Application of Tannic Acid and Fe3+ Crosslinking-Enhanced Pectin Films for Passion Fruit Preservation.

In this work, the role of tannic acid (TA) and Fe3+ in crosslinking pectin (PE) to enhance its physicochemical properties was investigated. Specifically, PE/TA/Fe3+ composite films were prepared using the solution casting method, and the UV-blocking properties, transparency, water content, physico-mechanical properties, antioxidant properties and degradability of the PE composite films were investigated. The microstructure of the PE composite films and the interactions between the contained components were analyzed using FTIR, X_crystal diffraction and SEM scanning electron microscopy. The results showed that the addition of TA and Fe3+ can significantly improve the UV barrier properties and antioxidant properties of PE films. Meanwhile, Fe3+ could form a metal phenol network with TA and crosslink with the PE film, which makes the structure of the PE film denser and thus significantly reduces the water vapor permeability of the PE film. In addition, this work also indicated that the PE composite coatings have a favorable preservation effect on passion fruit, which leads to the lowest weight loss rate and wrinkle index of the passion fruit within 7 days of storage and shows good appearance quality and commercial value. This work indicates that the addition of tannic acid and Fe3+ significantly improved the mechanical and barrier properties of pectin films, and the composite pectin coating extended the shelf life of passion fruit.

Investigation on epidermal structure and water migration of postharvest passion fruit during storage.

Passion fruit is a tropical fruit that has plenty of fruit fragrance. During storage, passion fruit quickly loses water, resulting in its poor quality. Researching the mechanism of water loss contributes to prolonging the storage time. In this study, passion fruit was stored at 7 or 25°C to analyze the relationship between epidermal structure and water migration. The epidermal wax and structure of passion fruit began to show signs of destruction from the middle stage (day 8) during storage. The mobility of free water was decreased at 7°C and increased at 25°C in passion fruit from the middle stage of storage (day 8). The migration rate of free water in passion fruit stored at 7°C was lower than that at 25°C. The mobility of immobile water was weaker in the late storage period but that of bound water changed barely. These results showed that the migration of free, immobile, and bound water had a connection with the epidermal structure. Incomplete epidermal structure promoted water loss in passion fruit, with the most pronounced loss of free water. PRACTICAL APPLICATION: Maintaining the epidermal structure of passion fruit well can decrease the water loss ratio. Passion fruit stored at low temperatures could better sustain the integrity of epidermal wax and structure; it was able to change the water migration rate in the epidermis of passion fruit, which was conducive to maintaining the water content.

Effects of Volatile Flavour Compound Variations on the Varying Aroma of Mangoes 'Tainong' and 'Hongyu' during Storage.

The aroma, taste, and flavour profiles of mango cultivars vary, directly influencing their marketability and consumer acceptance. In this study, we explored the effects of volatile organic compounds (VOCs) on the distinct aromas of two mango cultivars during storage using GC-IMS and HS-SPME-GC-MS combined with OPLS-DA analysis. Our findings revealed that the terpene and aldehyde contents were higher in the 'Tainong' mango cultivar, compared to the 'Hongyu' mango, while the ester content was lower. The aroma was attributed to the presence of terpinolene, 2-nonenal, delta-carene, and alpha-phellandrene in the early stages of storage, and later-between 5 and 11 days-to ethyl acetate, ethyl butyrate, and ethyl propanoate. Further analysis of characteristic VOCs using OPLS-DA demonstrated and explained the strong grassy aroma of the 'Tainong' mango, and the strong fruity and sweet aromas of the 'Hongyu' mango. Additionally, esters mainly accumulated during the later periods of storage, especially propyl butyrate, which was produced and accumulated when fruit quality deteriorated in the later storage period. Our study provides a theoretical basis for detecting mango VOCs during storage to determine the appropriate marketing time for the two mango cultivars and enables informed consumer choice.

Physiological and Transcriptome Analyses of CaCl2 Treatment to Alleviate Chilling Injury in Pineapple.

The post-harvest ripening of pineapples can be effectively postponed by refrigerated storage. Nevertheless, internal browning (IB) frequently appears in pineapples after refrigerated storage during the course of the shelf life at room temperature, which is known as chilling injury (CI). In this study, the chilling injury of pineapple fruit was induced by a low temperature (6 °C) and transferred to normal-temperature storage; the best concentration of 50 µmol/L of CaCl2 was selected by the IB appearance and electrical conductivity. Fruit quality, reactive oxygen species (ROS), antioxidants, and transcription factors were investigated. The physiological data results indicated that pineapples treated with 50 µmol/L of CaCl2 maintained fruit quality, decreased reactive oxygen species (ROS), and enhanced the antioxidant activity of fruits, alleviating internal browning (IB) symptoms in pineapple fruit. The expressions of related genes were also consistent with the physiological changes by the transcriptome data analysis. In addition, we focused on some related metabolic pathways, including phenylpropanoid biosynthesis, MAPK pathway, plant hormone, plant-pathogen interaction, tricarboxylic acid cycle (TAC), and fatty acid biosynthesis. We performed integrative analyses of transcriptome data combined with a series of physiology and experimental analyses on the internal browning of pineapples, which will be of great significance to extending the shelf life of pineapples through molecular biology in the future.

Silencing of Sly-miR171d increased the expression of GRAS24 and enhanced postharvest chilling tolerance of tomato fruit.

The role of Sly-miR171d on tomato fruit chilling injury (CI) was investigated. The results showed that silencing the endogenous Sly-miR171d effectively delayed the increase of CI and electrolyte leakage (EL) in tomato fruit, and maintained fruit firmness and quality. After low temperature storage, the expression of target gene GRAS24 increased in STTM-miR171d tomato fruit, the level of GA3 anabolism and the expression of CBF1, an important regulator of cold resistance, both increased in STTM-miR171d tomato fruit, indicated that silencing the Sly-miR171d can improve the resistance ability of postharvest tomato fruit to chilling tolerance.

Chilling injury of tomato fruit was alleviated under low-temperature storage by silencing Sly-miR171e with short tandem target mimic technology.

In this study, the role of Sly-miR171e on post-harvest cold tolerance of tomato fruit was researched. The results showed that overexpression of Sly-miR171e (miR171e-OE) promoted postharvest chilling injury (CI) of tomato fruit at the mature red (MR) and mature green (MG) stage. Contrasted with the wild type (WT) and miR171e-OE fruit, the knockdown of Sly-miR171e (miR171e-STTM) showed a lower CI index, lower hydrogen peroxide (H2O2) content, and higher fruit firmness after harvest. In the fruit of miR171e-STTM, the expression level of GRAS24, CBF1, GA2ox1, and COR, and the GA3 content were ascended, while the expression levels of GA20ox1 and GA3ox1 were descended. The research demonstrated that CI in tomato fruit was alleviated at low temperature storage by silencing Sly-miR171e with short tandem target mimic (STTM) technology. Furthermore, it also provided helpful information for genetic modification of miR171e and control of CI in the postharvest fruit.

Attenuation of Postharvest Browning in Rambutan Fruit by Melatonin Is Associated With Inhibition of Phenolics Oxidation and Reinforcement of Antioxidative Process.

Rambutan is a famous tropical fruit with a unique flavor and considerable economic value. However, the high vulnerability to postharvest browning leads to a short shelf life of rambutan fruit. Melatonin (MT) is an excellent bioactive molecule that possesses the potential to improve the storability of the harvested crops. In this study, the physiological mechanism of exogenous MT in affecting pericarp browning and senescence of postharvest rambutan fruit was investigated. Experimental results showed that the application of MT at 0.125 mmol L-1 appreciably retarded the advancement of pericarp browning and color parameters (L*, a*, and b*). MT treatment inhibited the increase in membrane relative electrolytes leakage (REL) while lowering the accumulation of reactive oxygen species (ROS) (■O2 - and H2O2) and malonaldehyde (MDA). Reduced phenolics oxidation, as indicated by higher contents of total phenolics, flavonoids, and anthocyanins along with fewer activities of peroxidase (POD) and polyphenol oxidase (PPO), was detected in MT fruit compared with control fruit. MT treatment maintained the cellular redox state by inducing antioxidant enzyme activity and reinforcing the ascorbate-glutathione (AsA-GSH) cycle. Furthermore, the ultrastructural observation revealed that the spoilage of cellular and subcellular structures was milder in MT fruit than that in control fruit. The results suggest that MT could ameliorate the browning and senescence of rambutan fruit by inhibiting phenolic oxidation and enhancing the antioxidative process.

SlBEL11 affects tomato carotenoid accumulation by regulating SlLCY-b2.

Extensive data have demonstrated that carotenoid accumulation in tomato fruit is influenced by environmental cues and hormonal signals. However, there is insufficient information on the mechanism of its transcriptional regulation, as many molecular roles of carotenoid biosynthetic pathways remain unknown. In this work, we found that the silence of the BEL1-like family transcription factor (TF) BEL1-LIKE HOMEODOMAIN 11 (SlBEL11) enhanced carotenoid accumulation in virus induced gene silencing (VIGS) analysis. In its RNA interference (RNAi) transgenic lines, a significant increase in the transcription level for the lycopene beta cyclase 2 (SlLCY-b2) gene was detected, which encoded a key enzyme located at the downstream branch of the carotenoid biosynthetic pathway. In Electrophoretic mobility shift assay (EMSA), SlBEL11 protein was confirmed to bind to the promoter of SlLCY-b2 gene. In addition, the dual-luciferase reporter assay showed its intrinsic transcriptional repression activity. Collectively, our findings added a new member to the carotenoid transcriptional regulatory network and expanded the functions of the SlBEL11 transcription factor.

A NAC transcription factor, NOR-like1, is a new positive regulator of tomato fruit ripening.

Ripening of the model fruit tomato (Solanum lycopersicum) is controlled by a transcription factor network including NAC (NAM, ATAF1/2, and CUC2) domain proteins such as No-ripening (NOR), SlNAC1, and SlNAC4, but very little is known about the NAC targets or how they regulate ripening. Here, we conducted a systematic search of fruit-expressed NAC genes and showed that silencing NOR-like1 (Solyc07g063420) using virus-induced gene silencing (VIGS) inhibited specific aspects of ripening. Ripening initiation was delayed by 14 days when NOR-like1 function was inactivated by CRISPR/Cas9 and fruits showed obviously reduced ethylene production, retarded softening and chlorophyll loss, and reduced lycopene accumulation. RNA-sequencing profiling and gene promoter analysis suggested that genes involved in ethylene biosynthesis (SlACS2, SlACS4), color formation (SlGgpps2, SlSGR1), and cell wall metabolism (SlPG2a, SlPL, SlCEL2, and SlEXP1) are direct targets of NOR-like1. Electrophoretic mobility shift assays (EMSA), chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR), and dual-luciferase reporter assay (DLR) confirmed that NOR-like1 bound to the promoters of these genes both in vitro and in vivo, and activated their expression. Our findings demonstrate that NOR-like1 is a new positive regulator of tomato fruit ripening, with an important role in the transcriptional regulatory network.

Role of the tomato TAGL1 gene in regulating fruit metabolites elucidated using RNA sequence and metabolomics analyses.

Fruit ripening is a complex biological process affecting fruit quality. In tomato the fruit ripening process is delicately regulated by transcription factors (TFs). Among these, the TOMATO AGAMOUS-LIKE 1 (TAGL1) gene plays an important role in both the development and ripening of fruit. In this study, the TAGL1 gene was successfully silenced by virus-induced gene silencing technology (VIGS), and the global gene expression and metabolites profiles of TAGL1-silenced fruits were analyzed by RNA-sequence analysis (RNA-seq) and liquid chromatography-mass spectrometry (LC-MS/MS). The TAGL1-silenced fruits phenotypically displayed an orange pericarp, which was in accordance with the results expected from the down-regulation of genes associated with carotenoid synthesis. Levels of several amino acids and organic acids were lower in the TAGL1-silenced fruits than in the wild-type fruits, whereas, α-tomatine content was greatly increased (more than 10-fold) in the TAGL1-silenced fruits compared to wild-type fruits. The findings of this study showed that TAGL1 not only regulates the ripening of tomato fruits, but also affects the synthesis and levels of nutrients in the fruit.

Manipulation of Light Signal Transduction Factors as a Means of Modifying Steroidal Glycoalkaloids Accumulation in Tomato Leaves.

Steroidal glycoalkaloids (SGAs) are cholesterol-derived specialized metabolites produced by Solanaceous plant species. They contribute to pathogen defense but are considered as anti-nutritional compounds and toxic to humans. Although the genes involved in the SGA biosynthetic pathway have been successfully cloned and identified, transcription factors regulating this pathway are still poorly understood. We report that silencing tomato light signal transduction transcription factors ELONGATED HYPOCOTYL 5 (SlHY5) and PHYTOCHROME INTERACTING FACTOR3 (SlPIF3), by virus-induced gene silencing (VIGS), altered glycoalkaloids levels in tomato leaves compared to control plant. Electrophoretic mobility shift assay (EMSA) and Chromatin immunoprecipitation (ChIP) analysis confirmed that SlHY5 and SlPIF3 bind to the promoter of target genes of GLYCOALKALOID METABOLISM (GAME1, GAME4, GAME17), affecting the steady-state concentrations of transcripts coding for SGA pathway enzymes. The results indicate that light-signaling transcription factors HY5 and PIF3 regulate the abundance of SGAs by modulating the transcript levels of these GAME genes. This insight into the regulation of SGA biosynthesis can be used for manipulating the level of these metabolites in crops.

BEL1-LIKE HOMEODOMAIN 11 regulates chloroplast development and chlorophyll synthesis in tomato fruit.

Chloroplast development and chlorophyll(Chl)metabolism in unripe tomato contribute to the growth and quality of the fruit, however these mechanisms are poorly understood. In this study, we initially investigated seven homeobox-containing transcription factors (TFs) with specific ripening-associated expression patterns using virus-induced gene silencing (VIGS) technology and found that inhibiting the expression of one of these TFs, BEL1-LIKE HOMEODOMAIN11 (SlBEL11), significantly increased Chl levels in unripe tomato fruit. This enhanced Chl accumulation was further validated by generating stable RNA interference (RNAi) transgenic lines. RNA sequencing (RNA-seq) of RNAi-SlBEL11 fruit at the mature green (MG) stage showed that 48 genes involved in Chl biosynthesis, photosynthesis and chloroplast development were significantly upregulated compared with the wild type (WT) fruit. Genomic global scanning for Homeobox TF binding sites combined with RNA-seq differential gene expression analysis showed that 22 of these 48 genes were potential target genes of SlBEL11 protein. These genes included Chl biosynthesis-related genes encoding for protochlorophyllide reductase (POR), magnesium chelatase H subunit (CHLH) and chlorophyllide a oxygenase (CAO), and chloroplast development-related genes encoding for chlorophyll a/b binding protein (CAB), homeobox protein knotted 2 (TKN2) and ARABIDOPSIS PSEUDO RESPONSE REGULATOR 2-LIKE (APRR2-like). Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation quantitative polymerase chain reaction (PCR) (ChIP-qPCR) assays were employed to verify that SlBEL11 protein could bind to the promoters for TKN2, CAB and POR. Taken together, our findings demonstrated that SlBEL11 plays an important role in chloroplast development and Chl synthesis in tomato fruit.

Transcriptome Analysis Provides a Preliminary Regulation Route of the Ethylene Signal Transduction Component, SlEIN2, during Tomato Ripening.

Ethylene is crucial in climacteric fruit ripening. The ethylene signal pathway regulates several physiological alterations such as softening, carotenoid accumulation and sugar level reduction, and production of volatile compounds. All these physiological processes are controlled by numerous genes and their expression simultaneously changes at the onset of ripening. Ethylene insensitive 2 (EIN2) is a key component for ethylene signal transduction, and its mutation causes ethylene insensitivity. In tomato, silencing SlEIN2 resulted in a non-ripening phenotype and low ethylene production. RNA sequencing of SlEIN2-silenced and wild type tomato, and differential gene expression analyses, indicated that silencing SlEIN2 caused changes in more than 4,000 genes, including those related to photosynthesis, defense, and secondary metabolism. The relative expression level of 28 genes covering ripening-associated transcription factors, ethylene biosynthesis, ethylene signal pathway, chlorophyll binding proteins, lycopene and aroma biosynthesis, and defense pathway, showed that SlEIN2 influences ripening inhibitor (RIN) in a feedback loop, thus controlling the expression of several other genes. SlEIN2 regulates many aspects of fruit ripening, and is a key factor in the ethylene signal transduction pathway. Silencing SlEIN2 ultimately results in lycopene biosynthesis inhibition, which is the reason why tomato does not turn red, and this gene also affects the expression of several defense-associated genes. Although SlEIN2-silenced and green wild type fruits are similar in appearance, their metabolism is significantly different at the molecular level.

Silencing of the SlNAP7 gene influences plastid development and lycopene accumulation in tomato.

Ripening is an important stage of fruit development. To screen the genes associated with pigment formation in tomato fruit, a suppression subtractive hybridization (SSH) cDNA library was constructed by using tomato fruit in the green ripe and break ripe stages, and 129 differential genes were obtained. Using redness as a screening marker, virus-induced gene silencing (VIGS) of the differential genes was performed with a sprout vacuum-infiltration system (SVI). The results showed that silencing the SlNAP7 gene affected the chloroplast development of tomato leaves, manifesting as a photo-bleaching phenotype, and silenced fruit significantly affected the accumulation of lycopene, manifested as a yellow phenotype. In our study, we found that silencing the SlNAP7 gene downregulates the expression of the POR and PORA genes and destroys the normal development of the chloroplast. The expression of related genes included in the lycopene biosynthesis pathway was not significantly changed, but lycopene accumulation was significantly reduced in tomato fruit. Perhaps it was caused by the destruction of the chromoplast, which leads to the oxidation of lycopene. The results show that the SlNAP7 gene influences chloroplast development and lycopene accumulation in tomato.

Efficient Virus-Induced Gene Silencing in Solanum rostratum.

Solanum rostratum is a "super weed" that grows fast, is widespread, and produces the toxin solanine, which is harmful to both humans and other animals. To our knowledge, no study has focused on its molecular biology owing to the lack of available transgenic methods and sequence information for S. rostratum. Virus-induced gene silencing (VIGS) is a powerful tool for the study of gene function in plants; therefore, in the present study, we aimed to establish tobacco rattle virus (TRV)-derived VIGS in S. rostratum. The genes for phytoene desaturase (PDS) and Chlorophyll H subunit (ChlH) of magnesium protoporphyrin chelatase were cloned from S. rostratum and used as reporters of gene silencing. It was shown that high-efficiency VIGS can be achieved in the leaves, flowers, and fruit of S. rostratum. Moreover, based on our comparison of three different types of infection methods, true leaf infection was found to be more efficient than cotyledon and sprout infiltration in long-term VIGS in multiple plant organs. In conclusion, the VIGS technology and tomato genomic sequences can be used in the future to study gene function in S. rostratum.