cluster biosynthesis genes during different fruit development stages. The development of ‘Xiahui8′ peaches last for an average period of 130days, followed by a rapid on-tree ripening during 7days. Notably, the Fe accumulation in peach flesh was negatively correlated to fruit weight and volume, but positively correlated to flesh firmness. Quantitative Real-Time PCR (qRT-PCR) analysis showed that Fe–S cluster biosynthesis genes were differentially expressed during distinct fruit development stages. A majority of plastid SUF and mitochondrial ISC machinery genes were gradually enhanced along with fruit growth, and began to decrease since commercial harvest phase. The highest expression level of all cytosolic CIA machinery genes were appeared in early fruitlet formation stage, and gradually reduced until fruit ripening. Moreover, foliar spraying of amino acid-Fe compound fertilizer significantly enhanced the total soluble solid (TSS) content in peaches, accompanied by strengthened flesh firmness, Fe concentration, and succinate dehydrogenase (SDH) and aconitase (ACO) activities. Thirteen Fe–S cluster biosynthesis genes were responsive to fertilizer treatment, whose expression level were significantly induced, with the exception of HSCA2 that was reduced. Our findings provided molecular basis for Fe metabolism in peach fruit development, and revealed potential genes for further functional verification.

Potential role of reactive oxygen species and antioxidant genes in the regulation of peach fruit development and ripening

The roles of reactive oxygen species (ROS) as both toxic by-products and as signaling molecules have been reported in fruit development and ripening. Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) play important roles in balancing the induction and removal of ROS in plants, and are respectively encoded by families of closely homologous genes. In the present study, we investigated the roles of ROS and the above-mentioned antioxidant genes during the development and ripening of peach fruit. The experimental results indicated that O2− and H2O2 acted as potential signaling molecules in the middle stage of fruit development, and only H2O2 might function as a main toxic molecule to stimulate lipid peroxidation and oxidative stress in the late stage of fruit ripening. PpaCu/Zn-SODs were the most abundant members in the PpaSOD gene family and they expressed steadily in peach fruit development and ripening. Low temperature (4 °C) postponed and suppressed the climacteric peaks of respiration and ethylene, significantly enhanced the activities of CAT and GPX, and up-regulated the expression of PpaCAT1 and PpaGPX6 in the late stage of fruit ripening. PpaCAT1 and PpaGPX6 were two key genes in alleviating oxidative stress in the late stage of fruit ripening.

Identification of Peach NAP Transcription Factor Genes and Characterization of their Expression in Vegetative and Reproductive Organs during Development and Senescence.

The NAP (NAC-like, activated by AP3/P1) transcription factor belongs to a subfamily of the NAC transcription factor family, and is believed to have an important role in regulating plant growth and development. However, there is very little information about this subfamily in Rosaceous plants. We identified seven NAP genes in the peach genome. PpNAP2 was categorized in the NAP I group, and contained a conserved transcription activation region. The other PpNAP genes belonged to the NAP II group. The expression patterns of the PpNAP genes differed in various organs and developmental stages. PpNAP1 and PpNAP2 were highly expressed in mature and senescing flowers, but not in leaves, fruits, and flower buds. PpNAP3 and PpNAP5 were only expressed in leaves. The PpNAP4 expression level was high in mature and senescing fruits, while PpNAP6 and PpNAP7 expression was up-regulated in mature and senescent leaves and flowers. During the fruit development period, the PpNAP4 and PpNAP6 expression levels rapidly increased during the S1 and S4 stages, which suggests these genes are involved in the first exponential growth phase and fruit ripening. During the fruit ripening and softening period, the PpNAP1, PpNAP4, and PpNAP6 expression levels were high during the early storage period, which was accompanied by a rapid increase in ethylene production. PpNAP1, PpNAP4, and PpNAP6 expression slowly increased during the middle or late storage periods, and peaked at the end of the storage period. Additionally, abscisic acid (ABA)-treated fruits were softer and produced more ethylene than the controls. Furthermore, the PpNAP1, PpNAP4, and PpNAP6 expression levels were higher in ABA-treated fruits. These results suggest that PpNAP1, PpNAP4, and PpNAP6 are responsive to ABA and may regulate peach fruit ripening.

Effect of blue light on ethylene biosynthesis, signalling and fruit ripening in postharvest peaches

The involvement of ethylene gas in the ripening of peach fruit is a symbolic phenomenon that has a place in the history of research on plant hormones. It is well documented that fruit ripening is developmentally regulated and affected by environmental factors such as temperature and light. Blue light has been shown to induce pigment synthesis in postharvest fruit. However, information on its effect on fruit ripening is still limited. This study aimed to investigate the effect of light-emitting diode blue light treatment at 40μmolm−2s−1 on fruit ripening, ethylene biosynthesis and signalling in postharvest peaches during storage at 10°C. Blue light exposure induced fruit ripening as expressed by the enhanced decline of fruit firmness and increases in skin colour parameters, which was associated with the increase in ethylene production because of the up-regulated expression of PpLOXs and ethylene biosynthetic genes such as PpACO1 and PpACS3. Meanwhile, six genes in relation to ethylene perception and signalling were also investigated using real-time PCR. Among them, blue light treatment significantly inhibited expression of PpERS1 and enhanced transcript levels of PpEIN2, PpEIL1, PpEIL2 and PpERF2, which led to an induction ethylene signalling pathway and resulted in turn into the promotion of ethylene production and fruit softening in postharvest peaches. Compared to control fruit stored at darkness, higher expression level of ethylene biosynthetic and signalling genes in blue light exposed peaches could be beneficial for its ethylene production and consequently fruit ripening.

Potential role of glutathione peroxidase gene family in peach fruit ripening under combined postharvest treatment with heat and 1-MCP

Glutathione peroxidases (GPXs) are central members in the antioxidant system and play an important role in response to oxidant stress. To understand the role of the major molecular players in peach fruit ripening, the GPX gene family was investigated in this study. Eight Glutathione peroxidase genes (PpaGPX1-8) in peach fruit were isolated from genome databases and characterized using bioinformatics analysis. The expression patterns of GPX genes were analyzed in peach fruit harvested at three different maturity classes and treated with heat+1-MCP (HM). The unripe fruit were found to have both higher enzymatic and transcriptional capacity compared with the more mature fruit, and the ripe fruit were more sensitive to HM treatment. PpaGPX6 and PpaGPX8 were the most abundantly expressed genes at all three maturity classes of peach fruit. All the PpaGPX genes (except PpaGPX1) showed up-regulated expression in the late stage of ripening (after the peak of respiratory climacteric). Moreover, HM treatment dramatically delayed the postharvest ripening process of peach fruit, by postponing the climacteric peak in respiration, enhancing firmness, increasing GPX activity and up-regulating PpaGPXs expression. These data indicated that PpaGPXs had a more important regulating function in the late stage of peach fruit ripening.

Molecular and biochemical responses to wounding in mesocarp of ripe peach (Prunus persica L. Batsch) fruit

The physiological and molecular responses of ripe fruit to wounding were evaluated in two peach (Prunus persica) varieties (‘Glohaven’, GH, melting and ‘BigTop’, BT, slow melting nectarine) by comparing mesocarp samples from wedges (as in minimal processing) and whole fruit as the control. Slight differences between the two varieties were detected in terms of ethylene production, whereas total phenol and flavonoid concentrations, and PPO and POD enzyme activities showed a general increase in wounded GH but not in BT. This was associated with the better appearance of the BT wedges at the end of the experimental period (72h). Microarray (genome-wide μPEACH3.0) analysis revealed that a total number of 2218 genes were differentially expressed (p<0.01, log2 fold change expression ratio >1 or <−1) in GH 24h after wounding compared to the control. This number was much lower (1208) in BT. According to the enrichment analysis, cell wall, plasma membrane, response to stress, secondary metabolic processes, oxygen binding were the GO categories over-represented among the GH up-regulated genes, whereas plasma membrane and response to endogenous stimulus were the categories over-represented among the down-regulated genes. Only 32 genes showed a common expression trend in the two varieties 24h after wounding, whereas a total of 512 genes (with highly represented transcription factors), displayed opposite behavior. Quantitative RT-PCR analysis confirmed the microarray data for 18 out of a total of 20 genes selected. Specific WRKY, AP2/ERF and HSP20 genes were markedly up-regulated in wounded GH, indicating the activation of regulatory and signaling mechanisms probably related to different hormone categories. Compared to BT, the expression of specific genes involved in phenylpropanoid and triterpenoid biosynthetic pathways showed a more pronounced induction in GH, highlighting the difference between the two peach varieties in terms of molecular responses to wounding in the mesocarp tissue.

Intracellular compartmentation and membrane permeability to sugars and acids at different growth stages of peach

The aim of the present work was to evaluate the distribution of sugars and acids in vacuoles, cytoplasm, and free space in peach fruits picked at premature (June 22) and mature (July 22) stages and assess the membrane permeability to sugars and acids. The results showed that sugars (sucrose, glucose, fructose and sorbitol) and acids (malate, citrate, quinate and shikimate) in vacuole, cytoplasm and free space were 1.0, 2.3 and 2.4mgg−1, and 0.15, 0.31 and 0.72mgg−1, respectively, in immature fruit, 27.4, 11.5 and 9.0mgg−1, and 1.97, 0.96 and 0.32mgg−1, respectively, in mature fruit. Vacuole was the main site for sugar and acid deposits in maturity. Sucrose and malate accounting for 80.6% and 77.3% of total sugars and acids, respectively, in mature fruit were principal accumulation form in ripe peach fruit. The permeability through plasma membrane and tonoplast decreased with peach fruit maturation. The tonoplast with lower permeability was the most resistant barrier to sugars and acids release. The permeability of sorbitol across plasma membrane in immature fruit with a releasing rate of 41.1×10−3mgg−1min−1 was the highest value among all velocity constants. The sweetness and sour distributed in vacuole accounted for 57.3% of total sweetness and 59.9% of total acidity, respectively, which indicated that sweetness and sour were mainly located in vacuole.

Changes in cell walls during fruit ripening in Chinese ‘Honey’ peach

SummaryModifications in cell wall ultrastructure, cell wall polysaccharides, and the activities of some enzymes involved in cell wall degration were evaluated during the development and ripening of ‘Honey’ peach (Prunus persica L., ‘Yuhuasanhao’) fruit from Stage I (very immature) to Stage V (over-ripe). Ultrastructural changes in the mesocarp of peach fruit were followed over the same time-course. The results showed that the decrease in fruit firmness was accompanied by an increase in ethylene production during peach ripening. Major changes in cell wall structure were noted, beginning with degradation of the middle lamella and the eventual disruption of the primary cell wall. During peach fruit softening, the trans-1, 2-cyclohexane-diamine-N, N, N’, N’-tetra-acetate (CDTA)-1 fraction decreased slightly during the initial ripening stage, then increased rapidly, whereas the contents of all other cell wall materials (CWM), namely the CDTA-2, Na2CO3-1, Na2CO3-2, KOH-1, KOH-2, and CWM-residue fractions decreased gradually during ripening. An analysis of sugar components suggested that not only did the main chains of pectin degrade, but the arabinose and galactose residues in the side-chains of pectin, hemicellulose, or cellulose were also degraded. β-Galactosidase activity was high in immature peach fruit, then declined during peach ripening. However, the activity of α-L-arabinofuranosidase was low from Stage I to Stage III, then increased rapidly in the later Stages (IV – V). These results demonstrate the dynamic changes that occur in cell wall components, and in some cell wall-modifying enzymes during ‘Honey’ peach fruit development and ripening.

Unique expression, processing regulation, and regulatory network of peach (Prunus persica) miRNAs

BackgroundMicroRNAs (miRNAs) have recently emerged as important gene regulators in plants. MiRNAs and their targets have been extensively studied in Arabidopsis and rice. However, relatively little is known about the characterization of miRNAs and their target genes in peach (Prunus persica), which is a complex crop with unique developmental programs.ResultsWe performed small RNA deep sequencing and identified 47 peach-specific and 47 known miRNAs or families with distinct expression patterns. Together, the identified miRNAs targeted 80 genes, many of which have not been reported previously. Like the model plant systems, peach has two of the three conserved trans-acting siRNA biogenesis pathways with similar mechanistic features and target specificity. Unique to peach, three of the miRNAs collectively target 49 MYBs, 19 of which are known to regulate phenylpropanoid metabolism, a key pathway associated with stone hardening and fruit color development, highlighting a critical role of miRNAs in the regulation of peach fruit development and ripening. We also found that the majority of the miRNAs were differentially regulated in different tissues, in part due to differential processing of miRNA precursors. Up to 16% of the peach-specific miRNAs were differentially processed from their precursors in a tissue specific fashion, which has been rarely observed in plant cells. The miRNA precursor processing activity appeared not to be coupled with its transcriptional activity but rather acted independently in peach.ConclusionsCollectively, the data characterizes the unique expression pattern and processing regulation of peach miRNAs and demonstrates the presence of a complex, multi-level miRNA regulatory network capable of targeting a wide variety of biological functions, including phenylpropanoid pathways which play a multifaceted spatial-temporal role in peach fruit development.

Heat treatment of peach fruit: Modifications in the extracellular compartment and identification of novel extracellular proteins

Ripening of peach (Prunus persica L. Batsch) fruit is accompanied by dramatic cell wall changes that lead to softening. Post-harvest heat treatment is effective in delaying softening and preventing some chilling injury symptoms that this fruit exhibits after storage at low temperatures. In the present work, the levels of twelve transcripts encoding proteins involved in cell wall metabolism, as well as the differential extracellular proteome, were examined after a post-harvest heat treatment (HT; 39°C for 3 days) of "Dixiland" peach fruit. A typical softening behaviour, in correlation with an increase in 1-aminocyclopropane-1-carboxylic acid oxidase-1 (PpACO1), was observed for peach maintained at 20°C for 3 days (R3). Six transcripts encoding proteins involved in cell wall metabolism significantly increased in R3 with respect to peach at harvest, while six showed no modification or even decreased. In contrast, after HT, fruit maintained their firmness, exhibiting low PpACO1 level and significant lower levels of the twelve cell wall-modifying genes than in R3. Differential proteomic analysis of apoplastic proteins during softening and after HT revealed a significant decrease of DUF642 proteins after HT; as well as an increase of glyceraldehyde-3-phosphate dehydrogenase (GAPC) after softening. The presence of GAPC in the peach extracellular matrix was further confirmed by in situ immunolocalization and transient expression in tomato fruit. Though further studies are required to establish the function of DUF642 and GAPC in the apoplast, this study contributes to a deeper understanding of the events during peach softening and after HT with a focus on this key compartment.

Metabolic Profiling during Peach Fruit Development and Ripening Reveals the Metabolic Networks That Underpin Each Developmental Stage

Fruit from rosaceous species collectively display a great variety of flavors and textures as well as a generally high content of nutritionally beneficial metabolites. However, relatively little analysis of metabolic networks in rosaceous fruit has been reported. Among rosaceous species, peach (Prunus persica) has stone fruits composed of a juicy mesocarp and lignified endocarp. Here, peach mesocarp metabolic networks were studied across development using metabolomics and analysis of key regulatory enzymes. Principal component analysis of peach metabolic composition revealed clear metabolic shifts from early through late development stages and subsequently during postharvest ripening. Early developmental stages were characterized by a substantial decrease in protein abundance and high levels of bioactive polyphenols and amino acids, which are substrates for the phenylpropanoid and lignin pathways during stone hardening. Sucrose levels showed a large increase during development, reflecting translocation from the leaf, while the importance of galactinol and raffinose is also inferred. Our study further suggests that posttranscriptional mechanisms are key for metabolic regulation at early stages. In contrast to early developmental stages, a decrease in amino acid levels is coupled to an induction of transcripts encoding amino acid and organic acid catabolic enzymes during ripening. These data are consistent with the mobilization of amino acids to support respiration. In addition, sucrose cycling, suggested by the parallel increase of transcripts encoding sucrose degradative and synthetic enzymes, appears to operate during postharvest ripening. When taken together, these data highlight singular metabolic programs for peach development and may allow the identification of key factors related to agronomic traits of this important crop species.

Effect of post-harvest heat treatment on proteome change of peach fruit during ripening

The extracted proteins from the heat-treated peach fruit (dipped in hot water at 48°C for 10min and then stored at room temperature (20°C-25°C) for up to 6 days) were used for proteomic analysis in order to understand the response of post-harvest peach fruit to heat treatment during ripening stage at proteomic level. After two dimensional gels electrophoresis (2-DE) was conducted, more than 600 protein spots were detected. Among them, 35 differently expressed spots (P<0.05) were selected to be excised and analyzed using MALDI-TOF/TOF, and finally 30 protein spots were confidently identified according to NCBI database. The results demonstrated that among the thirty protein spots expressed particularly induced by heat treatment, 43% were related to stress response, 17% to cell structure, 13% to protein fate, 7% to glycolytic pathway, 3% to ripening and senescence and 17% to unclassified. All of them are involved in the regulation of peach fruit development and ripening. All these indicated that the self-defense capability of peach fruit was improved by heat treatment. The study will enable future detailed investigation of gene expression and function linked with peach fruit ripening.