Xanthan gum-based edible coating effectively preserve postharvest quality of 'Gola' guava fruits by regulating physiological and biochemical processes.

BACKGROUND: Guava is a fruit prone to rapid spoilage following harvest, attributed to continuous and swift physicochemical transformations, leading to substantial postharvest losses. This study explored the efficacy of xanthan gum (XG) coatings applied at various concentrations (0.25, 0.5, and 0.75%) on guava fruits (Gola cultivar) over a 15-day storage period. RESULTS: The results indicated that XG coatings, particularly at 0.75%, substantially mitigated moisture loss and decay, presenting an optimal concentration. The coated fruits exhibited a modified total soluble soluble solids, an increased total titratable acidity, and an enhanced sugar-acid ratio, collectively enhancing overall quality. Furthermore, the XG coatings demonstrated the remarkable ability to preserve bioactive compounds, such as total phenolics, flavonoids, and antioxidants, while minimizing the levels of oxidative stress markers, such as electrolyte leakage, malondialdehyde, and H2O2. The coatings also influenced cell wall components, maintaining levels of hemicellulose, cellulose, and protopectin while reducing water-soluble pectin. Quantitative analysis of ROS-scavenging enzymes, including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, revealed significant increases in their activities in the XG-coated fruits compared to those in the control fruits. Specifically, on day 15, the 0.75% XG coating demonstrated the highest SOD and CAT activities while minimizing the reduction in APX activity. Moreover, XG coatings mitigated the activities of fruit-softening enzymes, including pectin methylesterase, polygalacturonase, and cellulase. CONCLUSIONS: This study concludes that XG coatings play a crucial role in preserving postharvest quality of guava fruits by regulating various physiological and biochemical processes. These findings offer valuable insights into the potential application of XG as a natural coating to extend the shelf life and maintain the quality of guava fruits during storage.

Analysis of Codon Usage Bias in Xyloglucan Endotransglycosylase (XET) Genes.

Xyloglucan endotransglycosylase (XET) genes are widely distributed in most plants, but the codon usage bias of XET genes has remained uncharacterized. Thus, we analyzed the codon usage bias using 4500 codons of 20 XET genes to elucidate the genetic and evolutionary patterns. Phylogenetic and hierarchical cluster analyses revealed that the 20 XET genes belonged to two groups. The closer the genetic distance, the more similar the codon usage preference. The codon usage bias of most XET genes was weak, but there was also some codon usage bias. AGA, AGG, AUC, and GUG were the top four codons (RSCU > 1.5) in the 20 XET genes. CitXET had a stronger codon usage bias, and there were eight optimal codons of CitXET (i.e., AGA, AUU, UCU, CUU, CCA, GCU, GUU, and AAA). The RSCU values underwent a correspondence analysis. The two main factors affecting codon usage bias (i.e., Axes 1 and 2) accounted for 54.8% and 17.6% of the total variation, respectively. Multiple correspondence analysis revealed that XET genes were widely distributed, with Group 1 genes being closer to Axis 1 than Group 2 genes, which were closer to Axis 2. Codons with A/U at the third codon position were distributed closer to Axis 1 than codons with G/C at the third codon position. PgXET, ZmXET, VlXET, VrXET, and PcXET were biased toward codons ending with G/C. In contrast, CitXET, DpXET, and BrpXET were strongly biased toward codons ending with A/U, indicating that these XET genes have a strong codon usage bias. Translational selection and base composition (especially A and U at the third codon position), followed by mutation pressure and natural selection, may be the most important factors affecting codon usage of 20 XET genes. These results may be useful in clarifying the codon usage bias of XET genes and the relevant evolutionary characteristics.

Identification of Photosynthesis Characteristics and Chlorophyll Metabolism in Leaves of Citrus Cultivar (Harumi) with Varying Degrees of Chlorosis.

In autumn and spring, citrus leaves with a Ponkan (Citrus reticulata Blanco cv. Ponkan) genetic background (Harumi, Daya, etc.) are prone to abnormal physiological chlorosis. The effects of different degrees of chlorosis (normal, mild, moderate and severe) on photosynthesis and the chlorophyll metabolism of leaves of Citrus cultivar (Harumi) were studied via field experiment. Compared with severe chlorotic leaves, the results showed that chlorosis could break leaf metabolism balance, including reduced chlorophyll content, photosynthetic parameters, antioxidant enzyme activity and enzyme activity related to chlorophyll synthesis, increased catalase and decreased enzyme activity. In addition, the content of chlorophyll synthesis precursors showed an overall downward trend expected for uroporphyrinogen III. Furthermore, the relative expression of genes for chlorophyll synthesis (HEMA1, HEME2, HEMG1 and CHLH) was down-regulated to some extent and chlorophyll degradation (CAO, CLH, PPH, PAO and SGR) showed the opposite trend with increased chlorosis. Changes in degradation were more significant. In general, the chlorosis of Harumi leaves might be related to the blocked transformation of uroporphyrinogen III (Urogen III) to coproporphyrinogen III (Coprogen III), the weakening of antioxidant enzyme system activity, the weakening of chlorophyll synthesis and the enhancement in degradation.

Dynamic Changes in Ascorbic Acid Content during Fruit Development and Ripening of Actinidia latifolia (an Ascorbate-Rich Fruit Crop) and the Associated Molecular Mechanisms.

Actinidia latifolia is one of the very few kiwifruit genotypes with extremely high ascorbic acid (AsA) content. However, a transcriptome atlas of this species is lacking. The accumulation of AsA during fruit development and ripening and the associated molecular mechanisms are still poorly understood. Herein, dynamic changes in AsA content at six different stages of A. latifolia fruit development and ripening were determined. AsA content of A. latifolia fruit reached 1108.76 ± 35.26 mg 100 g-1 FW at full maturity. A high-quality, full-length (FL) transcriptome of A. latifolia was successfully constructed for the first time using third-generation sequencing technology. The transcriptome comprises 326,926 FL non-chimeric reads, 15,505 coding sequences, 2882 transcription factors, 18,797 simple sequence repeats, 3328 long noncoding RNAs, and 231 alternative splicing events. The genes involved in AsA biosynthesis and recycling pathways were identified and compared with those in different kiwifruit genotypes. The correlation between the AsA content and expression levels of key genes in AsA biosynthesis and recycling pathways was revealed. LncRNAs that participate in AsA-related gene expression regulation were also identified. Gene expression patterns in AsA biosynthesis and metabolism exhibited a trend similar to that of AsA accumulation. Overall, this study paves the way for genetic engineering to develop kiwifruits with super-high AsA content.

Genome-Wide Identification of MYB Transcription Factors and Screening of Members Involved in Stress Response in Actinidia.

MYB transcription factors (TFs) play an active role in plant responses to abiotic stresses, but they have not been systematically studied in kiwifruit (Actinidia chinensis). In this study, 181 AcMYB TFs were identified from the kiwifruit genome, unevenly distributed on 29 chromosomes. The high proportion (97.53%) of segmental duplication events (Ka/Ks values less than 1) indicated that AcMYB TFs underwent strong purification selection during evolution. According to the conservative structure, 91 AcR2R3-MYB TFs could be divided into 34 subgroups. A combination of transcriptomic data under drought and high temperature from four AcMYB TFs (AcMYB2, AcMYB60, AcMYB61 and AcMYB102) was screened out in response to stress and involvement in the phenylpropanoid pathway. They were highly correlated with the expression of genes related to lignin biosynthesis. qRT-PCR analysis showed that they were highly correlated with the expression of genes related to lignin biosynthesis in different tissues or under stress, which was consistent with the results of lignin fluorescence detection. The above results laid a foundation for further clarifying the role of MYB in stress.

Melatonin improves heat tolerance in Actinidia deliciosa via carotenoid biosynthesis and heat shock proteins expression.

The whole-genome molecular mechanisms of melatonin (MT)-mediated enhancement of thermotolerance in plants has rarely been studied. In this study, the genome-wide gene expression profiles of kiwifruit seedlings primed with MT and non-MT at 45°C were analyzed by RNA-Seq. A total of 3299 differentially expressed genes (DEGs) were screened between MT and non-MT treatment, in which carotenoid biosynthesis was one of the high-enrichment pathways revealed by Kyoto Encyclopedia of Genes and Genomes analysis. Further, qRT-PCR verified that MT significantly induced the upregulated expression of the carotenoid biosynthesis gene, which was consistent with the increase of carotenoid content. In addition, 10 heat shock proteins (HSPs) were identified to have a highly upregulated expression by MT. These findings provide a set of informative and fundamental data on the role of MT in heat resistance.

Mowing enhances the phytoremediation ability of cadmium-contaminated soil in the post-grafting generations of potential cadmium-hyperaccumulator Solanum photeinocarpum.

The study aimed at accessing the effects of mowing on the growth and cadmium (Cd) accumulation of the first post-grafting generation of potential Cd-hyperaccumulator plant Solanum photeinocarpum through the pot and plot experiments. Four grafting treatments were employed such as ungrafted (UG), self-rooted grafting by the same S. photeinocarpum seedling (SG), self-rooted grafting by two different development stages of S. photeinocarpum seedlings (DG), and grafting on the rootstock of wild potato (PG). The biomass, Cd content, and Cd extraction amount of S. photeinocarpum shoots significantly decreased with the increase of mowing times in the pot and plot experiments. The order of the grafting on the biomass, Cd content, and Cd extraction amountof in the first, second, third mowing shoots were PG > DG > SG > UG. For the Cd extraction amountof total moving shoots, SG, DG, and PG increased by 20.42%, 35.54%, and 52.94%, respectively, in the pot experiment, and increased by 11.56%, 26.28%, and 44.90%, respectively, in the plot experiment, compared with the UG. Therefore, mowing provides an insight into the phytoremediation ability of S. photeinocarpum to Cd.

Alleviation of drought stress and the physiological mechanisms in Citrus cultivar (Huangguogan) treated with methyl jasmonate.

The role of exogenous methyl jasmonate (MeJA) in alleviating drought stress was investigated on Huangguogan. Except for intercellular CO2 concentration, MeJA had little effect on net photosynthetic rate, stomatal conductance, and transpiration rate under drought stress. Compared with drought stress, MeJA significantly alleviated the decrease of chlorophyll content. However, chlorophyll a/b ratio was significantly increased. MeJA significantly increased proline and soluble sugar contents, significantly decreased the O2 -· and H2O2 levels, and increased SOD and POD activities. In addition, the MDA content of drought stress was the highest of all treatments. MeJA significantly reduced MDA content in drought-stressed Huangguogan leaves. Although the Ascorbic acid (AsA) contents of 500 and 1000 mg L-1 MeJA treatments were lower than that of 250 mg L-1 MeJA, but all concentration of MeJA treatments delayed the decline of AsA content. Therefore, MeJA could induce drought stress tolerance by increasing the osmotic adjustment substances and antioxidant activities.

Melatonin Alleviates Drought Stress by a Non-Enzymatic and Enzymatic Antioxidative System in Kiwifruit Seedlings.

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.

Melatonin Accumulation in Sweet Cherry and Its Influence on Fruit Quality and Antioxidant Properties.

Although the effects of melatonin on plant abiotic and biotic stress resistance have been explored in recent decades, the accumulation of endogenous melatonin in plants and its influence on fruit quality remains unclear. In the present study, melatonin accumulation levels and the expression profiles of five synthesis genes were investigated during fruit and leaf development in sweet cherry (Prunus avium L.). Melatonin was strongly accumulated in young fruits and leaves, then decreased steadily with maturation. Transcript levels of PacTDC and PacSNAT were highly correlated with melatonin content in both fruit and leaves, indicating their importance in melatonin accumulation. Furthermore, application of 50 and 100 µmol·L-1 of melatonin to leaves had a greater influence on fruit quality than treatments applied to fruits, by significantly improving fruit weight, soluble solids content, and phenolic content including total phenols, flavanols, total anthocyanins, and ascorbic acid. Meanwhile, melatonin application promoted the antioxidant capacity of fruit assayed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylben zothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP). These results provide insights into the physiological and molecular mechanisms underlying melatonin metabolism of sweet cherry.

Effects of carboxymethyl chitosan on the growth and nutrient uptake in Prunus davidiana seedlings.

To determine the effects of carboxymethyl chitosan on plant growth and nutrient uptake, Prunus davidiana seedlings were treated with various concentrations of carboxymethyl chitosan. The biomass, physiological characteristics, and nutrient uptake of the treated P. davidiana seedlings were then examined. Compared with the control seedlings, the carboxymethyl chitosan-treated seedlings had a higher biomass and a greater abundance of photosynthetic pigments (i.e., chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), with the best concentration as 2 g/L carboxymethyl chitosan, which increased the shoot biomass and total chlorophyll content by 26.75% and 24.64%, respectively. Moreover, the application of carboxymethyl chitosan enhanced superoxide dismutase and catalase activities, increased the soluble protein content, and decreased the malondialdehyde and proline contents of the P. davidiana seedlings to some extent. Additionally, the carboxymethyl chitosan treatments decreased the total nitrogen content, but increased the total phosphorus and potassium contents in P. davidiana seedlings to some extent. The minimum of total nitrogen content and the maximum of total phosphorus and potassium contents in shoots of P. davidiana seedlings were the concentration of 2 g/L carboxymethyl chitosan, which was decreased by 12.96% and increased by 15.45% and 22.53%, respectively, compared with the control. Therefore, the application of a carboxymethyl chitosan solution may promote the growth, enhance the stress resistance, and alter the nutrient uptake of P. davidiana seedlings, especially at 2 g/L carboxymethyl chitosan.

Molecular cytogenetic analysis of genome-specific repetitive elements in Citrus clementina Hort. Ex Tan. and its taxonomic implications.

BACKGROUND: Clementine mandarin (Citrus clementina Hort. ex Tan.) is one of the most famous and widely grown citrus cultivars worldwide. Variations in relation to the composition and distribution of repetitive DNA sequences that dominate greatly in eukaryote genomes are considered to be species-, genome-, or even chromosome-specific. Repetitive DNA-based fluorescence in situ hybridization (FISH) is a powerful tool for molecular cytogenetic study. However, to date few studies have involved in the repetitive elements and cytogenetic karyotype of Clementine. RESULTS: A graph-based similarity sequence read clustering methodology was performed to analyze the repetitive DNA families in the Clementine genome. The bioinformatics analysis showed that repetitive DNAs constitute 41.95% of the Clementine genome, and the majority of repetitive elements are retrotransposons and satellite DNAs. Sequential multicolor FISH using a probe mix that contained CL17, four satellite DNAs, two rDNAs and an oligonucleotide of (TTTAGGG)3 was performed with Clementine somatic metaphase chromosomes. An integrated karyotype of Clementine was established based on unequivocal and reproducible chromosome discriminations. The distribution patterns of these probes in several Citrus, Poncirus and Fortunella species were summarized through extensive FISH analyses. Polymorphism and heterozygosity were commonly observed in the three genera. Some asymmetrical FISH loci in Clementine were in agreement with its hybrid origin. CONCLUSIONS: The composition and abundance of repetitive elements in the Clementine genome were reanalyzed. Multicolor FISH-based karyotyping provided direct visual proof of the heterozygous nature of Clementine chromosomes with conspicuous asymmetrical FISH hybridization signals. We detected some similar and variable distribution patterns of repetitive DNAs in Citrus, Poncirus, and Fortunella, which revealed notable conservation among these genera, as well as obvious polymorphism and heterozygosity, indicating the potential utility of these repetitive element markers for the study of taxonomic, phylogenetic and evolutionary relationships in the future.

Melatonin and 14-hydroxyed brassinosteroid combined promote kiwifruit seedling growth by improving soil microbial distribution, enzyme activity and nutrients uptake.

Kiwifruit, a nutrient-dense fruit, has become increasingly popular with consumers in recent decades. However, kiwifruit trees are prone to stunted growth after a few years of planting, called early tree decline. In this study, melatonin (MT), pollen polysaccharide (SF), 14-hydroxyed brassinosteroid (14-HBR) were applied alone or in combination to investigate their influence on plant growth, nutrition absorption and rhizosphere bacterial abundance in kiwifruit seedlings. The results revealed that MT, SF and 14-HBR alone treatments significantly increased leaf chlorophyll content, photosynthetic capacity and activities of dismutase and catalase compared with the control. Among them, MT treatment significantly increased the dry root biomass by 35.7%, while MT+14-HBR treatment significant enhanced the dry shoot biomass by 36.9%. Furthermore, both MT and MT+14-HBR treatments markedly improved the activities of invertase, urease, protease and phosphatase in soil, as well as the abundance of Proteobacteria and Acidobacteria in rhizosphere microorganisms based on 16S rDNA sequencing. In addition, MT treatment improved the content of available K and organic matter in soil, and increased the uptake of P, K and Fe by seedlings. In summary, 14-HBR and MT combined had the best effect on promoting rhizosphere bacterial distribution, nutrient absorption and plant growth. These findings may provide valuable guidance for solving growth weakness problem in kiwifruit cultivation.

A high-quality chromosome-scale genome assembly of blood orange, an important pigmented sweet orange variety.

Blood orange (BO) is a rare red-fleshed sweet orange (SWO) with a high anthocyanin content and is associated with numerous health-related benefits. Here, we reported a high-quality chromosome-scale genome assembly for Neixiu (NX) BO, reaching 336.63 Mb in length with contig and scaffold N50 values of 30.6 Mb. Furthermore, 96% of the assembled sequences were successfully anchored to 9 pseudo-chromosomes. The genome assembly also revealed the presence of 37.87% transposon elements and 7.64% tandem repeats, and the annotation of 30,395 protein-coding genes. A high level of genome synteny was observed between BO and SWO, further supporting their genetic similarity. The speciation event that gave rise to the Citrus species predated the duplication event found within them. The genome-wide variation between NX and SWO was also compared. This first high-quality BO genome will serve as a fundamental basis for future studies on functional genomics and genome evolution.

Integrated approaches for Solenopsis invicta (Hymenoptera: Formicidae) management: insights from laboratory studies with entomopathogenic nematodes and insecticides.

BACKGROUND: In agricultural pest management, especially in combatting the invasive red imported fire ant (RIFA, Solenopsis invicta), significant challenges emerge as a consequence of the constraints of solely depending on chemical insecticides or entomopathogenic nematodes (EPNs). The utilization of chemical insecticides carries environmental and ecological hazards, whereas EPNs, when applied independently, might not offer the immediate effectiveness necessary for adequate RIFA suppression. Acknowledging these hurdles, our study investigates a synergistic method that integrates EPNs with chemical insecticides, aiming to fulfill the urgent demand for more efficient and environmentally friendly pest control solutions. RESULTS: Our evaluation focused on the interaction between the highly pathogenic Steinernema riobrave 7-12 EPN strain and prevalent insecticides, specifically beta-cypermethrin and a mixture of bifenthrin and clothianidin, applied at highly diluted recommended concentrations. The findings revealed a notable increase in RIFA mortality rates when EPNs and these insecticides were used together, outperforming the results achieved with each method individually. Remarkably, this enhanced efficacy was especially evident at lower concentrations of the bifenthrin-clothianidin mixture, indicating a valuable approach to minimizing reliance on chemical insecticides in agriculture. Furthermore, the high survival rates of EPNs alongside the tested insecticides indicate their compatibility and potential for sustained use in integrated pest management programs. CONCLUSION: Our research underscores the effectiveness of merging EPNs with chemical insecticides as a powerful and sustainable strategy for RIFA management. This combined approach not only meets the immediate challenges of pest control in agricultural settings, but also supports wider environmental objectives by reducing the dependency on chemical insecticides. © 2024 Society of Chemical Industry.

Intercropping of Cyphomandra betacea with Different Ploidies of Solanum Sect. Solanum (Solanaceae) Wild Vegetables Increase Their Selenium Uptakes.

Selenium (Se) deficiency causes various diseases in humans. Se can be obtained from fruits and vegetables. In this study, the fruit tree Cyphomandra betacea was intercropped with three Solanum sect. Solanum (Solanaceae) wild vegetables [diploid (S. photeinocarpum), tetraploid (colchicine-induced S. photeinocarpum), and hexaploid (S. nigrum)], respectively, and Se uptakes of these plants were determined by a pot experiment. Intercropping decreased the biomass, photosynthetic pigment content, and superoxide dismutase activity of C. betacea, but increased the peroxidase (POD) activity, catalase (CAT) activity, and soluble protein content of C. betacea. These indicators' values of sect. Solanum increased after intercropping. The contents of Se increased in C. betacea and sect. Solanum after intercropping. Intercropped with diploid, tetraploid, and hexaploid increased the shoot Se contents in C. betacea by 13.73%, 17.49%, and 26.50%, respectively, relative to that of C. betacea monoculture. Intercropped with C. betacea increased the shoot Se contents in diploid, tetraploid, and hexaploid by 35.22%, 68.86%, and 74.46%, respectively, compared with their respective monoculture. The biomass and Se content of intercropped sect. Solanum showed linear relationships with the biomass and Se content of their monocultures. The biomass and Se content of intercropped C. betacea also exhibited linear relationships with that of sect. Solanum monocultures. Correlation and grey relational analyses revealed that the CAT activity, POD activity, and soluble protein content were the top three indicators closely associated with the C. betacea shoot Se content. The POD activity, soluble protein content, and translocation factor were the top three indicators closely associated with sect. Solanum shoot Se content. Therefore, intercropping can promote the Se uptake in C. betacea and sect. Solanum wild vegetables.

Chromosome-scale genome assembly of a natural diploid kiwifruit (Actinidia chinensis var. deliciosa).

The most commercialized kiwifruit, Actinidia chinensis var. deliciosa (Acd), is an allohexaploid (2n = 6x = 174), making high-quality assemblage genome challenging. We previously discovered a rare naturally occurring diploid Acd plant. Here, chromosome-level de novo genome assembly for this diploid Acd was reported, reaching approximately 621.98 Mb in length with contig and scaffold N50 values of 10.08 and 21.09 Mb, respectively, 99.66% of the bases anchored to 29 pseudochromosomes, and 38,990 protein-coding genes and 42.29% repetitive elements annotated. The divergence time of A. chinensis cv. 'Red5' and 'Hongyang' (11.1-27.7 mya) was more recent compared with the divergence time of them and Acd (19.9-41.2 mya), with the divergence time of A. eriantha cv. 'White' being the earliest (22.9-45.7 mya) among that of the four Actinidia species. The 4DTv distance distribution highlighted three recent whole-genome duplication events in Acd. This is the first high-quality diploid Acd genome, which lays an important foundation for not only kiwifruit functional genomics studies but also further elucidating genome evolution of allohexaploid Acd.

Comparative Analysis of Carotenoid Profiles and Biosynthetic Gene Expressions among Ten Plum Cultivars.

Plums are good sources of various bioactive phytochemical compounds such as vitamins, anthocyanins, and carotenoids, whereby all of which are noted for multiple potential health benefits. However, knowledge regarding plum carotenoid profiles remains limited. Hence, the total and individual carotenoids in the edible parts (skin and flesh) of ten plum cultivars were determined using a spectrophotometer and high-performance liquid chromatography-diode array detection, respectively. Total and individual carotenoid contents in skin were significantly higher (p < 0.05) than those in flesh among all plum cultivars tested. The cultivars with the highest content of total carotenoids in skin were Naili (36.73 µg/g FW), followed by Yinhongli (21.81 µg/g FW) and Yuhuangli (19.70 µg/g FW), with the lowest in Angeleno (8.97 µg/g FW). Lutein, zeaxanthine, ß-cryptoxanthin, α-carotene, and ß-carotene were the major types of carotenoids detected, with lutein and ß-carotene being the predominant constituents of the skin and flesh tissues, respectively. Lutein, zeaxanthine, and total carotenoid contents were positively correlated with the expressions of PSY, LCYB, and LCYE, and negatively correlated with the expressions of PDS and CRTISO. Characterizing the carotenoid profiles and investigating variations in carotenoid biosynthetic gene expressions among plum cultivars are crucial for advancing genetic improvements in plums.

Genome-wide identification of the AcMADS-box family and functional validation of AcMADS32 involved in carotenoid biosynthesis in Actinidia.

MADS-box is a large transcription factor family in plants and plays a crucial role in various plant developmental processes; however, it has not been systematically analyzed in kiwifruit. In the present study, 74 AcMADS genes were identified in the Red5 kiwifruit genome, including 17 type-I and 57 type-II members according to the conserved domains. The AcMADS genes were randomly distributed across 25 chromosomes and were predicted to be mostly located in the nucleus. A total of 33 fragmental duplications were detected in the AcMADS genes, which might be the main force driving the family expansion. Many hormone-associated cis-acting elements were detected in the promoter region. Expression profile analysis showed that AcMADS members had tissue specificity and different responses to dark, low temperature, drought, and salt stress. Two genes in the AG group, AcMADS32 and AcMADS48, had high expression levels during fruit development, and the role of AcMADS32 was further verified by stable overexpression in kiwifruit seedlings. The content of α-carotene and the ratio of zeaxanthin/ß-carotene was increased in transgenic kiwifruit seedlings, and the expression level of AcBCH1/2 was significantly increased, suggesting that AcMADS32 plays an important role in regulating carotenoid accumulation. These results have enriched our understanding of the MADS-box gene family and laid a foundation for further research of the functions of its members during kiwifruit development.

Dynamic Changes in Cell Wall Polysaccharides during Fruit Development and Ripening of Two Contrasting Loquat Cultivars and Associated Molecular Mechanisms.

Loquats have drawn much attention due to their essential nutrients and unusual phenology, which fills a market gap in early spring. Fruit firmness (FF) is one of the most important quality attributes. Dynamic changes in FF, cell wall (CW) polysaccharides, CW hydrolase activity, and expression of CW metabolism-related genes during the fruit development and ripening stages of two contrasting loquat cultivars were compared. Although the two cultivars possessed similar FF at the initial fruitlet stage, Dawuxing was significantly firmer than Ninghaibai at all subsequent time points. FF was positively correlated with the contents of covalent-soluble pectin and hemicellulose, activity of peroxidase, and gene expressions of PME, EG, CAD6, and POD; and negatively correlated with the contents of water-soluble pectin, activities of polygalacturonase, endo-glucanase, cellobiohydrolase, and xylanase, and gene expressions of PG, EG2, PAL1, PAL3, and CAD5. Identifying molecular mechanisms underlying the differences in FF is useful for fundamental research and crop improvement in future.