Melting Flesh Peach Research Articles

Deciphering aroma complexity between melting flesh and stony hard peach (Prunus persica L.) fruit through integrative analysis of volatile contributions

Stony hard peach is favored in production for resistance to storage and transportation, but presents a challenge of lacking fragrance compared to traditional fragrant peach i.e., melting flesh peach. Addressing this concern necessitates material composition analysis from the perspective of volatile composition and aroma characteristics. However, the complex relationship between volatile compounds and aroma profiles in melting flesh and stony hard peach cultivars remains poorly understood. To address this gap, we examined contribution of volatiles to their aroma. The application of multiple analysis methods, including distribution, odor importance, and partial least squares discriminant analysis facilitated a comprehensive understanding of the contribution of 30 volatiles to aroma; and hierarchical clustering analysis revealed relationships among the compounds within the two types of peaches. The primary differential volatiles between them were cis-3-hexenol, pentyl acetate, prenyl acetate, trans-2-hexenal, cis-3-hexenyl acetate, dihydro-β-ionone, benzaldehyde, and a range of lactones (γ-decalactone, γ-hexalactone, γ-octalactone, δ-decalactone and γ-undecalactone). Overall, the melting flesh peach exhibited more pronounced aroma than the stony hard type. This study underscores the significance of understanding the intricate interplay between volatile compounds and aroma characteristics across cultivars with different textures, offering valuable insights into cultivar selection, flavor enhancement, and consumer preference assessment within the peach industry.

Comparative Cell Wall Polysaccharide Analyses and Transcriptome Profiling during Fruit Ripening Reveal the Molecular Basis of Mealiness in Peach

Mealy peaches are dry and flavorless, which reduces their consumer acceptance. A deeper understanding of the mechanism underlying mealiness is crucial to enhancing peach fruit quality. In this study, comparative profiling was conducted on CP13, CP14, CM, and RM peaches. Sensory evaluation indicated that CP13 and CM are non-mealy clingstone and freestone peaches, respectively, and CP14 and RM are mealy freestone peaches. Both CP13 and CP14, identified as stony hard (SH) peaches, exhibited minimal ethylene release, whereas CM and RM, identified as melting flesh (MF) peaches, released high amounts of ethylene during the ripening process. Scanning electron microscopy (SEM) microstructure observation indicated that cells in the flesh tissue of mealy peaches, CP14 (SH) and RM (MF), were intact and separated, with large intercellular spaces and irregular arrangements. The main factor that promotes mealiness is differences in pectin metabolism, which impact cell wall composition. The fluctuations in polygalacturonase (PG) and pectin methylesterase (PME) activity between mealy and non-mealy peaches were the main factor contributing to mealiness. However, the changes in cell wall metabolism that caused these fluctuations did not have a clear direction. Using transcriptome analysis and weighted gene co-expression network analysis (WGCNA), we were able to identify forty differentially expressed genes (DEGs) that are associated with mealy patterns. Among these DEGs, genes encoding PG were significantly upregulated in mealy peaches (CP14 and RM) compared to non-mealy peaches (CP13 and CM). PpPG1 was the main effector gene for mealiness, while PpPG2, PpEGase2, PpEXP1, PpEXP3, PpAGP2, PpIAA4, and PpABA2 were identified as candidate genes regulating peach mealiness. These findings provide a solid experimental basis for understanding the textual distinctions between mealy and non-mealy peaches.

The Effect of Packaging Types on Fresh Peaches in the Direct‐To‐Consumer Environment: Distribution Testing, Life Cycle Assessment and Economic Impact

ABSTRACTThe direct‐to‐consumer (D2C) shipping mode presents new opportunity for fresh peach sales in North America where demand over the past four decades has steadily declined. The hazards in this distribution mode are severe, and fresh peaches are fragile emphasizing the need for proper protection. A full analysis that not only encompasses the effects of the D2C distribution environment but also incorporates analyses of the environmental and economic impact of the packages utilized for transit of peaches is necessary. In this study, we use the metrics of peach grade, firmness, soluble solids concentration and percent softness before and after the distribution simulation to compare the protective performance of six DTC packaging systems. All six packages consist of a single layer corrugated box with varying primary packaging. A life cycle analysis of each package system is performed as well as an economic analysis on the packaged materials and cost to ship. We conclude that peach damage in shock testing is related to the freedom of movement that peaches have within each package type and varies by package system. All the package types evaluated amplify input vibration in the frequency range commonly associated with the input from the tires of truck‐trailer systems. There are no statistical differences between package systems in the distribution simulation of the six package types except in peach softness and grade of melting flesh peaches. Finally, we found that a reduction in material use and change in format, that is, foam sheets to foam netting, provides for sufficient peach protection while reducing environmental and economic impact.

Nitrogen fertilization rates in a subtropical peach orchard: Effect on fruit nutritional value and flavor

AbstractBackgroundThe necessity to help farmers improve yields has resulted in many years of agricultural research focused on productivity and disease resistance, neglecting other areas of fruit quality such as flavor, health benefits, and external appearance. Nitrogen is required for several biochemical processes. However, reducing N fertilization can increase the synthesis of antioxidants and volatile aroma compounds. Four‐N rates (0 (N0), 45 (N1), 90 (N2), 179 (N3), and 269 (N4) kg ha−1) were tested each year from 2011 to 2017 in two peach varieties melting flesh (MF) ‘TropicBeauty’ (TB), a soft texture peach, and non‐melting flesh (NMF) ‘UFSharp’ (UFS), a crispy texture peach, to determine the effect of N on nutritional value and flavor.ResultsThe phytochemical composition of the NMF ‘UFSharp’ (UFS) and MF variety ‘TropicBeauty’ (TB) were not cleared affected by N rates. Volatile synthesis was little affected by N. The sensory evaluation showed that consumers preferred MF peaches compared with NMF, because of its juiciness.ConclusionsNitrogen fertilization had minor effects on peach fruit phytochemical composition, volatile aroma compounds, and consumer acceptability. The N effect could had been influence by pruning practices, training of the orchard, and the delay of fruit developmental period.

Low temperature inhibits pectin degradation by PpCBFs to prolong peach storage time.

Low-temperature storage is a widely used method for peach fruit storage. However, the impact of PpCBFs on pectin degradation during low-temperature storage is unclear. As such, in this study, we stored the melting-flesh peach cultivar "Fuli" at low temperature (LT, 6°C) and room temperature (RT, 25°C) to determine the effect of different temperatures on its physiological and biochemical changes. Low-temperature storage can inhibit the softening of "Fuli" peaches by maintaining the stability of the cell wall. It was found that the contents of water-soluble pectin and ionic-soluble pectin in peach fruit stored at RT were higher than those stored at LT. The enzyme activities of polygalacturonase (PG), pectate lyase (PL), and pectin methylesterase (PME) were all inhibited by LT. The expressions of PpPME3, PpPL2, and PpPG were closely related to fruit firmness, but PpCBF2 and PpCBF3 showed higher expression levels at LT than RT. The promoters of PpPL2 and PpPG contain the DER motif, which suggested that PpCBF2 and PpCBF3 might negatively regulate their expression by directly binding to their promoters. These results indicated that LT may maintain firmness by activating PpCBFs to repress pectin-degradation-related enzyme genes during storage.

Interaction between PpERF5 and PpERF7 enhances peach fruit aroma by upregulating PpLOX4 expression

Ethylene plays a critical role in peach (Prunus persica) fruit ripening; however, the molecular mechanism underlying ethylene-mediated aroma biosynthesis remains unclear. Here, we compared the difference in aroma-related volatiles and gene expression levels between melting-flesh (MF) and stony hard (SH) peach cultivars at S3, S4 I, S4 II, S4 III stages, and explored the relation between volatile biosynthesis related genes and ethylene response factor (ERF) genes. The concentration of fruity aromatic compounds such as lactones and terpenes increased significantly in MF peach during fruit ripening, while it was nearly undetectable in SH peach. LOX4 and FAD1 genes expressed concomitantly with ethylene emission and significantly downregulated by 1-MCP. Besides, 1-MCP treatment could sharply influence the fruity aromatic compounds, suggesting that these genes play key roles in volatile biosynthesis during fruit ripening. Furthermore, PpERF5 and PpERF7 could bind together to form a protein complex that enhanced the transcription of LOX4 more than each transcription factor individually. Overall, this work provides new insights into the transcriptional regulatory mechanisms associated with aroma formation during peach fruit ripening.

Methyl jasmonate treatment regulates α-linolenic acid metabolism and jasmonate acid signaling pathway to improve chilling tolerance in both stony hard and melting flesh peaches

Peach are susceptible to chilling injury (CI) when stored at a low temperature and the postharvest application of methyl jasmonate (MeJA) is well known to alleviate CI in peach fruit. However, the optimal dose for the treatment of MeJA is still debated in peaches and the underlying mechanism remains largely unknown. In this study, we screened the optimal concentration of MeJA treatment in stony hard and melting flesh peaches, then investigated the involvement of α-linolenic acid metabolism and jasmonate acid (JA) signaling pathway in the MeJA-induced chilling tolerance. The results showed that 10 mol L−1 was the broad-spectrum concentration of MeJA treatment for CI alleviation in the two peach cultivars. Also, MeJA treatment improved the degree of fatty acid unsaturation in cell membrane by delaying the decrease in unsaturated fatty acids (USFAs) and the increase in saturated fatty acids (SFAs), resulting in the activation of α-linolenic acid metabolism. Correspondingly, it maintained a higher concentration of α-linolenic acid and higher activities of lipoxygenase (LOX), allene oxide synthase (AOS) and allene oxide cyclase (AOC). It also induced the expressions of PpLOX, PpAOS, PpAOC, PpACOX and PpFadA in peaches during the end of the cold storage at 5 °C and the shelf-life at 20 ℃. Meanwhile, the increased α-linolenic acid metabolism in MeJA treated fruit led to accumulations in JA and jasmonic acid isoleucine (JA-Ile), which boosted the JA signaling pathway by up-regulating the expressions of PpCOI1, PpJAZ and PpMYC2. Thus, it was suggested that MeJA treatment activated α-linolenic acid metabolism and JA signaling pathway might be contributing to alleviating CI in peaches during cold storage.

Transcriptome analysis of peach fruit under 1-MCP treatment provides insights into regulation network in melting peach softening

Abstract Peach (Prunus persica L.) displays distinguish texture phenotype during postharvest, which could be classified into three types, including melting flesh (MF), non-melting flesh, and stony-hard. MF peach would soften rapidly with an outbreak of ethylene production, which causes huge wastage during fruit transportation and storage. 1-Methylcyclopropene (1-MCP) was used to alleviate fruit softening. In this study, we performed RNA-sequencing on two MF peach cultivars (‘YuLu’ and ‘Yanhong’) after 1-MCP treatment to identify the candidate genes participating in peach fruit softening. A total of 167 genes were identified by weighted gene coexpression network analysis and correlation analysis that could respond to 1-MCP treatment and might be related to softening. Among them, 5 auxin-related genes including 2 indole-3-acetic acid, 1 auxin response transcription factor and 2 small auxin-up RNAs, and 4 cell wall modifying genes (PpPG1, PpPG2, PpPG24 and PpPMEI) were characterized as key genes participating in MF peach softening. Furthermore, 2 transcription factors, which belong to HD-ZIP and MYB, were predicted as candidates regulating softening process by constructing a transcriptional network of these 4 cell wall modifying genes combined with expression pattern analysis, of which HD-ZIP could trans-activate the promoter of PpPG1.

The downregulation of PpPG21 and PpPG22 influences peach fruit texture and softening.

The downregulation of PpPG21 and PpPG22 expression in melting-flesh peach delays fruit softening and hinders texture changes by influencing pectin solubilization and depolymerization. The polygalacturonase (PG)-catalyzed solubilization and depolymerization of pectin plays a central role in the softening and texture formation processes in peach fruit. In this study, the expression characteristics of 15 PpPG members in peach fruits belonging to the melting flesh (MF) and non-melting flesh (NMF) types were analyzed, and virus-induced gene silencing (VIGS) technology was used to identify the roles of PpPG21 (ppa006839m) and PpPG22 (ppa006857m) in peach fruit softening and texture changes. In both MF and NMF peaches, the expression of PpPG1, 10, 12, 23, and 25 was upregulated, whereas that of PpPG14, 24, 35, 38, and 39 was relatively stable or downregulated during shelf life. PpPG1 was highly expressed in NMF fruit, whereas PpPG21 and 22 were highly expressed in MF peaches. Suppressing the expression of PpPG21 and 22 by VIGS in MF peaches significantly reduced PG enzyme activity, maintained the firmness of the fruit during the late shelf life stage, and suppressed the occurrence of the "melting" stage compared with the control fruits. Moreover, the downregulation of PpPG21 and 22 expression also reduced the water-soluble pectin (WSP) content, increased the contents of ionic-soluble pectin (ISP) and covalent-soluble pectin (CSP) and affected the expression levels of ethylene synthesis- and pectin depolymerization-related genes in the late shelf life stage. These results indicate that PpPG21 and 22 play a major role in the development of the melting texture trait of peaches by depolymerizing cell wall pectin. Our results provide direct evidence showing that PG regulates peach fruit softening and texture changes.

Postharvest Properties of Ultra-Late Maturing Peach Cultivars and Their Attributions to Melting Flesh (M) Locus: Re-evaluation of M Locus in Association With Flesh Texture.

The postharvest properties of two ultra-late maturing peach cultivars, “Tobihaku” (TH) and “Daijumitsuto” (DJ), were investigated. Fruit were harvested at commercial maturity and held at 25°C. TH exhibited the characteristics of normal melting flesh (MF) peach, including rapid fruit softening associated with appropriate level of endogenous ethylene production In contrast, DJ did not soften at all during 3 weeks experimental period even though considerable ethylene production was observed. Fruit of TH and DJ were treated with 5,000 ppm of propylene, an ethylene analog, continuously for 7 days. TH softened rapidly whereas DJ maintained high flesh firmness in spite of an increase in endogenous ethylene production, suggesting that DJ but not TH lacked the ability to be softened in response to endogenous and exogenous ethylene/propylene. DNA-seq analysis showed that tandem endo-polygalacturonase (endoPG) genes located at melting flesh (M) locus, Pp-endoPGM (PGM), and Pp-endoPGF (PGF), were deleted in DJ. The endoPG genes at M locus are known to control flesh texture of peach fruit, and it was suggested that the non-softening property of DJ is due to the lack of endoPG genes. On the other hand, TH possessed an unidentified M haplotype that is involved in determination of MF phenotype. Structural identification of the unknown M haplotype, designated as M0, through comparison with previously reported M haplotypes revealed distinct differences between PGM on M0 haplotype (PGM-M0) and PGM on other haplotypes (PGM-M1). Peach M haplotypes were classified into four main haplotypes: M0 with PGM-M0; M1 with both PGM-M1 and PGF; M2 with PGM-M1; and M3 lacking both PGM and PGF. Re-evaluation of M locus in association with MF/non-melting flesh (NMF) phenotypes in more than 400 accessions by using whole genome shotgun sequencing data on database and/or by PCR genotyping demonstrated that M0 haplotype was the common haplotype in MF accessions, and M0 and M1 haplotypes were dominant over M2 and M3 haplotypes and co-dominantly determined the MF trait. It was also assumed on the basis of structural comparison of M haplotypes among Prunus species that the ancestral haplotype of M0 diverged from those of the other haplotypes before the speciation of Prunus persica.

Optimum Harvest of Low-chill Melting and Non-melting Flesh Peach Cultivars for Direct Ripening and Ripening following Low Temperature Storage

The physical and chemical characteristics of two melting flesh (MF) cultivars, TropicBeauty and Flordaprince, and two non-melting flesh (NMF) cultivars, UFSun and Gulfking, with advancing maturities, were determined at harvest, after ripening at 20 °C for 7 days (i.e., direct ripening) and after storage at 0 °C for 14 days then ripening at 20 °C for 7 days (i.e., ripening following low temperature storage). The NMF cultivars were able to retain flesh firmness better than the MF cultivars as fruit matured and ripened on the tree and after the two storage treatments. The NMF fruit of the least mature to the most advanced maturity groups (MGs) were ≈2 to 7 times firmer than the MF fruit in the same MGs after ripening in both storage conditions. For both MF and NMF fruit, a significant reduction of titratable acidity (TA) occurred with no significant changes in soluble solids content (SSC) and total soluble sugar (TSS) as maturity and ripening progressed on the tree and after ripening in both storage conditions. Minimum quality standards of “ready for consumption” peaches were used as general guidelines to determine the optimum harvest maturity of all four cultivars. The NMF fruit ripened directly had wider optimum harvest maturity ranges and could be harvested at more advanced stages than the MF fruit. The MF fruit that ripened following low temperature storage needed to be picked at earlier maturity stages than those that were directly ripened. The optimum harvest maturity of NMF UFSun for the low temperature storage treatment was more advanced than that of the other three cultivars due to abnormal softening found in the lower MGs after ripening. Linear correlation analyses showed that the skin ground color (GC) a* values of both MF cultivars and NMF ‘UFSun’ were highly correlated with the flesh color (FC) a* values, suggesting that GC a* values can be an informative harvest indicator for this NMF cultivar instead of the traditionally used FC. The GC a* values also had high linear correlation with TA for all four cultivars, suggesting that TA can be a potential maturity index for both MF and NMF peaches. Significant correlations of GC a* values and flesh firmness (GC-FF) were found in all four cultivars in one year but only in MF peaches in both years, showing that flesh firmness was the most consistent maturity indicator for the MF cultivars in this study.

Genome-wide identification and transcriptome profiling reveal that E3 ubiquitin ligase genes relevant to ethylene, auxin and abscisic acid are differentially expressed in the fruits of melting flesh and stony hard peach varieties

BackgroundUbiquitin ligases (E3) are the enzymes in the ubiquitin/26S proteasome pathway responsible for targeting proteins to the degradation pathway and play major roles in multiple biological activities. However, the E3 family and their functions are yet to be identified in the fruit of peach.ResultsIn this study, genome-wide identification, classification and characterization of the E3 ligase genes within the genome of peach (Prunus persica) was carried out. In total, 765 E3 (PpE3) ligase genes were identified in the peach genome. The PpE3 ligase genes were divided into eight subfamilies according to the presence of known functional domains. The RBX subfamily was not detected in peach. The PpE3 ligase genes were not randomly distributed among the 8 chromosomes, with a greater concentration on the longer chromosomes. The primary mode of gene duplication of the PpE3 ligase genes was dispersed gene duplication (DSD). Four subgroups of the BTB subfamily never characterized before were newly identified in peach, namely BTBAND, BTBBL, BTBP and BTBAN. The expression patterns of the identified E3 ligase genes in two peach varieties that display different types of fruit softening (melting flesh, MF, and stony hard, SH) were analyzed at 4 different stages of ripening using Illumina technology. Among the 765 PpE3 ligase genes, 515 (67.3%) were expressed (FPKM > 1) in the fruit of either MF or SH during fruit ripening. In same-stage comparisons, 231 differentially expressed genes (DEGs) were identified between the two peach cultivars. The number of DEGs in each subfamily varied. Most DEGs were members of the BTB, F-box, U-box and RING subfamilies. PpE3 ligase genes predicted to be involved in ethylene, auxin, or ABA synthesis or signaling and DNA methylation were differentially regulated. Eight PpE3 ligase genes with possible roles in peach flesh texture and fruit ripening were discussed.ConclusionsThe results of this study provide useful information for further understanding the functional roles of the ubiquitin ligase genes in peach. The findings also provide the first clues that E3 ligase genes may function in the regulation of peach ripening.

Genetic algorithm optimized non-destructive prediction on property of mechanically injured peaches during postharvest storage by portable visible/shortwave near-infrared spectroscopy

The melting-flesh peach (Prunus persica, cv. 'Baihua') tends to rapidly decay after harvest in summer with a short after-ripening period. Although the use of preservatives can inhibit the growth of microorganisms, collisions during transportation greatly affect the shelf life for subsequent sales. To build a high-accuracy model to predict the inner physiological status of mechanically injured peaches during postharvest storage, visible/shortwave near-infrared (Vis/SWNIR) diffuse reflection spectra (300–1150 nm) were acquired for analysis. With 840 samples, two drop heights (30 cm and 60 cm) were applied to study the variations in total soluble solids (TSS) polyphenol oxidase (PPO), malondialdehyde (MDA) and relative electrolyte leakage (REL) by percussive tests. After multiplicative scatter correction and Savitzky-Golay smoothing pretreatments, optimal feature selections from a total of 1024 wavelengths were determined using genetic algorithm (GA) in PLS modeling. For TSS, the best correlation (rp) is 0.89, root mean square error of prediction (RMSEP) is 0.40 and relative percent deviation (RPD) is 2.94. For PPO, the best rp is 0.71, RMSEP is 20.34 and RPD is 2.75. For MDA, the best rp is 0.83, RMSEP is 0.17 and RPD is 1.90. For REL, the best rp is 0.92, RMSEP is 1.42 and RPD is 2.44. Through several verifications, the GA-PLS models showed good imitative effects and high precisions. They could predict the condition of peaches with minor injury, which are difficult to detect with the naked eye, to reduce loss in practical production.

Insertion of a transposon-like sequence in the 5'-flanking region of the YUCCA gene causes the stony hard phenotype.

Melting-flesh peaches produce large amounts of ethylene, resulting in rapid fruit softening at the late-ripening stage. In contrast, stony hard peaches do not soften and produce little ethylene. The indole-3-acetic acid (IAA) level in stony hard peaches is low at the late-ripening stage, resulting in low ethylene production and inhibition of fruit softening. To elucidate the mechanism of low IAA concentration in stony hard peaches, endogenous levels of IAA and IAA intermediates or metabolites were analysed by ultra-performance liquid chromatography-tandem mass spectrometry. Although the IAA level was low, the indole-3-pyruvic acid (IPyA) level was high in stony hard peaches at the ripening stage. These results indicate that YUCCA activity is reduced in ripening stony hard peaches. The expression of one of the YUCCA isogenes in peach, PpYUC11, was suppressed in ripening stony hard peaches. Furthermore, an insertion of a transposon-like sequence was found upstream of the PpYUC11 gene in the 5'-flanking region. Analyses of the segregation ratio of the stony hard phenotype and genotype in F1 progenies indicated that the transposon-inserted allele of PpYUC11, hd-t, correlated with the stony hard phenotype. On the basis of the above findings, we propose that the IPyA pathway (YUCCA pathway) is the main auxin biosynthetic pathway in ripening peaches of 'Akatsuki' and 'Manami' cultivars. Because IAA is not supplied from storage forms, IAAde novo synthesis via the IPyA pathway (YUCCA pathway) in mesocarp tissues is responsible for auxin generation to support fruit softening, and its disruption can lead to the stony hard phenotype.

Over-expression of Peach PpIAA19 in Tomato Alters Plant Growth, Parthenocarpy, and Fruit Shape

The auxin/indole acetic acid (Aux/IAA) genes encode a large family of short-lived proteins that regulate auxin signaling in plants. Previous attempts to understand the role of auxin during fruit development in peach (Prunus persica) found that expression of the Aux/IAA gene PpIAA19 was upregulated during fruit ripening, but the biological significance of the PpIAA19 protein is still unknown. The current study detected PpIAA19 transcripts in all peach plant tissues but found higher levels of accumulation in fruit S1 and S4II stages. During fruit ripening, the expression level of the PpIAA19 gene in melting flesh (MF) peach fruit was unsurprisingly higher than in stony hard (SH) peach fruit. Tomato (Solanum lycopersicum cv. ‘Micro-Tom’) was used as a model for investigating the phenotypic and molecular changes associated with over-expression of PpIAA19. This revealed that PpIAA19 was involved in regulating tomato lateral root number, stem elongation, parthenocarpy, and fruit shape. Molecular analyses of transgenic tomato plants over-expressing PpIAA19 indicated that the observed phenotypic changes were partially mediated by regulating the expression of auxin response genes. This result extends the functional characterization of PpIAA19 in tomato, and broadens our understanding of the role of auxin signaling in regulating plant growth and development.

Genes involved in ethylene signal transduction in peach (Prunus persica) and their expression profiles during fruit maturation

Ethylene is an essential regulator of fruit development. However, the role of this phytohormone in the development and maturation of peach (Prunus persica L. Batsch) fruit has not been systematically examined. In this study, through BLAST analysis of tomato (Solanum lycopersicum) protein sequences against the peach genome database and transcriptome analysis of all APETALA2/Ethylene Responsive Factor (AP2/ERF) genes in peach, we identified 15 ethylene signal transduction genes and 15 AP2/ERF genes and examined their expression levels in SH (stony hard) peaches and MF (melting flesh) peaches during fruit maturation. We investigated the expression patterns of six genes, including one ETR-like gene (Prupe.1G034300) and five AP2/ERF genes (Prupe.1G037700, Prupe.2G289500, Prupe.3G240000, Prupe.5G061800, and Prupe.7G194400), through quantitative RT-PCR expression analysis. The transcript levels of these genes were lower at the early stages of fruit development and increased dramatically at stage S4 in MF peaches, while they remained low in SH peaches, which mirrors the pattern of changes observed in ethylene production. Treatment of MF (‘Zhongyoutao 13’, ‘CN13’) fruit at stage S4 II with 1-MCP was ineffective in blocking ethylene production, and the expression of these genes was inhibited by 1-MCP treatment in ‘CN13’ on day 1, further demonstrating that these genes are closely related to fruit ripening. We detected a slight change in fruit firmness in ‘CN13’ after 1-MCP treatment, whereas ethylene production was not affected. By contrast, the transcript profile of gene Prupe.5G090800 exhibited the opposite trend. The comprehensive data generated in this study will improve our understanding of the ethylene receptor genes and ERF genes in peach and lay the foundation for further exploring the mechanisms underlying peach fruit ripening and softening.

Characteristics and regulatory pathway of the PrupeSEP1 SEPALLATA gene during ripening and softening in peach fruits

SEPALLATA genes are members of a subfamily of MADS-box transcription factors, and have essential roles in floral organ development and fruit ripening. In this study, the PrupeSEP1 gene was cloned from peach flesh. Its deduced amino acid sequence was very similar to that of MdMADS8 and MdMADS9 in apple and MADS-RIN-like in strawberry. During storage of melting flesh (MF) peach, the pattern of SEP1 expression was similar to that of ethylene biosynthesis and ethylene signal transduction-related gene expression (EIN2 and ETR2). The SEP1 expression level was correlated with that of EIN2 and ETR2. Furthermore, in MF, cell wall modification-related genes (Endo-PG3, EXP2 and PME3), N-glycan processing genes (β-Hex2 and α-Man) and Lox1 exhibited similar expression patterns to that of SEP1. However, in non-melting flesh (NMF) peach, the SEP1 expression pattern was different from that of MF peach. Moreover, in NMF, only EXP2, LOX1, and α-Man expression patterns were similar to that of SEP1. After SEP1 expression was inhibited by virus-induced gene silencing technique (VIGS) in MF peach, compared with the control, the fruit remained firm and fruit softening was delayed. While expression levels of the ripening and softening related genes, ACS2, EIN2, PME1, Endo-PG3, ACO1, ETR2,β-Hex2 and Lox1, were significantly decreased in SEP1-silenced peach, the transcription of EXP2 and PME3 were significantly enhanced except at the harvest stage. Yeast one-hybrid verification showed SEP1 can interact with promoter of target genes PGs. Our results indicate SEP1 may regulate fruit ripening and softening of MF peaches, while this regulation may be lost in the NMF peaches.

On the role of ethylene, auxin and a GOLVEN-like peptide hormone in the regulation of peach ripening.

BackgroundIn melting flesh peaches, auxin is necessary for system-2 ethylene synthesis and a cross-talk between ethylene and auxin occurs during the ripening process. To elucidate this interaction at the transition from maturation to ripening and the accompanying switch from system-1 to system-2 ethylene biosynthesis, fruits of melting flesh and stony hard genotypes, the latter unable to produce system-2 ethylene because of insufficient amount of auxin at ripening, were treated with auxin, ethylene and with 1-methylcyclopropene (1-MCP), known to block ethylene receptors. The effects of the treatments on the different genotypes were monitored by hormone quantifications and transcription profiling.ResultsIn melting flesh fruit, 1-MCP responses differed according to the ripening stage. Unexpectedly, 1-MCP induced genes also up-regulated by ripening, ethylene and auxin, as CTG134, similar to GOLVEN (GLV) peptides, and repressed genes also down-regulated by ripening, ethylene and auxin, as CTG85, a calcineurin B-like protein.The nature and transcriptional response of CTG134 led to discover a rise in free auxin in 1-MCP treated fruit. This increase was supported by the induced transcription of CTG475, an IAA-amino acid hydrolase. A melting flesh and a stony hard genotype, differing for their ability to synthetize auxin and ethylene amounts at ripening, were used to study the fine temporal regulation and auxin responsiveness of genes involved in the process. Transcriptional waves showed a tight interdependence between auxin and ethylene actions with the former possibly enhanced by the GLV CTG134. The expression of genes involved in the regulation of ripening, among which are several transcription factors, was similar in the two genotypes or could be rescued by auxin application in the stony hard. Only GLV CTG134 expression could not be rescued by exogenous auxin.Conclusions1-MCP treatment of peach fruit is ineffective in delaying ripening because it stimulates an increase in free auxin. As a consequence, a burst in ethylene production speeding up ripening occurs. Based on a network of gene transcriptional regulations, a model in which appropriate level of CTG134 peptide hormone might be necessary to allow the correct balance between auxin and ethylene for peach ripening to occur is proposed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0730-7) contains supplementary material, which is available to authorized users.

Specific Changes of Exocarp and Mesocarp Occurring during Softening Differently Affect Firmness in Melting (MF) and Non Melting Flesh (NMF) Fruits.

Melting (MF) and non melting flesh (NMF) peaches differ in their final texture and firmness. Their specific characteristics are achieved by softening process and directly dictate fruit shelf life and quality. Softening is influenced by various mechanisms including cell wall reorganization and water loss. In this work, the biomechanical properties of MF Spring Crest’s and NMF Oro A’s exocarp and mesocarp along with the amount and localization of hydroxycinnamic acids and flavonoids were investigated during fruit ripening and post-harvest. The objective was to better understand the role played by water loss and cell wall reorganization in peach softening. Results showed that in ripe Spring Crest, where both cell turgor loss and cell wall dismantling occurred, mesocarp had a little role in the fruit reaction to compression and probe penetration response was almost exclusively ascribed to the epidermis which functioned as a mechanical support to the pulp. In ripe Oro A’s fruit, where cell wall disassembly did not occur and the loss of cell turgor was observed only in mesocarp, the contribution of exocarp to fruit firmness was consistent but relatively lower than that of mesocarp, suggesting that in addition to cell turgor, the integrity of cell wall played a key role in maintaining NMF fruit firmness. The analysis of phenols suggested that permeability and firmness of epidermis were associated with the presence of flavonoids and hydroxycinnamic acids.

PpYUC11, a strong candidate gene for the stony hard phenotype in peach (Prunus persica L. Batsch), participates in IAA biosynthesis during fruit ripening.

High concentrations of indole-3-acetic acid (IAA) are required for climacteric ethylene biosynthesis to cause fruit softening in melting flesh peaches at the late ripening stage. By contrast, the fruits of stony hard peach cultivars do not soften and produce little ethylene due to the low IAA concentrations. To investigate the regulation of IAA accumulation during peach ripening [the transition from stage S3 to stage S4 III (climacteric)], a digital gene expression (DGE) analysis was performed. The expression patterns of auxin-homeostasis-related genes were compared in fruits of the melting flesh peach 'Goldhoney 3' and the stony hard flesh peach 'Yumyeong' during the ripening stage. It is revealed here that a YUCCA flavin mono-oxygenase gene (PpYUC11, ppa008176m), a key gene in auxin biosynthesis, displayed an identical differential expression profile to the profiles of IAA accumulation and PpACS1 transcription: the mRNA transcripts increased at the late ripening stage in melting flesh peaches but were below the limit of detection in mature fruits of stony hard peaches. In addition, the strong association between intron TC microsatellite genotypes of PpYUC11 and the flesh texture (normal or stony hard) is described in 43 peach varieties, indicating that this locus may be responsible for the stony hard phenotype in peach. These findings support the hypothesis that PpYUC11 may play an essential role in auxin biosynthesis during peach fruit ripening and is a candidate gene for the control of the stony hard phenotype in peach.