Effects of Acetylsalicylic Acid (ASA) and Ethylene Treatments onRipening and Softening of Postharvest Kiwifruit

Kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson cv. Bruno) was used toinvestigate the effects of acetylsalicylic acid (ASA, 1.0 mmol/L, pH 3.5) and ethylene (100 mL/L) treat-ments on changes at endogenous salicylic acid (SA) levels and other senescence-related factors duringfruit ripening and softening at 20 ℃. The level of endogenous SA in ripening fruits declined and a closerelationship was observed between the change at endogenous SA level and the rate of fruit ripening andsoftening. ASA treatment elevated SA level in the fruit, slowed down the increases in lipoxygenase (LOX)and allene oxide synthase (AOS) activities, decreased the O22-. production in the preclimacteric phase andthe early phase of ethylene climacteric rise, maintained the stability of cell membrane, inhibited ethylenebiosynthesis, postponed the onset of the ethylene climacteric, and delayed the process of fruit ripeningand softening. On the contrary, application of ethylene to ripening kiwifruit resulted at a lower SA level, anaccelerated increases in the activities of LOX and AOS and the rate of O22-. production, an elevated relativeelectric conductivity and an advanced onset of ethylene climacteric, and a quicker fruit ripening andsoftening. It is suggested that the effects of ASA on ripening kiwifruit can be attributed to its ability toscavenge O22-. and/or to maintain stability of cell membrane.

Transcriptomics and metabolomics analyses provide insights into postharvest ripening and senescence of tomato fruit under low temperature

Tomato is one of the most important vegetable crops in the world and is a model plant used to study the ripening of climacteric fleshy fruit.During the ripening process of tomato fruit,flavor and aroma metabolites,color,texture and plant hormones undergo significant changes.However,low temperatures delayed the ripening process of tomato fruit,inhibiting flavor compounds and ethylene production.Metabolomics and transcriptomics analyses of tomato fruit stored under low temperature(LT,5°C)and room temperature(RT,25°C)were carried out to investigate the effects of storage temperature on the physiological changes in tomato fruit after harvest.The results of transcriptomics changes revealed that the differentially expressed genes(DEGs)involved in tomato fruit ripening,including several kinds of transcription factors(TFs)(TCP,WRKY,MYB and bZIP),enzymes involved in cell wall metabolism[beta-galactosidase(β-GAL),pectinesterase(PE)and pectate lyase(PL),cellulose and cellulose synthase(CESA)],enzymes associated with fruit flavor and aroma[acetyltransferase(AT),malic enzyme(ME),lipoxygenase(LOX),aldehyde dehydrogenase(ALDH),alcohol dehydrogenase(ADH)and hexokinase(HK)],genes associated with heat stress protein 70 and genes involved in the production of plant hormones such as Ethylene responsive factor 1(ERF1),Auxin/indoleacetic acids protein(AUX/IAA),gibberellin regulated protein.Based on the above results,we constructed a regulatory network model of the effects of different temperatures during the fruit ripening process.According to the analysis of the metabolomics results,it was found that the contents of many metabolites in tomato fruit were greatly affected by storage temperature,including,organic acids(L-tartaric acid,a-hydroxyisobutyric acid and 4-acetamidobutyric acid),sugars(melezitose,beta-Dlactose,D-sedoheptulose 7-phosphate,2-deoxyribose 1-phosphate and raffinose)and phenols(coniferin,curcumin and feruloylputrescine).This study revealed the effects of storage temperature on postharvest tomato fruit and provided a basis for further understanding of the molecular biology and biochemistry of fruit ripening.

Elucidating the role of SlXTH5 in tomato fruit softening

Fruit softening in tomato(Solanum lycopersicum)is closely associated with cell wall disassembly,which is brought about through the action of a range of cell wall structure-related enzymes and other proteins such as expansins.Xyloglucan endotransglucosylase/hydrolase(XTH)(EC 2.4.1.207 and/or EC 3.2.1.151)has been proposed to be key player involved in xyloglucan metabolism.SlXTH5 showed the highest expression level among all SlXTHs during tomato ripening.In this study,the role of SlXTH5 involved in tomato softening was investigated in CRISPR-based knockout mutants of SlXTH5.Loss-of-function of SlXTH5 in transgenic tomato lines resulted in slightly firmer fruit pericarp,but significantly decreased their color index compared with azygous wild type(WT)control fruits.Increased paste viscosity was detected in CRISPR mutants,indicating that the activity of SlXTH5 is responsible for maintaining cell wall structural integrity.Immunocytochemistry studies were performed using the monoclonal antibody probe LM25 to examine the localization and distribution of xyloglucan in the pericarp cells of the CRISPR mutant fruits.The data indicated more xyloglucan was retained in the pericarp of CRISPR mutant fruit than in WT control fruit.This study revealed the link between SlXTH5 and xyloglucan metabolism and indicated the potential of manipulating SlXTH5 to regulate fruit softening.

Comparison of cell wall changes of two different types of apple cultivars during fruit development and ripening

Fruit development and ripening is a complex procedure(Malus×domestica Borkh.)and can be caused by various factors such as cell structure,cell wall components,and cell wall hydrolytic enzymes.In our study,we focused on the variations in fruit firmness,cell wall morphology and components,the activity of cell wall hydrolytic enzymes and the expression patterns of associated genes during fruit development in two different types of apple cultivars,the hard-crisp cultivar and the loose-crisp cultivar.In this paper,the aim was to find out the causes of the texture variations between the different type cultivars.Cell wall materials(CWMs),hemicellulose and cellulose content were strongly associated with variations in fruit firmness during the fruit development.The content of water soluble pectin(WSP)and chelator soluble pectin(CSP)gradually increased,while the content of ionic soluble pectin(ISP)showed inconsistent trends in the four cultivars.The activities of polygalacturonase(PG),β-galactosidase(β-gal),cellulase(CEL),and pectate lyase(PL)gradually increased in four cultivars.And the activities of PG,β-gal,and CEL were higher in‘Fuji’and‘Honeycrisp’fruit with the fruit development,while the activity of PL of‘Fuji’and‘Honeycrisp’was lower than that of‘ENVY’and‘Modi’.Both four cultivars of fruit cells progressively became bigger as the fruit expanded,with looser cell arrangements and larger cell gaps.According to the qRT-PCR,the relative expression levels of MdACO and Mdβ-gal were notably enhanced.Our study showed that there were large differences in the content of ISP and hemicellulose,the activity of PL and the relative expression of Mdβ-gal between two different types of apple cultivars,and these differences might be responsible for the variations in the texture of the four cultivars.

Over-expression of GhDWF4 gene improved tomato fruit quality and accelerated fruit ripening

Brassinosteroids（BRs）, a class of steroidal phytohormones are essential for many biological processes in plant. However, little is known about their roles in fruit development. Tomato is a highly valuable vegetable and has been adopted as the model species for studying fruit growth, development, and ripening. To understand the role of endogenous BRs in the development of tomato fruit, the expression patterns of three homologues of DWF4 gene were investigated and the transgenic tomato plants were generated in which the Gh DWF4 gene from upland cotton（Gossypium hirsutum L.） was ectopically expressed. The contents of main quality components were analyzed in fruits of transgenic tomato line and non-transgenic line（control plant, CP） when the fruit was mature. Sl CYP90B3 that possesses high homology with Gh DWF4 preferentially expressed in mature fruit. Significantly higher contents of soluble sugar, soluble proteins, and vitamin C were obtained in fruit of transgenic tomato lines compared with those in the CP. Furthermore, overexpressing Gh DWF4 promoted fruit growth and ripening. The weight per fruit was increased by about 23% in transgenic lines. In addition, overexpressing Gh DWF4 promoted the germination of transgenic tomato seeds and hypocotyl elongation of seedlings. These results indicated that overexpressing Gh DWF4 gene in tomato could increase the contents of many nutrients in fruit and accelerate fruit ripening. It is suggested that increased endogenous BRs in fruit affect the growth and development of tomato fruit and therefore improved the nutrient quality of tomato.

Molecular Cloning and Characterization of Fruit Softening Related Gene β-Mannanase from Banana Fruit

A 1 250 bp cDNA fragment encoding β-mannanase, named MaMAN, was cloned from banana （Musa spp cv. Baxi） fruit using degenerate primers designed with reference to the conserved nucleic acid sequences of known β-mannanase genes by RT-PCR. Sequence analysis showed that MaMAN cDNA encompassed a 1 085 bp open-reading frame （ORF）, encoding a predicted polypeptide of 395 amino acids. Alignment of the deduced amino acid sequence of MaMAN and other putative β-mannanases showed that MaMAN has an identity of 86, 70, 69, 54, and 57%, respectively, to β-mannanases from tomato, lettuce, arabidopsis, carrot and oryza sativa. The catalytic residues： Asn203, Glu204, Glu318 and the active site residues： Arg86, His277, Tyr279, and Trp360, which were strictly conserved in the glycoside hydrolase family 5 to which all β-mannanases belonged, were found in MaMAN. Semi-quantitative RT-PCR revealed that the level of MaMAN transcript in the pulp increased during banana fruit ripening, suggesting that MaMAN was likely to be involved highly in banana fruit softening.

ERF4 affects fruit ripening by acting as a JAZ interactor between ethylene and jasmonic acid hormone signaling pathways

The regulation of apple(Malus domestica)fruit texture during ripening is complex and a fundamental determinant of its commercial quality.In climacteric fruit,ripening-related processes are regulated by ethylene(ET),and jasmonate(JA)is also involved in the ethylene biosynthesis pathway,mainly through the transcription factor MYC2.However,the molecular genetic mechanism for fruit ripening processes between the JA and ET signaling pathways still needs to be elucidated.In order to explore how JA regulates apple fruit ripening through ERF4,we used’Gala’and’Ralls Janet’fruit at different developmental stages as experimental materials to determine the fruit firmness and related gene expression analysis.Meanwhile,we carried out different hormone treatments on’Gala’fruit at ripening stage.Here,we show that ERF4 is a core JA signaling hub protein JASMONATE ZIM-DOMAIN(JAZ)interactor that affects ethylene signaling pathways.During fruit development,ERF4 represses the expression of ACS1 and ACO1 by interacting with JAZ,as well as with the JA-activated transcription factor MYC2.Ripening is promoted in JAZ-suppressed apples.Thus,ERF4 acts as a molecular link between ethylene and JA hormone signals,and the natural variation of the ERF4Ethylene-responsive binding factor-associated amphiphilic repression(EAR)motif decreases repression of ethylene biosynthesis genes.

Transcriptional profiles underlying the effects of salicylic acid on fruit ripening and senescence in pear(Pyrus pyrifolia Nakai)

Salicylic acid(SA) plays a pivotal role in delaying fruit ripening and senescence. However, little is known about its underlying mechanism of action. In this study, RNA sequencing was conducted to analyze and compare the transcriptome profiles of SA-treated and control pear fruits. We found a total of 159 and 419 genes differentially expressed between the SA-treated and control pear fruits after 12 and 24 h of treatment, respectively. Among these differentially expressed genes(DEGs), 125 genes were continuously differentially expressed at both treatment times, and they were identified as candidate genes that might be associated with SA-regulated fruit ripening and senescence. Bioinformatics analysis results showed that 125 DEGs were mainly associated with plant hormone biosynthesis and metabolism, cell wall metabolism and modification, antioxidant systems, and senescence-associated transcription factors. Additionally, the expression of several candidate DEGs in ripening and senescent pear fruits after SA treatments were further validated by quantitative real-time PCR(qRT-PCR). This study provides valuable information and enhances the understanding of the comprehensive mechanisms of SA-meditated pear fruit ripening and senescence.

Effects of calcium application on apple fruit softening during storage revealed by proteomics and phosphoproteomics

Fruit ripening has been reported to be related to calcium(Ca),but the underlying mechanisms by which Ca regulates this process remain largely unknown.In order to study the changes of proteins and enriched phosphopeptides,we conducted TMT labeling,bio-material-based PTM enrichment based on mass spectrometry in Ca-treated‘Golden Delicious’(GD)apple fruit(Malus×domestica).This dataset presents a comprehensive overview of the critical pathways involved in fruit ripening.A total of 47 proteins and 124 phosphoproteins significantly changed in Ca-treated fruit,which are crucial for regulating the cell wall and cytoskeleton,Ca-mediated signaling and transport,ethylene production,protein fate,especially ubiquitination-based protein degradation,and primary and secondary metabolisms.Our results indicated that Ca inhibited the abundance of polygalacturonase(PG)activity and increased the phosphorylation level of CSLD3.PG and phosphorylation were involved in cell wall degradation,thereby delaying fruit softening.As a secondary messenger,Ca-mediated signaling subsequently triggered downstream mitogen-activated protein kinases(MAPK)cascades and activated the membrane,transport,and ROS signaling.Moreover,MdEIN2,a key enzyme involved in the ubiquitin of protein modification,increased at Ser753 and Ser758 in Ca-treated fruit.Furthermore,diverse primary and secondary metabolisms including glycolysis,fatty acid metabolism,and oxidation respiratory chain were modulated to prevent fruit softening.These results provide basic information from protein and phosphorylation levels for apple fruit ripening during storage,which may be helpful for apple fruit storage control.

PaPYL9 is involved in the regulation of apricot fruit ripening through ABA signaling pathway

Abscisic acid(ABA)is a major regulator of non-climacteric fruit ripening;however,the role of ABA in the ripening of climacteric fruit is not clear.Here,as a typical climacteric fruit,apricots were used to investigate the role of ABA in fruit ripening.Based on weighted gene coexpression network analysis(WGCNA)of our previous transcriptome data,we treated‘Danxing’fruit with exogenous ABA and obtained ABA receptor genes,genes related to ABA biosynthesis and signal transduction,and analyzed the response of these candidate genes to exogenous ABA during fruit ripening.Subsequently,the full length of candidate PYLs genes were cloned,and their putative function were analyzed by phylogenetic analysis and protein structure domain analysis.And then the function of one candidate gene PaPYL9 was verified by using transgenic tomato.Furthermore,the response genes in transgenic tomato were screened by transcriptome sequencing,and ultimately the related regulatory network was proposed.The results showed that the injection of exogenous 1.89 mmol·L^(-1) ABA remarkably promoted fruit coloration,and increased the color index for red grapes(CIRG)and the total soluble solids(TSS)content,but significantly decreased the firmness and titratable acid(TA)content(p<0.01).Nordihydroguaiaretic acid(NDGA),the inhibitor of ABA,appeared to have the converse role in TA,TSS,CIRG and firmness,during the ripening process.One NCED(9-cis-epoxycarotenoiddioxygenase)and five ABA receptor genes related to signal transduction were mined from the transcriptome data of apricot fruit through WGCNA.Compared with the control,the expression levels of NCED1,PYL9(PYR/PYL/RCAR),SnRK2(SUCROSE NON-FERMENTING1(SNF1)-RELATED PROTEIN KINASE 2S),and ABF2(ABRE-binding bZIP transcription)were induced dramatically by ABA treatment(p<0.01),while NDGA treatment significantly inhibited their expression.Based on gene expression and protein domain analysis,we inferred that PaPYL9 is putatively involved in apricot fruit ripening.Overexpression of PaPYL9 in Micro-TOM tomatoes resulted in the promotion of early ripening.Simultaneously,the expression levels of genes related ethylene biosynthesis,chlorophyll degradation,fruit softening,flavor formation,pigment synthesis,and metabolism were all significantly induced in overexpression of PaPYL9 tomatoes.This indicates the central role of ABA in climacteric fruit ripening.A regulatory network was tentatively proposed,laying the foundation to unveil the molecular mechanism of the regulatory role of PaPYL9 in fruit ripening.

Characteristics of fruit ripening in tomato mutant epi

The characteristics of fruit ripening and expression of ripening-related genes were investigated in epi, an ethylene overproduction mutant of tomato (Lycopersicon esculentum Mill.). The epi produces apparently more ethylene than its wild type VFN8 at every stage of vegetative and fruit growth and ripening; compared to VFN8, the epi fruit showed higher CO2 evolution, faster descending of chlorophyll, slightly quicker increase of carotenoid and lycopene, and faster reduction in pericarp firmness during maturation and ripening; and the mRNAs of three ripening-related genes including E8, pTOM5 and pTOM6 were at higher levels in epi. The ripening-related characteristics changing of the fruit are consistent with the increase of ethylene production and ripening-related genes expression. These results suggest that epi mutation possibly did not affect the ethylene perception and signaling during fruit ripening, and that the modified characteristics of fruit ripening possibly resulted from the ethylene over- production and increased expression of ripening-related genes.

The Influence of Co-Suppressing Tomato 1-Aminocyclopropane-1-Carboxylic Acid OxidaseⅠon the Expression of Fruit Ripening-Related and Pathogenesis-Related Protein Genes

The purpose of this study is to explore the influence of co-suppressing tomato ACC oxidase Ⅰ on the expression of fruit ripening-related and pathogenesis-related protein genes, and on the biosynthesis of endogenous ethylene and storage ability of fruits. Specific fragments of several fruit ripening-related and pathogenesis-related protein genes from tomato （Lycopersicon esculentum） were cloned, such as the l-aminocyclopropane-1-carboxylic acid oxidase 1 gene （LeAC01）, 1- aminocyclopropane-l-carboxylic acid oxidase 3 gene （LeAC03）, EIN3-binding F-box 1 gene （LeEBF1）, pathogenesis-related protein 1 gene （LePR1）, pathogenesis-related protein 5 gene （LePR5）, and pathogenesis-related protein osmotin precursor gene （LeNP24） by PCR or RT-PCR. Then these specific DNA fragments were used as probes to hybridize with the total RNAs extracted from the wild type tomato Ailsa Craig （AC＋＋） and the LeAC01 co-suppression tomatoes （V1187 and T4B）, respectively. At the same time, ethylene production measurement and storage experiment of tomato fruits were carded out. The hybridization results indicated that the expression of fruit ripening-related genes such as LeACO3 and LeEBF1, and pathogenesis-related protein genes such as LePR1, LePR5, and LeNP24, were reduced sharply, and the ethylene production in the fruits, wounded leaves decreased and the storage time of ripening fruits was prolonged, when the expression of LeACO1 gene in the transgenic tomato was suppressed. In the co-suppression tomatoes, the expression of fruit ripening-related and pathogenesis-related protein genes were restrained at different degrees, the biosynthesis of endogenous ethylene decreased and the storage ability of tomato fruits increased.

Changes of Reactive Oxygen Species and Related Enzymes in Mitochondria Respiratory Metabolism During the Ripening of Peach Fruit

The fruits of peach cultivar Yuhua 3 were used as materials to investigate the changes of active oxygen and related enzymes in mitochondria respiratory metabolism during ripening of peach fruit, involving their influence on the proceeding of peach fruit senescence. The results showed that the large decrease in firmness occurred between maturity II and IV. The decrease in firmness coincided with an increase in respiratory intensity. Obvious peaks of respiratory intensity lagging to the rapid change of fruit firmness could be shown during peach ripening. Reactive oxygen species （ROS） had a cumulative process and positively correlated with respiratory intensity. During peach ripening, the content of Ca^2＋ increased, the activities of succinic dehydrogenase （SDH）, cytochrome C oxidase （CCO）, H＋-ATPase, and Ca^2＋-ATPase decreased varying in different degree at the later step of ripening. These suggested a close relationship existed between ROS metabolism and mitochondrial respiration, namely, both ROS metabolism and mitochondrial respiration probably played important roles in ripening and senescing of peach fruit.

Changes of Activities in NAD Kinase and NADP PhosphataseDuring Ripening and Senescence of Tomatoand Strawberry Fruits

Activities of NAD kinase(NADK)and NADP phosphatase and relationship between the two enzymes and temperature, respiration, ethylene production and trifluoperazine(TFP) were studied during ripening and senescence of strawberry and tomato fruits after harvest at 4℃ and 20℃. The activity of NAD kinase in strawberry decreased slowly during first four days, then increased gradually. The NADP phosphatase activity increased at the second day, decreased the next day,then increased again. In tomato fruit, the activities of NAD kinase and NADP phosphatase increased at the second day, decreased with the ripening and senescence of the fruit. The change trend of NAD kinase and respiration in the two fruits were similar, the same were NADP phosphatase and ethylene production. TFP enhanced the activity of NAD kinase and had little effect on NADP phosphatase. Low temperature(4℃) activated the NAD kinase and reduced the activity of NADP phosphatase. These results indicated that the NAD kinase and NADP phosphatase were related to the ripening and senescence of strawberry and tomato fruits. The activation of NAD kinase probably postponed the ripening and senescence of the fruits.

Effect of Ethylene on Polygalacturonase,Lipoxygenase and Expansin in Ripening of Tomato Fruits

Fruit ripening is a complex process and is regulated by many factors. Ethylene and polygalacturonase （PG）, lipoxygenase （LOX）, expansin （EXP） are all critical regulating factors in fruit ripening and softening process. With antisense ACS tomato, Nr mutant tomato and cultivated tomato as materials, Northern blot hybridization showed that PG, LeEXP1 and LOXexpressed differently in different parts of cultivated tomato fruit during ripening, which was related to fruit ripening. The ripening process of columella and radial pericarp was faster than pericarp. In both Nr mutant and antisense ACS transgenic tomato fruit, expression levels ofPG, LeEXPI and LOXwere generally lower than those in cultivated fruit but still related to fruit ripening. The expression levels ofPG, LeEXP1 and LOX increased in the mature green tomato fruits after 0.5 h treatment with ethylene （100 μL/L）. These results indicate that gene expression ofPG, LeEXP1 and LOXwere positively regulated by ethylene. The time and cumulative effect of the concentration exists in the expression of PG regulated by ethylene. The regulation of LOX expression mainly depended on the fruit development after great amount of ethylene was produced. PG played a major role in ripening and softening of tomato fruit, and cooperated with the regulation of EXP and LOX.

Ripening and rot:How ripening processes influence disease susceptibility in fleshy fruits

Fleshy fruits become more susceptible to pathogen infection when they ripen;for example,changes in cell wall properties related to softening make it easier for pathogens to infect fruits.The need for high-quality fruit has driven extensive research on improving pathogen resistance in important fruit crops such as tomato(Solanum lycopersicum).In this review,we summarize current progress in understanding how changes in fruit properties during ripening affect infection by pathogens.These changes affect physical barriers that limit pathogen entry,such as the fruit epidermis and its cuticle,along with other defenses that limit pathogen growth,such as preformed and induced defense compounds.The plant immune system also protects ripening fruit by recognizing pathogens and initiating defense responses involving reactive oxygen species production,mitogen-activated protein kinase signaling cascades,and jasmonic acid,salicylic acid,ethylene,and abscisic acid signaling.These phytohormones regulate an intricate web of transcription factors(TFs)that activate resistance mechanisms,including the expression of pathogenesis-related genes.In tomato,ripening regulators,such as RIPENING INHIBITOR and NON_RIPENING,not only regulate ripening but also influence fruit defenses against pathogens.Moreover,members of the ETHYLENE RESPONSE FACTOR(ERF)family play pivotal and distinct roles in ripening and defense,with different members being regulated by different phytohormones.We also discuss the interaction of ripening-related and defense-related TFs with the Mediator transcription complex.As the ripening processes in climacteric and non-climacteric fruits share many similarities,these processes have broad applications across fruiting crops.Further research on the individual contributions of ERFs and other TFs will inform efforts to diminish disease susceptibility in ripe fruit,satisfy the growing demand for high-quality fruit and decrease food waste and related economic losses.

The brassinosteroid signaling component SlBZR1 promotes tomato fruit ripening and carotenoid accumulation

The plant hormone ethylene is essential for climacteric fruit ripening, although it is unclear how other phytohormones and their interactions with ethylene might affect fruit ripening. Here, we explored how brassinosteroids(BRs) regulate fruit ripening in tomato(Solanum lycopersicum) and how they interact with ethylene. Exogenous BR treatment and increased endogenous BR contents in tomato plants overexpressing the BR biosynthetic gene SlCYP90B3promoted ethylene production and fruit ripening.Genetic analysis indicated that the BR signaling regulators Brassinazole-resistant1(SlBZR1) and BRI1-EMS-suppressor1(SlBES1) act redundantly in fruit softening. Knocking out Sl BZR1 inhibited ripening through transcriptome reprogramming at the onset of ripening. Combined transcriptome deep sequencing and chromatin immunoprecipitation followed by sequencing identified 73 Sl BZR1-repressed targets and 203 Sl BZR1-induced targets involving major ripening-related genes, suggesting that Sl BZR1 positively regulates tomato fruit ripening.Sl BZR1 directly targeted several ethylene and carotenoid biosynthetic genes to contribute to the ethylene burst and carotenoid accumulation to ensure normal ripening and quality formation. Furthermore,knock-out of Brassinosteroid-insensitive2(Sl BIN2),a negative regulator of BR signaling upstream of Sl BZR1, promoted fruit ripening and carotenoid accumulation. Taken together, our results highlight the role of Sl BZR1 as a master regulator of tomato fruit ripening with potential for tomato quality improvement and carotenoid biofortification.

MaBEL1 regulates banana fruit ripening by activating cell wall and starch degradation-related genes

Banana is a typical subtropical fruit, sensitive to chilling injuries and prone to softening disorder.However, the underlying regulatory mechanisms of the softening disorder caused by cold stress remain obscure. Herein, we found that BEL1-LIKE HOMEODOMAIN transcription factor 1(MaBEL1)and its associated proteins regulate the fruit softening and ripening process. The transcript and protein levels of MaBEL1 were up-regulated with fruit ripening but severely repressed by the chilling stress. Moreover, the MaBEL1 protein interacted directly with the promoters of the cell wall and starch degradation-related genes, such as MaAMY3, MaXYL32, and MaEXP-A8. The transient overexpression of MaBEL1 alleviated fruit chilling injury and ripening disorder caused by cold stress and promoted fruit softening and ripening of “Fenjiao” banana by inducing ethylene production and starch and cell wall degradation. The accelerated ripening was also validated by the ectopic overexpression in tomatoes.Conversely, MaBEL1-silencing aggravated the chilling injury and ripening disorder and repressed fruit softening and ripening by inhibiting ethylene production and starch and cell wall degradation. MaABI5-like and MaEBF1, the two positive regulators of the fruit softening process,interacted with MaBEL1 to enhance the promoter activity of the starch and cell wall degradationrelated genes. Moreover, the F-box protein MaEBF1 does not modulate the degradation of MaBEL1, which regulates the transcription of MaABI5-like protein. Overall, we report a novel MaBEL1-MaEBF1-MaABI5-like complex system that mediates the fruit softening and ripening disorder in “Fenjiao” bananas caused by cold stress.

ClSnRK2.3 negatively regulates watermelon fruit ripening and sugar accumulation

Watermelon(Citrullus lanatus) as non-climacteric fruit is domesticated from the ancestors with inedible fruits. We previously revealed that the abscisic acid(ABA) signaling pathway gene ClSnRK2.3 might infuence watermelon fruit ripening. However,the molecular mechanisms are unclear. Here,we found that the selective variation of ClSnRK2.3 resulted in lower promoter activity and gene expression level in cultivated watermelons than ancestors, which indicated ClSnRK2.3 might be a negative regulator in fruit ripening. Overexpression (OE) of ClSnRK2.3 significantly delayed watermelon fruit ripening and suppressed the accumulation of sucrose, ABA and gibberellin GA4. Furthermore,we determined that the pyrophosphate-dependent phosphofructokinase(ClPFP1) in sugar metabolism pathway and GA biosynthesis enzyme GA20 oxidase(Cl GA20ox) could be phosphorylated by ClSnRK2.3 and thereby resulting in accelerated protein degradation in OE lines and finally led to low levels of sucrose and GA4. Besides that, ClSnRK2.3 phosphorylated homeodomain-leucine zipper protein(ClHAT1) and protected it from degradation to suppress the expression of the ABA biosynthesis gene 9’-cis-epoxycarotenoid dioxygenase 3(Cl NCED3). These results indicated that ClSnRK2.3 negatively regulated watermelon fruit ripening by manipulating the biosynthesis of sucrose, ABA and GA4. Altogether, these findings revealed a novel regulatory mechanism in non-climacteric fruit development and ripening.

Comparative transcriptome analysis of the climacteric of apple fruit uncovers the involvement of transcription factors affecting ethylene biosynthesis

Apple(Malus domestica)fruit generally undergoes a climacteric.During its ripening process,there is a peak in ethylene release and its firmness simultaneously decreases.Although more in-depth research into the mechanism of climacteric-type fruit ripening is being carried out,some aspects remain unclear.In this study,we compared the transcriptomes of 0-Pre and 15-Post(pre-and post-climacteric fruit),and 15-Post and 15-MCP[fruit treated with 1-MCP(1-methylcyclopropene)].Various transcription factors,such as MADS-box,ERF,NAC,Dof and SHF were identified among the DEGs(differential gene expressions).Furthermore,these transcription factors were selected for further validation analysis by qRT-PCR.Moreover,yeast one hybrid(Y1H),β-glucuronidase(GUS)transactivation assay and dual-luciferase reporter assay showed that MdAGL30,MdAGL104,MdERF008,MdNAC71,MdDof1.2,MdHSFB2a and MdHSFB3 bound to MdACS1 promoter and directly regulated its transcription,thereby regulating ethylene biosynthesis in apple fruit.Our results provide useful information and new insights for research on apple fruit ripening.