Search

Kiwifruit (Actinidia chinensis), a recently commercialized horticultural crop, is rich in various nutrient compounds. However, the regulatory networks controlling the dynamic changes in key metabolites among different tissues remain largely unknown. Here, high-resolution spatiotemporal datasets obtained by ultraperformance liquid chromatography-tandem mass spectrometry methodology and RNA-seq were employed to investigate the dynamic changes in the metabolic and transcriptional landscape of major kiwifruit tissues across different developmental stages, including from fruit skin, outer pericarp, inner pericarp, and fruit core. Kiwifruit spatiotemporal regulatory networks (KSRN) were constructed by integrating the 1,243 identified metabolites and co-expressed genes into 10 different clusters and 11 modules based on their biological functions. These networks allowed the generation of a global map for the major metabolic and transcriptional changes occurring throughout the life cycle of different kiwifruit tissues and discovery of the underlying regulatory networks. KSRN predictions confirmed previously established regulatory networks, including the spatiotemporal accumulation of anthocyanin and ascorbic acid (AsA). More importantly, the networks led to the functional characterization of three transcription factors: an A. chinensis ethylene response factor 1, which negatively controls sugar accumulation and ethylene production by perceiving the ripening signal, a basic-leucine zipper 60 (AcbZIP60) transcription factor, which is involved in the biosynthesis of AsA as part of the L-galactose pathway, and a transcription factor related to apetala 2.4 (RAP2.4), which directly activates the expression of the kiwi fruit aroma terpene synthase gene AcTPS1b. Our findings provide insights into spatiotemporal changes in kiwifruit metabolism and generate a valuable resource for the study of metabolic regulatory processes in kiwifruit as well as other fruits., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Dry matter content (DMC), firmness and soluble solid content (SSC) are important indicators for assessing the quality attributes and determining the maturity of kiwifruit. However, traditional measurement methods are time-consuming, labor-intensive, and destructive to the kiwifruit, leading to resource wastage. In order to solve this problem, this study has tracked the flowering, fruiting, maturing and collecting processes of Ya'an red-heart kiwifruit, and has proposed a non-destructive method for kiwifruit quality attribute assessment and maturity identification that combines fluorescence hyperspectral imaging (FHSI) technology and chemometrics. Specifically, first of all, three different spectral data preprocessing methods were adopted, and PLSR was used to evaluate the quality attributes (DMC, firmness, and SSC) of kiwifruit. Next, the differences in accuracy of different models in discriminating kiwifruit maturity were compared, and an ensemble learning model based on LightGBM and GBDT models was constructed. The results indicate that the ensemble learning model outperforms single machine learning models. In addition, the application effects of the 'Convolutional Neural Network'-'Multilayer Perceptron' (CNN-MLP) model under different optimization algorithms were compared. To improve the robustness of the model, an improved whale optimization algorithm (IWOA) was introduced by modifying the acceleration factor. Overall, the IWOA-CNN-MLP model performs the best in discriminating the maturity of kiwifruit, with Accuracy test of 0.916 and Loss of 0.23. In addition, compared with the basic model, the accuracy of the integrated learning model SG-MSC-SEL was improved by about 12%-20 %. The research findings will provide new perspectives for the evaluation of kiwifruit quality and maturity discrimination using FHSI and chemometric methods, thereby promoting further research and applications in this field., Competing Interests: Declaration of competing interest We declare that we have neither financial nor personal relationships with other people or organizations that can inappropriately influence our work. There is no professional or any personal interest of any nature or kind in any product, service or company that could be considered as influencing the position or the review presented in the manuscript entitled “Fluorescence hyperspectral imaging technology combined with chemometrics for kiwifruit quality attribute assessment and non-destructive judgment of maturity”., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study aimed to elucidate the effects of storage temperature on various fruit quality attributes, physiological disorders, and associated metabolites in the 0.5, 3, or 10 °C stored hardy kiwifruit. Peel pitting, which was highest in the 0.5 °C stored fruit, was identified as a chilling injury symptom of hardy kiwifruit. Proline and branched-chain amino acid contents showed higher values at 0.5 °C stored fruit as chilling responses. On the other hand, fruit shriveling and decay were highest in the 10 °C after 5 weeks of storage. The 10 °C storage induced fruit ripening during 3 weeks, but fruit shriveling and decay were severe after 5 weeks of storage. Therefore, storing the 'Autumn Sense' hardy kiwifruit at proper temperatures would be more beneficial, as it alters targeted metabolites and helps reduce the incidence of physiological disorders during cold storage., Competing Interests: Declaration of competing interest The authors have declared that no competing interests exist., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Previous research on the ripening process of many fruit crop varieties typically involved analyses of the conserved genetic factors among species. However, even for seemingly identical ripening processes, the associated gene expression networks often evolved independently, as reflected by the diversity in the interactions between transcription factors (TFs) and the targeted cis-regulatory elements (CREs). In this study, explainable deep learning (DL) frameworks were used to predict expression patterns on the basis of CREs in promoter sequences. We initially screened potential lineage-specific CRE-TF interactions influencing the kiwifruit ripening process, which is triggered by ethylene, similar to the corresponding processes in other climacteric fruit crops. Some novel regulatory relationships affecting ethylene-induced fruit ripening were identified. Specifically, ABI5-like bZIP, G2-like, and MYB81-like TFs were revealed as trans-factors modulating the expression of representative ethylene signaling/biosynthesis-related genes (e.g., ACS1, ERT2, and ERF143). Transient reporter assays and DNA affinity purification sequencing (DAP-Seq) analyses validated these CRE-TF interactions and their regulatory relationships. A comparative analysis with co-expression networking suggested that this DL-based screening can identify regulatory networks independently of co-expression patterns. Our results highlight the utility of an explainable DL approach for identifying novel CRE-TF interactions. These  imply that fruit crop species may have evolved lineage-specific fruit ripening-related cis-trans regulatory networks., (© 2024 The Author(s). The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Kiwifruit (Actinidia spp.), celebrated for its unique flavor and rich nutritional content, is a globally popular fruit. This fruit requires post-harvest ripening before consumption. However, the unpredictable ripening pace significantly impacts consumer acceptance and sales, thereby hindering the commercial growth of kiwifruit. To address this, understanding the key molecular mechanisms and metabolites governing postharvest ripening and senescence could offer valuable insights for developing storage strategies and breeding techniques in yellow-fleshed kiwifruits. We constructed two models that integrated these findings with existing theories. The first model suggests that, unlike the T6P-sucrose regulatory mechanism observed in plant leaves, the separation of harvested kiwifruit from the mother plant leads to an insufficient supply of T6P, which activates the SnRK1 kinase. This, in turn, inhibits the TOR kinase signaling pathway, regulating starch metabolism. The T6P-SnRK1-TOR-starch metabolism pathway plays a regulatory role during postharvest ripening, limiting excessive starch degradation that could accelerate aging and decay in yellow-fleshed kiwifruit. The second model highlights the role of abscisic acid (ABA), cytokinins (CKs), and ethylene in regulating the process, inducing the activation of ERFs and cell wall-degrading enzymes, promoting fruit postharvest softening. These findings indicate that at least two models, the T6P-SnRK1-TOR-starch metabolism model and the ABA-CKs-ethylene-cell wall degradation model, regulate postharvest fruit ripening, offering new insights into the artificial regulation of yellow-fleshed kiwifruit ripening speed., Competing Interests: Declarations. Ethics approval and consent to participate: The authors declare that the experimental research conducted on the plants described in this paper adheres to institutional, national, and international guidelines. The collection of fruits was carried out with full permission from the Jiangxi Academy of Sciences. Sampling was conducted at the Fengxin County Doctor Kiwifruit Base in Yichun City, China (114°45’ E, 28°34’ N), which is managed by the Jiangxi Academy of Sciences, with all necessary authorizations in place. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

The most widely cultivated species globally is Actinidia deliciosa cv. 'Hayward'. However, in recent years, consumers have shown greater demand for new varieties with novel flesh colour, flavour and appearance in international markets. To meet these expectations, one breeding study was started in 2016 at the University of Guilan in Iran to develop new kiwifruit cultivars with superior characteristics. In this breeding program, 201 female and 534 male hybrid genotypes were obtained from combinations of six different parents using the controlled cross-breeding technique. The evaluations were carried out over three consecutive stages. In the first stage, 201 female hybrid genotypes and control ('Golden') were evaluated based on 25 phenological and pomological traits. In the second stage, hybrids passed the desired threshold values in 7 key attributes were selected. Sensory testing in the next stage evaluated these selected hybrid genotypes more. As a result of the first stage, 30 hybrid genotypes with fruit weight (90 ≥ g) were selected. Then, in the second stage, 21 hybrids that showed acceptable dry matter, hue angle, flesh firmness, soluble solid content, acidity, and ascorbic acid were selected. Finally, 13 hybrid genotypes received high scores in sensory testing, and just two hybrid genotypes represented a 100% of novelty with positive texture. These genotypes were selected as potential cultivar candidates. In future studies, fruit yield, disease/pest resistance, and post-harvest performance trials of the 13 selected candidates will be evaluated at different sites. Thus, the ones that give the best results will be introduced to kiwifruit growers., (© 2024. The Author(s).)

Background: Kiwiberry is an emerging edible fruit with market potential owing to its advantages of small size, thin and hairless skin, and sweet taste. However, kiwiberry is highly susceptible to softening after harvest, which poses a challenge for storage and transport. To reveal the underlying cause of kiwiberry softening, it is essential to investigate the characteristics of postharvest fruit and the molecular mechanisms that affect changes in fruit firmness., Results: Morphological observations and analysis of physical parameters showed that the skin of kiwiberry did not change markedly from the 1st to the 7th day after harvest, while the colour of the inner pericarp gradually turned yellow. By the 9th day of room temperature storage, the kiwiberries began to rot. The hardness decreased rapidly from the 1st to the 5th day postharvest, reaching the low level on the 5th day. The starch and pectin contents of kiwiberry showed a downward trend with increasing storage time. Transcriptome sequencing and weighted gene co-expression network analysis identified 29 key genes associated with the changes in the hardness of kiwiberry after harvest. Gene Ontology enrichment analysis indicated that these 29 genes are mainly involved in pectin metabolism, starch synthesis, starch decomposition, and starch metabolism. In addition, three transcription factors, AGL31, HAT14, and ALC, were identified to be strongly positively correlated with the 29 genes that affect the hardness changes of kiwiberry after harvest, and 28 of the 29 key genes were predicted to be regulated by HAT14., Conclusions: These results reveal the changes in morphological characteristics and physiological indicators during the postharvest ripening and softening of kiwiberry stored under room temperature conditions. Transcriptome analysis identified 29 key genes and three transcription factors that affect the firmness changes of postharvest kiwiberry. The results of this study thus provide insight into the transcriptional regulatory mechanism of kiwiberry softening during storage to improve the postharvest quality., (© 2024. The Author(s).)

Background: Kiwifruit, belonging to the genus Actinidia, represents a unique fruit crop characterized by its modern cultivars being genetically diverse and exhibiting remarkable variations in morphological traits and adaptability to harsh environments. However, the genetic mechanisms underlying such morphological diversity remain largely elusive., Results: We report the high-quality genomes of five Actinidia species, including Actinidia longicarpa, A. macrosperma, A. polygama, A. reticulata, and A. rufa. Through comparative genomics analyses, we identified three whole genome duplication events shared by the Actinidia genus and uncovered rapidly evolving gene families implicated in the development of characteristic kiwifruit traits, including vitamin C (VC) content and fruit hairiness. A range of structural variations were identified, potentially contributing to the phenotypic diversity in kiwifruit. Notably, phylogenomic analyses revealed 76 cis-regulatory elements within the Actinidia genus, predominantly associated with stress responses, metabolic processes, and development. Among these, five motifs did not exhibit similarity to known plant motifs, suggesting the presence of possible novel cis-regulatory elements in kiwifruit. Construction of a pan-genome encompassing the nine Actinidia species facilitated the identification of gene DTZ79_23g14810 specific to species exhibiting extraordinarily high VC content. Expression of DTZ79_23g14810 is significantly correlated with the dynamics of VC concentration, and its overexpression in the transgenic roots of kiwifruit plants resulted in increased VC content., Conclusions: Collectively, the genomes and pan-genome of diverse Actinidia species not only enhance our understanding of fruit development but also provide a valuable genomic resource for facilitating the genome-based breeding of kiwifruit., (© 2024. The Author(s).)

Background: Ethylene plays a vital role in the ripening process of kiwifruit. A terrific amount of transcription factors (TFs) have been shown to regulate ethylene synthesis in various fruits., Results: In this research, two new NAC TFs, named AcNAC3 and AcNAC4, were isolated from kiwifruit, which belonged to NAM subfamily. Bioinformatics analysis showed that both AcNAC3 and AcNAC4 were hydrophilic proteins with similar three-dimensional structures. The expression levels of AcNAC3, AcNAC4 and AcACO1 increased during kiwifruit ripening, as well as were induced by ethylene and repressed by 1-methylcyclopropene (1-MCP). Correlation analysis exhibited that ethylene production was positively correlated with the expression levels of AcNAC3, AcNAC4 and AcACO1. Moreover, both AcNAC3 and AcNAC4 acted as transcriptional activators and could bind to and activate AcACO1 promoter., Conclusion: All results unveiled that the ethylene-induced AcNAC3 and AcNAC4 were transcriptional activators, and might participate in kiwifruit ripening and ethylene biosynthesis through activating AcACO1, providing a new insight of ethylene synthetic regulation during kiwifruit ripening. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Kiwifruit ripening is a complex and highly coordinated process that occurs in conjunction with the formation of fruit edible quality. The significance of epigenetic changes, particularly the impact of N6-methyladenosine (m6A) RNA modification on fruit ripening and quality formation, has been largely overlooked. We monitored m6A levels and gene expression changes in kiwifruit at four different stages using LC-MS/MS, MeRIP, RNA-seq, and validated the function of AcALKBH10 through heterologous transgenic expression in tomato. Notable m6A modifications occurred predominantly at the stop codons and the 3' UTRs and exhibited a gradual reduction in m6A levels during the fruit ripening process. Moreover, these m6A modifications in the aforementioned sites demonstrated a discernible inverse relationship with the levels of mRNA abundance throughout the ripening process, suggesting a repression effect of m6A modification in the modulation of kiwifruit ripening. We further demonstrated that AcALKBH10 rather than AcECT9 predominantly regulates m6A levels in ripening-related genes, thereby exerting the regulatory control over the ripening process and the accumulation of soluble sugars and organic acids, ultimately influencing fruit ripening and quality formation. In conclusion, our findings illuminate the epi-regulatory mechanism involving m6A in kiwifruit ripening, offering a fresh perspective for cultivating high-quality kiwifruit with enhanced nutritional attributes., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Background: Currently, organic farming has become a feasible approach for the production of high-quality fruits. To evaluate the response of fruit quality and mineral nutrition contents of Hayward Kiwifruit affected by different organic and inorganic fertilizers, the present study was conducted in Citrus and Subtropical Fruits Research Center, Iran, in 2017-2021, as a randomized block design with three replications. The studied treatments were organic fertilizers (cow, vermicompost and Azolla) and chemical fertilizers. After 4 years of fertilization, the fruit's nutritional elements content and some fruit bioactive compounds were evaluated after 3 months of cold storage and then analyzed by the principal component analysis (PCA) method., Results: The use of organic amendments boosted the calcium, phosphorus, potassium and iron content of the kiwifruits compared to chemical fertilizers. The highest fruit potassium and phosphorus content were recorded in the cow manure treatment. The lowest amount of nitrate and the highest calcium, zinc, copper and manganese accumulation were recorded in the fruits treated with vermicompost. In addition to mineral nutrients, the dry matter, total soluble solids, total phenolic and antioxidant capacity of kiwifruit were improved by the application of vermicompost amendment compared to the other fertilizer sources. However, the highest fruit vitamin C and total soluble carbohydrates were measured in the cow manure treatment. The PCA results of the fruit quality indices indicated that fertilization treatments were ranked as vermicompost (1.88) > cow manure (1.63) = chemical (1.60) > Azolla (1.54)., Conclusion: It is concluded that the application of 40 kg of vermicompost or 40 kg of cow manure in the next rank in Hayward kiwifruit orchards in March (growth stage beginning of bud swelling) may be a more suitable approach for improving the nutritional quality of the fruit. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Background: The changes in the physical structures of the products are the first things that consumers pay attention to. Therefore, it is essential and significant importance to take measures to improve the storage conditions of products and to minimize quality losses. The main objective of the study was to evaluate the effects of agro-ecological conditions on bioactive compounds and fruit quality of kiwifruit during cold storage. The 'Hayward' kiwifruit cultivar grown in Ordu, Giresun, Samsun, Rize, and Yalova provinces of Türkiye were kept at 0 ± 0.5 °C and relative humidity of 90 ± 5% for 150 d., Results: The kiwifruit obtained from the provinces of Yalova, Ordu, and Giresun experienced the least weight loss during cold storage. Kiwifruit from Samsun and Yalova provinces had the lowest fruit firmness, while those from Giresun had the highest on 150th d. The changes were observed in the skin and flesh colors of the kiwifruit belonging to all cultivation areas. The amount of vitamin C increased throughout the study in all ecological conditions, but the Yalova province's kiwifruit was found to have the highest levels. Additionally, in all ecologies, kiwifruit showed an increase in antioxidant activity, total phenolics, and total flavonoids, all known to have beneficial effects on human health. The total antioxidant activity and total phenolics were highest in the kiwifruit of Yalova province, but the total flavonoids were found in the kiwifruit of Rize and Ordu provinces., Conclusion: The study's results revealed that kiwifruit's bioactive compounds and quality parameters may vary depending on the cultivation area. Additionally, it can be stated that Yalova province kiwifruit experiences the least amount of postharvest quality losses., (© 2024. The Author(s).)

DNA-binding one zinc finger (DOF) transcription factors are crucial plant-specific regulators involved in growth, development, signal transduction, and abiotic stress response generation. However, the genome-wide identification and characterization of AcDOF genes and their regulatory elements in kiwifruit ( Actinidia chinensis ) has not been thoroughly investigated. In this study, we screened the kiwifruit genome database and identified 42 AcDOF genes ( AcDOF1 to AcDOF42 ). Phylogenetic analysis facilitated the categorization of these genes into five subfamilies ( DOF -a, DOF -b, DOF -c, DOF -d, and DOF -e). We further analyzed the motifs, conserved domains, gene structures, and collinearity of the AcDOF gene family. Gene ontology (GO) enrichment analysis indicated significant enrichment in the "flower development" term and the "response to abiotic stress" category. Promoter prediction analysis revealed numerous cis-regulatory elements related to responses to light, hormones, and low-temperature and drought stress in AcDOF promoters. RNA-seq expression profiles demonstrated the tissue-specific expression of AcDOF genes. Quantitative real-time PCR results showed that six selected genes ( AcDOF04 , AcDOF09 , AcDOF11 , AcDOF13 , AcDOF21 , and AcDOF22 ) were differentially induced by abscisic acid (ABA), methyl jasmonate (MeJA), and cold, salt, and drought stresses, with AcDOF22 specifically expressed at high levels in drought-tolerant cultivars. Further experiments indicated that transient AcDOF22 overexpression in kiwifruit leaf disks reduced water loss and chlorophyll degradation. Additionally, AcDOF22 was localized to the nucleus and exhibited transcriptional activation, enhancing drought resistance by activating the downstream drought marker gene AcDREB2A . These findings lay the foundation for elucidating the molecular mechanisms of drought resistance in kiwifruit and offer new insights into drought-resistant breeding.

Pollination is essential for achieving high yields and enhancing the quality of kiwifruit cultivation, both of which significantly influence growers' interests and consumers' preferences. However, compared to studies on yield, there are fewer studies exploring the impact of pollination methods on the flavor of kiwifruit Actinidia chinensis Planchon. This study examined the effects of bee (Apis mellifera L.) pollination and artificial pollination on the yield and flavor of kiwifruit in the main producing areas of China. Compared with those pollinated artificially, bee-pollinated kiwifruit exhibited a greater fruit set rate, heavier fruit weight, and greater number of seeds. Notably, the number of seeds was positively correlated with fruit weight in bee-pollinated kiwifruit, whereas no such correlation was detected in artificially pollinated fruit. Bee pollination not only enhanced the yield but also improved the flavor of kiwifruit. Specifically, bee-pollinated kiwifruit contained higher levels of sucrose and lower concentrations of glucose and fructose, while the acid content was less affected by pollination methods. Furthermore, significant differences were observed in the volatile organic compound (VOC) levels in kiwifruit subjected to different pollination treatments, with bee-pollinated fruit exhibiting a superior flavor. Our findings provide new insights into the beneficial role of bee pollination in enhancing kiwifruit yield and quality, underscoring the crucial importance of bees in kiwifruit pollination., (© 2024 Wiley Periodicals LLC.)

Intercropping systems have garnered attention as a sustainable agricultural approach for efficient land use, increased ecological diversity in farmland, and enhanced crop yields. This study examined the effect of intercropping on the kiwifruit rhizosphere to gain a deeper understanding of the relationships between cover plants and kiwifruit in this sustainable agricultural system. Soil physicochemical properties and bacterial communities were analyzed using the Kiwifruit-Agaricus blazei intercropping System. Moreover, a combined analysis of 16S rRNA gene sequencing and metabolomic sequencing was used to identify differential microbes and metabolites in the rhizosphere. Intercropping led to an increase in soil physicochemical and enzyme activity, as well as re-shaping the bacterial community and increasing microbial diversity. Proteobacteria, Bacteroidota, Myxococcota, and Patescibacteria were the most abundant and diverse phyla in the intercropping system. Expression analysis further revealed that the bacterial genera BIrii41, Acidibacter, and Altererythrobacter were significantly upregulated in the intercropping system. Moreover, 358 differential metabolites (DMs) were identified between the monocropping and intercropping cultivation patterns, with fatty acyls, carboxylic acids and derivatives, and organooxygen compounds being significantly upregulated in the intercropping system. The KEGG metabolic pathways further revealed considerable enrichment of DMs in ABC transporters, histidine metabolism, and pyrimidine metabolism. This study identified a significant correlation between 95 bacterial genera and 79 soil metabolites, and an interactive network was constructed to explore the relationships between these differential microbes and metabolites in the rhizosphere. This study demonstrated that Kiwifruit-Agaricus blazei intercropping can be an effective, labor-saving, economic, and sustainable practice for reshaping bacterial communities and promoting the accumulation and metabolism of beneficial microorganisms in the rhizosphere., (© 2024. The Author(s).)

Background: Potassium (K) is important in the regulation of plant growth and development. It is the most abundant mineral element in kiwifruit, and its content increases during fruit ripening. However, how K + transporter works in kiwifruit postharvest maturation is not yet clear., Results: Here, 12 K + transporter KT/HAK/KUP genes, AcKUP1 ~ AcKUP12, were isolated from kiwifruit, and their phylogeny, genomic structure, chromosomal location, protein properties, conserved motifs and cis-acting elements were analysed. Transcription analysis revealed that AcKUP2 expression increased rapidly and was maintained at a high level during postharvest maturation, consistent with the trend of K content; AcKUP2 expression was induced by ethylene, suggesting that AcKUP2 might play a role in ripening. Fluorescence microscopy showed that AcKUP2 is localised in the plasma membrane. Cis-elements, including DER or ethylene response element (ERE) responsive to ethylene, were found in the AcKUP2 promoter sequence, and ethylene significantly enhanced the AcKUP2 promoter activity. Furthermore, we verified that AcERF15, an ethylene response factor, directly binds to the AcKUP2 promoter to promote its expression. Thus, AcKUP2 may be an important potassium transporter gene which involved in ethylene-regulated kiwifruit postharvest ripening., Conclusions: Therefore, our study establishes the first genome-wide analysis of the kiwifruit KT/HAK/KUP gene family and provides valuable information for understanding the function of the KT/HAK/KUP genes in kiwifruit postharvest ripening., (© 2022. The Author(s).)

Background: Our previous study has demonstrated that the transcription of AchnKCS involved in suberin biosynthesis was up-regulated by exogenous abscisic acid (ABA) during the wound suberization of kiwifruit, but the regulatory mechanism has not been fully elucidated., Results: Through subcellular localization analysis in this work, AchnbZIP29 and AchnMYB70 transcription factors were observed to be localized in the nucleus. Yeast one-hybrid and dual-luciferase assay proved the transcriptional activation of AchnMYB70 and transcriptional suppression of AchnbZIP29 on AchnKCS promoter. Furthermore, the transcription level of AchnMYB70 was enhanced by ABA during wound suberization of kiwifruit, but AchnbZIP29 transcription was reduced by ABA., Conclusions: Therefore, it was believed that ABA enhanced the transcriptional activation of AchnMYB70 on AchnKCS by increasing AchnMYB70 expression. On the contrary, ABA relieved the inhibitory effect of AchnbZIP29 on transcription of AchnKCS by inhibiting AchnbZIP29 expression. These results gave further insight into the molecular regulatory network of ABA in wound suberization of kiwifruit., (© 2022. The Author(s).)

Kiwifruit plants have a fleshy, shallow root system which is sensitive to waterlogging stress, which results in a decrease in crop yield or even plants death. Although the waterlogging stress responses in kiwifruit have attracted much attention, the underlying molecular mechanism remains unclear. In this study, waterlogging led to drastic inhibition of root growth of 'Donghong' kiwifruit (Actinidia chinensis) plants grown in vitro, which was accompanied by significant elevation of endogenous acetaldehyde and ethanol contents. RNA-seq of roots of plants waterlogged for 0, 1 and 2 days revealed that a total of 149 genes were up- or down-regulated, including seven biosynthetic genes related to the glycolysis/gluconeogenesis pathway and 10 transcription factors. Analyses with real-time PCR, dual-luciferase assays and EMSA demonstrated that AcERF74 and AcERF75, two members of the ERF-VII subfamily, directly upregulated AcADH1 (alcohol dehydrogenase). Moreover, the overexpression of AcERF74/75 in transgenic calli resulted in dramatic increase of endogenous ethanol contents through the triggering of AcADH1 and AcADH2 expression. Although the AcPDC2 (pyruvate decarboxylase) expression was also enhanced in transgenic lines, the endogenous acetaldehyde contents showed no significant changes. These results illustrated that AcERF74/75 are two transcriptional activators on alcoholic fermentation related genes and are responsive to waterlogging stress in kiwifruit., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Actinidia (kiwifruit) is known as 'the king of vitamin C' due to its rich ascorbic acid (AsA) concentration, which makes it an important model for studying the regulation of AsA metabolism. Herein, transcriptomic analysis was employed to identify candidate genes that regulate AsA synthesis in Actinidia species with 100-fold variations in fruit AsA content ( A. latifolia and A. rufa ). Approximately 1.16 billion high-quality reads were generated, and an average of 66.68% of the data was uniquely aligned against the reference genome. AsA-associated DEGs that predominately respond to abiotic signals, and secondary metabolic pathways were identified. The key candidate genes, for instance, GDP-L-galactose phosphorylase-3 ( GGP3 ), were explored according to integrated analysis of the weighted gene co-expression network and L-galactose pathway. Transgenic kiwifruit plants were generated, and the leaves of GGP3 (OE- GGP3 ) overexpressing lines had AsA contents 2.0- to 6.4-fold higher than those of the wild type. Transcriptomic analysis of transgenic kiwifruit lines was further implemented to identify 20 potential downstream target genes and understand GGP3 -regulated cellular processes. As a result, two transcription factors (AcESE3 and AcMYBR) were selected to carry out yeast two-hybrid and BiFC assays, which verified that there were obvious AcESE3-AcMYBR and AcESE3- AcGGP3 protein-protein interactions. This study provides insight into the mechanism of AsA synthesis and provides candidate factors and genes involved in AsA accumulation in kiwifruit.

Sulfur has been previously reported to modulate plant growth and exhibit significant anti-microbial activities. However, the mechanism underlying its diverse effects on plant pathogens has not been elucidated completely. The present study conducted the two-year field experiment of sulfur application to control kiwifruit canker from 2017 to 2018. For the first time, our study uncovered activation of plant disease resistance by salicylic acid after sulfur application in kiwifruit. The results indicated that when the sulfur concentration was 1.5-2.0 kg m - 3 , the induced effect of kiwifruit canker reached more than 70%. Meanwhile, a salicylic acid high lever was accompanied by the decline of jasmonic acid. Further analysis revealed the high expression of the defense gene, especially AcPR-1 , which is a marker of the salicylic acid signaling pathway. Additionally, AcICS1, another critical gene of salicylic acid synthesis, was also highly expressed. All contributed to the synthesis of increasing salicylic acid content in kiwifruit leaves. Moreover, the first key lignin biosynthetic AcPAL gene was marked up-regulated. Thereafter, accumulation of lignin content in the kiwifruit stem and the higher deposition of lignin were visible in histochemical analysis. Moreover, the activity of the endochitinase activity of kiwifruit leaves increased significantly. We suggest that the sulfur-induced resistance against Pseudomonas syringae pv. actinidiae via salicylic activates systemic acquired resistance to enhance plant immune response in kiwifruit.

Background: Kiwifruit is an important horticultural crop all over the world and its development is important in Argentina. This dioecious crop has a short blooming period with nectarless flowers, and its fruit production depends on cross-pollination. Here, we tested whether kiwifruit quality increases by using honeybees exposed to female flowers treated with an artificial fragrance. The three experimental treatments were: A, sprinkled female flowers with 1:1 sugar syrup + Lavandula hybrida extract solution (a new attractant substance especially developed for this study named Lavandin Grosso); B, sprinkled female flowers with 1:1 water + sugar syrup (female flowers with additional sugar syrup reward); C (control; female flowers exposed to honeybees)., Results: The results showed a higher number of visits of honeybees to the female flowers sprinkled with the attractant substance, Lavandin Grosso, as well as higher fruit quality (weight, number of seeds, regularity in fruit size)., Conclusion: Our study demonstrates the potential of fragrance-treated flowers to improve yield production in kiwifruit. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

Background: Kiwifruit (Actinidia) has long been called the 'king of fruits' because of its unique flavor and the wide range of bioactive compounds which contains ascorbic acid, phenolics and minerals. These bioactivities are influenced by species and cultivar. However, to date few studies are concerned with the effect of ripening time on fruit quality. Here, early and late ripening kiwifruits were investigated to determine their content of ascorbic acid, organic acid, and phenolic compounds., Results: Early ripening cultivars contained higher quinic acid and malic acid, while citric acid were found in large amounts in late ripening kiwifruits. Most of the early ripening cultivars contained higher free phenolic fractions than the late ripening fruits, mainly due to the high levels of epicatechin. However, conjugated phenolics, mainly including caffeic and 2,3,4-trihydroxybenzoic acid, achieved higher levels in the late ripening cultivars. Free phenolics were higher than conjugated phenolics in the early ripening cultivars. Principal component analysis revealed some key compounds that differentiated the kiwifruits, and all the kiwifruits were divided into two subgroups as early and late ripening cultivars., Conclusion: Ripening time had a great impact on the accumulation of bioactive compounds. The early ripening cultivars, compared to the late ripening ones, were characterized by higher levels of free neochlorogenic acid and epicatechin, while the late ripening kiwifruits contained higher amounts of conjugated phenolics. Results from this study provide further insights into the health-promoting phenolic compounds in kiwifruit, and also provide good evidence to aid consumer selection. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

In this study, the co-application of chitosan and tetramycin against kiwifruit soft rot and its effects on the disease resistance, growth, quality and aroma of kiwifruit were investigated. The results show that chitosan could effectively enhance tetramycin against soft rot of kiwifruit with the field control efficacy of 85.33% for spraying chitosan 100 time + 0.3% tetramycin AS 5000-time dilution liquid, which was higher than 80.99% for 0.3% tetramycin AS 5000-time dilution liquid and significantly ( p < 0.01) higher than 40.66% for chitosan 100-time dilution liquid. Chitosan could significantly ( p < 0.05) improve the promoting effects of tetramycin on total phenolics, total flavonoids, SOD activity of kiwifruit compared to tetramycin during storage for 0-28 days and enhance the disease resistance of kiwifruit. Moreover, the co-application of chitosan and tetramycin was more effective than tetramycin or chitosan alone in enhancing fruit growth, improving fruit quality and increasing fruit aroma. This study highlights that chitosan can be used as an adjuvant to enhance tetramycin against soft rot of kiwifruit and promote tetramycin's improvement for the single fruit volume and weight, vitamin C, soluble sugar, soluble solid, dry matter, soluble protein, titratable acidity and aroma of kiwifruit.

A pot experiment was conducted with kiwifruit planting soil to evaluate the impacts of potassium solubilizing bacteria (KSB) and K-feldspar on the soil nutrient levels, enzyme activities, and microecological environment. The effects were investigated of three inoculation treatments (T1: K-feldspar, T2: KSB, and T3: KSB with K-feldspar) and a non-inoculation treatment (CK) on the enzyme activities and the metabolic activities of the bacterial communities in kiwifruit rhizosphere soil. The results showed that the total nitrogen, available phosphorus, available potassium, and organic matter contents in T3 were 18.19%, 45.22%, 15.06%, and 4.17% higher, respectively, than those in CK at the end of the experiment (90 days). Compared with CK, T3 significantly increased the invertase, urease, acid phosphatase, and polyphenol oxidase activities. T3 had a higher kiwifruit root activity, but there were no significant differences among the four treatments (P > 0.05). T3 significantly altered the bacterial community diversity, increased the utilization of phenolic compounds and polymers, and decreased the utilization of amino acids. Redundancy analysis indicated that soil nutrients (total nitrogen, available phosphorus, and available potassium) and enzyme activities (urease and acid phosphatase) had more important effects on the metabolic activities of the bacterial communities. Co-inoculation enhanced the soil nutrients, enzyme activities, and bacterial community diversity. KSB co-inoculated with K-feldspar has the potential to improve the soil fertility, microbial metabolic activity and plant growth.

Background: The skin (exocarp) of fleshy fruit is hugely diverse across species. Most fruit types have a live epidermal skin covered by a layer of cuticle made up of cutin while a few create an outermost layer of dead cells (peridermal layer)., Results: In this study we undertook crosses between epidermal and peridermal skinned kiwifruit, and showed that epidermal skin is a semi-dominant trait. Furthermore, backcrossing these epidermal skinned hybrids to a peridermal skinned fruit created a diverse range of phenotypes ranging from epidermal skinned fruit, through fruit with varying degrees of patches of periderm (russeting), to fruit with a complete periderm. Quantitative trait locus (QTL) analysis of this population suggested that periderm formation was associated with four loci. These QTLs were aligned either to ones associated with russet formation on chromosome 19 and 24, or cuticle integrity and coverage located on chromosomes 3, 11 and 24., Conclusion: From the segregation of skin type and QTL analysis, it appears that skin development in kiwifruit is controlled by two competing factors, cuticle strength and propensity to russet. A strong cuticle will inhibit russeting while a strong propensity to russet can create a continuous dead skinned periderm., (© 2021. The Author(s).)

Enzyme-based time-temperature integrators (TTIs) were applied to indicate the ripeness of plastic-container-packaged kiwifruit. The hypothesis was that the ethylene gas production, an indication of kiwifruit ripeness, depends on the time-temperature history. The market-purchased, unripe kiwifruit was assumed to be stored in a plastic container to ripen at home, as common practice in Korea. The kinetics of ethylene gas production and TTI color change was found to be suitable for the indication. The Arrhenius activation energy (E a ) of the ethylene gas production and color changes of lipase-, amylase-, and laccase-based TTIs were 41.60 ± 10.87 kJ/mol, and 42.76 ± 9.57, 100.28 ± 6.84, and 30.49 ± 4.41 kJ/mol, respectively. Kiwifruit firmness was also tested as a practical, major quality factor. The E a of the firmness changes was 39.66 ± 4.64 kJ/mol. In scenarios tests, the firmness could be most accurately predicted from the lipase-based TTI color. Overall, the lipase-based TTI was found to be the best in terms of the similarity of the E a and the prediction accuracy. PRACTICAL APPLICATION: Currently, there is no commercially available indicator that can determine the ripeness of packaged kiwifruit. Although an ethylene gas indicator is possible, it has been difficult to commercialize because the gas may leak in the package. An indicator on plastic containers with kiwifruit, as is common in Korea, has been developed using a conventional time-temperature integrator (TTI). The hypothesis was that the production of ethylene gas, indicating kiwi ripening, is also dependent on the time-temperature history. It was found that the TTI color change over time was suitable for judging suitable kiwifruit hardness, a major kiwifruit ripeness index., (© 2021 Institute of Food Technologists®.)

The aim of this study was to assess the enzymatic and non-enzymatic antioxidant status of kiwiberry ( Actinidia arguta ) leaf under different N regimes tested three times in field conditions during the 2015 growing season in two cultivars ('Weiki' and 'Geneva'). Leaf total antioxidant capacity using ABTS, DPPH and FRAP tests was evaluated in the years 2015 to 2017, which experienced different weather conditions. Both cultivars exhibited a significant fall in leaf L-ascorbic acid (L-AA) and reduced glutathione (GSH) as well as global content of these compounds during the growing season, while total phenolic contents slightly ('Weiki') or significantly ('Geneva') increased. There was a large fluctuation in antioxidative enzyme activity during the season. The correlation between individual antioxidants and trolox equivalent antioxidant capacity (TEAC) depended on the plant development phase. The study revealed two peaks of an increase in TEAC at the start and end of the growing season. Leaf L-AA, global phenolics, APX, CAT and TEAC depended on the N level, but thiol compounds were not affected. Over the three years, TEAC decreased as soil N fertility increased, and the strength of the N effect was year dependent. The relationship between leaf N content and ABTS and FRAP tests was highly negative. The antioxidant properties of kiwiberry leaves were found to be closely related to the plant development phase and affected by soil N fertility.

Kiwifruit has not been studied as much as other well-known fruits especially when it comes to studies about plant vigour and training systems. The aim of the study was to determine the importance of cane vigour of Actinidia chinensis var. deliciosa 'Hayward' and Actinidia arguta 'Issai' in order to develop the proper pruning technique that results in the best fruit quality. In addition, the effect of storage parameters such as weight, firmness and quality of the fruit was also studied. The study showed that the fruit size and weight are lower in low vigour canes in A. arguta, in contrast to A. chinensis, where the fruit size and weight are smaller on high-vigorous canes. For A. arguta, it is recommended to choose high-vigour canes as the optimal fruit wood during pruning. In this way, the fruits will ripen more evenly. The other possibility is to perform the harvest two to three times per season to achieve a more uniform fruit quality. In the case of A. chinensis the fruit are less variable between different cane vigour, so harvesting can be done in a single picking. In A. chinensis the less vigorous canes tend to show a slightly better fruit quality.

Ethylene interacts with other plant hormones to modulate many aspects of plant metabolism, including defence and stomata regulation. Therefore, its manipulation may allow plant pathogens to overcome the host's immune responses. This work investigates the role of ethylene as a virulence factor for Pseudomonas syringae pv. actinidiae (Psa), the aetiological agent of the bacterial canker of kiwifruit. The pandemic, highly virulent biovar of this pathogen produces ethylene, whereas the biovars isolated in Japan and Korea do not. Ethylene production is modulated in planta by light/dark cycle. Exogenous ethylene application stimulates bacterial virulence, and restricts or increases host colonisation if performed before or after inoculation, respectively. The deletion of a gene, unrelated to known bacterial biosynthetic pathways and putatively encoding for an oxidoreductase, abolishes ethylene production and reduces the pathogen growth rate in planta. Ethylene production by Psa may be a recently and independently evolved virulence trait in the arms race against the host. Plant- and pathogen-derived ethylene may concur in the activation/suppression of immune responses, in the chemotaxis toward a suitable entry point, or in the endophytic colonisation.

Background: Transcriptomic studies combined with a well annotated genome have laid the foundations for new understanding of molecular processes. Tools which visualise gene expression patterns have further added to these resources. The manual annotation of the Actinidia chinensis (kiwifruit) genome has resulted in a high quality set of 33,044 genes. Here we investigate gene expression patterns in diverse tissues, visualised in an Electronic Fluorescent Pictograph (eFP) browser, to study the relationship of transcription factor (TF) expression using network analysis., Results: Sixty-one samples covering diverse tissues at different developmental time points were selected for RNA-seq analysis and an eFP browser was generated to visualise this dataset. 2839 TFs representing 57 different classes were identified and named. Network analysis of the TF expression patterns separated TFs into 14 different modules. Two modules consisting of 237 TFs were correlated with floral bud and flower development, a further two modules containing 160 TFs were associated with fruit development and maturation. A single module of 480 TFs was associated with ethylene-induced fruit ripening. Three "hub" genes correlated with flower and fruit development consisted of a HAF-like gene central to gynoecium development, an ERF and a DOF gene. Maturing and ripening hub genes included a KNOX gene that was associated with seed maturation, and a GRAS-like TF., Conclusions: This study provides an insight into the complexity of the transcriptional control of flower and fruit development, as well as providing a new resource to the plant community. The Actinidia eFP browser is provided in an accessible format that allows researchers to download and work internally.

Understanding the metabolic modulation of major quality traits during ripening is critical for fruit quality improvement in kiwifruits. Here, integrated proteomic and metabolomic profiling was undertaken to comprehensively examine the dynamics of kiwifruit ripening. This data set presents a global view of the critical pathways involved in fruit ripening, and the contributions of key events to the regulation of kiwifruit ripening and softening, amino acid metabolism, balance in sugar accumulation and organic acid metabolism, glycolysis, and tricarboxylic acid (TCA) pathways were discussed. We suggested key enzymes for starch synthesis and degradation, including AGPase, SS, and SBE, especially for BMY, which was considered a key enzyme for starch degradation. In addition, our analysis implicated the key enzymes ACO4 and ACS9 in ethylene synthesis and the aspartate aminotransferase ASP3 in the conversion of amino acids. These results provide new insights into the modulation of fruit ripening, metabolism, and quality in post-harvest kiwifruits.

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.

Background: NAC transcription factors (TFs) are plant-specific proteins encoded by a large gene family. They play important roles in diverse biological processes, such as plant growth and development, leaf senescence, and responses to biotic or abiotic stresses. Functions of a number of NAC TFs have been identified mainly in model plants. However, very few studies on NAC TFs have been conducted in the fruit tree of kiwifruit., Results: Genome-wide NAC genes were identified and their phylogeny, genomic structure, chromosomal location, synteny relationships, protein properties and conserved motifs were analyzed. In addition, the fruit developmental process was evaluated in a new kiwifruit cultivar of Actinidia eriantha 'Ganlu 1'. And expressions for all those NAC genes were analyzed by quantitative real-time PCR method in fruits of 'Ganlu 1' during its developmental process. Our research identified 142 NAC TFs which could be phylogenetically divided into 23 protein subfamilies. The genomic structures of those NAC genes indicated that their exons were between one and ten. Analysis of chromosomal locations suggested that 116 out of 142 NACs distributed on all the 29 kiwifruit chromosomes. In addition, genome-wide gene expression analysis showed that expressions of 125 out of 142 NAC genes could be detected in fruit samples., Conclusion: Our comprehensive study provides novel information on NAC genes and expression patterns in kiwifruit fruit. This research would be helpful for future functional identification of NAC genes involved in kiwifruit fruit development.

According to the investigation of wild Actinidia eriantha in Jiangxi province of China, we found that soluble solids content of fruit was lower than edible standard (14%). However, we found a high-sugar type A. eriantha line (code was 'MM24', test material) during investigative process at Nancheng county (E 116° 48', N 26° 23', 845 m). We sheared its scions to asexual reproduction in Fengxin County (rootstock was A. deliciosa 'Miliang 1' with 7 years old) and at the same time DUS (Distinctness, Uniformity and Stability) test was also carried out. There were uncontested differences between the two comparative genotypes according to the results of polyacrylamide gel electrophoresis, it can be judged as a new cultivar. In addition, there was great similarity on most important morphological and quality characteristics. While, there was difference on SSC, DM and TS between the two materials on ripen fruit, these indicators were much higher on test material than on control. The sugar degree assessment showed that the sugar degree of test material was strong and retention time was long. Further, no sucrose was found before DAF 135 d in test material and sucrose were significantly higher than in control only at DAF 165 d and DAF 175 d. The qRT-PCR results of sucrose-related genes showed that the relative expression levels of AcSPS1, AcSPS3, AcSPS5 and AcSUS5 genes were consistent with the sucrose accumulation trend, which was probably the main genes for the difference in sugar degree.

The newly released Donghong kiwifruit is a promising commercial cultivar. The dynamic changes of major phenolic compounds (flavonols, flavanols, phenolic acids, and anthocyanins) during the representative stages of fruit development and ripening of the Donghong kiwifruit were determined by high-performance liquid chromatography. The corresponding time-course transcriptional changes were evaluated using the combined analysis of RNA-Seq and qRT-PCR. The most predominant phenolic compound in the Donghong kiwifruit was epicatechin. Cyanidin 3- O -[2- O -(β-xylosyl)- β -galactoside] and cyanidin 3- O - β -galactoside were two essential anthocyanins detected. Candidate genes and pathways involved in phenolic compounds biosynthesis were highlighted. The structural genes ( AcLDOX 2, Ac 5 GGT 1, and Ac 5 AT 2) and the transcription factor ( bHLH 74-2) were strongly associated with anthocyanin biosynthesis. AcMYB 4-1 may be a novel transcription factor that reduces anthocyanin accumulation. Results from the study may be a very useful supplement to current knowledge of molecular mechanisms to elucidate coloration in the red-fleshed kiwifruit and could help breeders modify the kiwifruit germplasm.

Kiwifruit (Actinidia chinensis) is a rich nutritious fruit crop owing to a markedly higher content of vitamin C and minerals. To promote fruit set and to increase the yield of kiwifruit, forchlorfenuron (CPPU) has been widely applied. However, the molecular details regarding CPPU controlling kiwifruit development, especially at the fastest fruit growth stage, remain unknown. In the present study, we measured the effect of CPPU on developmental regulation in red-fleshed kiwifruit (Actinidia chinensis 'Hongyang'). Additionally, a cytological analysis was performed to clarify the precise changes in the cell structure of the CPPU-treated kiwifruits. Moreover, the concentration of endogenous phytohormones, including indoleacetic acid (IAA), zeatin (ZT), gibberellic acid 3 (GA3), and abscisic acid (ABA), were measured by Enzyme-linked Immunosorbent Assay (ELISA). Furthermore, RNA-Seq was performed to dissect the complicated molecular mechanisms, with a focus on biosynthesis, metabolism, and signaling compounds, such as endogenous hormones, sugars, and L-ascorbic acid. Our results demonstrated that CPPU treatment not only regulates the size and weight of a single fruit but also improves the quality in 'Hongyang' kiwifruit through the accumulation of both soluble sugar and vitamin C. It was also seen that CPPU regulates kiwifruit development by enhancing cell expansion of epidermal cells and parenchyma cells, while, promoting cell division of subepidermal cells. Additionally, CPPU significantly increased the gibberellin and cytokinin biosynthetic pathway and signaling, while repressing auxin and ABA biosynthetic pathway; thus, signaling plays an essential role in CPPU controlling kiwifruit development. Notably, transcriptomic analysis revealed that a total of 2244 genes, including 352 unannotated genes, were differentially expressed in kiwifruits because of CPPU treatment, including 127 transcription factors. These genes are mainly enriched in plant hormone signal transduction, photosynthesis, MAPK signaling pathway, starch and sucrose metabolism, and phenylpropanoid biosynthesis. Overall, our results highlight that CPPU regulation of kiwifruit development is mainly associated with an antagonistic and/or synergistic regulatory role of endogenous phytohormones, and enhancing the energy supply. This provides new insights into the molecular details of CPPU controlling kiwifruit development at the fastest fruit growth stage, which is of agricultural importance for kiwifruit breeding and crop improvement., Competing Interests: The authors have declared that no competing interests exist.

Background: Actinidia arguta known as the 'kiwiberry' or 'mini kiwi' is relatively new among the cultivated berry species. Recent studies indicate the kiwiberry fruit could be an important source of many health-promoting compounds. A knowledge-based fertilisation concept was evolved to define optimal strategies for feeding Actinidia with nitrogen (N) because a deficit and excess of N both have a negative impact on plants and the surrounding environment., Results: Kiwiberry yield and fruit internal quality significantly depended on soil N level, cultivar and growing season. A higher soil N led to an increase in carotenoid content and a decrease in phenolic content, whereas ascorbic acid and glutathione contents were not affected by soil N fertility. Under the highest N dose, enzymatic antioxidants were activated. Trolox equivalent antioxidant capacity clearly decreased with an increasing N level., Conclusions: Competent and skilful fertilisation management should focus on balancing a high fruit yield and maintaining their high quality. Based on yield level and fruit antioxidant potential, the N guide values for A. arguta vary between 30 and 50 mg N per kg -1 of soil. The recommended N dose may depend on overall soil quality traits and cultivar N demand, as well as on weather conditions. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Background: Metabolites in kiwifruit greatly influence nutritional values; however, the dynamic changes in nutrient composition and the gene expression level of yellow kiwifruit have not been studied so far. To investigate the types and accumulation patterns of metabolites, a metabolomics approach utilizing liquid chromatography-electrospray ionization mass spectrometry and transcriptomics were used to analyze the yellow flesh of kiwifruit cultivar 'jinshi 1' collected at different stages of days after full bloom., Results: In total, 285 metabolites were identified over the kiwifruit developmental stages. The composition of the metabolites of kiwifruit at different stages of development was different. The organic acids contents and their derivatives were higher at the initial stage of development and then gradually decreased. The lipids and amino acids contents fluctuated at different stages of development but did not change significantly. Transcript profiles throughout yellow kiwifruit development were constructed and analyzed, with a focus on the biosynthesis and metabolism of compounds such as sugars, organic acids and ascorbic acid, which are indispensable for the development and formation of quality fruit. The transcript levels of genes involved in sucrose and starch metabolism were consistent with the change in soluble sugar and starch content throughout kiwifruit development. The metabolism of ascorbic acid was primarily through the l-galactose pathway., Conclusion: Our metabolome and transcriptome approach identified dynamic changes in five types of nutrient metabolite levels, and correlations among such levels, in developing fruit. The results provide information that can be used by metabolic engineers and molecular breeders to improve kiwifruit quality. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Background: Among the challenges for postharvest researchers is that of understanding the physiological and biochemical pathways associated with postharvest fruit decay. Fruit senescence directly affects sensorial and nutritional quality during postharvest life. It has been clarified that reactive oxygen species and oxidative damage are responsible for fruit senescence. Some cultivars of yellow-fleshed kiwifruit can be stored for a short period compared with green-fleshed kiwifruit. Postharvest performance is affected by the physiological state of the fruit at harvest, associated with its postharvest management. Among several postharvest applications, ozone treatment is considered as a cost-effective and eco-friendly food-processing technology to preserve the fruits' quality during cold storage. In this study, we investigated the influence of ozone, after gradual cooling treatment, on the antioxidant defense system in Actinidia chinensis, 'Soreli'., Results: Bioactive compound content decreased during cold storage, and ozone treatment enhanced the activities of superoxide dismutase and catalase during cold storage. This treatment preserved membrane integrity by inhibiting lipoxygenase activity and malondialdehyde accumulation. A multivariate statistical approach, using principal component analysis, provided the global response to the effect of ozone postharvest treatment during cold storage in kiwifruit 'Soreli'., Conclusion: Ozone treatment improves the efficiency of antioxidative system and storability of 'Soreli' kiwifruits. © 2019 Society of Chemical Industry., (© 2019 Society of Chemical Industry.)

Although melatonin was affirmed to alleviate drought stress in various plant species, the mechanism in kiwifruit remains to be elucidated. In this study, the transcriptomes of kiwifruit leaves under control (CK), DR (drought stress), and MTDR (drought plus melatonin) treatments were evaluated. After comparisons of the gene expression between DR and MTDR, the differentially expressed genes (DEGs) were screened. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated three significant pathways, which were mainly involved in the glutathione metabolism, ascorbate and aldarate metabolism, and carotenoid metabolism. Therefore, the content and metabolic gene expression level of ascorbic acid (AsA), glutathione, and carotenoid were higher in the MTDR treatment than that in others. Furthermore, the activity and mRNA expression level of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were also promoted in the MTDR group. Combined with these results of important secondary metabolites and protective enzymes measured in the seedlings in different treatments, it could be concluded that exogenous melatonin induced the ascorbic acid-glutathione (AsA-GSH) cycle, carotenoid biosynthesis, and protective enzyme system to improve seedling growth. Our results contribute to the development of a practical method for kiwifruit against drought stress.

Background: Artificial intelligence systems have been employed for the development of predictive models that estimate many agricultural processes., Results: In present study, the predictive capabilities of artificial neural networks (ANNs) were evaluated with respect to assessing fruit firmness as a postharvest life index, with determinations made at four stages of storage: 1, 60, 120 and 180 days after harvesting. Single concentrations of nitrogen (N), potassium (K), calcium (Ca) and magnesium (Mg) on fruit (D 1 ), all of these nutrient concentrations (D 2 ), the ratios of the nutrient concentrations alone (D 3 ), and a combination of nutrient concentrations and their ratios (D 4 ), were considered., Conclusion: The results obtained showed that fruit firmness at 1 and 60 days after harvesting was not influenced by nutrients. However, the ANN model estimated fruit firmness of 120 and 180 days, respectively, for D 1 and D 3 more accurately than for the D 2 and D 4 datasets. Application of D 3 (nitrogen/calcium ratio) as the input dataset improved predictions of fruit firmness, with a correlation coefficient of 0.85 between the measured and estimated data. © 2019 Society of Chemical Industry., (© 2019 Society of Chemical Industry.)

Key Message: The developmental morphology of male and female kiwifruit flowers is tracked to delimit a framework of events to aid the study of divergence in floral gene expression. The transition from hermaphrodite to unisexual development of kiwifruit (Actinidia chinensis Planch) flowers has been reported previously, but differences in gene expression controlling sexual development for this species have not been associated with the major developmental changes occurring within pistils. We investigated the key stages in male and female flower development to define the point at which meristematic activities diverge in the two sexes. A combination of scanning electron microscopy and light microscopy was used to investigate pistil development from the earliest stages. We identified seven distinct stages characterized by differences in ovary size and shape, macrosporogenesis, ovule primordium development, anther locule lengthening, microspore wall thickening, and pollen degeneration. Sex differences were evident from the initial stage of development, with a laterally compacted gynoecium in male flowers. However, the key developmental stage, at which tissue differentiation clearly deviated between the two sexes, was stage 3, when flowers were 3.5 to 4.5 mm in length at approximately 10 d from initiation of stamen development. At this stage, male flowers lacked evident carpel meristem development as denoted by a lack of ovule primordium formation. Pollen degeneration in female flowers, probably driven by programmed cell death, occurred at the late stage 6, while the final stage 7 was represented by pollen release. As the seven developmental stages are associated with specific morphological differences, including flower size, the scheme suggested here can provide the required framework for the future study of gene expression during the regulation of flower development in this crop species.

Annualization of woody perennials has the potential to revolutionize the breeding and production of fruit crops and rapidly improve horticultural species. Kiwifruit (Actinidia chinensis) is a recently domesticated fruit crop with a short history of breeding and tremendous potential for improvement. Previously, multiple kiwifruit CENTRORADIALIS (CEN)-like genes have been identified as potential repressors of flowering. In this study, CRISPR/Cas9- mediated manipulation enabled functional analysis of kiwifruit CEN-like genes AcCEN4 and AcCEN. Mutation of these genes transformed a climbing woody perennial, which develops axillary inflorescences after many years of juvenility, into a compact plant with rapid terminal flower and fruit development. The number of affected genes and alleles and severity of detected mutations correlated with the precocity and change in plant stature, suggesting that a bi-allelic mutation of either AcCEN4 or AcCEN may be sufficient for early flowering, whereas mutations affecting both genes further contributed to precocity and enhanced the compact growth habit. CRISPR/Cas9-mediated mutagenesis of AcCEN4 and AcCEN may be a valuable means to engineer Actinidia amenable for accelerated breeding, indoor farming and cultivation as an annual crop., (© 2018 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

The phenolics profile of two new kiwifruit cultivars, Zespri® SunGold and Zespri® Sweet Green, were characterized and quantified for the first time using cyclic voltammetry, an electrochemical method, combined with HPLC. Results from the cyclic voltammetry revealed high correlations with those obtained from the spectrophotometry and HPLC methods, providing evidence to support the application of cyclic voltammetry as a rapid method in determining the phenolic profile and reducing power of kiwifruit extracts. Catechol-containing phenolics were identified as the major phenolic sub-class in the skins while flavonoids and phenolic acids were abundant in flesh of the tested cultivars. Epicatechin was the predominant phenolic compound and contributor to antioxidant capacity in all samples. Results also showed that SunGold and Sweet Green (both flesh and skin) exhibited significantly higher phenolic contents and antioxidant activities comparing with the well-established commercial 'Hayward' cultivar, indicating their commercial value and potential applications in food and nutraceuticals., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Dioecy, the presence of male and female flowers on distinct individuals, has evolved independently in multiple plant lineages, and the genes involved in this differential development are just starting to be uncovered in a few species. Here, we used genomic approaches to investigate this pathway in kiwifruits (genus Actinidia ). Genome-wide cataloging of male-specific subsequences, combined with transcriptome analysis, led to the identification of a type-C cytokinin response regulator as a potential sex determinant gene in this genus. Functional transgenic analyses in two model systems, Arabidopsis thaliana and Nicotiana tabacum , indicated that this gene acts as a dominant suppressor of carpel development, prompting us to name it Shy Girl ( SyGI ). Evolutionary analyses in a panel of Actinidia species revealed that SyGI is located in the Y-specific region of the genome and probably arose from a lineage-specific gene duplication. Comparisons with the duplicated autosomal counterpart, and with orthologs from other angiosperms, suggest that the SyGI -specific duplication and subsequent evolution of cis -elements may have played a key role in the acquisition of separate sexes in this species., (© 2018 American Society of Plant Biologists. All rights reserved.)

Ascorbic acid (AsA), chlorophyll and carotenoid contents and their associated gene expression patterns were analysed in Actinidia chinensis 'Hongyang' outer pericarp. The results showed chlorophyll degradation during fruit development and softening, exposed the yellow carotenoid pigments. LHCB1 and CLS1 gene expressions were decreased, while PPH2 and PPH3 gene expressions were increased, indicating that downregulation of chlorophyll biosynthesis and upregulation of its degradation, caused chlorophyll degradation. A decrease in the expression of the late carotenoid biosynthesis and maintenance genes (LCYB1, LCYE1, CYP1, CYP2, ZEP1, VDE1, VDE2, and NCED2) and degradation gene (CCD1), showed biosynthesis and degradation of carotenoid could be regulatory factors involved in fruit development. Most genes expression data of L-galactose and recycling pathway were agreement with the AsA concentrations in the fruit, suggesting these are the predominant pathways of AsA biosynthesis. GMP1, GME1 and GGP1 were identified as the key genes controlling AsA biosynthesis in 'Hongyang' outer pericarp.

The appropriate reference genes are important and essential for reliable results of transcript normalization in real-time qRT-PCR. In the current study, we identified 1203 stably expressed genes from 35,286 genes' expression profiles in developmental fruits of Actinidia chinensis. We manually selected six candidate genes and assessed their expression levels, using two sets of fruit samples of A. chinensis: flesh fruits at four developmental stages and post-harvested fruits. The expression stability of these six genes was assessed by three independent algorithms: geNorm, NormFinder, and BestKeeper. Statistical results indicated these six genes can serve as internal control in both developmental and post-harvested fruits. Among these genes, UBQ&#95;CONJ&#95;E2 (Ubiquitin-conjugating enzyme E2 36) and TUB&#95;FCB (Tubulin folding cofactor B) were the two best reference genes identified in this study. The identification and validation of these reference genes can be helpful for elucidating the studies of fruit development and post-harvested fruits' storage in A. chinensis and other fruit crops of Actinidiaceae., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Key Message: Genome-wide targets of Actinidia chinensis SVP2 confirm roles in ABA- and dehydration-mediated growth repression and reveal a conservation in mechanism of action between SVP genes of taxonomically distant Arabidopsis and a woody perennial kiwifruit. The molecular mechanisms underlying growth and dormancy in woody perennials are largely unknown. In Arabidopsis, the MADS-box transcription factor SHORT VEGETATIVE PHASE (SVP) plays a key role in the progression from vegetative to floral development, and in woody perennials SVP-like genes are also proposed to be involved in controlling dormancy. During kiwifruit development SVP2 has a role in growth inhibition, with high-chill kiwifruit Actinidia deliciosa transgenic lines overexpressing SVP2 showing suppressed bud outgrowth. Transcriptomic analyses of these plants suggests that SVP2 mimics the well-documented abscisic acid (ABA) effect on the plant dehydration response. To corroborate the growth inhibition role of SVP2 in kiwifruit development at the molecular level, we analysed the genome-wide direct targets of SVP2 using chromatin immunoprecipitation followed by high-throughput sequencing in kiwifruit A. chinensis. SVP2 was found to bind to at least 297 target sites in the kiwifruit genome, and potentially modulates 252 genes that function in a range of biological processes, especially those involved in repressing meristem activity and ABA-mediated dehydration pathways. In addition, our ChIP-seq analysis reveals remarkable conservation in mechanism of action between SVP genes of taxonomically distant plant species.