'Movers and shakers' in the regulation of fruit ripening: a cross-dissection of climacteric versus non-climacteric fruit

Transcriptomic and metabolomic analyses reveal the importance of ethylene networks in mulberry fruit ripening

Mulberry (Morus alba L.) is a climacteric and highly perishable fruit. Ethylene has been considered to be an important trigger of fruit ripening process. However, the role of ethylene in the mulberry fruit ripening process remains unclear. In this study, we performed a comprehensive analysis of metabolomic and transcriptomic data of mulberry fruit and the physiological changes accompanying the fruit ripening process. Our study revealed that changes in the accumulation of specific metabolites at different stages of fruit development and ripening were closely correlated to transcriptional changes as well as underlying physiological changes and the development of taste biomolecules. The ripening of mulberry fruits was highly associated with the production of endogenous ethylene, and further application of exogenous ethylene assisted the ripening process. Transcriptomic analysis revealed that differential expression of diverse ripening-related genes was involved in sugar metabolism, anthocyanin biosynthesis, and cell wall modification pathways. Network analysis of transcriptomics and metabolomics data revealed that many transcription factors and ripening-related genes were involved, among which ethylene-responsive transcription factor 3 (MaERF3) plays a crucial role in the ripening process. The role of MaERF3 in ripening was experimentally proven in a transient overexpression assay in apples. Our study indicates that ethylene plays a vital role in modulating mulberry fruit ripening. The results provide a basis for guiding the genetic manipulation of mulberry fruits towards sustainable agricultural practices and improve post-harvest management, potentially enhancing the quality and shelf life of mulberry fruits for sustainable agriculture and forestry.

Ethylene biosynthesis and signal transduction during ripening and softening in non-climacteric fruits: an overview

In recent years, the ethylene-mediated ripening and softening of non-climacteric fruits have been widely mentioned. In this paper, recent research into the ethylene-mediated ripening and softening of non-climacteric fruits is summarized, including the involvement of ethylene biosynthesis and signal transduction. In addition, detailed studies on how ethylene interacts with other hormones to regulate the ripening and softening of non-climacteric fruits are also reviewed. These findings reveal that many regulators of ethylene biosynthesis and signal transduction are linked with the ripening and softening of non-climacteric fruits. Meanwhile, the perspectives of future research on the regulation of ethylene in non-climacteric fruit are also proposed. The overview of the progress of ethylene on the ripening and softening of non-climacteric fruit will aid in the identification and characterization of key genes associated with ethylene perception and signal transduction during non-climacteric fruit ripening and softening.

The Expression of Key Ethylene and Anthocyanin Biosynthetic Genes of 'Honeycrisp' Apples Subjected to the Combined Use of Reflective Groundcovers and Aminoethoxyvinylglycine in the Mid-Atlantic US

The decreased profitability of important apple cultivars, such as 'Honeycrisp', results from the poor red skin coloration and high fruit drop in the mid-Atlantic US. Apple red skin coloration is determined by the anthocyanin concentration. Reflective groundcovers promote red skin coloration, whereas aminoethoxyvinylglycine (AVG) decreases the ethylene production and fruit drop, thus reducing the coloration. Although our previous study showed that combinations of these practices impact the fruit quality and color, research is lacking regarding their effects at the gene and metabolite levels. In this work, for two years, we compared the differences in the internal ethylene concentration (IEC), red skin coloration, fruit drop, transcript accumulation of key ethylene and anthocyanin biosynthetic pathway-related genes, and total anthocyanin concentration of 'Honeycrisp' apples. The fruit was treated with combinations of reflective groundcover (Extenday) and AVG (130 mg L-1) and was assessed throughout ripening. Extenday-only-treated fruit displayed the highest upregulation of ethylene and anthocyanin biosynthetic-related genes and of total anthocyanins, exceeding 50% blush, while boosting the IEC. In contrast, AVG significantly decreased the expression of key ethylene and anthocyanin biosynthetic-related genes and total anthocyanins, thus preventing apples from reaching 50% blush, while also decreasing the IEC and fruit drop. The combination of Extenday x AVG fine-tuned the transcript accumulation of ethylene and anthocyanin biosynthetic-related genes as well as the total anthocyanins, allowing the 'Honeycrisp' fruit to exceed 50% blush, while increasing the IEC moderately and reducing the fruit drop (as compared to Extenday-only and control), thus enhancing the fruit economic value.

The roles of non-structural carbohydrates in fruiting: a review focusing on mango (Mangifera indica)

Reproductive development of fruiting trees, including mango (Mangifera indica L.), is limited by non-structural carbohydrates. Competition for sugars increases with cropping, and consequently, vegetative growth and replenishment of starch reserves may reduce with high yields, resulting in interannual production variability. While the effect of crop load on photosynthesis and the distribution of starch within the mango tree has been studied, the contribution of starch and sugars to different phases of reproductive development requires attention. This review focuses on mango and examines the roles of non-structural carbohydrates in fruiting trees to clarify the repercussions of crop load on reproductive development. Starch buffers the plant's carbon availability to regulate supply with demand, while sugars provide a direct resource for carbon translocation. Sugar signalling and interactions with phytohormones play a crucial role in flowering, fruit set, growth, ripening and retention, as well as regulating starch, sugar and secondary metabolites in fruit. The balance between the leaf and fruit biomass affects the availability and contributions of starch and sugars to fruiting. Crop load impacts photosynthesis and interactions between sources and sinks. As a result, the onset and rate of reproductive processes are affected, with repercussions for fruit size, composition, and the inter-annual bearing pattern.

Tracking the Variations in Trace Elements, Some Nutrients, Phenolics, and Anthocyanins in Grewia asiatica L. (Phalsa) at Different Fruit Development Stages

Grewia asiatica L. (phalsa) is a very prevalent berry in Pakistan and is consumed extensively as raw or in the form of juice. Here, for the first time, we assessed phalsa from Pakistan in terms of variations in macro and micro minerals, nutrients, and bio-active phyto-constituents including total phenolic and anthocyanin contents at different fruit developmental stages. It was found that the sugars in phalsa increased from D1 (small at the initial fruit setting stage) to D6 development stage (fully ripened fruit) where sugars at D5 (near to fully ripe) and D6 stages were many times greater than at D1, D2 (unripe close to full-size completion), D3 (close to semi ripe), and D4 stage (semi ripened and full-size attainment). Total acidity of was declined in all developmental stages, where the D1 stage displayed maximum and D6 with the lowest acidity. Ascorbic acid was decreased from D1 to D2 and then increased gradually from D3 to D5 stages. At the D6 stage, again a steep decline in ascorbic acid was observed. The total phenolics (mg gallic acid equivalents/100g) at stage D6 were higher (136.02 ± 1.17), whereas D1 being the lowermost in total phenolic content (79.89 ± 1.72). For anthocyanins (mg/100g), an increasing pattern of changes was observed in all stages of phalsa fruit where the D1 stage showed lower (13.97 ± 4.84) anthocyanin contents which then increased gradually at stage D2 (67.79 ± 6.73), but increased sharply at D3 (199.66 ± 4.90), D4 (211.02 ± 18.85), D5 (328.41 ±14.96) and D6 (532.30 ± 8.51) stages. A total of four anthocyanins such as cyanidin, delphidine-3-glucoside, pelargonidin, and malvidin in phalsa were identified using HPLC procedures, and a significant > 90 % DPPH inhibition in phalsa was observed at the D5 and D6 development stages. The macro and micro minerals including Ni, Zn, Fe, Ca, Cu, Mg, Na, P, and K contents were decreased from initial (D1) stage to the final (D6) development stage, while only Fe displayed an increasing trend from the initial to final fruit development stages (D1-D6). Conclusively, these findings could be of great interest for patients who are intended to consume phalsa as adjuvant therapy against diabetes and metabolic syndromes and other diseases involving reactive oxygen species with minimum metal toxicity.

Characterization and Potential Action Mode Divergences of Homologous ACO1 Genes during the Organ Development and Ripening Process between Non-Climacteric Grape and Climacteric Peach

Ethylene is one crucial phytohormone modulating plants' organ development and ripening process, especially in fruits, but its action modes and discrepancies in non-climacteric grape and climacteric peach in these processes remain elusive. This work is focused on the action mode divergences of ethylene during the modulation of the organ development and ripening process in climacteric/non-climacteric plants. We characterized the key enzyme genes in the ethylene synthesis pathway, VvACO1 and PpACO1, and uncovered that their sequence structures are highly conserved, although their promoters exhibit important divergences in the numbers and types of the cis-elements responsive to hormones, implying various responses to hormone signals. Subsequently, we found the two have similar expression modes in vegetative organ development but inverse patterns in reproductive ones, especially in fruits. Then, VvACO1 and PpACO1 were further validated in promoting fruit ripening functions through their transient over-expression/RNAi-expression in tomatoes, of which the former possesses a weaker role than the latter in the fruit ripening process. Our findings illuminated the divergence in the action patterns and function traits of the key VvACO1/PpACO1 genes in the tissue development of climacteric/non-climacteric plants, and they have implications for further gaining insight into the interaction mechanism of ethylene signaling during the modulation of the organ development and ripening process in climacteric/non-climacteric plants.

Dynamic shifts in primary metabolism across fruit development stages in Capsicum chinense (cv. Habanero)

The development of fleshy fruits involves changes in size and mass, followed by cell differentiation, which is associated with anatomical and histological changes. Parallel to these changes, metabolic alterations lead to the production of osmolytes and energy that modify cell turgor pressure, thereby promoting cell expansion and fruit growth. Detailed information is known about these processes in climacteric fruits (e.g. tomato); however, the regulation of metabolism and its association with anatomical changes in non-climacteric fruit development are poorly understood. In this study, we used detailed anatomical and histological analyses to define three developmental phases of chili pepper (Capsicum chinense cv. Habanero): cell division, cell expansion, and ripening. We showed that each was marked by distinct metabolic profiles, underpinning the switches in energy metabolism to support cellular processes. Interestingly, mitochondrial activity was high in the early stages of development and declined over time, with a modest increase in O2 consumption by pericarp tissues at the beginning of the ripening stage. This respiratory-like burst was associated with the degradation of starch and malate, which are the sources of energy and carbon required for other processes associated with fruit maturation.

Molecular regulation of apple and grape ripening: exploring common and distinct transcriptional aspects of representative climacteric and non-climacteric fruits

Fleshy fruits of angiosperms are organs specialized for promoting seed dispersal by attracting herbivores and enticing them to consume the organ and the seeds it contains. Ripening can be broadly defined as the processes serving as a plant strategy to make the fleshy fruit appealing to animals, consisting of a coordinated series of changes in color, texture, aroma, and flavor that result from an intricate interplay of genetically and epigenetically programmed events. The ripening of fruits can be categorized into two types: climacteric, which is characterized by a rapid increase in respiration rate typically accompanied by a burst of ethylene production, and non-climacteric, in which this pronounced peak in respiration is absent. Here we review current knowledge of transcriptomic changes taking place in apple (Malus × domestica, climacteric) and grapevine (Vitis vinifera, non-climacteric) fruit during ripening, with the aim of highlighting specific and common hormonal and molecular events governing the process in the two species. With this perspective, we found that specific NAC transcription factor members participate in ripening initiation in grape and are involved in restoring normal physiological ripening progression in impaired fruit ripening in apple. These elements suggest the existence of a common regulatory mechanism operated by NAC transcription factors and auxin in the two species.

Induced Resistance in Fruit and Vegetables: A Host Physiological Response Limiting Postharvest Disease Development

Harvested fruit and vegetables are perishable, subject to desiccation, show increased respiration during ripening, and are colonized by postharvest fungal pathogens. Induced resistance is a strategy to control diseases by eliciting biochemical processes in fruits and vegetables. This is accomplished by modulating the progress of ripening and senescence, which maintains the produce in a state of heightened resistance to decay-causing fungi. Utilization of induced resistance to protect produce has been improved by scientific tools that better characterize physiological changes in plants. Induced resistance slows the decline of innate immunity after harvest and increases the production of defensive responses that directly inhibit plant pathogens. This increase in defense response in fruits and vegetables contributes to higher amounts of phenols and antioxidant compounds, improving both the quality and appearance of the produce. This review summarizes mechanisms and treatments that induce resistance in harvested fruits and vegetables to suppress fungal colonization. Moreover, it highlights the importance of host maturity and stage of ripening as limiting conditions for the improved expression of induced-resistance processes.

Changes in the Fruit Quality Parameters of Medlar Fruit (Mespilus germanica L.) after Heat Treatment, Storage, Freezing or Hoarfrost

The present study deals with the comparison of traditional fruit processing methods on medlar fruits and their effects on sugar content, organic acids, and phenolic composition in the medlar fruit variety 'Domača nešplja'. The study aimed to analyze which processing methods can be used to make technologically mature medlar fruits that are not yet suitable for consumption edible and to maintain their good chemical quality. The two major sugars in medlars are fructose (59.30 g/kg FW) and glucose (54.43 g/kg FW), and the most abundant organic acids present are malic (8.44 g/kg FW) and quinic acid (8.77 g/kg FW). A total of 38 different phenolic compounds were identified in the medlar fruits: 13 phenolic acids, 9 flavanols, 1 flavone, 3 flavanones, and 12 flavonol glycosides. To explicate: phenolic acids (532.85 mg/kg FW) and flavanols (375.21 mg/kg FW) predominated; neochlorogenic acid had the highest content among phenolic acids; and procyanidins were the most abundant flavanols. The analysis observed statistical differences in metabolite content amongst fruits treated differently (technologically ripe fruits (harvested from the three fruits), edible fruits (technologically ripe fruits stored at 8 °C for 25 days), fruits exposed to the hoarfrost (temperature -1 °C to -4 °C), fruits heated at 60 °C (3 h), and frozen fruits (at -20 °C for 2 months). The lowest levels of fructose (191.77-195.1 g/kg DW) and sorbitol (29.35-31.3 g/kg DW) were detected in the heated and edible fruits. Edible fruits had a 30% lower content of organic acids than technologically ripe fruits and a five times lower content of flavanols, whereas flavonols had an 18.7 times lower content of phenolic acids than technologically ripe fruits. Heating the fruits to 60 °C resulted in a 40% increase in total phenolic compounds in medlars. The results of the study indicate that exposure of medlar fruit to hoarfrost does not significantly affect the chemical quality of the fruit and only minimally alters the composition of sugars, acids, and phenolic compounds. The processing of medlar fruit with hoarfrost, therefore, remains the most suitable method of fruit bletting.

Current insights into posttranscriptional regulation of fleshy fruit ripening

Fruit ripening is a complicated process that is accompanied by the formation of fruit quality. It is not only regulated at the transcriptional level via transcription factors or DNA methylation but also fine-tuned after transcription occurs. Here, we review recent advances in our understanding of key regulatory mechanisms of fleshy fruit ripening after transcription. We mainly highlight the typical mechanisms by which fruit ripening is controlled, namely, alternative splicing, mRNA N6-methyladenosine RNA modification methylation, and noncoding RNAs at the posttranscriptional level; regulation of translation efficiency and upstream open reading frame-mediated translational repression at the translational level; and histone modifications, protein phosphorylation, and protein ubiquitination at the posttranslational level. Taken together, these posttranscriptional regulatory mechanisms, along with transcriptional regulation, constitute the molecular framework of fruit ripening. We also critically discuss the potential usage of some mechanisms to improve fruit traits.

FvWRKY50 is an important gene that regulates both vegetative growth and reproductive growth in strawberry

The WRKY transcription factors play important roles in plant growth and resistance, but only a few members have been identified in strawberry. Here we identified a WRKY transcription factor, FvWRKY50, in diploid strawberry which played essential roles in strawberry vegetative growth, and reproductive growth. Knocking out FvWRKY50 by genome editing accelerated flowering time and leaf senescence but delayed anthocyanin accumulation in fruit. Further analysis showed that FvWRKY50 acted as a transcriptional repressor to negatively regulate the expression of flowering- and leaf senescence-related genes, including FvFT2, FvCO, FvFT3, and FvSAUR36. Notably, FvWRKY50 directly upregulated the expression of FvCHI and FvDFR by binding their promoter under normal conditions, but at low temperature FvWRKY50 was phosphorylated by FvMAPK3 and then induced protein degradation by ubiquitination, delaying anthocyanin accumulation. In addition, the homozygous mutant of FvWRKY50 was smaller while the biallelic mutant showed normal size. These new findings provide important clues for us to further reveal the regulatory mechanisms of strawberry growth and fruit ripening.

NADP-Dependent Malic Enzyme Genes in Sweet Pepper Fruits: Involvement in Ripening and Modulation by Nitric Oxide (NO)

NADPH is an indispensable cofactor in a wide range of physiological processes that is generated by a family of NADPH dehydrogenases, of which the NADP-dependent malic enzyme (NADP-ME) is a member. Pepper (Capsicum annuum L.) fruit is a horticultural product consumed worldwide that has great nutritional and economic relevance. Besides the phenotypical changes that pepper fruit undergoes during ripening, there are many associated modifications at transcriptomic, proteome, biochemical and metabolic levels. Nitric oxide (NO) is a recognized signal molecule with regulatory functions in diverse plant processes. To our knowledge, there is very scarce information about the number of genes encoding for NADP-ME in pepper plants and their expression during the ripening of sweet pepper fruit. Using a data mining approach to evaluate the pepper plant genome and fruit transcriptome (RNA-seq), five NADP-ME genes were identified, and four of them, namely CaNADP-ME2 to CaNADP-ME5, were expressed in fruit. The time course expression analysis of these genes during different fruit ripening stages, including green immature (G), breaking point (BP) and red ripe (R), showed that they were differentially modulated. Thus, while CaNADP-ME3 and CaNADP-ME5 were upregulated, CaNADP-ME2 and CaNADP-ME4 were downregulated. Exogenous NO treatment of fruit triggered the downregulation of CaNADP-ME4. We obtained a 50-75% ammonium-sulfate-enriched protein fraction containing CaNADP-ME enzyme activity, and this was assayed via non-denaturing polyacrylamide gel electrophoresis (PAGE). The results allow us to identify four isozymes designated from CaNADP-ME I to CaNADP-ME IV. Taken together, the data provide new pieces of information on the CaNADP-ME system with the identification of five CaNADP-ME genes and how the four genes expressed in pepper fruits are modulated during ripening and exogenous NO gas treatment.

Abscisic Acid Synthesis and Signaling during the Ripening of Raspberry (Rubus idaeus 'Heritage') Fruit

The raspberry (Rubus idaeus L.) fruit is characterized by its richness in functional molecules and high nutritional value, but the high rate of fruit softening limits its quality during postharvest. Raspberry drupelets have a particular ripening regulation, depending partially on the effect of ethylene produced from the receptacle. However, the possible role of abscisic acid (ABA) in the modulation of quality parameters during the ripening of raspberry is unclear. This study characterized the fruit quality-associated parameters and hormonal contents during fruit development in two seasons. The quality parameters showed typical changes during ripening: a drastic loss of firmness, increase in soluble solids content, loss of acidity, and turning to a red color from the large green stage to fully ripe fruit in both seasons. A significant increase in the ABA content was observed during the ripening of drupelets and receptacles, with the higher content in the receptacle of ripe and overripe stages compared to the large green stage. Moreover, identification of ABA biosynthesis-(9-cis-epoxycarotenoid dioxygenase/NCED) and ABA receptor-related genes (PYRs-like receptors) showed three genes encoding RiNCEDs and nine genes for RiPYLs. The expression level of these genes increased from the large green stage to the full-ripe stage, specifically characterized by a higher expression of RiNCED1 in the receptacle tissue. This study reports a consistent concomitant increase in the ABA content and the expression of RiNCED1, RiPYL1, and RiPYL8 during the ripening of the raspberry fruit, thus supporting the role for ABA signaling in drupelets.

Molecular dynamics simulation of the interaction of a raspberry polygalacturonase (RiPG) with a PG inhibiting protein (RiPGIP) isolated from ripening raspberry (Rubus idaeus cv. Heritage) fruit as a model to understand proteins interaction during fruit softening

Polygalacturonase (PG) is an important hydrolytic enzyme involved in pectin disassembly and the subsequent textural changes during fruit ripening. Although the interaction of fungal PGs with other proteins has been documented, the interaction of plant PGs with other plant proteins has not yet been studied. In this study, the molecular mechanisms involved in raspberry fruit ripening, particularly the polygalacturonase (RiPG) interaction with polygalacturonase inhibiting protein (RiPGIP) and substrate, were investigated with a structural approach. The 3D model of RiPG2 and RiPGIP3 was built using a comparative modeling strategy and validated using molecular dynamics (MD) simulations. The RiPG2 model structure comprises 11 complete coils of right-handed parallel β-helix architecture, with an average of 27 amino acid residues per turn. The structural model of the RiPGIP3 displays a typical structure of LRR protein, with the right-handed superhelical fold with an extended parallel β-sheet. The conformational interaction between the RiPG2 protein and RiPGIP3 showed that RiPGIP3 could bind to the enzyme and thereby leave the active site cleft accessible to the substrate. All this evidence indicates that RiPG2 enzyme could interact with RiPGIP3 protein. It can be a helpful model for evaluating protein-protein interaction as a potential regulator mechanism of hydrolase activity during pectin disassembly in fruit ripening.

Effect of Methyl Jasmonate on the Biosynthesis of Volatile Compounds Associated with the Ripening of Grape Tomato Fruits

The present work aims to evaluate the roles of methyl jasmonate (MeJA) in the formation of volatile organic compounds (VOC) from grape tomatoes during ripening. Fruits were treated with MeJA, ethylene, 1-MCP (1-methylcyclopropene), and MeJA+1-MCP, with analyses of the VOC and levels of the gene transcripts for the enzymes lipoxygenase (LOX), alcohol dehydrogenase (ADH), and hydroperoxide lyase (HPL). An intimate relationship between MeJA and ethylene in aroma formation was detected, mainly among the VOC from the carotenoid pathway. Expression of the fatty acid transcripts, LOXC, ADH, and HPL pathway genes, was reduced by 1-MCP, even when associated with MeJA. In ripe tomato, MeJA increased most of the volatile C6 compounds, except 1-hexanol. The MeJA+1-MCP treatment followed most of the increases in volatile C6 compounds that were increased by MeJA alone, which evidenced some ethylene-independent mechanism in the production of the volatile C6 compounds. In ripe tomato, MeJA and MeJA+1-MCP increased the levels of 6-methyl-5-hepten-2-one, which is derived from lycopene, evidencing an ethylene-independent biosynthetic process.

Physiological and Metabolic Changes in Tamarillo (Solanum betaceum) during Fruit Ripening

Physiological and metabolic profiles in tamarillo were investigated to reveal the molecular changes during fruit maturation. The firmness, ethylene production, soluble sugar contents, and metabolomic analysis were determined in tamarillo fruit at different maturity stages. The firmness of tamarillo fruit gradually decreased during fruit ripening with increasing fructose and glucose accumulation. The rapid increase in ethylene production was found in mature fruit. Based on the untargeted metabolomic analysis, we found that amino acids, phospholipids, monosaccharides, and vitamin-related metabolites were identified as being changed during ripening. The contents of malic acid and citric acid were significantly decreased in mature fruits. Metabolites involved in phenylpropanoid biosynthesis, phenylalanine metabolism, caffeine metabolism, monoterpenoid biosynthesis, and thiamine metabolism pathways showed high abundance in mature fruits. However, we also found that most of the mature-enhanced metabolites showed reduced abundance in over-mature fruits. These results reveal the molecular profiles during tamarillo fruit maturing and suggest tamarillos have potential benefits with high nutrition and health function.

Applications of CRISPR/Cas genome editing in economically important fruit crops: recent advances and future directions

Fruit crops, consist of climacteric and non-climacteric fruits, are the major sources of nutrients and fiber for human diet. Since 2013, CRISPR/Cas (Clustered Regularly Interspersed Short Palindromic Repeats and CRISPR-Associated Protein) genome editing system has been widely employed in different plants, leading to unprecedented progress in the genetic improvement of many agronomically important fruit crops. Here, we summarize latest advancements in CRISPR/Cas genome editing of fruit crops, including efforts to decipher the mechanisms behind plant development and plant immunity, We also highlight the potential challenges and improvements in the application of genome editing tools to fruit crops, including optimizing the expression of CRISPR/Cas cassette, improving the delivery efficiency of CRISPR/Cas reagents, increasing the specificity of genome editing, and optimizing the transformation and regeneration system. In addition, we propose the perspectives on the application of genome editing in crop breeding especially in fruit crops and highlight the potential challenges. It is worth noting that efforts to manipulate fruit crops with genome editing systems are urgently needed for fruit crops breeding and demonstration.

Recent trends and advances of RNA interference (RNAi) to improve agricultural crops and enhance their resilience to biotic and abiotic stresses

Over the last two decades, significant advances have been made using genetic engineering technology to modify genes from various exotic origins and introduce them into plants to induce favorable traits. RNA interference (RNAi) was discovered earlier as a natural process for controlling the expression of genes across all higher species. It aims to enhance precision and accuracy in pest/pathogen resistance, quality improvement, and manipulating the architecture of plants. However, it existed as a widely used technique recently. RNAi technologies could well be used to down-regulate any genes' expression without disrupting the expression of other genes. The use of RNA interference to silence genes in various organisms has become the preferred method for studying gene functions. The establishment of new approaches and applications for enhancing desirable characters is essential in crops by gene suppression and the refinement of knowledge of endogenous RNAi mechanisms in plants. RNAi technology in recent years has become an important and choicest method for controlling insects, pests, pathogens, and abiotic stresses like drought, salinity, and temperature. Although there are certain drawbacks in efficiency of this technology such as gene candidate selection, stability of trigger molecule, choice of target species and crops. Nevertheless, from past decade several target genes has been identified in numerous crops for their improvement towards biotic and abiotic stresses. The current review is aimed to emphasize the research done on crops under biotic and abiotic stress using RNAi technology. The review also highlights the gene regulatory pathways/gene silencing, RNA interference, RNAi knockdown, RNAi induced biotic and abiotic resistance and advancements in the understanding of RNAi technology and the functionality of various components of the RNAi machinery in crops for their improvement.

An Integrated Metabolomic and Gene Expression Analysis of 'Sachinoka' Strawberry and Its Somaclonal Mutant Reveals Fruit Color and Volatiles Differences

Plant tissue culture produces a wide range of genetic variations which are useful for quality improvement of the plant species. However, the differences in metabolic components and the key genes responsible for the difference in metabolic components between somaclonal variation and the original parent are still largely unknown. In this study, a mutant named 'Mixue' was identified with somaclonal variation of the 'Sachinoka' strawberry. The contents of pelargonidin-3-O-glucoside and cyanidin-3-O-glucoside in the red fruit of 'Mixue' were significantly decreased compared with 'Sachinoka'. In comparison with 'Sachinoka', the expression levels of FaMYB10, FaMYB11.2, FaWD40 and FaTT19 in the turning fruit of 'Mixue' were significantly down-regulated, while the expression of FaMYB1 was significantly up-regulated in the red fruit. 'Sachinoka' and 'Mixue' fruits were found to have 110 volatile components. Among them, 15 volatile components in the red fruit of 'Mixue' were significantly increased compared with 'Sachinoka', such as nerolidol, benzaldehyde, ethyl hexanoate, ethyl isovalerate, which led to an enhanced aroma in 'Mixue' and might result from the up-regulated expression of FaNES1, FaCNL and FaAATs in 'Mixue'. These results provide useful information on the effect of somaclonal variation on metabolic components of strawberry fruit and lay the foundation for the improvement in quality of strawberry.

FvNST1b NAC Protein Induces Secondary Cell Wall Formation in Strawberry

Secondary cell wall thickening plays a crucial role in plant growth and development. Diploid woodland strawberry (Fragaria vesca) is an excellent model for studying fruit development, but its molecular control of secondary wall thickening is largely unknown. Previous studies have shown that Arabidopsis NAC secondary wall thickening promoting factor1 (AtNST1) and related proteins are master regulators of xylem fiber cell differentiation in multiple plant species. In this study, a NST1-like gene, FvNST1b, was isolated and characterized from strawberry. Sequence alignment and phylogenetic analysis showed that the FvNST1b protein contains a highly conserved NAC domain, and it belongs to the same family as AtNST1. Overexpression of FvNST1b in wild-type Arabidopsis caused extreme dwarfism, induced ectopic thickening of secondary walls in various tissues, and upregulated the expression of genes related to secondary cell wall synthesis. In addition, transient overexpression of FvNST1b in wild-type Fragaria vesca fruit produced cells resembling tracheary elements. These results suggest that FvNST1b positively regulates secondary cell wall formation as orthologous genes from other species.

Copper Amine Oxidase (CuAO)-Mediated Polyamine Catabolism Plays Potential Roles in Sweet Cherry (Prunus avium L.) Fruit Development and Ripening

Copper amine oxidases (CuAOs) play important roles in PA catabolism, plant growth and development, and abiotic stress response. In order to better understand how PA affects cherry fruit, four potential PavCuAO genes (PavCuAO1–PavCuAO4) that are dispersed over two chromosomes were identified in the sweet cherry genome. Based on phylogenetic analysis, they were classified into three subclasses. RNA-seq analysis showed that the PavCuAO genes were tissue-specific and mostly highly expressed in flowers and young leaves. Many cis-elements associated with phytohormones and stress responses were predicted in the 2 kb upstream region of the promoter. The PavCuAOs transcript levels were increased in response to abscisic acid (ABA) and gibberellin 3 (GA₃) treatments, as well as abiotic stresses (NaCl, PEG, and cold). Quantitative fluorescence analysis and high-performance liquid chromatography confirmed that the Put content fell, and the PavCuAO4 mRNA level rose as the sweet cherry fruit ripened. After genetically transforming Arabidopsis with PavCuAO4, the Put content in transgenic plants decreased significantly, and the expression of the ABA synthesis gene NCED was also significantly increased. At the same time, excessive H₂O₂ was produced in PavCuAO4 transiently expressed tobacco leaves. The above results strongly proved that PavCuAO4 can decompose Put and may promote fruit ripening by increasing the content of ABA and H₂O₂ while suppressing total free PA levels in the fruit.

Interactions of melatonin, reactive oxygen species, and nitric oxide during fruit ripening: an update and prospective view

Fruit ripening is a physiological process that involves a complex network of signaling molecules that act as switches to activate or deactivate certain metabolic pathways at different levels, not only by regulating gene and protein expression but also through post-translational modifications of the involved proteins. Ethylene is the distinctive molecule that regulates the ripening of fruits, which can be classified as climacteric or non-climacteric according to whether or not, respectively, they are dependent on this phytohormone. However, in recent years it has been found that other molecules with signaling potential also exert regulatory roles, not only individually but also as a result of interactions among them. These observations imply the existence of mutual and hierarchical regulations that sometimes make it difficult to identify the initial triggering event. Among these 'new' molecules, hydrogen peroxide, nitric oxide, and melatonin have been highlighted as prominent. This review provides a comprehensive outline of the relevance of these molecules in the fruit ripening process and the complex network of the known interactions among them.

Signal transduction in non-climacteric fruit ripening

Fleshy fruit ripening involves changes in numerous cellular processes and metabolic pathways, resulting from the coordinated actions of diverse classes of structural and regulatory proteins. These include enzymes, transporters and complex signal transduction systems. Many aspects of the signaling machinery that orchestrates the ripening of climacteric fruits, such as tomato (Solanum lycopersicum), have been elucidated, but less is known about analogous processes in non-climacteric fruits. The latter include strawberry (Fragaria x ananassa) and grape (Vitis vinifera), both of which are used as non-climacteric fruit experimental model systems, although they originate from different organs: the grape berry is a true fruit derived from the ovary, while strawberry is an accessory fruit that is derived from the floral receptacle. In this article, we summarize insights into the signal transduction events involved in strawberry and grape berry ripening. We highlight the mechanisms underlying non-climacteric fruit ripening, the multiple primary signals and their integrated action, individual signaling components, pathways and their crosstalk, as well as the associated transcription factors and their signaling output.

Ripening of Pomegranate Skin as Revealed by Developmental Transcriptomics

The appearance of pomegranate (Punica granatum L.) fruit is highly important for its marketing. The primary concerns are obtaining sufficient red pigment accumulation and minimal cracking of the fruit skin (the outer red layer of the peel). We analyzed the skin transcriptome of pomegranate cv. Wonderful at distinct time points of fruit development to characterize the processes that occur in the skin during fruit ripening and which may reflect on processes in the whole fruit, such as the non-climacteric nature of pomegranate. The data suggested a ripening mechanism in pomegranate skin that differs from that in strawberry—the model plant for non-climacteric fruit where abscisic acid is the growth regulator that drives ripening—involving ethylene, polyamine, and jasmonic acid pathways. The biosynthetic pathways of important metabolites in pomegranate—hydrolyzable tannins and anthocyanins—were co-upregulated at the ripening stage, in line with the visual enhancement of red coloration. Interestingly, cuticle- and cell-wall-related genes that showed differential expression between the developmental stages were mainly upregulated in the skin of early fruit, with lower expression at mid-growth and ripening stages. Nevertheless, lignification may be involved in skin hardening in the mature fruit.

Atypical Climacteric and Functional Ethylene Metabolism and Signaling During Fruit Ripening in Blueberry (Vaccinium sp.)

Climacteric fruits display an increase in respiration and ethylene production during the onset of ripening, while such changes are minimal in non-climacteric fruits. Ethylene is a primary regulator of ripening in climacteric fruits. The ripening behavior and role of ethylene in blueberry (Vaccinium sp.) ripening is controversial. This work aimed to clarify the fruit ripening behavior and the associated role of ethylene in blueberry. Southern highbush (Vaccinium corymbosum hybrids) and rabbiteye (Vaccinium ashei) blueberry displayed an increase in the rate of respiration and ethylene evolution, both reaching a maxima around the Pink and Ripe stages of fruit development, consistent with climacteric fruit ripening behavior. Increase in ethylene evolution was associated with increases in transcript abundance of its biosynthesis genes, AMINOCYCLOPROPANE CARBOXYLATE (ACC) SYNTHASE1 (ACS1) and ACC OXIDASE2 (ACO2), implicating them in developmental ethylene production during ripening. Blueberry fruit did not display autocatalytic system 2 ethylene during ripening as ACS transcript abundance and ACC concentration were not enhanced upon treatment with an ethylene-releasing compound (ethephon). However, ACO transcript abundance was enhanced in response to ethephon, suggesting that ACO was not rate-limiting. Transcript abundance of multiple genes associated with ethylene signal transduction was upregulated concomitant with developmental increase in ethylene evolution, and in response to exogenous ethylene. As these changes require ethylene signal transduction, fruit ripening in blueberry appears to involve functional ethylene signaling. Together, these data indicate that blueberry fruit display atypical climacteric ripening, characterized by a respiratory climacteric, developmentally regulated but non-autocatalytic increase in ethylene evolution, and functional ethylene signaling.

Do Non-climacteric Fruits Share a Common Ripening Mechanism of Hormonal Regulation?

Fleshy fruits have been traditionally categorized into climacteric (CL) and non-climacteric (NC) groups. CL fruits share a common ripening mechanism of hormonal regulation, i.e., the ethylene regulation, whereas whether NC fruits share a common mechanism remains controversial. Abscisic acid (ABA) has been commonly thought to be a key regulator in NC fruit ripening; however, besides ABA, many other hormones have been increasingly suggested to play crucial roles in NC fruit ripening. NC fruits vary greatly in their organ origin, constitution, and structure. Development of different organs may be different in the pattern of hormonal regulation. It has been well demonstrated that the growth and development of strawberry, the model of NC fruits, is largely controlled by a hormonal communication between the achenes and receptacle; however, not all NC fruits contain achenes. Accordingly, it is particularly important to understand whether strawberry is indeed able to represent a universal mechanism for the hormonal regulation of NC fruit ripening. In this mini-review, we summarized the recent research advance on the hormone regulation of NC ripening in relation to fruit organ origination, constitution, and structure, whereby analyzing and discussing whether NC fruits may share a common mechanism of hormonal regulation.

Effect of Magnetic and Electrical Fields on Yield, Shelf Life and Quality of Fruits

The presented article is a review of the literature reports on the influence of magnetic and electric fields on the growth, yield, ripening, and durability of fruits and their quality. The article shows the potential application of MF and EF in agricultural production. Magnetic and electrical fields increase the shelf life of the fruit and improve its quality. Alternating magnetic fields (AMF) with a value of 0.1–200 mT and a power frequency of 50 Hz or 60 Hz improve plant growth parameters. MF cause an increase in firmness, the rate of maturation, the content of beta-carotene, lycopene, and fructose, sugar concentration, and a reduction in acidity and respiration. The most common is a high-voltage electric field (HVEF) of 2–3.61 kV/cm. These fields extend the shelf life and improve the quality of fruit by decreasing respiration rate and ethylene production. The presented methods seem to be a promising way to increase the quantity and quality of crops in agricultural and fruit production. They are suitable for extending the shelf life of fruit and vegetables during their storage. Further research is needed to develop an accessible and uncomplicated way of applying MF and AEF in agricultural and fruit production.

Autocatalytic biosynthesis of abscisic acid and its synergistic action with auxin to regulate strawberry fruit ripening

Abscisic acid (ABA) plays a major role in the regulation of strawberry fruit ripening; however, the origin of the ABA signal is largely unknown. Here, we report an autocatalytic mechanism for ABA biosynthesis and its synergistic interaction with the auxin to regulate strawberry fruit ripening. We demonstrate that ABA biosynthesis is self-induced in the achenes, but not in the receptacle, which results its substantial accumulation during ripening. ABA was found to regulate both IAA transport and biosynthesis, thereby modulating IAA content during both early fruit growth and later during ripening. Taken together, these results reveal the origins of the ABA signal and demonstrate the importance of its coordinated action with IAA in the regulation of strawberry fruit development and ripening.

Horticultural innovation by viral-induced gene regulation of carotenogenesis

Multipartite viral vectors provide a simple, inexpensive and effective biotechnological tool to transiently manipulate (i.e. reduce or increase) gene expression in planta and characterise the function of genetic traits. The development of virus-induced gene regulation (VIGR) systems usually involve the targeted silencing or overexpression of genes involved in pigment biosynthesis or degradation in plastids, thereby providing rapid visual assessment of success in establishing RNA- or DNA-based VIGR systems in planta. Carotenoids pigments provide plant tissues with an array of yellow, orange, and pinkish-red colours. VIGR-induced transient manipulation of carotenoid-related gene expression has advanced our understanding of carotenoid biosynthesis, regulation, accumulation and degradation, as well as plastid signalling processes. In this review, we describe mechanisms of VIGR, the importance of carotenoids as visual markers of technology development, and knowledge gained through manipulating carotenogenesis in model plants as well as horticultural crops not always amenable to transgenic approaches. We outline how VIGR can be utilised in plants to fast-track the characterisation of gene function(s), accelerate fruit tree breeding programs, edit genomes, and biofortify plant products enriched in carotenoid micronutrients for horticultural innovation.

Metabolomic and transcriptomic analyses reveal new insights into the role of abscisic acid in modulating mango fruit ripening

Mango (Mangifera indica L.) is a climacteric tropical fruit consumed around the world. Although ethylene and abscisic acid (ABA) have been considered to be stimulators that trigger mango fruit ripening, their regulation mechanisms in modulating mango fruit ripening remain uncertain. In this study, we performed integrative analyses of metabolome and transcriptome data combined with a series of physiological and experimental analyses in the 'Keitt' mango, and we characterized changes in accumulation of specific metabolites at different stages during fruit development and ripening, which were strongly correlated with transcriptional changes and embodied physiological changes as well as taste formation. Specifically, we found that ABA, rather than ethylene, was highly associated with mango ripening, and exogenous ABA application promoted mango fruit ripening. Transcriptomic analysis identified diverse ripening-related genes involved in sugar and carotenoid biosynthesis and softening-related metabolic processes. Furthermore, networks of ABA- and ripening-related genes (such as MiHY5, MiGBF4, MiABI5, and MibZIP9) were constructed, and the direct regulation by the key ABA-responsive transcription factor MiHY5 of ripening-related genes was experimentally confirmed by a range of evidence. Taken together, our results indicate that ABA plays a key role in directly modulating mango fruit ripening through MiHY5, suggesting the need to reconsider how we understand ABA function in modulating climacteric fruit ripening.

Flavonoid biosynthesis is differentially altered in detached and attached ripening bilberries in response to spectral light quality

Light spectral quality is known to affect flavonoid biosynthesis during fruit ripening. However, the response of fruits to different light conditions, when ripening autonomously from the parent plant (detached), has been less explored. In this study, we analyzed the effect of light quality on detached and naturally ripening (attached) non-climacteric wild bilberry (Vaccinium myrtillus L.) fruits accumulating high amounts of anthocyanins and flavonols. Our results indicated contrasting responses for the accumulation of phenolic compounds in the berries in response to red and blue light treatments. For detached berries, supplemental blue light resulted in the highest accumulation of anthocyanins, while naturally ripening berries had elevated accumulation under supplemental red light treatment. Both red and blue supplemental light increased the expression levels of all the major structural genes of the flavonoid pathway during ripening. Notably, the key regulatory gene of anthocyanin biosynthesis, VmMYBA1, was found to express fivefold higher under blue light treatment in the detached berries compared to the control. The red light treatment of naturally ripening berries selectively increased the delphinidin branch of anthocyanins, whereas in detached berries, blue light increased other anthocyanin classes along with delphinidins. In addition, red and far-red light had a positive influence on the accumulation of flavonols, especially quercetin and myricetin glycoside derivatives, in both ripening conditions. Our results of differential light effects on attached and detached berries, which lacks signaling from the mother plant, provide new insights in understanding the light-mediated regulatory mechanisms in non-climacteric fruit ripening.

FvMYB79 Positively Regulates Strawberry Fruit Softening via Transcriptional Activation of FvPME38

Strawberry is a soft fruit with short postharvest life, due to a rapid loss of firmness. Pectin methylesterase (PME)-mediated cell wall remodeling is important to determine fruit firmness and softening. Previously, we have verified the essential role of FvPME38 in regulation of PME-mediated strawberry fruit softening. However, the regulatory network involved in PME-mediated fruit softening is still largely unknown. Here, we identified an R2R3-type MYB transcription factor FvMYB79, which activates the expression level of FvPME38, thereby accelerating fruit softening. During fruit development, FvMYB79 co-expressed with FvPME38, and this co-expression pattern was opposite to the change of fruit firmness in the fruit of 'Ruegen' which significantly decreased during fruit developmental stages and suddenly became very low after the color turning stage. Via transient transformation, FvMYB79 could significantly increase the transcriptional level of FvPME38, leading to a decrease of firmness and acceleration of fruit ripening. In addition, silencing of FvMYB79 showed an insensitivity to ABA-induced fruit ripening, suggesting a possible involvement of FvMYB79 in the ABA-dependent fruit softening process. Our findings suggest FvMYB79 acts as a novel regulator during strawberry ripening via transcriptional activation of FvPME38, which provides a novel mechanism for improvement of strawberry fruit firmness.

Aloe-Based Edible Coating to Maintain Quality of Fresh-Cut Italian Pears (Pyrus communis L.) during Cold Storage

Pear fruits are known for their antioxidant and nutritional characteristics. However, they are very susceptible to rapid decay. Edible coating (EC) represents a good strategy to maintain postharvest quality. The effects of two EC in slowing down the senescence processes in fresh-cut ‘Coscia’ pears were investigated: EC1 (A. vera gel, hydroxypropyl-methylcellulose and pomegranate seeds oil (PSO), EC2 (A. vera gel and hydroxypropyl-methylcellulose). Weight loss, firmness and colour decrease more slowly in both EC-treated than in untreated (CTR) slices; soluble solid content increases faster in CTR, indicating a faster ripening process. The specific investigation of undesired microorganisms did not generate any colony in all analysed samples. Sensory analysis confirmed that the tasters preferred the EC2-treated samples, as they were the only ones that did not show undesirable flavours until the last day of storage.

Exploring diverse roles of micro RNAs in banana: Current status and future prospective

Micro RNAs (miRNAs) are 20-24 nucleotides long non-coding RNA sequences identified and characterized in multiple plant and animal systems. miRNAs play multifarious roles ranging from plant development to stress tolerance by synchronizing physiological processes at the level of transcription and translation. Banana is a major horticultural crop with colossal production worldwide. Despite the recent encouraging developments, the information on functions of miRNAs in banana plants is still in its infancy. The available literature pertaining to miRNAs in banana plants hints towards their contribution as master regulators in crucial physiological processes for instance abiotic stress responses, pathogenic defence response, fruit ripening and so on. This review is focused on biogenesis of miRNAs, their identification and deciphering their respective roles in banana plants with special emphasis on abiotic stress responses, plant immune responses, fruit ripening and storage. Based on the prior reports, we identified a few miRNAs with prospective roles in stress tolerance and illustrated the potential applications of miRNAs in banana crop improvement utilizing recent biotechnological tools such as CRISPR cas9, RNAi and the nano particle based foliar spray of miRNAs. The review briefly explained the future directions in banana research with a special emphasis on miRNA regulatory networks and agronomic traits improvement. Finally, future domains in miRNA research in plants and their possible applications towards crop improvement in agriculture are described briefly.

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.

A Method for Assaying of Protein Kinase Activity In Vivo and Its Use in Studies of Signal Transduction in Strawberry Fruit Ripening

Strawberry (Fragaria × ananassa) fruit ripening is regulated by a complex of cellular signal transduction networks, in which protein kinases are key components. Here, we report a relatively simple method for assaying protein kinase activity in vivo and specifically its application to study the kinase, FaMPK6, signaling in strawberry fruit. Green fluorescent protein (GFP)-tagged FaMPK6 was transiently expressed in strawberry fruit and after stimuli were applied to the fruit it was precipitated using an anti-GFP antibody. The precipitated kinase activity was measured in vitro using ³²P-ATP and myelin basic protein (MBP) as substrates. We also report that FaMPK6 is not involved in the abscisic acid (ABA) signaling cascade, which is closely associated with FaMPK6 signaling in other plant species. However, methyl jasmonate (MeJA), low temperature, and high salt treatments were all found to activate FaMPK6. Transient manipulation of FaMPK6 expression was observed to cause significant changes in the expression patterns of 2749 genes, of which 264 were associated with MeJA signaling. The data also suggest a role for FaMPK6 in modulating cell wall metabolism during fruit ripening. Taken together, the presented method is powerful and its use will contribute to a profound exploration to the signaling mechanism of strawberry fruit ripening.

Postharvest Treatment of Hydrogen Sulfide Delays the Softening of Chilean Strawberry Fruit by Downregulating the Expression of Key Genes Involved in Pectin Catabolism

Hydrogen sulfide (H₂S) plays several physiological roles in plants. Despite the evidence, the role of H₂S on cell wall disassembly and its implications on fleshy fruit firmness remains unknown. In this work, the effect of H₂S treatment on the shelf-life, cell wall polymers and cell wall modifying-related gene expression of Chilean strawberry (Fragaria chiloensis) fruit was tested during postharvest storage. The treatment with H₂S prolonged the shelf-life of fruit by an effect of optimal dose. Fruit treated with 0.2 mM H₂S maintained significantly higher fruit firmness than non-treated fruit, reducing its decay and tripling its shelf-life. Additionally, H₂S treatment delays pectin degradation throughout the storage period and significantly downregulated the expression of genes encoding for pectinases, such as polygalacturonase, pectate lyase, and expansin. This evidence suggests that H₂S as a gasotransmitter prolongs the post-harvest shelf-life of the fruit and prevents its fast softening rate by a downregulation of the expression of key pectinase genes, which leads to a decreased pectin degradation.

Exogenous 2,4-Epibrassinolide Treatment Maintains the Quality of Carambola Fruit Associated With Enhanced Antioxidant Capacity and Alternative Respiratory Metabolism

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.

Alternative postharvest pre-treatment strategies for quality and microbial safety of 'Granny Smith' apple

Over the years, chemical pre-treatments have been used intensively to maintain apple quality and reduce decay during postharvest. This conduct has been reported to have a negative impact on environment and human health. This study aimed to investigate alternative approaches such as hot water (HW) and electrolyzed water (WE) treatments for decay management of 'Granny Smith' apples. Two different sets of experiments were set up for this study. In experiment 1, the effects of HW treatment (45 °C) under varying dipping durations (5, 10 and 15 min) on physicochemical quality of apple were investigated. In experiment 2, the curative efficacy of slightly alkaline electrolyzed water (SAl-EW) (50, 100, 200, 300, 400 and 500 mg L^-1) against Botrytis cinerea was investigated. Hot water treatment duration (15 min) had beneficial effects on flesh firmness, fruit colour, total soluble solid (TSS) and titritable acidity (TA) by the end of the storage. In contrast, a significant reduction in fruit weight and TA values (p < 0.05) were observed in control fruit. The SAl-EW treatments against B. cinerea resulted in a significant reduction in lesion zones compared to the untreated control fruit. Curative efficacy was most effective at concentrations of 200-500 mg L^-1 for 5 °C and 300-500 mg L^-1 for 24 °C. These findings suggest the potential of combining lower concentrations of SAl-EW with other hurdle techniques for better preservation of fresh apples.

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.

Ethylene application at the immature stage of Fragaria chiloensis fruit represses the anthocyanin biosynthesis with a concomitant accumulation of lignin

Ethylene seems to play a secondary role in non-climacteric strawberry ripening compared to abscisic acid. However, this does not exclude that ethylene can regulate some specific events related to the ripening process. Preliminary experiments of applications of ethylene or its inhibitor 1-MCP to strawberry fruits have reinforced this hypothesis. Here, we reveal some previously non-covered physiological effects of ethylene using an in vitro strawberry ripening system. Fruits of Fragaria chiloensis treated with ethephon at the large green developmental stage showed inhibition of anthocyanin biosynthesis and downregulation of essential anthocyanin biosynthesis genes during the ripening. At the same time, ethylene stimulated lignin biosynthesis and remarkably upregulated the expression of FcPOD27. Since contrasting results have been reported when ethylene was applied at late ripening developmental stages, our findings support the hypothesis of a temporal-specific ethylene role in the ripening of strawberry fruits.

An effector-reporter system to study cellular signal transduction in strawberry fruit (Fragaria ananassa)

An effector-reporter system is a powerful tool used to study cellular signal transduction, but this technique has been traditionally used in protoplasts. A similar system to study cellular signal transduction in fruits has not yet been established. In this study, we aimed to establish an effector-reporter system for strawberry fruit, a model nonclimacteric fruit. We first investigated the characteristics of transient gene expression in strawberry fruits and found marked variation in gene expression levels among individual fruits, and this variation has complicated the establishment of a technical system. To overcome this difficulty, we investigated a sampling strategy based on a statistical analysis of the activity pattern of four different reporters (GUS, GFP, FLuc, and RLuc) among individual fruits and combinations of pairs of reporters (GUS/GFP and RLuc/FLuc). Based on an optimized sampling strategy, we finally established a step-by step protocol for the effector/reporter assay. Using FaMYB10 and FaWRKY71 as the effectors and GUS driven by the FaCHS promoter as the reporter, we demonstrated that this effector/reporter system was practical and reliable. This effector/reporter technique will contribute to an in-depth exploration of the signaling mechanism for the regulation of strawberry fruit ripening.

Multifaceted roles of nitric oxide in tomato fruit ripening: NO-induced metabolic rewiring and consequences for fruit quality traits

Nitric oxide (NO) has been implicated as part of the ripening regulatory network in fleshy fruits. However, very little is known about the simultaneous action of NO on the network of regulatory events and metabolic reactions behind ripening-related changes in fruit color, taste, aroma and nutritional value. Here, we performed an in-depth characterization of the concomitant changes in tomato (Solanum lycopersicum) fruit transcriptome and metabolome associated with the delayed-ripening phenotype caused by NO supplementation at the pre-climacteric stage. Approximately one-third of the fruit transcriptome was altered in response to NO, including a multilevel down-regulation of ripening regulatory genes, which in turn restricted the production and tissue sensitivity to ethylene. NO also repressed hydrogen peroxide-scavenging enzymes, intensifying nitro-oxidative stress and S-nitrosation and nitration events throughout ripening. Carotenoid, tocopherol, flavonoid and ascorbate biosynthesis were differentially affected by NO, resulting in overaccumulation of ascorbate (25%) and flavonoids (60%), and impaired lycopene production. In contrast, the biosynthesis of compounds related to tomato taste (sugars, organic acids, amino acids) and aroma (volatiles) was slightly affected by NO. Our findings indicate that NO triggers extensive transcriptional and metabolic rewiring at the early ripening stage, modifying tomato antioxidant composition with minimal impact on fruit taste and aroma.

Identification and Functional Analysis of Tomato TPR Gene Family

Tomato (Solanum lycopersicum) as an important vegetable grown around the world is threatened by many diseases, which seriously affects its yield. Therefore, studying the interaction between tomato and pathogenic bacteria is biologically and economically important. The TPR (Tetratricopeptide repeat) gene family is a class of genes containing TPR conserved motifs, which are widely involved in cell cycle regulation, gene expression, protein degradation and other biological processes. The functions of TPR gene in Arabidopsis and wheat plants have been well studied, but the research on TPR genes in tomato is not well studied. In this study, 26 TPR gene families were identified using bioinformatics based on tomato genome data, and they were analyzed for subcellular localization, phylogenetic evolution, conserved motifs, tissue expression, and GO (Gene Ontology) analysis. The qRT-PCR was used to detect the expression levels of each member of the tomato TPR gene family (SlTPRs) under biological stress (Botrytis cinerea) and abiotic stress such as drought and abscisic acid (ABA). The results showed that members of the tomato TPR family responded to various abiotic stresses and Botrytis cinerea stress, and the SlTPR2 and SlTPR4 genes changed significantly under different stresses. Using VIGS (Virus-induced gene silencing) technology to silence these two genes, the silenced plants showed reduced disease resistance. It was also shown that TPR4 can interact with atpA which encodes a chloroplast ATP synthase CF1 α subunit. The above results provide a theoretical basis for further exploring the molecular mechanism of TPR-mediated resistance in disease defense, and also provide a foundation for tomato disease resistance breeding.