Chromosome-level genome of putative autohexaploid Actinidia deliciosa provides insights into polyploidisation and evolution.

Actinidia ('Mihoutao' in Chinese) includes species with complex ploidy, among which diploid Actinidia chinensis and hexaploid Actinidia deliciosa are economically and nutritionally important fruit crops. Actinidia deliciosa has been proposed to be an autohexaploid (2n = 174) with diploid A. chinensis (2n = 58) as the putative parent. A CCS-based assembly anchored to a high-resolution linkage map provided a chromosome-resolved genome for hexaploid A. deliciosa yielded a 3.91-Gb assembly of 174 pseudochromosomes comprising 29 homologous groups with 6 members each, which contain 39 854 genes with an average of 4.57 alleles per gene. Here we provide evidence that much of the hexaploid genome matches diploid A. chinensis; 95.5% of homologous gene pairs exhibited >90% similarity. However, intragenome and intergenome comparisons of synteny indicate chromosomal changes. Our data, therefore, indicate that if A. deliciosa is an autoploid, chromosomal rearrangement occurred following autohexaploidy. A highly diversified pattern of gene expression and a history of rapid population expansion after polyploidisation likely facilitated the adaptation and niche differentiation of A. deliciosa in nature. The allele-defined hexaploid genome of A. deliciosa provides new genomic resources to accelerate crop improvement and to understand polyploid genome evolution.

Comprehensive assessment of drought resistance and recovery in kiwifruit genotypes using multivariate analysis.

As global climate change persists, ongoing warming exposes plants, including kiwifruit, to repeated cycles of drought stress and rewatering, necessitating the identification of drought-resistant genotypes for breeding purposes. To better understand the physiological mechanisms underlying drought resistance and recovery in kiwifruit, moderate (40-45% field capacity) and severe (25-30% field capacity) drought stresses were applied, followed by rewatering (80-85% field capacity) to eight kiwifruit rootstocks in this study. We then conducted a multivariate analysis of 20 indices for the assessment of drought resistance and recovery capabilities. Additionally, we identified four principal components, each playing a vital role in coping with diverse water conditions. Three optimal indicator groups were pinpointed, enhancing precision in kiwifruit drought resistance and recovery assessment and simplifying the evaluation system. Finally, MX-1 and HW were identified as representative rootstocks for future research on kiwifruit's responses to moderate and severe drought stresses. This study not only enhances our understanding of the response mechanisms of kiwifruit rootstocks to progressive drought stress and recovery but also provides theoretical guidance for reliable screening of drought-adaptive kiwifruit genotypes.

Genomic analyses reveal dead-end hybridization between two deeply divergent kiwifruit species rather than homoploid hybrid speciation.

Despite the importance of hybridization in evolution, the evolutionary consequence of homoploid hybridizations in plants remains poorly understood. Specially, homoploid hybridization events have been rarely documented due to a lack of genomic resources and methodological limitations. Actinidia zhejiangensis was suspected to have arisen from hybridization of Actinidia eriantha and Actinidia hemsleyana or Actinidia rufa. However, this species was very rare in nature and exhibited sympatric distribution with its potential parent species, which implied it might be a spontaneous hybrid of ongoing homoploid hybridization. Here, we illustrate the dead-end homoploid hybridization and genomic basis of isolating barriers between A. eriantha and A. hemsleyana through whole genome sequencing and population genomic analyses. Chromosome-scale genome assemblies of A. zhejiangensis and A. hemsleyana were generated. The chromosomes of A. zhejiangensis are confidently assigned to the two haplomes, and one of them originates from A. eriantha and the other originates from A. hemsleyana. Whole genome resequencing data reveal that A. zhejiangensis are mainly F1 hybrids of A. hemsleyana and A. eriantha and gene flow initiated about 0.98 million years ago, implying both strong genetic barriers and ongoing hybridization between these two deeply divergent kiwifruit species. Five inversions containing genes involved in pollen germination and pollen tube growth might account for the fertility breakdown of hybrids between A. hemsleyana and A. eriantha. Despite its distinct morphological traits and long recurrent hybrid origination, A. zhejiangensis does not initiate speciation. Collectively, our study provides new insights into homoploid hybridization in plants and provides genomic resources for evolutionary and functional genomic studies of kiwifruit.

Genome-wide analysis and expression profiling of the HD-ZIP gene family in kiwifruit.

The homeodomain-leucine zipper (HD-Zip) gene family plays a pivotal role in plant development and stress responses. Nevertheless, a comprehensive characterization of the HD-Zip gene family in kiwifruit has been lacking. In this study, we have systematically identified 70 HD-Zip genes in the Actinidia chinensis (Ac) genome and 55 in the Actinidia eriantha (Ae) genome. These genes have been categorized into four subfamilies (HD-Zip I, II, III, and IV) through rigorous phylogenetic analysis. Analysis of synteny patterns and selection pressures has provided insights into how whole-genome duplication (WGD) or segmental may have contributed to the divergence in gene numbers between these two kiwifruit species, with duplicated gene pairs undergoing purifying selection. Furthermore, our study has unveiled tissue-specific expression patterns among kiwifruit HD-Zip genes, with some genes identified as key regulators of kiwifruit responses to bacterial canker disease and postharvest processes. These findings not only offer valuable insights into the evolutionary and functional characteristics of kiwifruit HD-Zips but also shed light on their potential roles in plant growth and development.

Genome-wide identification and expression pattern analysis of the kiwifruit GRAS transcription factor family in response to salt stress.

BACKGROUND: GRAS is a family of plant-specific transcription factors (TFs) that play a vital role in plant growth and development and response to adversity stress. However, systematic studies of the GRAS TF family in kiwifruit have not been reported. RESULTS: In this study, we used a bioinformatics approach to identify eighty-six AcGRAS TFs located on twenty-six chromosomes and phylogenetic analysis classified them into ten subfamilies. It was found that the gene structure is relatively conserved for these genes and that fragmental duplication is the prime force for the evolution of AcGRAS genes. However, the promoter region of the AcGRAS genes mainly contains cis-acting elements related to hormones and environmental stresses, similar to the results of GO and KEGG enrichment analysis, suggesting that hormone signaling pathways of the AcGRAS family play a vital role in regulating plant growth and development and adversity stress. Protein interaction network analysis showed that the AcGRAS51 protein is a relational protein linking DELLA, SCR, and SHR subfamily proteins. The results demonstrated that 81 genes were expressed in kiwifruit AcGRAS under salt stress, including 17 differentially expressed genes, 13 upregulated, and four downregulated. This indicates that the upregulated AcGRAS55, AcGRAS69, AcGRAS86 and other GRAS genes can reduce the salt damage caused by kiwifruit plants by positively regulating salt stress, thus improving the salt tolerance of the plants. CONCLUSIONS: These results provide a theoretical basis for future exploration of the characteristics and functions of more AcGRAS genes. This study provides a basis for further research on kiwifruit breeding for resistance to salt stress. RT-qPCR analysis showed that the expression of 3 AcGRAS genes was elevated under salt stress, indicating that AcGRAS exhibited a specific expression pattern under salt stress conditions.

Dynamic m6A mRNA methylation reveals the involvement of AcALKBH10 in ripening-related quality regulation in kiwifruit.

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.

AcHZP45 is a repressor of chlorophyll biosynthesis and activator of chlorophyll degradation in kiwifruit.

The degradation of chlorophyll during fruit development is essential to reveal a more 'ripe' color that signals readiness to wild dispersers of seeds and the human consumer. Here, comparative biochemical analysis of developing fruit of Actinidia deliciosa cv. Xuxiang ('XX', green-fleshed) and Actinidia chinensis cv. Jinshi No.1 ('JS', yellow-fleshed) indicated that variation in chlorophyll content is the major contributor to differences in flesh color. Four differentially expressed candidate genes were identified: the down-regulated genes AcCRD1 and AcPOR1 involved in chlorophyll biosynthesis, and the up-regulated genes AcSGR1 and AcSGR2 driving chlorophyll degradation. Prochlorophyllide and chlorophyllide, the metabolites produced by AcCRD1 and AcPOR1, progressively reduced in 'JS', but not in 'XX', indicating that chlorophyll biosynthesis was less active in yellow-fleshed fruit. AcSGR1 and AcSGR2 were verified to be involved in chlorophyll degradation, using both transient expression in tobacco and stable overexpression in kiwifruit. Furthermore, a homeobox-leucine zipper (HD-Zip II), AcHZP45, showed significantly increased expression during 'JS' fruit ripening, which led to both repressed expression of AcCRD1 and AcPOR1 and activated expression of AcSGR1 and AcSGR2. Collectively, the present study indicated that different dynamics of chlorophyll biosynthesis and degradation coordinate the changes in chlorophyll content in kiwifruit flesh, which are orchestrated by the key transcription factor AcHZP45.

Simultaneous inoculation of non-Saccharomyces yeast and lactic acid bacteria for aromatic kiwifruit wine production.

To further explore strain potential and develop an aromatic kiwifruit wine fermentation technique, the feasibility of simultaneous inoculation by non-Saccharomyces yeast and lactic acid bacteria was investigated. Lacticaseibacillus paracasei, Lactiplantibacillus plantarum, and Limosilactobacillus fermentum, which have robust ß-glucosidase activity as well as good acid and ethanol tolerance, were inoculated for simultaneous fermentation with Zygosaccharomyces rouxii and Meyerozyma guilliermondii, respectively. Subsequently, the chemical compositions and sensory characteristics of the wines were comprehensively evaluated. The results showed that the majority of the simultaneous protocols effectively improved the quality of kiwifruit wines, increasing the content of polyphenols and volatile compounds, thereby enhancing sensory acceptability compared to the fermentation protocols inoculated with non-Saccharomyces yeast individually. Particularly, the collaboration between Lacp. plantarum and Z. rouxii significantly increased the diversity and content of esters, alcohols, and ketones, intensifying floral and seeded fruit odors, and achieving the highest overall acceptability. This study highlights the potential significance of simultaneous inoculation in kiwifruit wine production.

First Report of Fusarium fujikuroi Causing Postharvest Rot of Kiwifruit (Actinidia chinensis) in Jiangxi Province, China.

Kiwifruits (Actinidia chinensis) are among the most widely planted fruit in Jiangxi Province, China. Infected kiwifruits of the cultivars 'Hongyang' and 'Jinyan' were obtained from a commercial orchard in Fengxin county, Jiangxi Province (28°67' N; 115°42' E) from September to November 2022. The 1200 kiwifruits were collected from cold storage (cold stored for 3 months at 2°C), and moved to room temperatures (15 to 20°C), approximately 20% had symptoms of postharvest soft rot 7 days later. The infected fruits had brown or dark gray spots on the peel. Most were round or oval, with a diameter of approximately 1~3 cm. The pulp was milky white, and there was a waterlogged ring at the junction of decay. The pathogen was isolated by removing several small pieces (3×3 mm) of infected tissue from the diseased kiwifruits, which were sterilized with 75% ethanol for 30 s, dipped in 1% NaClO for 1 min, and rinsed three times with sterile distilled water. These pieces were transferred onto potato dextrose agar (PDA) and incubated for 5 days at 28°C, 75% relative humidity (RH), separated, and repurified. Eight unidentified isolates with similar morphology were obtained on PDA (D3-1 to D3-8). These isolates had abundant aerial fluffy mycelia. The colonies were white during the early stage of culture and turned light purple in the later stage. The mycelia grew 5.8 mm day-1 (n=5) on average and produced abundant conidia 10 days later. The microconidia were solitary, transparent, ovoid, with 0 to 1 septa, and 3.6 to 11.2 × 1.6 to 3.5 µm (average 6.5 × 2.9 µm, n = 50). The macroconidia were sickle-shaped, slender and slightly curved, with 3 to 5 septa, and 22.3 to 53.9 × 2.6 to 5.4 µm (average 39.5 × 4.3 µm, n = 50). Chlamydospores were absent. The morphological characteristics enabled the identification of the pathogen as Fusarium spp. (Leslie and Summerell, 2006). Isolate D3-2 was further confirmed, and the primers ITS1/ITS4 (White et al. 1990), 5F2/7CR and EF1/EF2 (O'Donnell et al. 2022) were used to amplify the internal transcribed spacer (ITS) region, RNA polymerase II largest subunit (RPB2) gene and translation elongation factor-1 alpha regions (TEF-1α). The ITS (accession no. PP077075), RPB2 (PP566653) and TEF-1α (PP566654) sequences shared 99.62 to 100% identities with ITS (ON564593.1), RPB2 (ON734380.1) and TEF-1α (ON697186.1) of F. fujikuroi from NCBI, respectively. Thus, the pathogen was identified as F. fujikuroi based on morphological and molecular characteristics. Each of the three isolates was inoculated on surface-disinfected (75% ethanol, 5 min) disease-free kiwifruits of cv. 'Jinyan' and 'Hongyang'. The six kiwifruits were pierced by a sterile inoculation needle and inoculated with 20 µl spore suspension (1×106 spores/ml), and six kiwifruits were treated with spore suspension without any wounds, four control fruits were inoculated with sterile distilled water. All the fruits were sealed in a storage box, kept at an RH of 90%-95%, and incubated at a constant temperature of 28°C for 5 days. After 3 days, the fruit rotted at the inoculation site, and after 5 days, the lesions gradually increased, and the symptoms were the same as those of the original sample. The control fruits remained disease-free. The pathogenicity tests were repeated three times. Koch's postulates were completed by reisolating the fungus from infected kiwifruits, which was identified as F. fujikuroi by sequencing. Although F. solani (Yang et al. 2018) and F. acuminatum (Wang et al. 2015) have been previously reported to rot kiwifruits in China, this is the first report of F. fujikuroi causing postharvest rot on kiwifruits in China. This discovery can alert agronomists to prevent and control this pathogen.

Combining thermotherapy with shoot tip culture or cryotherapy for improved virus eradication from in vitro Actinidia macrosperma.

In recent years, kiwifruit viral diseases have become increasingly prevalent in kiwifruit producing regions of China, significantly impacting both the yield and quality of kiwifruit. This has emerged as a significant constraint on the healthy and sustainable development of the kiwifruit industry. The use of virus-free propagation materials has been proven to be an effective strategy for controlling plant viral diseases. In the present study, shoot tip culture (STC), shoot tip cryotherapy (Cryo), and their combinations with thermotherapy were established to eradicate AcVA, AcVB and AcCRaV from Actinidia macrosperma. Additionally, the impact of shoot tip size on virus eradication was evaluated. Among the three confirmed viruses, AcVB was the easiest to eradicate, followed by AcVA and AcCRaV. Combining thermotherapy with shoot tip culture or cryotherapy resulted in higher virus elimination rates than shoot tip culture or cryotherapy alone. Notably, the combination of thermotherapy and 0.5-1 mm shoot tip cryotherapy was shown to be the most effective protocol which produced 50% of regenerated shoots free from all the tested viruses. To the best of our knowledge, this is the first report on virus elimination from kiwifruit infected with multiple viruses based on conventional shoot tip culture and shoot tip cryotherapy.

Genome-Wide Identification and Expression Analysis of Kiwifruit Leucine-Rich Repeat Receptor-Like Proteins Reveal Their Roles in Biotic and Abiotic Stress Responses.

Leucine-rich repeat receptor-like proteins (LRR-RLPs), a major group of receptor-like proteins in plants, have diverse functions in plant physiology, including growth, development, signal transduction, and stress responses. Despite their importance, the specific roles of kiwifruit LRR-RLPs in response to biotic and abiotic stresses remain poorly understood. In this study, we performed family identification, characterization, transcriptome data analysis, and differential gene expression analysis of kiwifruit LRR-RLPs. We identified totals of 101, 164, and 105 LRR-RLPs in Actinidia chinensis 'Hongyang', Actinidia eriantha 'Huate', and Actinidia chinensis 'Red5', respectively. Synteny analysis revealed that the expansion of kiwifruit LRR-RLPs was primarily attributed to segmental duplication events. Based on RNA-seq data from pathogen-infected kiwifruits, we identified specific LRR-RLP genes potentially involved in different stages of pathogen infection. Additionally, we observed the potential involvement of kiwifruit LRR-RLPs in abiotic stress responses, with upstream transcription factors possibly regulating their expression. Furthermore, protein interaction network analysis unveiled the participation of kiwifruit LRR-RLP in the regulatory network of abiotic stress responses. These findings highlight the crucial roles of LRR-RLPs in mediating both biotic and abiotic stress responses in kiwifruit, offering valuable insights for the breeding of stress-resistant kiwifruit varieties.

Physicochemical and Volatile Compounds Analysis of Fruit Wines Fermented with Saccharomyces cerevisiae: FTIR and Microscopy Study with Focus on Anti-Inflammatory Potential.

The growing trend in fruit wine production reflects consumers' interest in novel, diverse drinking experiences and the increasing demand for healthier beverage options. Fruit wines made from kiwi, pomegranates, and persimmons fermented using S. bayanus Lalvin strain EC1118 demonstrate the versatility of winemaking techniques. Kiwifruit, persimmon, and pomegranate wines were analyzed using HPLC and GC-TOFMS analyses to determine their concentrations of phenolic acids and volatile compounds. These results were supported by Fourier transform infrared (FTIR) spectroscopy to characterize and compare chemical shifts in the polyphenol regions of these wines. The wines' characterization included an anti-inflammatory assay based on NO, TNF-alpha, and IL-6 production in the RAW 264.7 macrophage model. FTIR spectroscopy predicted the antioxidant and phenolic contents in the wines. In terms of polyphenols, predominantly represented by chlorogenic, caffeic, and gallic acids, pomegranate and kiwifruit wines showed greater benefits. However, kiwifruit wines exhibited a highly diverse profile of volatile compounds. Further analysis is necessary, particularly regarding the use of other microorganisms in the fermentation process and non-Saccharomyces strains methods. These wines exhibit high biological antioxidant potential and health properties, providing valuable insights for future endeavors focused on designing healthy functional food products.

Utilizing the Banana S-Adenosyl-L-Homocysteine Hydrolase Allergen to Identify Cross-Reactive IgE in Ryegrass-, Latex-, and Kiwifruit-Allergic Individuals.

Food allergies mediated by specific IgE (sIgE) have a significant socioeconomic impact on society. Evaluating the IgE cross-reactivity between allergens from different allergen sources can enable the better management of these potentially life-threatening adverse reactions to food proteins and enhance food safety. A novel banana fruit allergen, S-adenosyl-L-homocysteine hydrolase (SAHH), has been recently identified and its recombinant homolog was heterologously overproduced in E. coli. In this study, we performed a search in the NCBI (National Center for Biotechnology Information) for SAHH homologs in ryegrass, latex, and kiwifruit, all of which are commonly associated with pollen-latex-fruit syndrome. In addition, Western immunoblot analysis was utilized to identify the cross-reactive IgE to banana SAHH in the sera of patients with a latex allergy, kiwifruit allergy, and ryegrass allergy. ClustalOmega analysis showed more than 92% amino acid sequence identity among the banana SAHH homologs in ryegrass, latex, and kiwifruit. In addition to five B-cell epitopes, in silico analysis predicted eleven T-cell epitopes in banana SAHH, seventeen in kiwifruit SAHH, twelve in ryegrass SAHH, and eight in latex SAHH, which were related to the seven-allele HLA reference set (HLA-DRB1*03:01, HLA-DRB1*07:01, HLA-DRB1*15:01, HLA-DRB3*01:01, HLA-DRB3*02:02, HLA-DRB4*01:01, HLA-DRB5*01:01). Four T-cell epitopes were identical in banana and kiwifruit SAHH (positions 328, 278, 142, 341), as well as banana and ryegrass SAHH (positions 278, 142, 96, and 341). All four SAHHs shared two T-cell epitopes (positions 278 and 341). In line with the high amino acid sequence identity and B-cell epitope homology among the analyzed proteins, the cross-reactive IgE to banana SAHH was detected in three of three latex-allergic patients, five of six ryegrass-allergic patients, and two of three kiwifruit-allergic patients. Although banana SAHH has only been studied in a small group of allergic individuals, it is a novel cross-reactive food allergen that should be considered when testing for pollen-latex-fruit syndrome.

Efficient three phase partitioning of actinidin from kiwifruit (Actinidia deliciosa) and its characterization.

Three phase partitioning (TPP) method was effectively utilized for the extraction and purification of milk clotting protease (actinidin) from the kiwifruit pulp. The different purification parameters of TPP such as ammonium sulfate saturation, ratio of the crude kiwifruit extract to tert-butanol, and the pH value of extract were optimized. The 40% (w/v) salt saturation having 1.0:0.75 (v/v) ratio of crude kiwifruit extract to tert-butanol at 6.0 pH value exhibited 3.14 purification fold along with 142.27% recovery, and the protease was concentrated exclusively at intermediate phase (IP). This fraction showed milk-clotting activity (MCA), but there was no such activity in lower aqueous phase (AP). The enzyme molecular weight was found to be 24 kDa from Tricine SDS-PAGE analysis. Recovered protease demonstrated greater stability at pH 7.0 and temperature 50 °C. The Vmax and Km values were 121.9 U/ml and 3.2 mg/ml respectively. Its cysteine nature was demonstrated by inhibition studies. This study highlighted that the TPP is an economic and effective method for extraction and purification of actinidin from kiwifruit, and it could be used as a vegetable coagulant for cheesemaking.

Development of a polyphenol-enriched whole kiwifruit dietary supplement and its potential in ameliorating hyperlipidemia.

BACKGROUND: Kiwifruit pomace, which contains abundant phenolic compounds, is typically discarded during the juicing process, leading to wastage of valuable resources. To address this issue, various indicators (including total acidity, sugar/acid ratio, vitamin C, total polyphenols, polyphenol monomers, and soluble solids content) of 15 kiwifruit cultivars were evaluated and juiced. Then, a polyphenol-concentrated solution from kiwifruit pomace was backfilled into kiwi juice to prepare whole nutritious compound kiwi juice, and its anti-hyperlipidemic activity on obese model mice was then investigated. RESULTS: Through grey relational analysis and the technique for order preference by similarity to an ideal solution (TOPSIS), Kuimi and Huayou were identified as the predominant varieties for juicing, with weighted relevance scores of 0.695 and 0.871 respectively and TOPSIS scores of 0.6509 and 0.8220 respectively. The polyphenol content of Cuixiang pomace was 43.97 mg g-1 , making it the most suitable choice for polyphenol extraction. By backfilling a polyphenol-concentrated solution derived from Cuixiang pomace into compound kiwi juice of Huayou and Kuimi, the whole nutritious compound kiwi juice with polyphenols was produced and exhibited superior bioactivities, including enhanced hepatic oxidative stress defense, and alleviated serum lipid abnormalities. Furthermore, whole nutritious compound kiwi juice with polyphenols ameliorated host intestinal microbiota dysbiosis by increasing the relative abundance of the phyla Bacteroidota and Verrucomicrobiota. CONCLUSION: A hypolipidemic dietary supplement based on kiwifruit pomace polyphenols has been successfully developed, providing an effective solution for hyperlipidemia intervention. © 2023 Society of Chemical Industry.

Kiwifruit Peel Extract Improves the Alterations in Lipid Metabolism in High-fat Diet-fed Model Rats.

Previous studies have demonstrated that the kiwifruit peel, which is usually discarded by consumers and factories, has the highest polyphenol content among all parts of the kiwifruit. To maximize the utilization of these waste resources, the aim of this study was to examine the regulatory effects of polyphenols extracted from kiwifruit peel (KPE) on lipid metabolism and investigate their underlying mechanisms. Thirty-two male Sprague‒Dawley rats were divided into four groups: those fed a normal diet, those fed a high-fat (HF) diet, and those fed a HF diet with a low dose of KPE solution (50 mg/kg) or a high dose of KPE (100 mg/kg) by gavage. The findings of the study revealed that KPE effectively reduced body weight gain and the increases in triglycerides and total cholesterol in serum induced by the HF diet (HFD). Additionally, KPE supplementation led to a significant decrease in hepatic fat accumulation, potentially by increasing hepatic oxidation abilities. Hepatic lipidomics demonstrated that KPE influenced various metabolic pathways, including linoleic acid metabolism, steroid biosynthesis, and the biosynthesis of unsaturated fatty acids in HFD-induced rats, which were associated with the downregulation of FATP2, ACC, FAS, GPAT, DGTA1, DGTA2, and PPARγ expression as well as the upregulation of AMPK, PGC-1α, CPT-1, and PPARα expression. These findings suggest that KPE has considerable regulatory effects in rats with dyslipidaemia, which may provide supporting information for the reuse of kiwifruit peel.

Genomic architecture of resistance to latania scale (H. lataniae) in kiwifruit (A. chinensis var. chinensis).

BACKGROUND: Latania scale (Hemiberlesia lataniae Signoret) is an armoured scale insect known to cause damage to kiwifruit plants and fruit, which ultimately reduces crop values and creates post-harvest export and quarantine issues. Resistance to H. lataniae does exist in some commercial cultivars of kiwifruit. However, some of the commercial cultivars bred in New Zealand have not inherited alleles for resistance to H. lataniae carried by their parents. To elucidate the architecture of resistance in the parents and develop molecular markers to assist breeding, these experiments analysed the inheritance of resistance to H. lataniae from families related to commercial cultivars. RESULTS: The first experiment identified a 15.97 Mb genomic region of interest for resistance to H. lataniae in rtGBS data of 3.23 to 19.20 Mb on chromosome 10. A larger population was then QTL mapped, which confirmed the region of interest as the sole locus contributing to H. lataniae resistance. inDel markers mapping the region of low recombination under the QTL peak further narrowed the region associated with H. lataniae resistance to a 5.73 Mb region. CONCLUSIONS: The kiwifruit populations and genomic methods used in this study identify the same non-recombinant region of chromosome 10 which confers resistance of A. chinensis var. chinensis to H. lataniae. The markers developed to target the H. lataniae resistance loci will reduce the amount of costly and time-consuming phenotyping required for breeding H. lataniae scale resistance into new kiwifruit cultivars.

Genome-wide identification and expression patterns of the laccase gene family in response to kiwifruit bacterial canker infection.

BACKGROUND: Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease worldwide. Resistance genes that respond to Psa infection urgently need to be identified for controlling this disease. Laccase is mainly involved in the synthesis of lignin in the plant cell wall and plays a prominent role in plant growth and resistance to pathogen infection. However, the role of laccase in kiwifruit has not been reported, and whether laccase is pivotal in the response to Psa infection remains unclear. RESULTS: We conducted a bioinformatics analysis to identify 55 laccase genes (AcLAC1-AcLAC55) in the kiwifruit genome. These genes were classified into five cluster groups (I-V) based on phylogenetic analysis, with cluster groups I and II having the highest number of members. Analysis of the exon-intron structure revealed that the number of exons varied from 1 to 8, with an average of 5 introns. Our evolutionary analysis indicated that fragment duplication played a key role in the expansion of kiwifruit laccase genes. Furthermore, evolutionary pressure analysis suggested that AcLAC genes were under purifying selection. We also performed a cis-acting element analysis and found that AcLAC genes contained multiple hormone (337) and stress signal (36) elements in their promoter regions. Additionally, we investigated the expression pattern of laccase genes in kiwifruit stems and leaves infected with Psa. Our findings revealed that laccase gene expression levels in the stems were higher than those in the leaves 5 days after inoculation with Psa. Notably, AcLAC2, AcLAC4, AcLAC17, AcLAC18, AcLAC26, and AcLAC42 showed significantly higher expression levels (p < 0.001) compared to the non-inoculated control (0 d), suggesting their potential role in resisting Psa infection. Moreover, our prediction indicated that 21 kiwifruit laccase genes are regulated by miRNA397, they could potentially act as negative regulators of lignin biosynthesis. CONCLUSIONS: These results are valuable for further analysis of the resistance function and molecular mechanism of laccases in kiwifruit.

Development of a 135K SNP genotyping array for Actinidia arguta and its applications for genetic mapping and QTL analysis in kiwifruit.

Kiwifruit (Actinidia spp) is a woody, perennial and deciduous vine. In this genus, there are multiple ploidy levels but the main cultivated cultivars are polyploid. Despite the availability of many genomic resources in kiwifruit, SNP genotyping is still a challenge given these different levels of polyploidy. Recent advances in SNP array technologies have offered a high-throughput genotyping platform for genome-wide DNA polymorphisms. In this study, we developed a high-density SNP genotyping array to facilitate genetic studies and breeding applications in kiwifruit. SNP discovery was performed by genome-wide DNA sequencing of 40 kiwifruit genotypes. The identified SNPs were stringently filtered for sequence quality, predicted conversion performance and distribution over the available Actinidia chinensis genome. A total of 134 729 unique SNPs were put on the array. The array was evaluated by genotyping 400 kiwifruit individuals. We performed a multidimensional scaling analysis to assess the diversity of kiwifruit germplasm, showing that the array was effective to distinguish kiwifruit accessions. Using a tetraploid F1 population, we constructed an integrated linkage map covering 3060.9 cM across 29 linkage groups and performed QTL analysis for the sex locus that has been identified on Linkage Group 3 (LG3) in Actinidia arguta. Finally, our dataset presented evidence of tetrasomic inheritance with partial preferential pairing in A. arguta. In conclusion, we developed and evaluated a 135K SNP genotyping array for kiwifruit. It has the advantage of a comprehensive design that can be an effective tool in genetic studies and breeding applications in this high-value crop.

A dramatic decline in fruit citrate induced by mutagenesis of a NAC transcription factor, AcNAC1.

Citrate is a common primary metabolite which often characterizes fruit flavour. The key regulators of citrate accumulation in fruit and vegetables are poorly understood. We systematically analysed the dynamic profiles of organic acid components during the development of kiwifruit (Actinidia spp.). Citrate continuously accumulated so that it became the predominate contributor to total acidity at harvest. Based on a co-expression network analysis using different kiwifruit cultivars, an Al-ACTIVATED MALATE TRANSPORTER gene (AcALMT1) was identified as a candidate responsible for citrate accumulation. Electrophysiological assays using expression of this gene in Xenopus oocytes revealed that AcALMT1 functions as a citrate transporter. Additionally, transient overexpression of AcALMT1 in kiwifruit significantly increased citrate content, while tissues showing higher AcALMT1 expression accumulated more citrate. The expression of AcALMT1 was highly correlated with 17 transcription factor candidates. However, dual-luciferase and EMSA assays indicated that only the NAC transcription factor, AcNAC1, activated AcALMT1 expression via direct binding to its promoter. Targeted CRISPR-Cas9-induced mutagenesis of AcNAC1 in kiwifruit resulted in dramatic declines in citrate levels while malate and quinate levels were not substantially affected. Our findings show that transcriptional regulation of a major citrate transporter, by a NAC transcription factor, is responsible for citrate accumulation in kiwifruit, which has broad implications for other fruits and vegetables.