Banana MabHLH28 positively regulates the expression of softening-related genes to mediate fruit ripening independently or via cooperating with MaWRKY49/111

Texture softening is a physiological indicator of fruit ripening, which eventually contributes to fruit quality and the consumer's acceptance. Despite great progress having been made in identification of the genes related to fruit softening, the upstream transcriptional regulatory pathways of these softening-related genes are not fully elucidated. Here, a novel bHLH gene, designated as MabHLH28, was identified because of its significant upregulation in banana fruit ripening. DAP-Seq analysis revealed that MabHLH28 bound to the core sequence of 'CAYGTG' presented in promoter regions of fruit softening-associated genes, such as the genes related to cell wall modification (MaPG3, MaPE1, MaPL5, MaPL8, MaEXP1, MaEXP2, MaEXPA2, and MaEXPA15) and starch degradation (MaGWD1 and MaLSF2), and these bindings were validated by EMSA and DLR assays. Transient overexpression and knockdown of MabHLH28 in banana fruit resulted in up- and down-regulation of softening-related genes, thereby hastening and postponing fruit ripening. Furthermore, overexpression of MabHLH28 in tomato accelerated the ripening process by elevating the accumulation of softening-associated genes. In addition, MabHLH28 showed interaction withMaWRKY49/111 and itself to form protein complexes, which could combinatorically strengthen the transcription of softening-associated genes. Taken together, our findings suggest that MabHLH28 mediates fruit softening by upregulating the expression of softening-related genes either alone or in combination with MaWRKY49/111.

Revealing the specific regulations of nitric oxide on the postharvest ripening and senescence of bitter melon fruit

Bitter melon fruit is susceptible to yellowing, softening, and rotting under room-temperature storage conditions, resulting in reduced commercial value. Nitric oxide (NO) is an important signaling molecule and plays a crucial role in regulating the fruit postharvest quality. In this study, we investigated the effects of NO treatment on changes in sensory and firmness of bitter melon fruit during postharvest storage. Moreover, transcriptomic, metabolomic, and proteomic analyses were performed to elucidate the regulatory mechanisms through which NO treatment delays the ripening and senescence of bitter melon fruit. Our results show that differentially expressed genes (DEGs) were involved in fruit texture (CSLE, β-Gal, and PME), plant hormone signal transduction (ACS, JAR4, and AUX28), and fruit flavor and aroma (SUS2, LOX, and GDH2). In addition, proteins differentially abundant were associated with fruit texture (PLY, PME, and PGA) and plant hormone signal transduction (PBL15, JAR1, and PYL9). Moreover, NO significantly increased the abundance of key enzymes involved in the phenylpropanoid biosynthetic pathway, thus enhancing the disease resistance and alleviating softening of bitter melon fruit. Finally, differential metabolites mainly included phenolic acids, terpenoids, and flavonoids. These results provide a theoretical basis for further studies on the physiological changes associated with postharvest ripening and senescence of bitter melon fruit.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00110-y.

Expansin SlExp1 and endoglucanase SlCel2 synergistically promote fruit softening and cell wall disassembly in tomato

Fruit softening, an irreversible process that occurs during fruit ripening, can lead to losses and waste during postharvest transportation and storage. Cell wall disassembly is the main factor leading to loss of fruit firmness, and several ripening-associated cell wall genes have been targeted for genetic modification, particularly pectin modifiers. However, individual knockdown of most cell wall-related genes has had minimal influence on cell wall integrity and fruit firmness, with the notable exception of pectate lyase. Compared to pectin disassembly, studies of the cell wall matrix, the xyloglucan-cellulose framework, and underlying mechanisms during fruit softening are limited. Here, a tomato (Solanum lycopersicum) fruit ripening-associated α-expansin (SlExpansin1/SlExp1) and an endoglucanase (SlCellulase2/SlCel2), which function in the cell wall matrix, were knocked out individually and together using clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing. Simultaneous knockout of SlExp1 and SlCel2 enhanced fruit firmness, reduced depolymerization of homogalacturonan-type pectin and xyloglucan, and increased cell adhesion. In contrast, single knockouts of either SlExp1 or SlCel2 did not substantially change fruit firmness, while simultaneous overexpression of SlExp1 and SlCel2 promoted early fruit softening. Collectively, our results demonstrate that SlExp1 and SlCel2 synergistically regulate cell wall disassembly and fruit softening in tomato.

SlERF109-like and SlNAC1 Coordinately Regulated Tomato Ripening by Inhibiting ACO1 Transcription

As a typical climacteric fruit, tomato (Solanum lycopersicum) is widely used for studying the ripening process. The negative regulation of tomato fruits by transcription factor SlNAC1 has been reported, but its regulatory network was unclear. In the present study, we screened a transcription factor, SlERF109-like, and found it had a stronger relationship with SlNAC1 at the early stage of tomato fruit development through the use of transcriptome data, RT-qPCR, and correlation analysis. We inferred that SlERF109-like could interact with SlNAC1 to become a regulatory complex that co-regulates the tomato fruit ripening process. Results of transient silencing (VIGS) and transient overexpression showed that SlERF109-like and SlNAC1 could regulate chlorophyll degradation-related genes (NYC1, PAO, PPH, SGR1), carotenoids accumulation-related genes (PSY1, PDS, ZDS), ETH-related genes (ACO1, E4, E8), and cell wall metabolism-related genes expression levels (CEL2, EXP, PG, TBG4, XTH5) to inhibit tomato fruit ripening. A dual-luciferase reporter and yeast one-hybrid (Y1H) showed that SlNAC1 could bind to the SlACO1 promoter, but SlERF109-like could not. Furthermore, SlERF109-like could interact with SlNAC1 to increase the transcription for ACO1 by a yeast two-hybrid (Y2H) assay, a luciferase complementation assay, and a dual-luciferase reporter. A correlation analysis showed that SlERF109-like and SlNAC1 were positively correlated with chlorophyll contents, and negatively correlated with carotenoid content and ripening-related genes. Thus, we provide a model in which SlERF109-like could interact with SlNAC1 to become a regulatory complex that negatively regulates the tomato ripening process by inhibiting SlACO1 expression. Our study provided a new regulatory network of tomato fruit ripening and effectively reduced the waste of resources.

The apple transcription factor MdZF-HD11 regulates fruit softening by promoting Mdβ-GAL18 expression

Fruit ripening and the associated softening are major determinants of fruit quality and post-harvest shelf life. Although the mechanisms underlying fruit softening have been intensively studied, there are limited reports on the regulation of fruit softening in apples (Malus domestica). Here, we identified a zinc finger homeodomain transcription factor MdZF-HD11that trans-activates the promoter of Mdβ-GAL18, which encodes a pectin-degradation enzyme associated with cell wall metabolism. Both MdZF-HD11 and Mdβ-GAL18 genes were up-regulated by exogenous ethylene treatment and repressed by 1-methylcyclopropene treatment. Further experiments revealed that MdZF-HD11 binds directly to the Mdβ-GAL18 promoter and up-regulates its transcription. Moreover, using transgenic apple fruit calli, we found that overexpression of Mdβ-GAL18 or MdZF-HD11 significantly enhanced β-galactosidase activity, and overexpression of MdZF-HD11 induced the expression of Mdβ-GAL18. We also discovered that transient overexpression of Mdβ-GAL18 or MdZF-HD11 in 'Golden Delicious' apple significantly increased the release of ethylene, reduced fruit firmness, promoted the transformation of skin color from green to yellow, and accelerated ripening and softening of the fruit. Finally, the overexpression of MdZF-HD11 in tomato also promoted fruit softening. Collectively, these results indicate that ethylene-induced MdZF-HD11 interacts with Mdβ-GAL18 to promote the post-harvest softening of apple.

Transcriptional regulation of tomato fruit ripening

An intrinsic and genetically determined ripening program of tomato fruits often depends upon the appropriate activation of tissue- and stage-specific transcription factors in space and time. The past two decades have yielded considerable progress in detailing these complex transcriptional as well as hormonal regulatory circuits paramount to fleshy fruit ripening. This non-linear ripening process is strongly controlled by the MADS-box and NOR family of proteins, triggering a transcriptional response associated with the progression of fruit ripening. Deepening insights into the connection between MADS-RIN and plant hormones related transcription factors, such as ERFs and ARFs, further conjugates the idea that several signaling units work in parallel to define an output fruit ripening transcriptome. Besides these TFs, the role of other families of transcription factors such as MYB, GLK, WRKY, GRAS and bHLH have also emerged as important ripening regulators. Other regulators such as EIN and EIL proteins also determine the transcriptional landscape of ripening fruits. Despite the abundant knowledge of the complex spectrum of ripening networks in the scientific domain, identifying more ripening effectors would pave the way for a better understanding of fleshy fruit ripening at the molecular level. This review provides an update on the transcriptional regulators of tomato fruit ripening.

Abscisic acid biosynthesis, metabolism and signaling in ripening fruit

Fruits are highly recommended nowadays in human diets because they are rich in vitamins, minerals, fibers and other necessary nutrients. The final stage of fruit production, known as ripening, plays a crucial role in determining the fruit's quality and commercial value. This is a complex physiological process, which involves many phytohormones and regulatory factors. Among the phytohormones involved in fruit ripening, abscisic acid (ABA) holds significant importance. ABA levels generally increase during the ripening process in most fruits, and applying ABA externally can enhance fruit flavor, hasten softening, and promote color development through complex signal regulation. Therefore, gaining a deeper understanding of ABA's mechanisms in fruit ripening is valuable for regulating various fruit characteristics, making them more suitable for consumption or storage. This, in turn, can generate greater economic benefits and reduce postharvest losses. This article provides an overview of the relationship between ABA and fruit ripening. It summarizes the effects of ABA on ripening related traits, covering the biochemical aspects and the underlying molecular mechanisms. Additionally, the article discusses the interactions of ABA with other phytohormones during fruit ripening, especially ethylene, and provides perspectives for future exploration in this field.

Fruit ripening under heat stress: The intriguing role of ethylene-mediated signaling

Crop production is significantly influenced by climate, and even minor climate changes can have a substantial impact on crop yields. Rising temperature due to climate change can lead to heat stress (HS) in plants, which not only hinders plant growth and development but also result in significant losses in crop yields. To cope with the different stresses including HS, plants have evolved a variety of adaptive mechanisms. In response to these stresses, phytohormones play a crucial role by generating endogenous signals that regulate the plant's defensive response. Among these, Ethylene (ET), a key phytohormone, stands out as a major regulator of stress responses in plants and regulates many plant traits, which are critical for crop productivity and nutritional quality. ET is also known as a ripening hormone for decades in climacteric fruit and many studies are available deciphering the function of different ET biosynthesis and signaling components in the ripening process. Recent studies suggest that HS significantly affects fruit quality traits and perturbs fruit ripening by altering the regulation of many ethylene biosynthesis and signaling genes resulting in substantial loss of fruit yield, quality, and postharvest stability. Despite the significant progress in this field in recent years the interplay between ET, ripening, and HS is elusive. In this review, we summarized the recent advances and current understanding of ET in regulating the ripening process under HS and explored their crosstalk at physiological and molecular levels to shed light on intricate relationships.

Comparative Physiological and Transcriptome Analyses Reveal Mechanisms of Salicylic-Acid-Reduced Postharvest Ripening in 'Hosui' Pears (Pyrus pyrifolia Nakai)

Postharvest ripening of sand pear fruit leads to quality deterioration, including changes in texture, flavor, and fruit color. Salicylic acid (SA), an important defense-related hormone, delays fruit ripening and maintains fruit quality, but the underling mechanism remains unclear. Herein, we evaluated the efficacy of SA in delaying the ripening process of Pyrus pyrifolia cv. 'Hosui' pear fruit, as evidenced by the reduction in fruit weight loss, inhibition of firmness loss, cell wall degradation and soluble sugars, and retention of total phenols. Based on comparative transcriptomic data, a total of 3837 and 1387 differentially expressed genes (DEGs) were identified during room-temperature storage of control fruit and between SA-treated and control fruit, respectively. Further KEGG analysis revealed that the DEGs were mainly implicated in plant hormone signal transduction, starch and sugar metabolism, and cell wall modification. Moreover, exogenous SA treatment also altered the expression of many transcription factor (TF) families, including those in the ethylene-responsive factor (ERF), NAM, ATAF, CUC (NAC), basic helix-loop-helix (bHLH), basic leucine zipper (bZIP), and v-myb avian myeloblastosis viral oncogene homolog (MYB) families. Together, the results offer important insights into the role of SA-responsive genes in controlling fruit ripening in sand pears.

Exogenous gibberellin delays maturation in persimmon fruit through transcriptional activators and repressors

As the harvest season of most fruit is concentrated, fruit maturation manipulation is essential for the fresh fruit industry to prolong sales time. Gibberellin (GA), an important phytohormone necessary for plant growth and development, has also shown a substantial regulatory effect on fruit maturation; however, its regulatory mechanisms remain inconclusive. In this research, preharvest GA3 treatment effectively delayed fruit maturation in several persimmon (Diospyros kaki) cultivars. Among the proteins encoded by differentially expressed genes, 2 transcriptional activators (NAC TRANSCRIPTION FACTOR DkNAC24 and ETHYLENE RESPONSIVE FACTOR DkERF38) and a repressor (MYB-LIKE TRANSCRIPTION FACTOR DkMYB22) were direct regulators of GERANYLGERANYL DIPHOSPHATE SYNTHASE DkGGPS1, LYSINE HISTIDINE TRANSPORTER DkLHT1, and FRUCTOSE-BISPHOSPHATE ALDOLASE DkFBA1, respectively, resulting in the inhibition of carotenoid synthesis, outward transport of an ethylene precursor, and consumption of fructose and glucose. Thus, the present study not only provides a practical method to prolong the persimmon fruit maturation period in various cultivars but also provides insights into the regulatory mechanisms of GA on multiple aspects of fruit quality formation at the transcriptional regulation level.

Exogenous BR delayed peach fruit softening by inhibiting pectin degradation enzyme genes

Peach fruit deteriorates and senesces rapidly when stored at room temperature. Brassinosteroids (BRs) play an important role in regulating plant growth and development and maintaining fruit quality. However, little information is available on the effect of BRs on the senescence of harvested peach fruit. In this study, different concentrations of BR were used to treat 'Hongniang' peach fruit, and the results showed that 10 μM BR was the most beneficial concentration to delay the senescence of peach fruits. BR treatment delayed the decrease of fruit firmness, the release of ethylene, the increase in water-soluble pectin (WSP) and ionic-soluble pectin (ISP) content and the decrease in covalently bound pectin (CBP) content, inhibited the activities of pectin degradation enzymes, and inhibited the gene expression of PpPME1/3, PpPG, PpARF2, and PpGAL2/16. In addition, BR treatment also inhibited the expression of PpBES1-5/6. Cis-acting regulatory element analysis of pectin degradation enzyme promoters showed that many of them contained BES1 binding elements. All the above results showed that BR treatment had a positive effect on delaying the senescence of peach fruit and prolonging its storage period.

Ethylene enhances MdMAPK3-mediated phosphorylation of MdNAC72 to promote apple fruit softening

The phytohormone ethylene plays an important role in promoting the softening of climacteric fruits, such as apples (Malus domestica); however, important aspects of the underlying regulatory mechanisms are not well understood. In this study, we identified apple MITOGEN-ACTIVATED PROTEIN KINASE 3 (MdMAPK3) as an important positive regulator of ethylene-induced apple fruit softening during storage. Specifically, we show that MdMAPK3 interacts with and phosphorylates the transcription factor NAM-ATAF1/2-CUC2 72 (MdNAC72), which functions as a transcriptional repressor of the cell wall degradation-related gene POLYGALACTURONASE1 (MdPG1). The increase in MdMAPK3 kinase activity was induced by ethylene, which promoted the phosphorylation of MdNAC72 by MdMAPK3. Additionally, MdPUB24 functions as an E3 ubiquitin ligase to ubiquitinate MdNAC72, resulting in its degradation via the 26S proteasome pathway, which was enhanced by ethylene-induced phosphorylation of MdNAC72 by MdMAPK3. The degradation of MdNAC72 increased the expression of MdPG1, which in turn promoted apple fruit softening. Notably, using variants of MdNAC72 that were mutated at specific phosphorylation sites, we observed that the phosphorylation state of MdNAC72 affected apple fruit softening during storage. This study thus reveals that the ethylene-MdMAPK3-MdNAC72-MdPUB24 module is involved in ethylene-induced apple fruit softening, providing insights into climacteric fruit softening.

Hormonal regulation of ethylene response factors in tomato during storage and distribution

Introduction

Ethylene response factors (ERFs) play a critical role in regulating hormone interactions that affect the shelf life of tomatoes. Understanding their regulation during storage and distribution can be highly beneficial.

Methods

This study examined the effects of treatment with ethylene (ET), brassinosteroid (BR), auxin (AUX), and gibberellin (GA) on fruit ripening and the expression of 18 ripening-associated ERFs in tomato stored at 20°C (room temperature) for 10 d or 4°C (cold storage) for 14 d followed by 2 d at 20°C (retailer conditions).

Results

The results showed that ripening was accelerated by ET and BR but was delayed by AUX and GA at room temperature. Cold storage delayed ripening in all groups, with ET and GA treatments showing the highest and lowest a* values, respectively. The effects of hormone treatment were consistent with room temperature when the fruits were transferred from cold storage to retail conditions. At room temperature, ERFs responsive to ET (ERF.B1, B2, B6, E2, and F1) and BR (ERF.E5, F2, and F3) were inhibited by AUX. ET-induced genes (ERF.C1, E1, F4, and H7) could be co-regulated by other hormones at cold storage. When the fruits were transferred from cold storage to retailer conditions, ERFs responsive to ET and BR were inhibited by GA. Additionally, ET-responsive ERFs could be inhibited by BR at room temperature, whereas ET could inhibit BR-responsive ERFs at retailer conditions. The same ERFs that were regulated by ET at room temperature were instead regulated by BR under retailer conditions, and vice versa.

Discussion

These findings can help provide a better understanding of the complex hormone interactions regulating the postharvest physiology of tomato and in maintaining its quality and shelf life during storage and distribution.

Transcriptomic Analysis Reveals Genes Associated with the Regulation of Peach Fruit Softening and Senescence during Storage

Peach (Prunus persica (L.) Batsch) is a highly desirable fruit that is consumed around the world. However, the peach fruit is highly perishable after harvest, a characteristic that limits the distribution and supply to the market and causes heavy economic losses. Thus, peach fruit softening and senescence after harvest urgently need to be addressed. In the current study, transcriptomic analysis was performed to identify candidate genes associated with peach fruit softening and senescence, comparing peach fruit from cultivars with different flesh textures, namely melting and stony hard (SH) flesh textures during storage at room temperature. The mitogen-activated protein kinase signaling pathway-plant and plant hormone signal transduction pathways were associated with peach fruit softening and senescence according to the Venn diagram analysis and weighted gene co-expression network analysis. The expression levels of seven genes, including Prupe.1G034300, Prupe.2G176900, Prupe.3G024700, Prupe.3G098100, Prupe.6G226100, Prupe.7G234800, and Prupe.7G247500, were higher in melting peach fruit than in SH peach fruit during storage. Furthermore, the SH peach fruit softened rapidly after 1-naphthylacetic acid treatment, during which the levels of expression of these seven genes, determined by a quantitative reverse transcription polymerase chain reaction, were strongly induced and upregulated. Thus, these seven genes may play essential roles in regulating peach fruit softening and senescence.

Differential gene expression associated with flower development of mango (Mangifera indica L.) varieties with different shelf-life

Mango (Mangifera indica L.) is one of the most important commercial fruit crop grown in many parts of the world. Major challenges affecting mango trade are short shelf-life, high susceptibility to chilling injury, post-harvest diseases and consumer demand for improved fruit quality. The objective of the present study was to reveal the key regulators present in bud and flower tissues during flower development stage, associated with fruit development and affect the shelf-life of the mango fruit. RNA-sequencing of contrasting genotypes having short and long shelf-life, was carried out. Comparative differential expression pathway studies of long shelf-life (Totapuri) and short shelf-life (Bombay Green) mango genotypes revealed a total of 177 highly differentially expressed genes. Out of 177 total genes, 101 genes from endoplasmic reticulum pathway and very few from gibberellins (3) and jasmonic acid (1) pathway were identified. Genes from endoplasmic reticulum pathway like hsp 90, SRC2, DFRA, CHS, BG3 and ASPG1 mainly up regulated in Bombay Green. Uniprotein B9R8D3 also shows up regulation in Bombay Green. Ethylene insensitive pathway gene EIL1 up regulated in Bombay Green. Gene CAD1 from phenylpropanoid pathway mainly up regulated in Bombay Green. A total of 4 SSRs and 227 SNPs were mined from these pathways specific to the shelf-life. Molecular studies of endoplasmic reticulum, phenylpropanoid, ethylene, polygalacturonase and hormone pathways at the time of bud and flower formation revealed key regulators that determine the shelf-life of mango fruit.

Insights into cell wall changes during fruit softening from transgenic and naturally occurring mutants

Excessive softening during fleshy fruit ripening leads to physical damage and infection that reduce quality and cause massive supply chain losses. Changes in cell wall (CW) metabolism, involving loosening and disassembly of the constituent macromolecules, are the main cause of softening. Several genes encoding CW metabolizing enzymes have been targeted for genetic modification to attenuate softening. At least nine genes encoding CW modifying proteins have increased expression during ripening. Any alteration of these genes could modify CW structure and properties and contribute to softening, but evidence for their relative importance is sparse. The results of studies with transgenic tomato (Solanum lycopersicum), the model for fleshy fruit ripening, investigations with strawberry (Fragaria spp.) and apple (Malus domestica), and results from naturally occurring textural mutants provide direct evidence of gene function and the contribution of CW biochemical modifications to fruit softening. Here we review the revised CW structure model and biochemical and structural changes in CW components during fruit softening and then focus on and integrate the results of changes in CW characteristics derived from studies on transgenic fruits and mutants. Potential strategies and future research directions to understand and control the rate of fruit softening are also discussed.

Targeting ripening regulators to develop fruit with high quality and extended shelf life

Fruit quality directly impacts fruit marketability and consumer acceptance. Breeders have focused on fruit quality traits to extend shelf life, primarily through fruit texture, but, in some cases, have neglected other qualities such as flavor and nutrition. In recent years, integrative biotechnology and consumer-minded approaches have surfaced, aiding in the development of flavorful, long-lasting fruit. Here, we discussed how specific transcription factors and hormones involved in fruit ripening can be targeted to generate high-quality fruit through traditional breeding and bioengineering. We highlight regulators that can be used to generate novel-colored fruit or biofortify fresh produce with health-promoting nutrients, such as vitamin C. Overall, we argue that addressing grower and industry needs must be balanced with consumer-based traits.

The development progress of multi-array colourimetric sensors based on the M13 bacteriophage

Techniques for detecting chemicals dispersed at low concentrations in air continue to evolve. These techniques can be applied not only to manage the quality of agricultural products using a post-ripening process but also to establish a safety prevention system by detecting harmful gases and diagnosing diseases. Recently, techniques for rapid response to various chemicals and detection in complex and noisy environments have been developed using M13 bacteriophage-based sensors. In this review, M13 bacteriophage-based multi-array colourimetric sensors for the development of an electronic nose is discussed. The self-templating process was adapted to fabricate a colour band structure consisting of an M13 bacteriophage. To detect diverse target chemicals, the colour band was utilised with wild and genetically engineered M13 bacteriophages to enhance their sensing abilities. Multi-array colourimetric sensors were optimised for application in complex and noisy environments based on simulation and deep learning analysis. The development of a multi-array colourimetric sensor platform based on the M13 bacteriophage is likely to result in significant advances in the detection of various harmful gases and the diagnosis of various diseases based on exhaled gas in the future.

Telomere-to-telomere genome assembly of bitter melon (Momordica charantia L. var. abbreviata Ser.) reveals fruit development, composition and ripening genetic characteristics

Momordica charantia L. var. abbreviata Ser. (Mca), known as bitter gourd or bitter melon, is a Momordica variety with medicinal value and belongs to the Cucurbitaceae family. In view of the lack of genomic information on bitter gourd and other Momordica species and to promote Mca genomic research, we assembled a 295.6-Mb telomere-to-telomere (T2T) high-quality Mca genome with six gap-free chromosomes after Hi-C correction. This genome is anchored to 11 chromosomes, which is consistent with the karyotype information, and comprises 98 contigs (N50 of 25.4 Mb) and 95 scaffolds (N50 of 25.4 Mb). The Mca genome harbors 19 895 protein-coding genes, of which 45.59% constitute predicted repeat sequences. Synteny analysis revealed variations involved in fruit quality during the divergence of bitter gourd. In addition, assay for transposase-accessible chromatin by high-throughput sequencing and metabolic analysis showed that momordicosides and other substances are characteristic of Mca fruit pulp. A combined transcriptomic and metabolomic analysis revealed the mechanisms of pigment accumulation and cucurbitacin biosynthesis in Mca fruit peels, providing fundamental molecular information for further research on Mca fruit ripening. This report provides a new genetic resource for Momordica genomic studies and contributes additional insights into Cucurbitaceae phylogeny.

Using Fuzzy Logic to Increase Accuracy in Mango Maturity Index Classification: Approach for Developing a Portable Near-Infrared Spectroscopy Device

Grading is a decisive step in the successful distribution of mangoes to customers according to their preferences for the maturity index. A non-destructive method using near-infrared spectroscopy has historically been used to predict the maturity of fruit. This research classifies the maturity indexes in five classes using a new approach involving classification modeling and the application of fuzzy logic and indirect classification by measuring four parameters: total acidity, soluble solids content, firmness, and starch. These four quantitative parameters provide guidelines for maturity indexes and consumer preferences. The development of portable devices uses a neo spectra micro development kit with specifications for the spectrum of 1350-2500 nm. In terms of computer technology, this study uses a Raspberry Pi and Python programming. To improve the accuracy performance, preprocessing is carried out using 12 spectral transformation operators. Next, these operators are collected and combined to achieve optimal performance. The performance of the classification model with direct and indirect approaches is then compared. Ultimately, classification of the direct approach with preprocessing using linear discriminant analysis offered an accuracy of 91.43%, and classification of the indirect approach using partial least squares with fuzzy logic had an accuracy of 95.7%.

Morphological Variation of Strychnos spinosa Lam. Morphotypes: A Case Study at Bonamanzi Game Reserve, KwaZulu-Natal, South Africa

Strychnos spinosa Lam. of the Loganiaceae family is associated with versatility, poverty eradication, and rural economic development. However, the morphological diversity of S. spinosa is not well documented. This limits efforts toward its improvement and commercial exploitation. This study aimed to characterize the variability, vegetative and reproductive traits, and heritability of S. spinosa morphotypes at Bonamanzi Game Reserve. The majority of the morphotypes had green, rough, round immature fruits with dark green, elongated, open fully developed leaves. Fruits varied between roundish and pyriform shape as well as green and purple colour. Positive correlation was mainly seen between fruit and seed traits. Principal component analysis indicated fruit and seed traits as major discriminating factors for morphotypes, followed by leaf size and seed thickness. A dendrogram primarily grouped morphotypes according to fruit texture. Genotypic variance and genotypic coefficient of variation were higher than environmental variance and environmental coefficient variation in reproductive traits of S. spinosa. A rough pericarp texture and purple tinge on the immature leaves of some morphotypes was recorded for the first time. Differences in morphological features across S. spinosa morphotypes indicate a high level of diversity that could be utilized by breeders to generate new cultivars. This first report on variability and heritability among S. spinosa morphotypes forms the basis of available germplasm essential for future breeding programs.

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage

INTRODUCTION

Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant.

OBJECTIVES

This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness.

METHODS

The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca²⁺ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit.

RESULTS

The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0°C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca²⁺ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals.

CONCLUSION

PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca²⁺ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Transcriptional regulation of fleshy fruit texture

Fleshy fruit texture is a critically important quality characteristic of ripe fruit. Softening is an irreversible process which operates in most fleshy fruits during ripening which, together with changes in color and taste, contributes to improvements in mouthfeel and general attractiveness. Softening results mainly from the expression of genes encoding enzymes responsible for cell wall modifications but starch degradation and high levels of flavonoids can also contribute to texture change. Some fleshy fruit undergo lignification during development and post-harvest, which negatively affects eating quality. Excessive softening can also lead to physical damage and infection, particularly during transport and storage which causes severe supply chain losses. Many transcription factors (TFs) that regulate fruit texture by controlling the expression of genes involved in cell wall and starch metabolism have been characterized. Some TFs directly regulate cell wall targets, while others act as part of a broader regulatory program governing several aspects of the ripening process. In this review, we focus on advances in our understanding of the transcriptional regulatory mechanisms governing fruit textural change during fruit development, ripening and post-harvest. Potential targets for breeding and future research directions for the control of texture and quality improvement are discussed.

Determining the Effects of Light on the Fruit Peel Quality of Photosensitive and Nonphotosensitive Eggplant

With the development of facility agriculture, low-light stress is a prominent problem and a popular research topic currently. In this study, transcriptome analysis was used to analyze the genes in the fruit peel of photosensitive and nonphotosensitive eggplant and to explore the mechanism of changes in fruit color, texture, hormone content, aroma, and taste of these two different types of eggplant. We identified 51, 65, 66, and 66 genes involved in synthesizing anthocyanins, texture, hormone content, and aroma and flavor, respectively, in the two different types of eggplant based on the variation in gene expression trends in the fruit peel. These results provide a basis for further analysis of the molecular mechanism underlying the regulatory processes in eggplant fruits under low-light stress.

MaMYB4 is a negative regulator and a substrate of RING-type E3 ligases MaBRG2/3 in controlling banana fruit ripening

Fruit ripening is a complex developmental process, which is modulated by both transcriptional and post-translational events. Control of fruit ripening is important in maintaining moderate quality traits and minimizing postharvest deterioration. In this study, we discovered that the transcription factor MaMYB4 acts as a negative regulator of fruit ripening in banana. The protein levels of MaMYB4 decreased gradually with banana fruit ripening, paralleling ethylene production, and decline in firmness. DNA affinity purification sequencing combined with RNA-sequencing analyses showed that MaMYB4 preferentially binds to the promoters of various ripening-associated genes including ethylene biosynthetic and cell wall modifying genes. Furthermore, ectopic expression of MaMYB4 in tomato delayed tomato fruit ripening, which was accompanied by downregulation of ethylene biosynthetic and cell wall modifying genes. Importantly, two RING finger E3 ligases MaBRG2/3, whose protein accumulation increased progressively with fruit ripening, were found to interact with and ubiquitinate MaMYB4, contributing to decreased accumulation of MaMYB4 during fruit ripening. Transient overexpression of MaMYB4 and MaBRG2/3 in banana fruit ripening delayed or promoted fruit ripening by inhibiting or stimulating ethylene biosynthesis, respectively. Taken together, we demonstrate that MaMYB4 negatively modulates banana fruit ripening, and that MaMYB4 abundance could be regulated by protein ubiquitination, thus providing insights into the role of MaMYB4 in controlling fruit ripening at both transcriptional and post-translational levels.

Rhamnogalacturonan Endolyase Family 4 Enzymes: An Update on Their Importance in the Fruit Ripening Process

Fruit ripening is a process that produces fruit with top sensory qualities that are ideal for consumption. For the plant, the final objective is seed dispersal. One of the fruit characteristics observed by consumers is texture, which is related to the ripening and softening of the fruit. Controlled and orchestrated events occur to regulate the expression of genes involved in disassembling and solubilizing the cell wall. Studies have shown that changes in pectins are closely related to the loss of firmness and fruit softening. For this reason, studying the mechanisms and enzymes that act on pectins could help to elucidate the molecular events that occur in the fruit. This paper provides a review of the enzyme rhamnogalacturonan endolyase (RGL; EC 4.2.2.23), which is responsible for cleavage of the pectin rhamnogalacturonan I (RGL-I) between rhamnose (Rha) and galacturonic acid (GalA) through the mechanism of β-elimination during fruit ripening. RGL promotes the loosening and weakening of the cell wall and exposes the backbone of the polysaccharide to the action of other enzymes. Investigations into RGL and its relationship with fruit ripening have reliably demonstrated that this enzyme has an important role in this process.

Quantitative Determination of Ethylene Using a Smartphone-Based Optical Fiber Sensor (SOFS) Coupled with Pyrene-Tagged Grubbs Catalyst

For rapid and portable detection of ethylene in commercial fruit ripening storage rooms, we designed a smartphone-based optical fiber sensor (SOFS), which is composed of a 15 mW 365 nm laser for fluorescence signal excitation and a bifurcated fiber system for signal flow direction from probe to smartphone. Paired with a pyrene-tagged Grubbs catalyst (PYG) probe, our SOFS showed a wide linearity range up to 350 ppm with a detection limit of 0.6 ppm. The common gases in the warehouse had no significant interference with the results. The device is portable (18 cm × 8 cm × 6 cm) with an inbuilt power supply and replaceable optical fiber sensor tip. The images are processed with a dedicated smartphone application for RGB analysis and ethylene concentration. The device was applied in detection of ethylene generated from apples, avocados, and bananas. The linear correlation data showed agreement with data generated from a fluorometer. The SOFS provides a rapid, compact, cost-effective solution for determination of the fruit ethylene concentration dynamic during ripening for better fruit harvest timing and postharvest management to minimize wastage.

MdMADS6 Recruits Histone Deacetylase MdHDA19 to Repress the Expression of the Carotenoid Synthesis-Related Gene MdCCD1 during Fruit Ripening

Fruit ripening is regulated by epigenetic modifications and transcription factors, which may function independently or as protein complexes. Our previous study showed that the apple histone deacetylase19 (MdHDA19) suppresses fruit ripening through the deacetylation of histones in related genes. Here, a MADS-box transcription factor (MdMADS6) was identified using a yeast two-hybrid (Y2H) assay as a candidate protein that interacts with MdHDA19 during apple fruit ripening. Furthermore, Y2H, bimolecular fluorescence complementation (BiFC) and pull-down assays were used to confirm the interaction between MdHDA19 and MdMADS6. Agrobacterium-mediated transient transformation and yeast one-hybrid assays showed that MdMADS6 promoted carotenoid accumulation in apple fruit by acting on the downstream target genes related to carotenoid biosynthesis. In summary, we conclude that, in the early stages of fruit development, the expression of MdMADS6 was maintained at lower levels, where it interacted with MdHDA19 to form a protein complex that inhibited the expression of the downstream genes. At the late stages of fruit development, active expression of MdMADS6 dissociated the protein complex of MdMADS6 and MdHDA19 and consequently promoted the expression of carotenoid biosynthesis genes as well as carotenoid accumulation.

NAC Transcription Factor Family Regulation of Fruit Ripening and Quality: A Review

The NAC transcription factor (TF) family is one of the largest plant-specific TF families and its members are involved in the regulation of many vital biological processes during plant growth and development. Recent studies have found that NAC TFs play important roles during the ripening of fleshy fruits and the development of quality attributes. This review focuses on the advances in our understanding of the function of NAC TFs in different fruits and their involvement in the biosynthesis and signal transduction of plant hormones, fruit textural changes, color transformation, accumulation of flavor compounds, seed development and fruit senescence. We discuss the theoretical basis and potential regulatory models for NAC TFs action and provide a comprehensive view of their multiple roles in modulating different aspects of fruit ripening and quality.

The Emergence and Impact of Ethylene Scavengers Techniques in Delaying the Ripening of Fruits and Vegetables

As the top grocery list priorities, the primary challenge when purchasing fruits and vegetables from supermarkets is obtaining fresh, minimally processed perishable goods. This source of diet is critical for obtaining vitamins, minerals, antioxidants, and fibres. However, the short shelf life caused by moisture content in rapid deterioration and decay caused by microbial growth, results in unappealing appearances. Fruits and vegetables undergo ripening and eventually the ageing process, in which the tissues of the plants degrade. Even after harvesting, numerous biological processes occur, generating a significant variation of ethylene production along with respiration rates between fruits and vegetables. Thus, the utilization of ethylene scavengers in food packaging or films has been revealed to be beneficial. The synergistic effects of these biomaterials have been demonstrated to reduce microorganisms and prolong the shelf life of greens due to antimicrobial activity, oxygen scavenging capacity, enzyme immobilization, texture enhancers, and nutraceuticals. The current review fills this void by discussing the most recent advances in research on ethylene scavengers and removal mechanisms of ethylene, including oxidation in fruit and vegetable packaging. The application and advantages of ethylene scavengers in packaging are then discussed with the addition of how the efficiency related to ethylene scavengers can be increased through atmospheric packaging tools. In this context, the article discusses characteristics, types of applications, and efficacy of ethylene control strategies for perishable commodities with the inclusion of future implications.

Cucurbitaceae genome evolution, gene function and molecular breeding

The Cucurbitaceae is one of the most genetically diverse plant families in the world. Many of them are important vegetables or medicinal plants and are widely distributed worldwide. The rapid development of sequencing technologies and bioinformatic algorithms has enabled the generation of genome sequences of numerous important Cucurbitaceae species. This has greatly facilitated research on gene identification, genome evolution, genetic variation and molecular breeding of cucurbit crops. So far, genome sequences of 18 different cucurbit species belonging to tribes Benincaseae, Cucurbiteae, Sicyoeae, Momordiceae and Siraitieae have been deciphered. This review summarizes the genome sequence information, evolutionary relationship, and functional genes associated with important agronomic traits (e.g., fruit quality). The progress of molecular breeding in cucurbit crops and prospects for future applications of Cucurbitaceae genome information are also discussed.

QTL mapping and genomic analyses of earliness and fruit ripening traits in a melon Recombinant Inbred Lines population supported by de novo assembly of their parental genomes

Earliness and ripening behavior are important attributes of fruits on and off the vine, and affect quality and preference of both growers and consumers. Fruit ripening is a complex physiological process that involves metabolic shifts affecting fruit color, firmness, and aroma production. Melon is a promising model crop for the study of fruit ripening, as the full spectrum of climacteric behavior is represented across the natural variation. Using Recombinant Inbred Lines (RILs) population derived from the parental lines "Dulce" (reticulatus, climacteric) and "Tam Dew" (inodorus, non-climacteric) that vary in earliness and ripening traits, we mapped QTLs for ethylene emission, fruit firmness and days to flowering and maturity. To further annotate the main QTL intervals and identify candidate genes, we used Oxford Nanopore long-read sequencing in combination with Illumina short-read resequencing, to assemble the parental genomes de-novo. In addition to 2.5 million genome-wide SNPs and short InDels detected between the parents, we also highlight here the structural variation between these lines and the reference melon genome. Through systematic multi-layered prioritization process, we identified 18 potential polymorphisms in candidate genes within multi-trait QTLs. The associations of selected SNPs with earliness and ripening traits were further validated across a panel of 177 diverse melon accessions and across a diallel population of 190 F1 hybrids derived from a core subset of 20 diverse parents. The combination of advanced genomic tools with diverse germplasm and targeted mapping populations is demonstrated as a way to leverage forward genetics strategies to dissect complex horticulturally important traits.

Multi-omics data integration provides insights into the post-harvest biology of a long shelf-life tomato landrace

In this study we investigated the transcriptome and epigenome dynamics of the tomato fruit during post-harvest in a landrace belonging to a group of tomatoes (Solanum lycopersicum L.) collectively known as "Piennolo del Vesuvio", all characterized by a long shelf-life. Expression of protein-coding genes and microRNAs as well as DNA methylation patterns and histone modifications were analysed in distinct post-harvest phases. Multi-omics data integration contributed to the elucidation of the molecular mechanisms underlying processes leading to long shelf-life. We unveiled global changes in transcriptome and epigenome. DNA methylation increased and the repressive histone mark H3K27me3 was lost as the fruit progressed from red ripe to 150 days post-harvest. Thousands of genes were differentially expressed, about half of which were potentially epi-regulated as they were engaged in at least one epi-mark change in addition to being microRNA targets in ~5% of cases. Down-regulation of the ripening regulator MADS-RIN and of genes involved in ethylene response and cell wall degradation was consistent with the delayed fruit softening. Large-scale epigenome reprogramming that occurred in the fruit during post-harvest likely contributed to delayed fruit senescence.

APETALA2/ethylene responsive factor in fruit ripening: Roles, interactions and expression regulation

Insects and animals are attracted to, and feed on ripe fruit, thereby promoting seed dispersal. As a vital vitamin and nutrient source, fruit make up an indispensable and enjoyable component of the human diet. Fruit ripening involves a series of physiological and biochemical changes in, among others, pigmentation, chlorophyll (Chl) degradation, texture, sugar accumulation, and flavor. Growing evidence indicates that the coordinated and ordered trait changes during fruit ripening depend on a complex regulatory network consisting of transcription factors, co-regulators, hormonal signals, and epigenetic modifications. As one of the predominant transcription factor families in plants and a downstream component of ethylene signaling, more and more studies are showing that APETALA2/ethylene responsive factor (AP2/ERF) family transcription factors act as critical regulators in fruit ripening. In this review, we focus on the regulatory mechanisms of AP2/ERFs in fruit ripening, and in particular the recent results on their target genes and co-regulators. We summarize and discuss the role of AP2/ERFs in the formation of key fruit-ripening attributes, the enactment of their regulatory mechanisms by interaction with other proteins, their role in the orchestration of phytohormone-signaling networks, and the epigenetic modifications associated with their gene expression. Our aim is to provide a multidimensional perspective on the regulatory mechanisms of AP2/ERFs in fruit ripening, and a reference for understanding and furthering research on the roles of AP2/ERF in fruit ripening.

Triggered and controlled release of active gaseous/volatile compounds for active packaging applications of agri-food products: A review

Gaseous and volatile active compounds are versatile to enhance safety and preserve quality of agri-food products during storage and distribution. However, the use of these compounds is limited by their high vapor pressure and/or chemical instability, especially in active packaging (AP) applications. Various approaches for stabilizing and controlling the release of active gaseous/volatile compounds have been developed, including encapsulation (e.g., into supramolecular matrices, polymer-based films, electrospun nonwovens) and triggered release systems involving precursor technology, thereby allowing their safe and effective use in AP applications. In this review, encapsulation technologies of gases (e.g., CO₂ , ClO₂ , SO₂ , ethylene, 1-methylcyclopropene) and volatiles (e.g., ethanol, ethyl formate, essential oils and their constituents) into different solid matrices, polymeric films, and electrospun nonwovens are reviewed, especially with regard to encapsulation mechanisms and controlled release properties. Recent developments on utilizing precursor compounds of bioactive gases/volatiles to enhance their storage stability and better control their release profiles are discussed. The potential applications of these controlled release systems in AP of agri-food products are presented as well.

Consensus co-expression network analysis identifies AdZAT5 regulating pectin degradation in ripening kiwifruit

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CCNA was advanced by introducing physiological traits.

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Six cell wall genes and four transcription factors were identified for pectin degradation.

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A series of experiments validated the regulations of AdZAT5 on AdPL5 and Adβ-Gal5.

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CCNA would be powerful for phishing the unknown regulators with higher efficiency and accuracy.

Introduction

Cell wall degradation and remodeling is the key factor causing fruit softening during ripening.

Objectives

To explore the mechanism underlying postharvest cell wall metabolism, a transcriptome analysis method for more precious prediction on functional genes was needed.

Methods

Kiwifruits treated by ethylene (a conventional and effective phytohormone to accelerate climacteric fruit ripening and softening as kiwifruits) or air were taken as materials. Here, Consensus Coexpression Network Analysis (CCNA), a procedure evolved from Weighted Gene Co-expression Network Analysis (WGCNA) package in R, was applied and generated 85 consensus clusters from twelve transcriptome libraries. Advanced and comprehensive modifications were achieved by combination of CCNA and WGCNA with introduction of physiological traits, including firmness, cell wall materials, cellulose, hemicellulose, water soluble pectin, covalent binding pectin and ionic soluble pectin.

Results

As a result, six cell wall metabolisms related structural genes AdGAL1, AdMAN1, AdPL1, AdPL5, Adβ-Gal5, AdPME1 and four transcription factors AdZAT5, AdDOF3, AdNAC083, AdMYBR4 were identified as hub candidate genes for pectin degradation. Dual-luciferase system and electrophoretic mobility shift assays validated that promoters of AdPL5 and Adβ-Gal5 were recognized and trans-activated by transcription factor AdZAT5. The relatively higher enzyme activities of PL and β-Gal were observed in ethylene treated kiwifruit, further emphasized the critical roles of these two pectin related genes for fruit softening. Moreover, stable transient overexpression AdZAT5 in kiwifruit significantly enhanced AdPL5 and Adβ-Gal5 expression, which confirmed the in vivo regulations between transcription factor and pectin related genes.

Conclusion

Thus, modification and application of CCNA would be powerful for the precious phishing the unknown regulators. It revealed that AdZAT5 is a key factor for pectin degradation by binding and regulating effector genes AdPL5 and Adβ-Gal5.

An ethylene-hypersensitive methionine sulfoxide reductase regulated by NAC transcription factors increases methionine pool size and ethylene production during kiwifruit ripening

Ethylene plays an important role in regulating fruit ripening by triggering dynamic changes in expression of ripening-associated genes, but the functions of many of these genes are still unknown. Here, a methionine sulfoxide reductase gene (AdMsrB1) was identified by transcriptomics-based analysis as the gene most responsive to ethylene treatment in ripening kiwifruit. The AdMsrB1 protein exhibits a stereospecific activity toward the oxidative stress-induced R enantiomer of methionine sulfoxide (MetSO), reducing it to methionine (Met). Stable overexpression of AdMsrB1 in kiwifruit significantly increased the content of free Met and 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, and increased ethylene production. Dual-luciferase assays indicated that the AdMsrB1 promoter was not directly upregulated by ethylene treatment but was modulated by two ethylene-inducible NAM/ATAF/CUC transcription factors (AdNAC2 and AdNAC72) that bind directly to the AdMsrB1 promoter. Overexpression of AdNAC72 in kiwifruit not only enhanced AdMsrB1 expression, but also increased free Met and ACC content and ethylene production rates. This finding establishes an unexpected regulatory loop that enhances ethylene production and the concentration of its biosynthetic intermediates.

Transcriptome analysis of low-temperature-affected ripening revealed MYB transcription factors-mediated regulatory network in banana fruit

Low temperature leads to abnormal ripening and poor quality of the harvested banana fruit, which is an urgent problem limiting the development of industry in China. To comprehensively understand the mechanism underlying low-temperature-affected ripening, we performed comparative RNA-Seq analysis of ethylene-induced ripening of banana fruit after 3 days of pre-storage at 7 °C and 22 °C. A total of 986 differentially expressed genes (DEGs) were identified in both RT-0 d versus RT-3 d, LT-0 d versus LT-3 d, RT-0 d versus LT-0 d and RT-3 d versus LT-3 d, and the RNA-Seq outputs of 15 randomly selective DEGs were verified using qRT-PCR. Among the 986 DEGs obtained in the four groups, 9 MYB genes (MaMYB75/281/219/4/151/156/3/37 and MaMYB3R1) and 32 genes related to carotenoid biosynthesis (MaPSY1/2a), flavor formation (MaLOX6, MaADH7, MaAAT1), sucrose transport (MaSUS2/4), ethylene production (MaSAM1, MaACO9/10/12, MaACS1/12), starch degradation (MaAMY1A/1B, MaPHS1/2, MaMEX2, MapGlcT1) and cell wall degradation (MaPG3/X1, MaPME25/41, MaXTH5/7/22/23/25, MaEXP2/20/A1/A15) were characterized. Combining transcription factor binding site (TFBS) analysis as well as cis-acting element analysis, the regulatory network of low-temperature-affected ripening mediated by MYBs were constructed. The data generated in this study may unravel the transcriptional regulatory network of MYBs associated with low-temperature-affected ripening and provide a solid foundation for future studies.

Systems Biology Applied to the Study of Papaya Fruit Ripening: The Influence of Ethylene on Pulp Softening

Papaya is a fleshy fruit that undergoes fast ethylene-induced modifications. The fruit becomes edible, but the fast pulp softening is the main factor that limits the post-harvest period. Papaya fast pulp softening occurs due to cell wall disassembling coordinated by ethylene triggering that massively expresses pectinases. In this work, RNA-seq analysis of ethylene-treated and non-treated papayas enabled a wide transcriptome overview that indicated the role of ethylene during ripening at the gene expression level. Several families of transcription factors (AP2/ERF, NAC, and MADS-box) were differentially expressed. ACO, ACS, and SAM-Mtase genes were upregulated, indicating a high rate of ethylene biosynthesis after ethylene treatment. The correlation among gene expression and physiological data demonstrated ethylene treatment can indeed simulate ripening, and regulation of changes in fruit color, aroma, and flavor could be attributed to the coordinated expression of several related genes. Especially about pulp firmness, the identification of 157 expressed genes related to cell wall metabolism demonstrated that pulp softening is accomplished by a coordinated action of several different cell wall-related enzymes. The mechanism is different from other commercially important fruits, such as strawberry, tomato, kiwifruit, and apple. The observed behavior of this new transcriptomic data confirms ethylene triggering is the main event that elicits fast pulp softening in papayas.

A tomato LATERAL ORGAN BOUNDARIES transcription factor, SlLOB1, predominantly regulates cell wall and softening components of ripening

A tomato fruit ripening–specific transcription factor, SlLOB1 predominantly influences fruit cell wall–related gene regulation and textural changes during fruit maturation and thus is distinct from broadly acting ripening transcription factors described to date that influence many ripening processes. As such, SlLOB1 is an intermediate regulator primarily influencing a physiological subdomain of the overall ripening transition.

Fruit softening is a key component of the irreversible ripening program, contributing to the palatability necessary for frugivore-mediated seed dispersal. The underlying textural changes are complex and result from cell wall remodeling and changes in both cell adhesion and turgor. While a number of transcription factors (TFs) that regulate ripening have been identified, these affect most canonical ripening-related physiological processes. Here, we show that a tomato fruit ripening–specific LATERAL ORGAN BOUNDRIES (LOB) TF, SlLOB1, up-regulates a suite of cell wall–associated genes during late maturation and ripening of locule and pericarp tissues. SlLOB1 repression in transgenic fruit impedes softening, while overexpression throughout the plant under the direction of the 35s promoter confers precocious induction of cell wall gene expression and premature softening. Transcript and protein levels of the wall-loosening protein EXPANSIN1 (EXP1) are strongly suppressed in SlLOB1 RNA interference lines, while EXP1 is induced in SlLOB1-overexpressing transgenic leaves and fruit. In contrast to the role of ethylene and previously characterized ripening TFs, which are comprehensive facilitators of ripening phenomena including softening, SlLOB1 participates in a regulatory subcircuit predominant to cell wall dynamics and softening.

Molecular and Hormonal Mechanisms Regulating Fleshy Fruit Ripening

This article focuses on the molecular and hormonal mechanisms underlying the control of fleshy fruit ripening and quality. Recent research on tomato shows that ethylene, acting through transcription factors, is responsible for the initiation of tomato ripening. Several other hormones, including abscisic acid (ABA), jasmonic acid (JA) and brassinosteroids (BR), promote ripening by upregulating ethylene biosynthesis genes in different fruits. Changes to histone marks and DNA methylation are associated with the activation of ripening genes and are necessary for ripening initiation. Light, detected by different photoreceptors and operating through ELONGATED HYPOCOTYL 5(HY5), also modulates ripening. Re-evaluation of the roles of 'master regulators' indicates that MADS-RIN, NAC-NOR, Nor-like1 and other MADS and NAC genes, together with ethylene, promote the full expression of genes required for further ethylene synthesis and change in colour, flavour, texture and progression of ripening. Several different types of non-coding RNAs are involved in regulating expression of ripening genes, but further clarification of their diverse mechanisms of action is required. We discuss a model that integrates the main hormonal and genetic regulatory interactions governing the ripening of tomato fruit and consider variations in ripening regulatory circuits that operate in other fruits.