Analysis of β-Galactosidase During Fruit Development and Ripening in Two Different Texture Types of Apple Cultivars

Predicting the role of β-GAL genes in bean under abiotic stress and genome-wide characterization of β-GAL gene family members

Β-Gals are a subgroup of the glycoside hydrolase (GH) family of enzymes, which possess the Glyco_hydro_35 (GH35) domain. Although studies have been conducted on the β-Gal gene family in numerous plant species, no such research has been conducted on beans. The purpose of this study was to determine the gene expression levels of β-Gal genes in the leaf tissue of P. vulgaris under salt and drought stress using quantitative real-time polymerase chain reaction (qRT-PCR) and to perform a comprehensive analysis of β-Gal gene family members using bioinformatics tools. In the bean genome, 25 Pvul-βGAL proteins with amino acid numbers ranging from 291 to 1119, molecular weights from 32.94 to 126.56 kDa, and isoelectric points from 5.46 to 9.08 were identified. Both segmental and tandem duplication have occurred in β-Gal genes in the bean genome, and Pvul-BGAL genes have been subject to negative selection in the evolutionary process. For a deeper comprehension of the evolutionary proximity of Pvul-BGAL genes, a phylogenetic tree and synteny map were drawn together with Arabidopsis thaliana and Glycine max β-Gal genes. The expression profiles of β-Gal genes in different tissues of the bean were determined in silico. In addition, the expression profiles of β-Gal genes in the leaves of bean plants subjected to drought and salt stress were analyzed, and the role of β-Gal genes in salt and drought stress was estimated. In this study, the role of β-Gal gene family in abiotic stress response and the characterization of β-Gal genes in beans were determined for the first time and will provide a basis for future functional genomics studies.

Changes in the proteomics and metabolomics profiles of Cormus Domestica (L.) fruits during the ripening process

BACKGROUND

Cormus domestica (L.) is a monophyletic wild fruit tree belonging to the Rosaceae family, with well-documented use in the Mediterranean region. Traditionally, these fruits are harvested and stored for at least 2 weeks before consumption. During this period, the fruit reaches its well-known and peculiar organoleptic and texture characteristics. However, the spread of more profitable fruit tree species, resulted in its progressive erosion. In this work we performed proteomic and metabolomic fruit analyses at three times after harvesting, to characterise postharvest physiological and molecular changes, it related to nutritional and organoleptic properties at consumption.

RESULTS

Proteomics and metabolomics analysis were performed on fruits harvested at different time points: freshly harvested fruit (T0), fruit two weeks after harvest (T1) and fruit four weeks after harvest (T2). Proteomic analysis (Shotgun Proteomic in LC-MS/MS) resulted in 643 proteins identified. Most of the differentially abundant proteins between the three phases observed were involved in the softening process, carbohydrate metabolism and stress responses. Enzymes, such as xyloglucan endotransglucosylase/hydrolase, pectin acetylesterase, beta-galactosidase and pectinesterase, accumulated during fruit ripening and could explain the pulp breakdown observed in C. domestica. At the same time, enzymes abundant in the early stages (T0), such as sucrose synthase and malic enzyme, explain the accumulation of sugars and the lowering of acidity during the process. The metabolites extraction from C. domestica fruits enabled the identification of 606 statistically significant differentially abundant metabolites. Some compounds such as piptamine and resorcinol, well-known for their antimicrobial and antifungal properties, and several bioactive compounds such as endocannabinoids, usually described in the leaves, accumulate in C. domestica fruit during the post-harvest process.

CONCLUSIONS

The metabolomic and proteomic profiling of the C. domestica fruit during the postharvest process, evaluated in the study, provides a considerable contribution to filling the existing information gap, enabling the molecular and phytochemical characterisation of this erosion-endangered fruit. Data show biochemical changes that transform the harvested fruit into palatable consumable product.

An activatable fluorescence probe for rapid detection and in situ imaging of β-galactosidase activity in cabbage roots under heavy metal stress

β-Galactosidase (β-gal), an enzyme related to cell wall degradation, plays an important role in regulating cell wall metabolism and reconstruction. However, activatable fluorescence probes for the detection and imaging of β-gal fluctuations in plants have been less exploited. Herein, we report an activatable fluorescent probe based on intramolecular charge transfer (ICT), benzothiazole coumarin-bearing β-galactoside (BC-βgal), to achieve distinct in situ imaging of β-gal in plant cells. It exhibits high sensitivity and selectivity to β-gal with a fast response (8 min). BC-βgal can be used to efficiently detect the alternations of intracellular β-gal levels in cabbage root cells with considerable imaging integrity and imaging contrast. Significantly, BC-βgal can assess β-gal activity in cabbage roots under heavy metal stress (Cd2+, Cu2+, and Pb2+), revealing that β-gal activity is negatively correlated with the severity of heavy metal stress. Our work thus facilitates the study of β-gal biological mechanisms.

Integrative Analysis of Transcriptomic Profiles and Physiological Responses Provide New Insights into Drought Stress Tolerance in Oil Palm (Elaeis guineensis Jacq.)

Oil palm (Elaeis guineensis Jacq.) is a highly productive crop economically significant for food, cosmetics, and biofuels. Abiotic stresses such as low water availability, salt accumulation, and high temperatures severely impact oil palm growth, physiology, and yield by restricting water flux among soil, plants, and the environment. While drought stress's physiological and biochemical effects on oil palm have been extensively studied, the molecular mechanisms underlying drought stress tolerance remain unclear. Under water deficit conditions, this study investigates two commercial E. guineensis cultivars, IRHO 7001 and IRHO 2501. Water deficit adversely affected the physiology of both cultivars, with IRHO 2501 being more severely impacted. After several days of water deficit, there was a 40% reduction in photosynthetic rate (A) for IRHO 7001 and a 58% decrease in IRHO 2501. Further into the drought conditions, there was a 75% reduction in A for IRHO 7001 and a 91% drop in IRHO 2501. Both cultivars reacted to the drought stress conditions by closing stomata and reducing the transpiration rate. Despite these differences, no significant variations were observed between the cultivars in stomatal conductance, transpiration, or instantaneous leaf-level water use efficiency. This indicates that IRHO 7001 is more tolerant to drought stress than IRHO 2501. A differential gene expression and network analysis was conducted to elucidate the differential responses of the cultivars. The DESeq2 algorithm identified 502 differentially expressed genes (DEGs). The gene coexpression network for IRHO 7001 comprised 274 DEGs and 46 predicted HUB genes, whereas IRHO 2501's network included 249 DEGs and 3 HUB genes. RT-qPCR validation of 15 DEGs confirmed the RNA-Seq data. The transcriptomic profiles and gene coexpression network analysis revealed a set of DEGs and HUB genes associated with regulatory and transcriptional functions. Notably, the zinc finger protein ZAT11 and linoleate 13S-lipoxygenase 2-1 (LOX2.1) were overexpressed in IRHO 2501 but under-expressed in IRHO 7001. Additionally, phytohormone crosstalk was identified as a central component in the response and adaptation of oil palm to drought stress.

Root cell wall polysaccharides and endodermal barriers restrict long-distance Cd translocation in the roots of Kentucky bluegrass

Soil Cd pollution is a significant environmental issue faced by contemporary society. Kentucky bluegrass is considered a potential phytoremediation species, as some varieties have excellent cadmium (Cd) tolerance. However, the mechanisms of Cd accumulation and transportation in Kentucky bluegrass are still not fully understood. The Cd-tolerant Kentucky bluegrass cultivar 'Midnight' (M) exhibits lower Cd translocation efficiency and a higher leaf Cd concentration compared to the Cd-sensitive cultivar 'Rugby II' (R). We hypothesized that Cd translocation from roots to shoots in cultivar M is hindered by the endodermal barriers and cell wall polysaccharides; hence, we conducted Cd distribution, cytological observation, cell wall component, and transcriptomic analyses under Cd stress conditions using the M and R cultivars. Cd stress resulted in the thickening of the endodermis and increased synthesis of cell wall polysaccharides in both the M and R cultivars. Endodermis development restricted the radical transport of Cd from the root cortex to the stele, while the accumulation of cell wall polysaccharides promoted the binding of Cd to the cell wall. These changes further inhibited the long-distance translocation of Cd from the roots to the aerial parts. Furthermore, the M cultivar exhibited limited long-distance Cd translocation efficiency compared to the R cultivar, which was attributed to the enhanced development of endodermal barriers and increased Cd binding by cell wall polysaccharides. This study provides valuable insights for screening high Cd transport efficiency in Kentucky bluegrass based on anatomical structure and genetic modification.

Haplotype-resolved genome assembly for tetraploid Chinese cherry (Prunus pseudocerasus) offers insights into fruit firmness

Chinese cherry (Prunus pseudocerasus) holds considerable importance as one of the primary stone fruit crops in China. However, artificially improving its traits and genetic analysis are challenging due to lack of high-quality genomic resources, which mainly result from difficulties associated with resolving its tetraploid and highly heterozygous genome. Herein, we assembled a chromosome-level, haplotype-resolved genome of the cultivar 'Zhuji Duanbing', comprising 993.69 Mb assembled into 32 pseudochromosomes using PacBio HiFi, Oxford Nanopore, and Hi-C. Intra-haplotype comparative analyses revealed extensive intra-genomic sequence and expression consistency. Phylogenetic and comparative genomic analyses demonstrated that P. pseudocerasus was a stable autotetraploid species, closely related to wild P. pusilliflora, with the two diverging ~18.34 million years ago. Similar to other Prunus species, P. pseudocerasus underwent a common whole-genome duplication event that occurred ~139.96 million years ago. Because of its low fruit firmness, P. pseudocerasus is unsuitable for long-distance transportation, thereby restricting its rapid development throughout China. At the ripe fruit stage, P. pseudocerasus cv. 'Zhuji Duanbing' was significantly less firm than P. avium cv. 'Heizhenzhu'. The difference in firmness is attributed to the degree of alteration in pectin, cellulose, and hemicellulose contents. In addition, comparative transcriptomic analyses identified GalAK-like and Stv1, two genes involved in pectin biosynthesis, which potentially caused the difference in firmness between 'Zhuji Duanbing' and 'Heizhenzhu'. Transient transformations of PpsGalAK-like and PpsStv1 increase protopectin content and thereby enhance fruit firmness. Our study lays a solid foundation for functional genomic studies and the enhancement of important horticultural traits in Chinese cherries.

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

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

Supplementary Information

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

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

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

Physiological and transcriptomic analysis of IAA-induced antioxidant defense and cell wall metabolism in postharvest mango fruit

Mango fruit tend to oxidize and senescence rapidly after harvesting, significantly reducing their commercial value. This study investigated the effect of exogenous auxin indole-3-acetic acid (IAA) on fruit quality, antioxidant system, and cell wall metabolism of mango fruit during storage. The results showed that the 1.0 mM IAA treatment delayed weight loss and maintained the firmness, pH and contents of total soluble solids (TSS) and titratable acidity (TA) of the mango fruit. The 1.0 mM IAA treatment increased the peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activities and the ascorbic acid (AsA) and total phenols (TP) contents but decreased the polyphenol oxidase (PPO) activity in postharvest mango fruit. Moreover, beta-galactosidase (β-Gal) and polygalacturonase (PG) activities were increased, but the pectinesterase (PME) activity was decreased in the IAA-treated fruit. Transcriptome analysis showed that the differentially expressed genes (DEGs) in the IAA vs. control groups were mainly associated with oxidative stress responses, cell wall metabolism, and transcription factors (TFs). The IAA treatment upregulated the antioxidant-related genes (SOD, CAT1, PODs, GSTs, Prxs, and Trxs) and MYB TFs, and downregulated cell wall metabolism-related genes (PG, PME31 and two PME63) and 11 ethylene-responsive transcription factors (ERFs). These results suggested that exogenous IAA could improve the antioxidant system and maintain the storage quality of mango fruit by regulating gene expression and metabolic pathways. The results provide insights into the mechanisms involved in IAA-mediated delayed ripening and senescence of mango fruit.

Comparative physiological and transcriptomic analyses provide insights into fruit softening in Chinese cherry [Cerasus pseudocerasus (Lindl.) G.Don]

Fruit softening is a complex, genetically programmed and environmentally regulated process, which undergoes biochemical and physiological changes during fruit development. The molecular mechanisms that determine these changes in Chinese cherry [Cerasus peseudocerasus (Lindl.) G.Don] fruits are still unknown. In the present study, fruits of hard-fleshed 'Hongfei' and soft-fleshed 'Pengzhoubai' varieties of Chinese cherry were selected to illustrate the fruit softening at different developmental stages. We analyzed physiological characteristics and transcriptome profiles to identify key cell wall components and candidate genes related to fruit softening and construct the co-expression networks. The dynamic changes of cell wall components (cellulose, hemicellulose, pectin, and lignin), the degrading enzyme activities, and the microstructure were closely related to the fruit firmness during fruit softening. A total of 6,757 and 3,998 differentially expressed genes (DEGs) were screened between stages and varieties, respectively. Comprehensive functional enrichment analysis supported that cell wall metabolism and plant hormone signal transduction pathways were involved in fruit softening. The majority of structural genes were significantly increased with fruit ripening in both varieties, but mainly down-regulated in Hongfei fruits compared with Pengzhoubai, especially DEGs related to cellulose and hemicellulose metabolism. The expression levels of genes involving lignin biosynthesis were decreased with fruit ripening, while mainly up-regulated in Hongfei fruits at red stage. These obvious differences might delay the cell all degrading and loosening, and enhance the cell wall stiffing in Hongfei fruits, which maintained a higher level of fruit firmness than Pengzhoubai. Co-expressed network analysis showed that the key structural genes were correlated with plant hormone signal genes (such as abscisic acid, auxin, and jasmonic acid) and transcription factors (MADS, bHLH, MYB, ERF, NAC, and WRKY). The RNA-seq results were supported using RT-qPCR by 25 selected DEGs that involved in cell wall metabolism, hormone signal pathways and TF genes. These results provide important basis for the molecular mechanism of fruit softening in Chinese cherry.

Pre-Treatment of Rice Plants with ABA Makes Them More Tolerant to Multiple Abiotic Stress

Multiple abiotic stress is known as a type of environmental unfavourable condition maximizing the yield and growth gap of crops compared with the optimal condition in both natural and cultivated environments. Rice is the world's most important staple food, and its production is limited the most by environmental unfavourable conditions. In this study, we investigated the pre-treatment of abscisic acid (ABA) on the tolerance of the IAC1131 rice genotype to multiple abiotic stress after a 4-day exposure to combined drought, salt and extreme temperature treatments. A total of 3285 proteins were identified and quantified across the four treatment groups, consisting of control and stressed plants with and without pre-treatment with ABA, with 1633 of those proteins found to be differentially abundant between groups. Compared with the control condition, pre-treatment with the ABA hormone significantly mitigated the leaf damage against combined abiotic stress at the proteome level. Furthermore, the application of exogenous ABA did not affect the proteome profile of the control plants remarkably, while the results were different in stress-exposed plants by a greater number of proteins changed in abundance, especially those which were increased. Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing the rice seedlings' tolerance against combined abiotic stress, mainly by affecting stress-responsive mechanisms dependent on ABA signalling pathways in plants.

The Key Metabolic Network and Genes Regulating the Fresh Fruit Texture of Jujube (Ziziphus jujuba Mill.) Revealed via Metabolomic and Transcriptomic Analysis

The texture of fresh jujube fruit is related to its popularity and commercial value. The metabolic networks and essential genes that regulate the texture of jujube (Ziziphus jujuba) fruit are still unknown. In this study, two jujube cultivars with significantly different textures were selected by a texture analyzer. The four developmental stages of the exocarp and mesocarp of jujube fruit were studied separately using metabolomic and transcriptomic analyses. Differentially accumulated metabolites were enriched in several critical pathways related to cell wall substance synthesis and metabolism. Transcriptome analysis confirmed this by finding enriched differential expression genes in these pathways. Combined analysis showed that 'Galactose metabolism' was the most overlapping pathway in two omics. Genes such as β-Gal, MYB and DOF may affect fruit texture by regulating cell wall substances. Overall, this study provides an essential reference for the establishment of texture-related metabolic and gene networks of jujube fruit.

Molecular mechanisms involved in fruit cracking: A review

Several fleshy fruits are highly affected by cracking, a severe physiological disorder that compromises their quality and causes high economical losses to the producers. Cracking can occur due to physiological, genetic or environmental factors and may happen during fruit growth, development and ripening. Moreover, in fleshy fruits, exocarp plays an important role, acting as a mechanical protective barrier, defending against biotic or abiotic factors. Thus, when biochemical properties of the cuticle + epidermis + hypodermis are affected, cracks appear in the fruit skin. The identification of genes involved in development such as cell wall modifications, biosynthesis and transport of cuticular waxes, cuticular membrane deposition and associated transcription factors provides new insights to better understand how fruit cracking is affected by genetic factors. Amongst the major environmental stresses causing cracking are excessive water during fruit development, leading to imbalances in cations such as Ca. This review focus on expression of key genes in these pathways, in their influence in affected fruits and the potential for molecular breeding programs, aiming to develop cultivars more resistant to cracking under adverse environmental conditions.

Galactosyltransferase GhRFS6 interacting with GhOPR9 involved in defense against Verticillium wilt in cotton

The soil-borne fungus Verticillium dahliae causes Verticillium wilt (VW), one of the most devastating diseases of cotton. In a previous study showed that GhOPR9 played a positive role in resistance of cotton to VW through the regulation of the Jasmonic acid (JA) pathway. Furtherly, we also found that GhOPR9 interacted with a sucrose galactosyltransferase GhRFS6. Raffinose synthase (RFS) plays a key role in plant innate immunity, including the abiotic stress of drought, darkness. However, there were few reports on the effects of RFS on biotic stress. In this study, we verified the function of GhRFS6 to VW. The expression analysis showed that the GhRFS6 may be regulated by various stresses, and it was upregulated under Vd076 and Vd991 pressures. Inhibition of GhRFS6 expression, hydrogen peroxide (H₂O₂) content, lignin content, cell wall thickness and a series of defense responses were decreased, and the resistance of cotton to V. dahliae was decreased. In addition, this study showed that GhRFS6 has glycosyltransferase activity and can participate in the regulation of α-galactosidase activity and raffinose and inositol synthesis. And that galactose was accumulated in cotton roots after GhRFS6 silencing, which is beneficial for the colonization and growth of V. dahliae. Furthermore, overexpression of GhRFS6 in Arabidopsis thaliana enhanced plant resistance to V. dahliae. In GUS staining, the promoter expression position of GhRFS6 was also altered after V. dahliae infection. Meanwhile, GhRFS6 has also been shown to resist VW through the regulation of the JA pathway. These results suggest that GhRFS6 is a potential molecular target for improving cotton resistance to VW.

Identification and Characterization of Long Non-Coding RNAs: Implicating Insights into Their Regulatory Role in Kiwifruit Ripening and Softening during Low-Temperature Storage

Long non-coding RNAs (lncRNAs) are crucial players regulating many biological processes in plants. However, limited knowledge is available regarding their roles in kiwifruit ripening and softening. In this study, using lncRNA-seq technology, 591 differentially expressed (DE) lncRNAs (DELs) and 3107 DE genes (DEGs) were identified from kiwifruit stored at 4 °C for 1, 2, and 3 weeks in comparison with non-treated control fruits. Of note, 645 DEGs were predicted to be targets of DELs (DEGTLs), including some DE protein-coding genes (such as β-amylase and pectinesterase). DEGTL-based GO enrichment analysis revealed that these genes were significantly enriched in cell wall modification and pectinesterase activity in 1 W vs. CK and 3 W vs. CK, which might be closely related to the fruit softening during low-temperature storage. Moreover, KEGG enrichment analysis revealed that DEGTLs were significantly associated with starch and sucrose metabolism. Our study revealed that lncRNAs play critical regulatory roles in kiwifruit ripening and softening under low-temperature storage, mainly by mediating the expression of starch and sucrose metabolism and cell wall modification related genes.

Beta-galactosidase gene family genome-wide identification and expression analysis of members related to fruit softening in melon (Cucumis melo L.)

BACKGROUND

Texture quality is impotent for melon (Cucumis melo L.) fruit. β-galactosidase (β-Gal, EC 3.2.1.23) is an important cell wall glycosyl hydrolase involved in fruit softening, However, the β-Gal gene (BGALs) family hasn't been identified genome-wide in melon. Thus, it's necessary to conduct an in-depth bioinformatic analysis on melon BGALs family and to seek out the key members who participated in melon fruit softening.

RESULTS

A total of 21 BGALs members designated as CmBGAL1-CmBGAL21 were identified genome-wide in melon, clustered into A-G seven clades. Among them, three duplications CmBGAL1:CmBGAL3, CmBGAL19:CmBGAL21, and CmBGAL20:CmBGAL21 happened. For conserved domains, besides the Glyco_hydro_35 domain (PF01301), all the members also contained the GHD domain (PF17834) except for CmBGAL12, and the Gal_Lectin (PF02140) domain existed in most CmBGALs at the C-termini. Motifs, protein secondary and tertiary structure analysis showed that the CmBGAL12 is a unique member. Moreover, protein-protein association network analysis showed that the CmBGAL12 is the only node protein. Furthermore, spatiotemporal expression pattern analysis by quantitative real-time PCR (qRT-PCR) suggested that most of CmBGALs expressed in tissues with vigorous cell wall remodeling/disassembly. In addition, cis-acting regulatory elements analysis in promoters inferred that CmBGALs might participate in diverse responsiveness to phytohormone, biotic and abiotic signaling.

CONCLUSIONS

A novel clade of CmBGAL members (Clade F) related to melon fruit softening was discovered, since their expression showed a specific surge in the mature fruit of 'HPM' with mealy texture (softening sharply), but not in 'HDB' with crisp texture (softening bluntly). The homologous CmBGAL7-11 in Clade F exhibited identical spatiotemporal expression patterns may multiple genes leading to melon fruit softening.

Abscisic acid-responsive transcription factors PavDof2/6/15 mediate fruit softening in sweet cherry

Softening is a key step during fruit ripening that is modulated by the interplay between multiple phytohormones. The antagonistic action of abscisic acid (ABA) and auxin determines the rate of fruit ripening and softening. However, the transcription factors that integrate ABA and auxin signals to regulate fruit softening remain to be determined. In this study, we identified several DNA-binding with One Finger (Dof) transcription factors essential for ABA-promoted fruit softening, based on transcriptome analysis of two sweet cherry (Prunus avium L.) varieties with different fruit firmness. We show that PavDof6 directly binds to the promoters of genes encoding cell wall-modifying enzymes to activate their transcription, while PavDof2/15 directly repress their transcription. Transient overexpression of PavDof6 and PavDof2/15 in sweet cherry fruits resulted in precocious and delayed softening, respectively. In addition, we show that the auxin response factor PavARF8, the expression of whose encoding gene is repressed by ABA, activates PavDof2/15 transcription. Furthermore, PavDof2/6/15 and PavARF8 directly bind to the 9-cis-epoxycarotenoid dioxygenase 1 (PavNCED1) promoter and regulate its expression, forming a feedback mechanism for ABA-mediated fruit softening. These findings unveil the physiological framework of fruit softening and establish a direct functional link between the ABA-PavARF8-PavDofs module and cell-wall-modifying genes in mediating fruit softening.

Variation in Cell Wall Metabolism and Flesh Firmness of Four Apple Cultivars during Fruit Development

Fruit ripening and softening are highly complex processes, and there is an interplay and coordination between the metabolic pathways that are involved in the biological processes. In this study, we aimed to elucidate the variation in the characters and possible causes of cell wall materials and morphological structure during apple fruits development. We studied the cell wall material (CWM), structure, cellular morphology, hydrolase activity, and the transcriptional levels of the related genes in four apple varieties 'Ruixue' and 'Ruixianghong' and their parents ('Pink Lady' and 'Fuji') during fruit development. The decrease in the contents of CWMs, sodium carbonate soluble pectin, hemicellulose, and cellulose were positively correlated with the decline in the hardness during the fruit development. In general, the activities of polygalacturonase, β-galactosidase, and cellulase enzymes increased during the late developmental period. As the fruit grew, the fruit cells of all of the cultivars gradually became larger, and the cell arrangement became more relaxed, the fruit cell walls became thinner, and the intercellular space became larger. In conclusion, the correlation analysis indicated that the up-regulation of the relative expression levels of ethylene synthesis and cell wall hydrolase genes enhanced the activity of the cell wall hydrolase, resulting in the degradation of the CWMs and the depolymerization of the cell wall structure, which affected the final firmness of the apple cultivars in the mature period.

B, Iquebal MA, Bhattacharya RC, Rai A, Kumar D. Genome wide identification of lncRNAs and circRNAs having regulatory role in fruit shelf life in health crop cucumber (Cucumis sativus L.)

Cucumber is an extremely perishable vegetable; however, under room conditions, the fruits become unfit for consumption 2-3 days after harvesting. One natural variant, DC-48 with an extended shelf-life was identified, fruits of which can be stored up to 10-15 days under room temperature. The genes involved in this economically important trait are regulated by non-coding RNAs. The study aims to identify the long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) by taking two contrasting genotypes, DC-48 and DC-83, at two different fruit developmental stages. The upper epidermis of the fruits was collected at 5 days and 10 days after pollination (DAP) for high throughput RNA sequencing. The differential expression analysis was performed to identify differentially expressed (DE) lncRNAs and circRNAs along with the network analysis of lncRNA, miRNA, circRNA, and mRNA interactions. A total of 97 DElncRNAs were identified where 18 were common under both the developmental stages (8 down regulated and 10 upregulated). Based on the back-spliced reads, 238 circRNAs were found to be distributed uniformly throughout the cucumber genomes with the highest numbers (71) in chromosome 4. The majority of the circRNAs (49%) were exonic in origin followed by inter-genic (47%) and intronic (4%) origin. The genes related to fruit firmness, namely, polygalacturonase, expansin, pectate lyase, and xyloglucan glycosyltransferase were present in the target sites and co-localized networks indicating the role of the lncRNA and circRNAs in their regulation. Genes related to fruit ripening, namely, trehalose-6-phosphate synthase, squamosa promoter binding protein, WRKY domain transcription factors, MADS box proteins, abscisic stress ripening inhibitors, and different classes of heat shock proteins (HSPs) were also found to be regulated by the identified lncRNA and circRNAs. Besides, ethylene biosynthesis and chlorophyll metabolisms were also found to be regulated by DElncRNAs and circRNAs. A total of 17 transcripts were also successfully validated through RT PCR data. These results would help the breeders to identify the complex molecular network and regulatory role of the lncRNAs and circRNAs in determining the shelf-life of cucumbers.

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

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

Ozone Treatment Improves the Texture of Strawberry Fruit during Storage

The major aim of this study was to check whether a cyclic ozonation process will affect the preservation of the texture of strawberries stored at room temperature. Strawberry fruit was stored for 3 days at room temperature and ozonated with gaseous ozone at a concentration of 10 and 100 ppm for 30 min, every 12 h of storage. Research showed that the ozonation process inhibited the texture deterioration of the fruit during storage. The positive effect of ozone was directly related to the inhibition of the activity of enzymes involved in the degradation of the fruit cell walls, as well as indirectly from the improved energy metabolism of the fruit. The higher level of energy charge corresponded to the higher resistance of ozonated fruit to abiotic stress, leading to the maintenance of the integrity of cell membranes and, consequently, to maintaining good hardness of the fruit throughout the storage period.

Immobilized fungal enzymes: Innovations and potential applications in biodegradation and biosynthesis

Microbial enzymes catalyze various reactions inside and outside living cells. Among the widely studied enzymes, fungal enzymes have been used for some of the most diverse purposes, especially in bioremediation, biosynthesis, and many nature-inspired commercial applications. To improve their stability and catalytic ability, fungal enzymes are often immobilized on assorted materials, conventional as well as nanoscale. Recent advances in fungal enzyme immobilization provide effective and sustainable approaches to achieve improved environmental and commercial outcomes. This review aims to provide a comprehensive overview of commonly studied fungal enzymes and immobilization technologies. It also summarizes recent advances involving immobilized fungal enzymes for the degradation or assembly of compounds used in the manufacture of products, such as detergents, food additives, and fossil fuel alternatives. Furthermore, challenges and future directions are highlighted to offer new perspectives on improving existing technologies and addressing unexplored fields of applications.

Identification in silico and expression analysis of a β-1-4-endoglucanase and β-galactosidase genes related to ripening in guava fruit

BACKGROUND

Guava fruit softening is a crucial process during ripening and this process involves a number of enzymes that modifies the cell wall. Two of the enzymes that regulate this process are (a) the β-1, 4-endoglucanase 17 (BEG) which hydrolyze β-1, 4 bonds from cellulose and hemicellulose, and (b) β-galactosidase (BGA) that hydrolyzes pectin chains. Bioinformatics and expression analysis information on these genes is limited in guava fruit.

RESULTS

A fragment of a β-1, 4-endoglucanase 17 (PgE17), and another of a β-galactosidase (PgGa1) were identified. These sequences have a similarity of more than 85% with those reported in the NCBI database. In the guava genome, one homologous sequence was found for PgE17 in Chr 4 and two homologous to PgGa1: one in Chr 3 and the other one in Chr 6. Putative protein PgE17 contains part of the glyco_hydro_9 domain. Putative protein PgGa1 has a part of the glyco_hydro_35 domain. Phylogenetic analysis of PgE17 and PgGa1 revealed that both are highly conserved inside the Myrtaceae family. In silico expression analysis showed that both PgE17 and PgGa1 work in a coordinated way with other cell wall modifier enzymes. Expression of these genes was found in all the guava samples analyzed. However, the highest expression was found in the fruit in the breaking and ripe states.

CONCLUSIONS

A β-1, 4-endoglucanase 17, and β-galactosidase 1 sequences were identified. PgE17 and PgGa1 are expressed in all the plant tissues, and fruit ripening states. Although, the highest expression was on breaker and ripe states.

Genome-Wide Association Study of Root Mealiness and Other Texture-Associated Traits in Cassava

Cassava breeders have made significant progress in developing new genotypes with improved agronomic characteristics such as improved root yield and resistance against biotic and abiotic stresses. However, these new and improved cassava (Manihot esculenta Crantz) varieties in cultivation in Nigeria have undergone little or no improvement in their culinary qualities; hence, there is a paucity of genetic information regarding the texture of boiled cassava, particularly with respect to its mealiness, the principal sensory quality attribute of boiled cassava roots. The current study aimed at identifying genomic regions and polymorphisms associated with natural variation for root mealiness and other texture-related attributes of boiled cassava roots, which includes fibre, adhesiveness (ADH), taste, aroma, colour, and firmness. We performed a genome-wide association (GWAS) analysis using phenotypic data from a panel of 142 accessions obtained from the National Root Crops Research Institute (NRCRI), Umudike, Nigeria, and a set of 59,792 high-quality single nucleotide polymorphisms (SNPs) distributed across the cassava genome. Through genome-wide association mapping, we identified 80 SNPs that were significantly associated with root mealiness, fibre, adhesiveness, taste, aroma, colour and firmness on chromosomes 1, 4, 5, 6, 10, 13, 17 and 18. We also identified relevant candidate genes that are co-located with peak SNPs linked to these traits in M. esculenta. A survey of the cassava reference genome v6.1 positioned the SNPs on chromosome 13 in the vicinity of Manes.13G026900, a gene recognized as being responsible for cell adhesion and for the mealiness or crispness of vegetables and fruits, and also known to play an important role in cooked potato texture. This study provides the first insights into understanding the underlying genetic basis of boiled cassava root texture. After validation, the markers and candidate genes identified in this novel work could provide important genomic resources for use in marker-assisted selection (MAS) and genomic selection (GS) to accelerate genetic improvement of root mealiness and other culinary qualities in cassava breeding programmes in West Africa, especially in Nigeria, where the consumption of boiled and pounded cassava is low.

Nanoparticle-based amplification for sensitive detection of β-galactosidase activity in fruits

Development of fast and sensitive assays for enzyme activity detection has received a great deal of attention because of the wide spread applications in measurements of numerous clinical, food and environmental processes. Herein, a novel amplification approach to enhance the sensitivity of colorimetric assays for detection of β-galactosidase (β-Gal) activity is proposed. β-Gal detection is important in biomedical applications and in food industry, where it is associated with the ripening process of fruits. The method is based on the use of multivalent cerium oxide nanoparticles (CeNPs) which catalyze the oxidation of 4-aminophenol (4-AP) produced in the hydrolysis process of the 4-aminophenyl-β-d-galactopyranoside substrate (4-APG) by β-Gal, thus enhancing detection sensitivity of β-Gal in the visible range. The developed assay is highly sensitive and easy to use. Using the optimized procedure, a limit of detection of 0.06 mU/mL was obtained with a linearity range up to 2.0 mU/mL. The feasibility of the method was demonstrated for detection of β-Gal activity in fruits and the results were compared with the conventional assay, providing over a 30-fold amplification as compared to a commercially available β-Gal protocol. The advantage of the presented assay is its biocatalytic event amplified by a secondary reaction, which enables much more sensitive detection of the enzymatic product. The sensing platform can be applied broadly to a variety of applications that rely on β-Gal activity measurements.

Colletotrichum fioriniae and Colletotrichum godetiae Causing Postharvest Bitter Rot of Apple in South Tyrol (Northern Italy)

South Tyrol (northern Italy) harbors one of the largest interconnected apple farming areas in Europe, contributing approximately 10% to the apple production of the European Union. Despite the availability of sophisticated storage facilities, postharvest diseases occur, one of which is bitter rot of apple. In Europe, this postharvest disease is mainly caused by the Colletotrichum acutatum species complex. This study aimed to characterize the Colletotrichum spp. isolated from decayed apple fruit collected in 2018 and 2019 in South Tyrol. The characterization of Colletotrichum spp. was accomplished based on multilocus DNA sequences of four different genomic regions-actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), histone H3 (HIS3), and the internal transcribed spacer (ITS) region-as well as morphological and pathogenicity assessment. A phylogenetic analysis based on multilocus DNA sequences showed that the isolates obtained from apples with symptoms of bitter rot belonged to the species Colletotrichum godetiae and Colletotrichum fioriniae, which are part of the Colletotrichum acutatum species complex. A third species isolated from apples belonging to the same species complex, Colletotrichum salicis, was described in this area. Moreover, the Colletotrichum isolates found in this study proved to be virulent on Cripps Pink, Golden Delicious, and Roho 3615/Evelina. To the best of our knowledge, C. godetiae and C. fioriniae have so far never been mentioned as postharvest pathogens of apple in Italy, although the reanalysis of samples collected in the past indicates that these pathogens have been occurring in Italy for at least a decade. So far, bitter rot seems to play a minor role as a postharvest disease in South Tyrol, but it was disproportionately represented on a few scab-resistant apple cultivars, which are increasingly planted in organically managed orchards. Considering that the expansion of organic apple production and the conversion to new potentially Colletotrichum-susceptible cultivars will continue, the present study represents an important contribution toward a better understanding of bitter rot in this geographic area.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Genome-Wide Analysis of Glycoside Hydrolase Family 35 Genes and Their Potential Roles in Cell Wall Development in Medicago truncatula

Plant β-galactosidases (BGAL) function in various cell wall biogeneses and modifications, and they belong to the glycoside hydrolase family. However, the roles of BGAL family members in Medicago truncatula cell wall remodeling remain unclear. In this study, a total of 25 MtBGAL members of the glycoside hydrolase gene family 35 were identified, and they were clustered into nine sub-families. Many cis-acting elements possibly related to MeJA and abscisic acid responses were identified in the promoter region of the MtBGAL genes. Transcript analyses showed that these MtBGAL genes exhibited distinct expression patterns in various tissues and developing stem internodes. Furthermore, a stem-specific expression module associated with cell wall metabolic pathways was identified by weighted correlation network analysis (WGCNA). In particular, MtBGAL1 and MtBGAL23 within the stem-specific expression module were highly expressed in mature stems. In addition, several genes involved in lignin, cellulose, hemicellulose and pectin pathways were co-expressed with MtBGAL1 and MtBGAL23. It was also found that MtBGAL1 and MtBGAL23 were localized to the cell wall at the subcellular level, indicating their roles in the modification of cell wall metabolites in Medicago. As a whole, these results will be useful for further functional characterization and utilization of BGAL genes in cell wall modifications aiming to improve the quality of legume forage crops.

Why Consumers Prefer Green Friariello Pepper: Changes in the Protein and Metabolite Profiles Along the Ripening

Fruit ripening is a physiologically complex process altering texture, color, flavor, nutritional value, and aroma. However, some fruits are consumed at an early stage of ripening due to the very peculiar characteristics varying during ripening. An example is a particular ecotype of pepper, the Friariello pepper, among the most important representatives of Campania (Southern Italy) agro-alimentary culture. In this study, for the first time, the physiological variations during Friariello ripening (green, veraison, and fully ripe) were evaluated by hyphenated mass spectrometric techniques in a proteomic and metabolomic approach. We found that Lutein and Thaumatin are particularly abundant in the green Friariello. Friariello at an early stage of ripening, is rich in volatile compounds like butanol, 1 3 5-cycloheptatriene, dimethylheptane, α-pinene, furan-2-penthyl, ethylhexanol, 3-carene, detected by gas chromatography-mass spectrometry (GC-MS) analysis, which give it the peculiar fresh and pleasant taste. The detected features of Friariello may justify its preferential consumption in the early ripening stage and outline new knowledge aimed at preserving specific agro-cultural heritage.

Integrated analysis of lncRNA and mRNA transcriptomes reveals the potential regulatory role of lncRNA in kiwifruit ripening and softening

Kiwifruit has gained increasing attention worldwide for its unique flavor and high nutritional value. Rapid softening after harvest greatly shortens its shelf-life and reduces the commercial value. Therefore, it is imperative and urgent to identify and clarify its softening mechanism. This study aimed to analyze and compare the long noncoding RNA (lncRNA) and mRNA expression patterns in ABA-treated (ABA) and room temperature (RT)-stored fruits with those in freshly harvested fruits (CK) as control. A total of 697 differentially expressed genes (DEGs) and 81 differentially expressed lncRNAs (DELs) were identified while comparing ABA with CK, and 458 DEGs and 143 DELs were detected while comparing RT with CK. The Kyoto Encyclopedia of Genes and Genomes analysis of the identified DEGs and the target genes of DELs revealed that genes involved in starch and sucrose metabolism, brassinosteroid biosynthesis, plant hormone signal transduction, and flavonoid biosynthesis accounted for a large part. The co-localization networks, including 38 DEGs and 31 DELs in ABA vs. CK, and 25 DEGs and 25 DELs in RT vs. CK, were also performed. Genes related to fruit ripening, such as genes encoding β-galactosidase, mannan endo-1,4-β-mannosidase, pectinesterase/pectinesterase inhibitor, and NAC transcription factor, were present in the co-localization network, suggesting that lncRNAs were involved in regulating kiwifruit ripening. Notably, several ethylene biosynthesis- and signaling-related genes, including one 1-aminocyclopropane-1-carboxylic acid oxidase gene and three ethylene response factor genes, were found in the co-localization network of ABA vs. CK, suggesting that the promoting effect of ABA on ethylene biosynthesis and fruit softening might be embodied by increasing the expression of these lncRNAs. These results may help understand the regulatory mechanism of lncRNAs in ripening and ABA-induced fruit softening of kiwifruit.

Changes in cell wall components and polysaccharide-degrading enzymes in relation to differences in texture during sweetpotato storage root growth

Sweetpotato has special texture characteristics, which directly affect the eating quality and post-production processing quality of sweetpotato. To investigate the texture change mechanism of sweetpotato during the growth process, this study selected two varieties with significant differences in texture from 35 varieties. The storage roots were sampled at 50, 80, 110, and 140 days after planting. Measure the texture parameters, the cell wall composition content, cell wall-related enzyme activities and the expression of expansin genes of sweetpotato storage roots. The results show that the hardness, adhesiveness and chewiness parameters of 'Yushu No 10' were significantly lower than those of 'Mianfen No 1', they have significantly different texture properties. In terms of cell wall composition, the soluble pectin content of 'Yushu No 10' was more than twice that of 'Mianfen No 1', whereas the insoluble pectin content was lower than that of 'Mianfen No 1', with the cellulose content of 'Yushu No 10' being significantly higher than that of 'Mianfen No 1'. In terms of cell wall-related enzymes, 'Yushu No 10' hardness gumminess and chewiness had a significant correlation with hemicellulose activity, and 'Mianfen No 1' had insignificant correlation with four cell wall-related enzymes. Expansin genes were also expressed differently during the various stages of root tubers expansin. The expressions of IbEXP1, IbEXP2 and IbEXPL1 were significantly correlated with the changes in cell wall component content, and were related to the qualitative structure changes. The research conclusion shows that the texture changes during the growth of sweetpotato are related to cell wall composition, cell wall-related enzyme activity changes, and the expression of expansin genes. This study provides theoretical guidance for in-depth study of texture changes of sweetpotato, post-harvest processing and utilization and quality improvement of storage roots.

Identification of Candidate Genes Involved in Fruit Ripening and Crispness Retention Through Transcriptome Analyses of a 'Honeycrisp' Population

Crispness retention is a postharvest trait that fruit of the 'Honeycrisp' apple and some of its progeny possess. To investigate the molecular mechanisms of crispness retention, progeny individuals derived from a 'Honeycrisp' × MN1764 population with fruit that either retain crispness (named "Retain"), lose crispness (named "Lose"), or that are not crisp at harvest (named "Non-crisp") were selected for transcriptomic comparisons. Differentially expressed genes (DEGs) were identified using RNA-Seq, and the expression levels of the DEGs were validated using nCounter®. Functional annotation of the DEGs revealed distinct ripening behaviors between fruit of the "Retain" and "Non-crisp" individuals, characterized by opposing expression patterns of auxin- and ethylene-related genes. However, both types of genes were highly expressed in the fruit of "Lose" individuals and 'Honeycrisp', which led to the potential involvements of genes encoding auxin-conjugating enzyme (GH3), ubiquitin ligase (ETO), and jasmonate O-methyltransferase (JMT) in regulating fruit ripening. Cell wall-related genes also differentiated the phenotypic groups; greater numbers of cell wall synthesis genes were highly expressed in fruit of the "Retain" individuals and 'Honeycrisp' when compared with "Non-crisp" individuals and MN1764. On the other hand, the phenotypic differences between fruit of the "Retain" and "Lose" individuals could be attributed to the functioning of fewer cell wall-modifying genes. A cell wall-modifying gene, MdXTH, was consistently identified as differentially expressed in those fruit over two years in this study, so is a major candidate for crispness retention.

Genome-Wide Association Study Reveals Candidate Genes Involved in Fruit Trait Variation in Persian Walnut (Juglans regia L.)

Elucidating the genetic determinants of fruit quality traits in walnut is essential to breed new cultivars meeting the producers and consumers' needs. We conducted a genome-wide association study (GWAS) using multi-locus models in a panel of 170 accessions of Juglans regia from the INRAE walnut germplasm collection, previously genotyped using the Axiom^TM J. regia 700K SNP array. We phenotyped the panel for 25 fruit traits related to morphometrics, shape, volume, weight, ease of cracking, and nutritional composition. We found more than 60 marker-trait associations (MTAs), including a highly significant SNP associated with nut face diameter, nut volume and kernel volume on chromosome 14, and 5 additional associations were detected for walnut weight. We proposed several candidate genes involved in nut characteristics, such as a gene coding for a beta-galactosidase linked to several size-related traits and known to be involved in fruit development in other species. We also confirmed associations on chromosomes 5 and 11 with nut suture strength, recently reported by the University of California, Davis. Our results enhance knowledge of the genetic control of important agronomic traits related to fruit quality in walnut, and pave the way for the development of molecular markers for future assisted selection.

Cell type-specific gene expression underpins remodelling of cell wall pectin in exocarp and cortex during apple fruit development

In apple (Malus×domestica) fruit, the different layers of the exocarp (cuticle, epidermis, and hypodermis) protect and maintain fruit integrity, and resist the turgor-driven expansion of the underlying thin-walled cortical cells during growth. Using in situ immunolocalization and size exclusion epitope detection chromatography, distinct cell type differences in cell wall composition in the exocarp were revealed during apple fruit development. Epidermal cell walls lacked pectic (1→4)-β-d-galactan (associated with rigidity), whereas linear (1→5)-α-l-arabinan (associated with flexibility) was exclusively present in the epidermal cell walls in expanding fruit and then appeared in all cell types during ripening. Branched (1→5)-α-l-arabinan was uniformly distributed between cell types. Laser capture microdissection and RNA sequencing (RNA-seq) were used to explore transcriptomic differences controlling cell type-specific wall modification. The RNA-seq data indicate that the control of cell wall composition is achieved through cell-specific gene expression of hydrolases. In epidermal cells, this results in the degradation of galactan side chains by possibly five β-galactosidases (BGAL2, BGAL7, BGAL10, BGAL11, and BGAL103) and debranching of arabinans by α-arabinofuranosidases AF1 and AF2. Together, these results demonstrate that flexibility and rigidity of the different cell layers in apple fruit during development and ripening are determined, at least in part, by the control of cell wall pectin remodelling.

Transcriptome analysis of acerola fruit ripening: insights into ascorbate, ethylene, respiration, and softening metabolisms

The first transcriptome coupled to metabolite analyses reveals major trends during acerola fruit ripening and shed lights on ascorbate, ethylene signalling, cellular respiration, sugar accumulation, and softening key regulatory genes. Acerola is a fast growing and ripening fruit that exhibits high amounts of ascorbate. During ripening, the fruit experience high respiratory rates leading to ascorbate depletion and a quickly fragile and perishable state. Despite its growing economic importance, understanding of its developmental metabolism remains obscure due to the absence of genomic and transcriptomic data. We performed an acerola transcriptome sequencing that generated over 600 million reads, 40,830 contigs, and provided the annotation of 25,298 unique transcripts. Overall, this study revealed the main metabolic changes that occur in the acerola ripening. This transcriptional profile linked to metabolite measurements, allowed us to focus on ascorbate, ethylene, respiration, sugar, and firmness, the major metabolism indicators for acerola quality. Our results suggest a cooperative role of several genes involved in AsA biosynthesis (PMM, GMP1 and 3, GME1 and 2, GGP1 and 2), translocation (NAT3, 4, 6 and 6-like) and recycling (MDHAR2 and DHAR1) pathways for AsA accumulation in unripe fruits. Moreover, the association of metabolites with transcript profiles provided a comprehensive understanding of ethylene signalling, respiration, sugar accumulation and softening of acerola, shedding light on promising key regulatory genes. Overall, this study provides a foundation for further examination of the functional significance of these genes to improve fruit quality traits.