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In the ethylene signalling pathway, EIN2 is an essential signal transducer linking ethylene perception on endoplasmic reticulum to transcriptional regulation in the nucleus, EIN3/EIL1 transcription...

As an inhibitor of ethylene receptors, 1-methylcyclopropene (1-MCP) can delay the ripening of papaya. However, improper 1-MCP treatment will cause a rubbery texture in papaya. Understanding of the underlying mechanism is still lacking. In the present work, a comparative sRNA analysis was conducted after different 1-MCP treatments and identified a total of 213 miRNAs, of which 44 were known miRNAs and 169 were novel miRNAs in papaya. Comprehensive functional enrichment analysis indicated that plant hormone signal pathways play an important role in fruit ripening. Through the comparative analysis of sRNAs and transcriptome sequencing, a total of 11 miRNAs and 12 target genes were associated with the ethylene and auxin signaling pathways. A total of 1741 target genes of miRNAs were identified by degradome sequencing, and nine miRNAs and eight miRNAs were differentially expressed under the ethylene and auxin signaling pathways, respectively. The network regulation diagram of miRNAs and target genes during fruit ripening was drawn. The expression of 11 miRNAs and 12 target genes was verified by RT-qPCR. The target gene verification showed that cpa-miR390a and cpa-miR396 target CpARF19-like and CpERF RAP2-12-like, respectively, affecting the ethylene and auxin signaling pathways and, therefore, papaya ripening.

Brassinosteroids act by delaying fruit ripening. The effects of different concentrations of 2,4-epibrassinolide (eBL) treatments on carambola fruit ripening were investigated. The results show that treatment of 2.8 mg L–1, eBL with 10 min effectively delays ripening and maintains the quality of carambola fruit. This is achieved by retarding color changes and firmness losses while maintaining high level of soluble protein content and vitamin C, and low organic acid content. eBL-delayed senescence may be due to the inhibition of respiration rate and enhanced antioxidant system. It is noteworthy that eBL treatment markedly reduces the content of fructose-6-phosphate (6-P-F) and enhances the activity of cytochrome oxidase (CCO), and the total activity of glucose-6-phosphate dehydrogenase (G-6-PDH) and 6-phosphate gluconate dehydrogenase (6-PGDH). eBL treatment induces the IAA and GA contents but reduces that of ABA. In general, senescence retardation and quality improvement by eBL treatment may be due to the enhanced antioxidant capacity and altered respiratory pathways.

Calcium ions (Ca2+) is an important element for plant cells and serve as second messengers, playing an important role in the regulation of plant physiology, specifically in postharvest fruits and vegetables. The roles of calcium and calcium-sensing receptors have been exhaustively studied in plants, and some of these receptors have been found to play a role in fruit ripening as well. However, a comprehensive overview of the manner in which calcium participates in regulating fruit development, ripening and the molecular mechanisms underlying fruit physiology and ripening have not been conducted. In this study, we reviewed the comprehensive roles of calcium in fruit development and ripening, attempting to elucidate the possible physiological and molecular mechanisms in fruit ripening. The roles of calcium sensors, including calmodulin (CaM), calmodulin-like (CML) proteins, calcineurin B-like proteins (CBL), and calcium-dependent protein kinases (CDPK), are discussed in fruit development and ripening. The interaction between the calcium signal and phytohormone signal pathways in fruit development and fruit ripening was also reviewed. The integral associations among calcium, calcium sensors, and fruit ripening were highlighted. This study provides a comprehensive overview of calcium signals in fruit development and ripening and may contribute to possible areas of interest for future research.

Calcium (Ca2+) is an important second messenger involved in diverse developmental and adaptive processes in plants. Calmodulin (CaM) and calmodulin-like (CML) proteins are primary Ca2+ sensors that control diverse cellular functions. In this study, 41 genes encoding CaM and CML proteins were identified in the papaya genome, three of which were CaM and others were CML. Sequence alignment, gene structural and phylogenetic analyses revealed that all CaM/CMLs contained the EF-hand, but not other functional domains, and CaM proteins were quite conservative while CML proteins exhibited sequence diversity and structural multiformity. Promoter analysis identified different types of cis-elements related to plant growth and development, hormone response, light response, stress response and transcriptional enhancement in promoter regions of CpCaM/CML genes. Gene expression analysis showed distinctive expression profiles of the CaM/CMLs in different tissue types, different fruit developmental stages and different fruit storage conditions. Several groups of CaM/CML genes were positively or negatively regulated by high and low temperature stresses, such as CML16, CML17.1, CML24 and CML36, indicating that they may play a role in temperature stress adaption. Notably, some CaM/CML genes were rigorously regulated by ethylene (ethephon and 1-MCP treatment), either in a positive or a negative manner, such as CaM7, CML15, CML16, CML17.1, CML37 and CML46. All these results indicated that CaM and CML gene families might play important roles in fruit development, in response to temperature stresses and in fruit ripening process.

Pineapple (Ananas comosus (L.) Merr.) fruit ripen and soften rapidly after harvest. This study focused on examining the effect of wax application on the ripening and storage quality of the fruit. An optimized waxing treatment (65 g L−1 for 1 min) could effectively control fruit ripening by delaying fruit color change, decreasing the respiration rate and ethylene production, decreasing content of organic acids and relieving the symptoms of internal browning of pineapple fruit. Waxing enhanced the relative level of pentose phosphate pathway of respiration and affected the enzymes involved in organic acid metabolism. Waxing also reinforced the antioxidant system and enhanced the expression levels of genes related to defense, such as PGIP. These results indicated that wax treatment could effectively improve the fruit quality, mainly through the reduction of organic acid content.

Low-temperature storage is a common strategy for preserving and transporting vegetables and fruits. However, many fruits are hypersensitive to chilling injury, including bananas. In the present study, storage conditions of 11 &deg, C delayed the ripening of Fenjiao (Musa ABB Pisang Awak) banana, and the pulp could be softened after ethephon treatment. Storage conditions of 7 &deg, C prevented fruit from fully softening, and fruit contained a significantly higher starch content and lower soluble sugar content. MaEBF1, a critical gene component in the ethylene signaling pathway, was repressed during ripening after fruit had been stored for 12 days at 7 &deg, C. The expression of a series of starch degradation-related genes and a MaNAC67-like gene were also severely repressed. Both MaEBF1 and MaNAC67-like genes were ethylene-inducible and localized in the nucleus. MaNAC67-like protein was able to physically bind to the promoter of genes associated with starch degradation, including MaBAM6, MaSEX4, and MaMEX1. Yeast two-hybrid, GST-pull down, and BiFC assays showed that MaEBF1 interacted with the MaNAC67-like protein, and their interaction further activated the promoters of MaBAM6 and MaSEX4. The current study indicates that MaNAC67-like is a direct regulator of starch degradation and potential for involvement in regulating chilling-inhibited starch degradation by interacting with the ethylene signaling components in banana fruit. The present work paves the way for further functional analysis of MaEBF1 and MaNAC67-like in banana, which will be useful for understanding the regulation of banana starch metabolism and fruit ripening.

Background Ethylene promotes fruit ripening whereas 1-methylcyclopropene (1-MCP), a non-toxic antagonist of ethylene, delays fruit ripening via the inhibition of ethylene receptor. However, unsuitable 1-MCP treatment can cause fruit ripening disorders. Results In this study, we show that short-term 1-MCP treatment (400 nL•L− 1, 2 h) significantly delays papaya fruit ripening with normal ripening characteristics. However, long-term 1-MCP treatment (400 nL•L− 1, 16 h) causes a “rubbery” texture of fruit. The comparative transcriptome analysis showed that a total of 5529 genes were differently expressed during fruit ripening compared to freshly harvested fruits. Comprehensive functional enrichment analysis showed that the metabolic pathways of carbon metabolism, plant hormone signal transduction, biosynthesis of amino acids, and starch and sucrose metabolism are involved in fruit ripening. 1-MCP treatment significantly affected fruit transcript levels. A total of 3595 and 5998 differently expressed genes (DEGs) were identified between short-term 1-MCP, long-term 1-MCP treatment and the control, respectively. DEGs are mostly enriched in the similar pathway involved in fruit ripening. A large number of DEGs were also identified between long-term and short-term 1-MCP treatment, with most of the DEGs being enriched in carbon metabolism, starch and sucrose metabolism, plant hormone signal transduction, and biosynthesis of amino acids. The 1-MCP treatments accelerated the lignin accumulation and delayed cellulose degradation during fruit ripening. Considering the rubbery phenotype, we inferred that the cell wall metabolism and hormone signal pathways are closely related to papaya fruit ripening disorder. The RNA-Seq output was confirmed using RT-qPCR by 28 selected genes that were involved in cell wall metabolism and hormone signal pathways. Conclusions These results showed that long-term 1-MCP treatment severely inhibited ethylene signaling and the cell wall metabolism pathways, which may result in the failure of cell wall degradation and fruit softening. Our results reveal multiple ripening-associated events during papaya fruit ripening and provide a foundation for understanding the molecular mechanisms underlying 1-MCP treatment on fruit ripening and the regulatory networks. Electronic supplementary material The online version of this article (10.1186/s12870-019-1904-x) contains supplementary material, which is available to authorized users.

Ethylene plays a pivotal role in climacteric fruit ripening; whereas 1-MCP, a non-toxic antagonist of ethylene, prevents ethylene-dependent responses and fruit ripening. In this study, a short-term treatment (1 h) with 400 nL L−1 1-MCP delayed the ripening of harvested papaya. However, long-term application of 1-MCP (400 nL L−1, 16 h) resulted in abnormal fruit ripening, with the fruits exhibiting normal yellowing without softening, significantly higher cellulose and lignin contents, and intact cell walls (CW). Furthermore, we found that long-term treatment with 1-MCP significantly inhibited the expression of CpEBF1, an EIN3-binding F-box-1 gene. A protein interaction analysis using yeast two-hybrid, BiFC and GST pull-down assays showed that CpEBF1 interacts with the CpMADS1/3 and CpEIL1 proteins. The interaction of CpEBF1 with CpMADS1/3 further activated the activities of CW-degradation gene promoters. Subcellular localization showed that these proteins were localized in the nucleus. Additionally, the expression levels of CpMADS1/3, CpEIL1, and several CW-degradation-related genes were significantly downregulated by long-term 1-MCP treatment. Therefore, we propose that the inhibited expression of CpEBF1 and CpMADS1/3 resulted in the repressed activation of CW-degradation-related genes via their interaction, thereby resulting in fruit softening disorders., Papaya: Anti-ripening treatment prevents degradation of cell wall Long-term treatment with an anti-ripening agent inhibits the expression of regulatory genes that normally break down the cell wall of the papaya fruit. A team from Guangzhou’s South China Agricultural University led by Xueping Li and Weixin Chen applied a hormone inhibitor to papayas at the breaker stage of fruit ripening. 1 h of treatment delayed ripening, whereas 16 h of treatment caused the fruit to become rubbery, with significantly higher levels of cellulose and lignin, both structural components of the cell wall. The researchers identified two genes with reduced expression following extended hormone-blocking treatment. Both normally encode proteins that aid in degrading the cell wall to promote fruit ripening. The findings thus offer a molecular explanation for why misuse of anti-ripening agents on papaya fruits can lead to undesirable characteristics.

1-Methylcyclopropene (1-MCP) has been widely used to manipulate fruit ripening. However, inappropriate treatment with 1-MCP may cause ripening disorders. In this study, we observed that the appropriate concentration of 1-MCP (400 nl L−1, 6 h) (1-MCP400) significantly delayed the ripening of Fenjiao banana. However, a high concentration of 1-MCP (3200 nl L−1, 6 h) (1-MCP3200) resulted in abnormal Fenjiao banana that ripened with softened fruit that had a green peel. An RNA sequencing analysis showed that a large number of differentially expressed genes (DEGs) in the fruit peel and pulp were screened out from fruit that were ripened as controls. A KEGG analysis revealed that the metabolic pathways of plant hormone signal transduction, starch and sucrose metabolism, phenylpropanoid biosynthesis, photosynthesis and biosynthesis of amino acids were significantly enriched during fruit ripening. The fruit transcript level of fruit was markedly altered by 1-MCP treatment. Large numbers of DEGs were also detected between high and appropriate concentrations of 1-MCP in the peel and pulp. A comprehensive functional enrichment analysis showed that most of the DEGs involved in photosynthesis, cysteine and methionine metabolism, phenylpropanoid biosynthesis, amino sugar and nucleotide sugar metabolism, plant hormone signal transduction, starch and sucrose metabolism were enriched. RT-qPCR verified the RNA-Seq results, which indicated that 1-MCP3200 severely repressed the expression of genes involved in ethylene (MaACS1, MaACO1, MaETR2-like, MaERF003, MaERF012 and MaERF113), auxin (MaARF19-like, MaSAUR71-like and MaSAUR72-like) and abscisic acid (MaPYL3-like and MaABI5-like) signaling pathways, chlorophyll and cell wall degradation, and starch and sucrose metabolism but induced the expression of genes in lignin synthesis. These genes were consistently expressed in the pulp and peel following control and 1-MCP400 treatment, but their expression was inconsistent following 1-MCP3200 treatment, which may result in the failure of the peel to turn yellow in the 1-MCP3200 group.

Papaya fruits accumulate carotenoids during fruit ripening. Although many papaya carotenoid biosynthesis pathway genes have been identified, the transcriptional regulators of these genes have not been characterized. In this study, a NAC transcription factor, designated as CpNAC1, was characterized from papaya fruit. CpNAC1 was localized exclusively in nucleus and possessed transcriptional activation activity. Expression of carotenoid biosynthesis genes phytoene desaturases (CpPDSs) and CpNAC1 was increased during fruit ripening and by propylene treatment, which correlates well with the elevated carotenoid content in papaya. The gel mobility shift assays and transient expression analyses demonstrated that CpNAC1 directly binds to the NAC binding site (NACBS) motifs in CpPDS2/4 promoters and activates them. Collectively, these data suggest that CpNAC1 may act as a positive regulator of carotenoid biosynthesis during papaya fruit ripening possibly via transcriptional activation of CpPDSs such as CpPDS2/4.

Benzothiadiazole (BTH) works as a plant activator. The effects of different BTH treatments and fungicides SPORGON on fruit ripening and disease incidence were investigated. The results showed that BTH treatment significantly delayed fruit ripening, maintained fruit firmness, color, and good fruit quality, and dramatically reduced the incidence of disease. BTH effectively inhibited the invasion and development of pathogenic bacteria and controlled the occurrence of disease. BTH treatment enhanced the activities of defense-related enzymes, including chitinase, phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase, increased the content of hydrogen peroxide and total antioxidant capacity, and reduced malondialdehyde content. Cellular structure analysis after inoculation confirmed that BTH treatment effectively maintained the cell structural integrity. SPORGON did not provide benefits for delaying fruit ripening or for the resistance system, while it can control the disease only during the earlier stage and not at later stages.

Fenjiao (Musa ABB Pisang Awak) is a popular banana cultivar due to its good taste and stress resistance, but it has a short shelf-life and deteriorates rapidly post-harvest. The effects of 1-methylcyclopropene (1-MCP) treatment on fruit physiology and quality and transcriptomic profiles are investigated in this study. The results showed that 1-MCP significantly delayed fruit ripening by repressing fruit softening and inhibiting the respiratory rate and ethylene production. The 1-MCP treatment delayed sugar accumulation and influenced the content of the precursors of the biosynthesis of aroma volatiles. 1-MCP reduced the production of flavor-contributing volatile esters isoamyl isobutyrate, isoamyl acetate and trans-2-hexenal and hexanal, but dramatically increased the hexyl acetate production at the full-ripening stage. The transcriptomic analysis showed that 1-MCP dramatically affected the transcript profiles during fruit ripening, especially the KEGG pathways involved in amino acid metabolism, biosynthesis of other secondary metabolites, carbohydrate metabolism, lipid metabolism, signal transduction, and translation classes. The key genes and the corresponding enzyme activities involved in the volatile and ethylene synthesis were severely repressed due to the 1-MCP treatment. The 1-MCP treatment effectively delayed Fenjiao fruit ripening, but affected volatile production by reducing the precursor production and expression level of genes involved in the metabolism pathways of ethylene, auxin and volatiles.

Aromatic compounds are important for fruit quality and can vary among fruit cultivars. Volatile compounds formed during the ripening of two banana cultivars, Brazilian and Fenjiao, were determined using headspace solid-phase micro-extraction (SPME) and gas chromatography coupled with mass spectrometry (GC-MS). These two cultivars exhibited different physiological characteristics during storage. Fenjiao fruit exhibited faster yellowing and softening, a higher respiration rate and greater ethylene production. Also, the soluble sugar content in Fenjiao fruit was much higher than in Brazilian fruit. In total, 62 and 59 volatile compounds were detected in Fenjiao and Brazilian fruits, respectively. The predominant volatile components isoamyl acetate, butanoic acid, 3-methyl-3-methylbutyl ester, hexanal, trans-2-hexenal and 1-hexanol varied during ripening stages. Moreover, esters were more abundant in Fenjiao, and propanoic acid 2-methylbutyl ester, and octanoic acid were only detected in Fenjiao. These compounds contribute to the unique flavors and aromas of the two cultivars.

1-methylcyclopropene (1-MCP) has obvious effects on delaying the ripening of harvested banana fruit. However, improper concentration, treatment time and handling methods could affect normal ripening, yellowing, softening and formation of volatiles, which are important components of banana fruit quality. This study was performed to screen and test the effect of a combination of low concentration ethephon with 1-MCP on the ripening of banana fruit, as well as on physiological and biochemical changes. The results showed that a combination of 50 μL L−1 ethephon with 400 nL L−1 1-MCP (16 h) was the most suitable treatment, which significantly delayed the ripening and maintained the commodity value of harvested banana fruit without detrimentally affecting normal ripening after ripening acceleration treatment. This treatment effectively delayed and decreased respiration rate and ethylene production, inhibited the activity of pectin lyase (PL), pectin methylesterase (PME), cellulase (CX) and polygalacturonase (PG), and delayed the peak activity of ACC synthase (ACS) and ACC oxidase (ACO). It also delayed the formation of volatile compounds, but did not detrimentally affect the amount of volatiles, especially the esters. The combined treatment significantly delayed the ripening and prolonged the shelf life of banana fruit with normal coloring and volatile development, which effectively maintained the commercial value of banana fruit.

Harvested papaya fruit are perishable due to rapid ripening and softening and susceptibility to biotic or abiotic stresses. Hot water treatment (HWT) can preserve fruit quality by reducing decay. The present study investigated effects of HWT on controlling fungal pathogens of papaya fruit and the possible mechanism by which HWT induced disease resistance. HWT (54 °C, 4 min) of papaya fruit had a pronounced effect on reducing the carrier rate of Colletotrichum gloeosporioides ( C. gloeosporioides ) in fruit peel, significantly inhibited the incidence of anthracnose and stem-end rot, effectively delayed fruit softening, but slightly promoted the rate of fruit coloring. HWT reduced the anthracnose index and fruit ripeness to a certain extent and induced changes in the wax arrangement on the surface of treated fruit, causing the wax to melt. The cracks and most stomata appeared to be partially or completely plugged by the melted wax, thereby providing a mechanical barrier against wound pathogens. HWT induced the expression of CpPGIP and promptly induced the expression of CpNPR1 , and then regulated the expression of the CpPR1 gene, which may enhance the resistance of the fruit to anthracnose disease and reduce the decay rate. Together, these results confirm that HWT could reduce disease incidence and induce resistance, and thus maintain postharvest quality during storage and prolong the shelf-life of papaya fruit.

Fruit softening is an ethylene-dependent ripening event. 1-Methylcyclopropene (1-MCP), a synthetic plant growth regulator structurally related to the natural plant hormone ethylene, is used to slow down the fruit ripening. However, inappropriate 1-MCP treatment tends to cause the elastic texture in papaya fruit. Constitutive triple response 1 (CTR1), a downstream protein of the ethylene receptors, acts as a negative regulator of ethylene signaling. To elucidate the signal transduction pathway involved in the ethylene regulation during papaya ripening and softening, four genes homologous to Arabidopsis CTR1 were isolated from papaya fruit and designated as CpCTR1–4. Their molecular and biochemical properties were characterized, and their expression patterns in papaya fruit after treatments with 1-MCP were investigated. Four CTR1-like genes differ in sequence length and molecular size, and have a relative distance relationship in the evolutionary tree analysis. However, sequences analysis showed that the C-terminus of CpCTR1–4 proteins contained the highly conserved kinase domains, including a protein kinase ATP-binding signature (IGAGSFGTVH) and a serine/threonine protein kinase active site signature (IVHRDLKSPNLLV). Their N-terminus contains the conserved motifs (CN box) that exist in all CTR1-like proteins. CpCTR1–4 proteins were predicted to be located differently in either chloroplast or nuclei or both. Gene expression analysis showed that 1-MCP treatment significantly repressed the expression of CpCTRs and high concentration of 1-MCP treatment had a more significant effect. These results suggested that CpCTR1–4 genes may play different roles in papaya fruit ripening and softening and that the rubbery fruit might be relate to the expression of CpCTRs genes.

Papaya fruits ( Carica papaya L. cv ‘Sui you 2’) harvested with

The present study was performed to investigate the effect of nitric oxide (NO) fumigation on fruit ripening of harvested “Sui you 2” Carica papayas in relation to postharvest quality and soluble sugar content. Fruits were fumigated for 3 h with 60 μL/L NO and stored at 20C and 75% relative humidity for 20 days. NO treatment effectively suppressed ethylene formation and respiratory rate (CO2 levels), reduced weight loss, maintained firmness and delayed changes in peel color and soluble solid contents during 20 days of storage. The level of vitamin C initially increased and then declined slightly during storage at a slower rate in the NO-treated fruits than in controls. Exposure to 60 μL/L NO resulted in significant decreases in fructose and sucrose content. Glucose content in NO-treated fruits was higher than that in controls. Our results indicate that NO gas can be used to prolong fruit storage life and delay changes in soluble sugar content in papaya fruit. Practical Applications Nitric oxide (NO) gas, a highly reactive free radical, is being studied to resist vegetative stress and senescence of horticultural products. NO was initially regarded as an environmental pollutant, but since 1996, when emission of NO from plants was reported by Leshem and Haramaty, it has drawn much worldwide attention. The present study was performed to investigate the effect of NO fumigation on fruit ripening of harvested “Sui you 2” Carica papaya in relation to the postharvest quality and content of soluble sugars. Our results indicate that NO gas can be potentially applied for prolonging the storage life and delaying soluble sugar change of papaya fruit.

The plant-specific NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) play important roles in plant growth, development, and stress responses. However, the precise role of NAC TFs in relation to fruit ripening is poorly understood. In this study, six NAC genes, designated MaNAC1–MaNAC6, were isolated and characterized from banana fruit. Subcellular localization showed that MaNAC1–MaNAC5 proteins localized preferentially to the nucleus, while MaNAC6 was distributed throughout the entire cell. A transactivation assay in yeast demonstrated that MaNAC4 and MaNAC6, as well as their C-terminal regions, possessed trans-activation activity. Gene expression profiles in fruit with four different ripening characteristics, including natural, ethylene-induced, 1-methylcyclopropene (1-MCP)-delayed, and a combination of 1-MCP with ethylene treatment, revealed that the MaNAC genes were differentially expressed in peel and pulp during post-harvest ripening. MaNAC1 and MaNAC2 were apparently upregulated by ethylene in peel and pulp, consistent with the increase in ethylene production. In contrast, MaNAC3 in peel and pulp and MaNAC5 in peel were constitutively expressed, and transcripts of MaNAC4 in peel and pulp and MaNAC6 in peel decreased, while MaNAC5 or MaNAC6 in pulp increased slightly during fruit ripening. Furthermore, the MaNAC2 promoter was activated after ethylene application, further enhancing the involvement of MaNAC2 in fruit ripening. More importantly, yeast two-hybrid and bimolecular fluorescence complementation analyses confirmed that MaNAC1/2 physically interacted with a downstream component of ethylene signalling, ethylene insensitive 3 (EIN3)-like protein, termed MaEIL5, which was downregulated during ripening. Taken together, these results suggest that MaNACs such as MaNAC1/MaNAC2, may be involved in banana fruit ripening via interaction with ethylene signalling components.

BACKGROUND: Little attention has been paid to characterising the ethylene-signalling pathway genes in relation to abnormal ripening of harvested banana fruit during storage at high temperature. The aim of the present study was to investigate banana fruit abnormal ripening and the expression of ten genes associated with the ethylene-signalling pathway, namely MaACS1, MaACO1, MaERS1–4 and MaEIL1–4, at high temperature. Changes in these parameters of banana fruit at high temperature in response to 1-MCP pretreatment were also investigated. RESULTS: High temperature accelerated the decline in fruit firmness, increased ethylene production and inhibited degreening in banana fruit, resulting in fruit abnormal ripening. In addition, the expression of MaACS1, MaACO1, MaERS2, MaERS3, MaERS4, MaEIL1, MaEIL3 and MaEIL4 was enhanced in banana fruit stored at high temperature. However, application of 1-MCP prior to high temperature storage delayed fruit abnormal ripening and simultaneously suppressed the expression of MaACS1, MaERS2, MaERS3, MaEIL1, MaEIL3 and MaEIL4. CONCLUSION: The findings of this study suggested that the expression of genes associated with the ethylene-signalling pathway might be involved in banana fruit abnormal ripening at high temperature. Application of 1-MCP suppressed the expression of genes associated with the ethylene-signalling pathway, which may be attributed at least partially to 1-MCP delaying fruit abnormal ripening at high temperature. Copyright © 2010 Society of Chemical Industry

Ethylene response factors (ERFs) play important roles in fruit development, ripening, defense responses and stress signaling pathways. After harvest, climacteric fruit such as papaya are subject to a range of problems associated with postharvest handling and storage treatments. There have been few attempts to evaluate the role of ERFs in fruit's responses to environmental stimuli. To investigate the transcriptional mechanisms underlying fruit developmental, ripening and stresses, we cloned four ERFs from papaya. The deduced amino acid sequence of CpERFs contained the conserved apetalous (AP2)/ERF domain, which shared high similarity with other reported AP2/ERF domains. The phylogeny, gene structures, and putatively conserved motifs in papaya ERF proteins were analyzed, and compared with those of Arabidopsis. Expression patterns of CpERFs were examined during fruit development, under 1-MCP treatment, ethephon treatment, biotic stress (temperature stress) and pathogen stress. CpERFs displayed differential expression patterns and expression levels under different experimental conditions. CpERF2 and CpERF3 showed a close association with fruit ripening and CpERFs had a high expression level in the earlier stages during the fruit development period. The expression of CpERFs strongly associated with stress response. These results support the role for papaya ERFs in transcriptional regulation of ripening-related or stress-respond genes and thus, in the regulation of papaya fruit-ripening processes and stress responses.

Papaya (Carica papaya L.) is sensitive to low temperature and easy to be subjected to chilling injury, which causes fruit ripening disorder. This study aimed to investigate the relationship between the expression of genes related to ethylene and fruit ripening disorder caused by chilling injury. Papaya fruits were firstly stored at 7°C and 12°C for 25 and 30 days, respectively, then treated with exogenous ethylene and followed by ripening at 25°C for 5 days. Chilling injury symptoms such as pulp water soaking were observed in fruit stored at 7°C on 20 days, whereas the coloration and softening were completely blocked after 25 days, Large differences in the changes in the expression levels of twenty two genes involved in ethylene were seen during 7°C-storage with chilling injury. Those genes with altered expression could be divided into three groups: the group of genes that were up-regulated, including ACS1/2/3, EIN2, EIN3s/EIL1, CTR1/2/3, and ERF1/3/4; the group of genes that were down-regulated, including ACO3, ETR1, CTR4, EBF2, and ERF2; and the group of genes that were un-regulated, including ACO1/2, ERS, and EBF1. The results also showed that pulp firmness had a significantly positive correlation with the expression of ACS2, ACO1, CTR1/4, EIN3a/b, and EBF1/2 in fruit without chilling injury. This positive correlation was changed to negative one in fruit after storage at 7°C for 25 days with chilling injury. The coloring index displayed significantly negative correlations with the expression levels of ACS2, ACO1/2, CTR4, EIN3a/b, ERF3 in fruit without chilling injury, but these correlations were changed into the positive ones in fruit after storage at 7°C for 25 days with chilling injury. All together, these results indicate that these genes may play important roles in the abnormal softening and coloration with chilling injury in papaya.