The transcriptional control of LcIDL1-LcHSL2 complex by LcARF5 integrates auxin and ethylene signaling for litchi fruitlet abscission.

At the physiological level, the interplay between auxin and ethylene has long been recognized as crucial for the regulation of organ abscission in plants. However, the underlying molecular mechanisms remain unknown. Here, we identified transcription factors involved in indoleacetic acid (IAA) and ethylene (ET) signaling that directly regulate the expression of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) and its receptor HAESA (HAE), which are key components initiating abscission. Specifically, litchi IDA-like 1 (LcIDL1) interacts with the receptor HAESA-like 2 (LcHSL2). Through in vitro and in vivo experiments, we determined that the auxin response factor LcARF5 directly binds and activates both LcIDL1 and LcHSL2. Furthermore, we found that the ETHYLENE INSENSITIVE 3-like transcription factor LcEIL3 directly binds and activates LcIDL1. The expression of IDA and HSL2 homologs was enhanced in LcARF5 and LcEIL3 transgenic Arabidopsis plants, but reduced in ein3 eil1 mutants. Consistently, the expressions of LcIDL1 and LcHSL2 were significantly decreased in LcARF5- and LcEIL3-silenced fruitlet abscission zones (FAZ), which correlated with a lower rate of fruitlet abscission. Depletion of auxin led to an increase in 1-aminocyclopropane-1-carboxylic acid (the precursor of ethylene) levels in the litchi FAZ, followed by abscission activation. Throughout this process, LcARF5 and LcEIL3 were induced in the FAZ. Collectively, our findings suggest that the molecular interactions between litchi AUXIN RESPONSE FACTOR 5 (LcARF5)-LcIDL1/LcHSL2 and LcEIL3-LcIDL1 signaling modules play a role in regulating fruitlet abscission in litchi and provide a long-sought mechanistic explanation for how the interplay between auxin and ethylene is translated into the molecular events that initiate abscission.

Diet with different concentrations of lychee peel flour modulates oxidative stress parameters and antioxidant activity in zebrafish.

The agri-food industry generates substantial waste, leading to significant environmental impacts. Lychee (Litchi chinensis Sonnerat), which is rich in bioactive compounds in its peel, pulp, and seeds, offers an opportunity for waste use. This study aimed to evaluate the effects of supplementing a high-carbohydrate diet with varying levels of lychee peel flour on lipid metabolism biomarkers and oxidative stress in a zebrafish (Danio rerio) model. A total of 225 zebrafish, approximately four months old, were divided into five groups: control, high-carbohydrate (HC), HC2%, HC4%, and HC6%. The study did not find significant differences in the growth performance of zebrafish in any group. However, the HC6% group exhibited a significant decrease in glucose and triglyceride levels compared with the HC group. Furthermore, this group showed enhanced activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), along with reduced levels of malondialdehyde (MDA). Increased antioxidant activity was also evidenced by DPPH-, ABTS+, and ß-carotene/Linoleic acid assays in the HC6% group. A positive correlation was identified between SOD/CAT activity and in vitro antioxidant assays. These findings suggest that dietary supplementation with 6% lychee peel flour can significantly modulate glucose homeostasis, lipid metabolism, and antioxidant activity in zebrafish.

The SOC1 gene plays an important role in regulating litchi flowering time.

Litchi (Litchi chinensis Sonn.) is a valuable subtropical fruit tree with high-quality fruit. However, its economic benefits and sustainable development are restrained by a number of challenges. One major challenge is the lack of extremely early and late maturing high-quality varieties due to limited availability of varieties suitable for commercial cultivation and outdated breeding methods, resulting in an imbalanced supply and low price of litchi. Flowering time is a crucial genetic factor influencing the maturation period of litchi. Our previous research has highlighted the pivotal role of the LcFT1 gene in regulating the flowering time of litchi and identified a gene associated with LcFT1 (named as LcSOC1) based on RNA-Seq and weight gene co-expression network (WGCNA) analysis. This study further investigated the function of LcSOC1. Subcellular localization analysis revealed that LcSOC1 is primarily localized in the nucleus, where it acts as a transcription factor. LcSOC1 overexpression in Nicotiana tabacum and Arabidopsis thaliana resulted in significant early flowering. Furthermore, LcSOC1 was found to be expressed in various tissues, with the highest expression in mature leaves. Analysis of spatial and temporal expression patterns of LcSOC1 in litchi varieties with different flowering time under low temperature treatment and across an annual cycle demonstrated that LcSOC1 is responsive to low temperature induction. Interestingly, early maturing varieties exhibited higher sensitivity to low temperature, with significantly premature induction of LcSOC1 expression relative to late maturing varieties. Activation of LcSOC1 triggered the transition of litchi into the flowering phase. These findings demonstrate that LcSOC1 plays a pivotal role in regulating the flowering process and determining the flowering time in litchi. Overall, this study provides theoretical guidance and important target genes for molecular breeding to regulate litchi production period.

A plant cell death-inducing protein from litchi interacts with Peronophythora litchii pectate lyase and enhances plant resistance.

Cell wall degrading enzymes, including pectate lyases (PeLs), released by plant pathogens, break down protective barriers and/or activate host immunity. The direct interactions between PeLs and plant immune-related proteins remain unclear. We identify two PeLs, PlPeL1 and PlPeL1-like, critical for full virulence of Peronophythora litchii on litchi (Litchi chinensis). These proteins enhance plant susceptibility to oomycete pathogens in a PeL enzymatic activity-dependent manner. However, LcPIP1, a plant immune regulator secreted by litchi, binds to PlPeL1/PlPeL1-like, and attenuates PlPeL1/PlPeL1-like induced plant susceptibility to Phytophthora capsici. LcPIP1 also induces cell death and various immune responses in Nicotiana benthamiana. Conserved in plants, LcPIP1 homologs bear a conserved "VDMASG" motif and exhibit immunity-inducing activity. Furthermore, SERK3 interacts with LcPIP1 and is required for LcPIP1-induced cell death. NbPIP1 participates in immune responses triggered by the PAMP protein INF1. In summary, our study reveals the dual roles of PlPeL1/PlPeL1-like in plant-pathogen interactions: enhancing pathogen virulence through PeL enzymatic activity while also being targeted by LcPIP1, thus enhancing plant immunity.

Total flavonoids of Litchi chinensis Sonn. seed inhibit prostate cancer growth in bone by regulating the bone microenvironment via inactivation of the HGFR/NF-κB signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Litchi chinensis Sonn. (Litchi) seed, a traditional Chinese medicine, is habitually used in the clinical treatment of prostate cancer (PCa)-induced bone pain. In our previous study, flavonoids have been identified as the active ingredient of litchi seed against PCa. However, its anti-tumor activities in bone and associated molecular mechanisms are still unclear. AIM OF THE STUDY: To investigate the effects and underlying mechanisms of total flavonoids of litchi seed (TFLS) on the growth of PCa in bone. MATERIALS AND METHODS: The effect of TFLS on the growth of PCa in bone was observed using a mouse model constructed with tibial injection of luciferase-expressing RM1-luc cells. Conditioned medium (CM) from bone marrow stromal cells OP9 and CM treated with TFLS (T-CM) was used to investigate the effect on the proliferation, colony formation, and apoptosis of PCa cells (LNCaP, PC3, RM1). An antibody microarray was performed to detect cytokine expression in the supernatant fraction of OP9 cell cultures treated with TFLS or left untreated. Western blot assay was employed to determine the expression and activity of HGFR and its key downstream proteins, Akt, mTOR, NF-κB, and Erk, in PCa cells. The potential target was further verified using immunofluorescence and immunohistochemistry assays. RESULTS: Treatment with TFLS (80 mg/kg, 24 days) significantly suppressed the growth of RM1 cells in bone. CM from bone marrow stromal cells OP9 stimulated the proliferation and colony formation of the PCa cells as well as inhibited the apoptosis of PC3 cells, while T-CM reversed the effects mediated by OP9 cells in vitro. In an antibody array assay, TFLS regulated the majority of cytokines in OP9 cell culture supernatant, among which HGF, HGFR, IGF-1R, and PDGF-AA showed the greatest fold changes. Mechanistically, CM upregulated HGFR and promoted phosphorylation of NF-κB while T-CM induced reduction of HGFR and dephosphorylation of NF-κB in PC3 cells. Moreover, T-CM inhibited NF-κB entry into PC3 cell nuclei. Data from in vivo experiments further confirmed the inhibitory effects of TFLS on NF-κB. CONCLUSION: TFLS suppresses the growth of PCa in bone through regulating bone microenvironment and the underlying mechanism potentially involves attenuation of the HGFR/NF-κB signaling axis.

An LcMYB111-LcHY5 Module Differentially Activates an LcFLS Promoter in Different Litchi Cultivars.

Flavonol synthase (FLS) is the crucial enzyme of the flavonol biosynthetic pathways, and its expression is tightly regulated in plants. In our previous study, two alleles of LcFLS,LcFLS-A and LcFLS-B, have been identified in litchi, with extremely early-maturing (EEM) cultivars only harboring LcFLS-A, while middle-to-late-maturing (MLM) cultivars only harbor LcFLS-B. Here, we overexpressed both LcFLS alleles in tobacco, and transgenic tobacco produced lighter-pink flowers and showed increased flavonol levels while it decreased anthocyanin levels compared to WT. Two allelic promoters of LcFLS were identified, with EEM cultivars only harboring proLcFLS-A, while MLM cultivars only harbor proLcFLS-B. One positive and three negative R2R3-MYB transcription regulators of LcFLS expression were identified, among which only positive regulator LcMYB111 showed a consistent expression pattern with LcFLS, which both have higher expression in EEM than that of MLM cultivars. LcMYB111 were further confirmed to specifically activate proLcFLS-A with MYB-binding element (MBE) while being unable to activate proLcFLS-B with mutated MBE (MBEm). LcHY5 were also identified and can interact with LcMYB111 to promote LcFLS expression. Our study elucidates the function of LcFLS and its differential regulation in different litchi cultivars for the first time.

Litchi procyanidins inhibit colon cancer proliferation and metastasis by triggering gut-lung axis immunotherapy.

Litchi chinensis seed, as a valuable by-product of the subtropical fruit litchi (Litchi chinensis Sonn.), has been confirmed to be rich in procyanidins (LPC). The anticarcinogenic properties of procyanidins has been primarily attributed to their antioxidant and anti-inflammatory activities. However, there is a comparative paucity of information on if and how LPC inhibits colon cancer. Here, LPC significantly inhibited CT26 colon cancer cells proliferation and metastasis in vivo and in vitro. In CT26 lung metastatic mice, the anti-metastatic effect of LPC relied on its regulation of gut microbiota such as increase of Lachnospiraceae UCG-006, Ruminococcus, and their metabolites such as acetic acid, propionic acid and butyric acid. In addition, LPC significantly inhibited CT26 colon cancer cells metastasis through increasing CD8+ cytotoxic T lymphocytes infiltration and decreasing the number of macrophages. Antibiotics treatment demonstrated that the therapeutic effect of LPC depended on the gut microbiota, which regulated T cells immune response. Taken together, LPC had strong inhibitory effects on colon cancer pulmonary metastasis by triggering gut-lung axis to influence the T cells immune response. Our research provides a novel finding for the utilization of procyanidins in the future, that is, supplementing more fruits and vegetables rich in procyanidins is beneficial to the treatment of colon cancer, or it can be used as an adjuvant drug in clinical anti-tumor immunotherapy.

Involvement of miRNAs-mediated senescence and salicylic acid defense in postharvest litchi downy blight.

Litchi downy blight, caused by Peronophythora litchii, results in decline of market value of litchi fruit. In this study, roles of microRNAs (miRNAs) in regulating litchi fruit response to P. litchii infection was investigated. Results showed that P. litchii infection decreased anthocyanin content while accelerating fruit senescence. Salicylic acid (SA) content was also altered by P. litchii infection. Meanwhile, expression levels of LcmiR159, LcmiR828, LcmiR160 and LcmiR167 were investigated using stem-loop real-time quantitative PCR (RT-qPCR). Then, we identified LcGAMYB, LcTT2, LcARF18 and LcARF8 as their target genes, respectively, based on RNA Ligase-Mediated (RLM)-5'-RACE, transient co-expression assay in Nicotiana benthamiana as well as expression change of target genes. Our results suggested that LcmiR159-LcGAMYB and LcmiR828-LcTT2 modules participated in litchi downy blight possibly through regulating fruit senescence while LcmiR160-LcARF18 and LcmiR167-LcARF8 through SA-mediated defense response. This study provides new knowledge on deployment of miRNAs to increase litchi fruit resistance against fungal disease.

R3-MYB transcription factor LcMYBx from Litchi chinensis negatively regulates anthocyanin biosynthesis by ectopic expression in tobacco.

Anthocyanin accumulation is one of the remarkable physiological changes during fruit ripening. In plants, anthocyanin synthesis is regulated by MYB activators, but the MYB repressors has been recognized recently. Here, we isolated a repressor of anthocyanin synthesis, LcMYBx, from Litchi chinensis Sonn. LcMYBx encoded a typical R3-MYB protein and contained a conserved [D/E]Lx2[R/K]x3Lx6Lx3R motif for interacting with bHLH proteins. Overexpression of LcMYBx in tobacco suppressed anthocyanin accumulation resulting in faded petals from pale-pink to almost white. Gene expression analysis showed the strong down-regulation of endogenous anthocyanin structural and regulatory genes by LcMYBx overexpression. Yeast two-hybrid and bimolecular fluorescence complementation assays indicated that LcMYBx could interact with the transcription factors LcbHLH1 and LcbHLH3. Transient promoter activation assays showed that LcMYBx could inhibit the activation capacity of LcMYB1-LcbHLH3 complex for LcDFR gene. These results suggest that LcMYBx competed with LcMYB1 to LcbHLHs, thus preventing the activation of LcDFR by LcMYB1-LcbHLHs complex and negatively controlling anthocyanin biosynthesis.

Physical Characterization, Nutrient, Phenolic Profiles and Antioxidant Activities of 16 litchi Cultivars Grown in the Upper Yangtze River Region.

Litchi grown in the upper Yangtze River region have the advantage of being late-maturing owing to the geographical location. This study aimed to evaluate the physical characteristics, nutritional values, phenolic composition and antioxidant activities of 16 litchi cultivars grown in the upper Yangtze River region. Litchi grown in this region had total soluble solid and ascorbic acid contents comparable with those of cultivars grown in other locations. The total polyphenol contents were determined using the Folin-Ciocalteu assay, and the phenolic profiles were determined using UPLC-QqQ-MS/MS. Nine phenolic compounds were identified and quantified in this study. Naringin, rutin and p-coumaric acid were the major phenolic compounds in all the litchi cultivars. Statistical analysis of all the physiochemical results was performed using principal component analysis. Our results indicated that litchi grown in the upper Yangtze River region not only showed the late-maturity characteristic but were also good dietary sources of phenolic compounds and antioxidants. In particular, 'Fei Zi Xiao' and 'Jing Gang Hong Nuo', characterized by high polyphenol contents and high antioxidant capacities, were of superior comprehensive quality. This study provides important information for the development of late-maturing litchi industry.

Diabetes diminishes a typical metabolite of litchi pericarp oligomeric procyanidins (LPOPC) in urine mediated by imbalanced gut microbiota.

Animal studies and clinical trials have shown that dietary polyphenols and polyphenol-rich foods can reduce the risk of type 2 diabetes (T2D) and its complications, but how diabetes regulates the metabolism of polyphenol has not been fully elucidated. This study investigated the effects of diabetes on litchi pericarp oligomeric procyanidin (LPOPC) dynamic metabolism and its major static metabolites in urine. First, a high-fat and streptozotocin (STZ)-induced diabetic Sprague Dawley (SD) rat model was established. In the diabetic rat model, elevated fasting blood glucose, severely impaired glucose tolerance test, and increased reactive oxygen species (ROS) levels in serum and the liver were observed. Subsequently, 200 mg per kg body weight of LPOPC was administrated to control and diabetic SD rats, and the gastrointestinal tract was collected at 0.5 h, 1 h, 3 h, and 6 h. The results showed that the retention time of LPOPC was not changed in our diabetic rat model. However, the gut microbiota were significantly altered, with elevated Proteobacteria and Verrucomicrobia abundance in diabetic rats and decreased short chain fatty acid (SCFA)-producing bacteria. Interestingly, after one dose of 300 mg per kg body weight LPOPC, the total antioxidant capacity of urine in diabetic rats significantly decreased. We then tested the static metabolites of LPOPC, demonstrating that epicatechin had not changed in urine in diabetic rats, but that shikimic acid was significantly reduced in urine in diabetic rats. The changes in shikimic acid may be due to the alteration of gut microbiota and elevated ROS levels in serum.

The Mitogen-Activated Protein Kinase PlMAPK2 Is Involved in Zoosporogenesis and Pathogenicity of Peronophythoralitchii.

As an evolutionarily conserved pathway, mitogen-activated protein kinase (MAPK) cascades function as the key signal transducers that convey information by protein phosphorylation. Here we identified PlMAPK2 as one of 14 predicted MAPKs encoding genes in the plant pathogenic oomycete Peronophythora litchii. PlMAPK2 is conserved in P.litchii and Phytophthora species. We found that PlMAPK2 was up-regulated in sporangium, zoospore, cyst, cyst germination and early stage of infection. We generated PlMAPK2 knockout mutants using the CRISPR/Cas9 method. Compared with wild-type strain, the PlMAPK2 mutants showed no significant difference in vegetative growth, oospore production and sensitivity to various abiotic stresses. However, the sporangium release was severely impaired. We further found that the cleavage of the cytoplasm into uninucleate zoospores was disrupted in the PlMAPK2 mutants, and this developmental phenotype was accompanied by reduction in the transcription levels of PlMAD1 and PlMYB1 genes. Meanwhile, the PlMAPK2 mutants exhibited lower laccase activity and reduced virulence to lychee leaves. Overall, this study identified a MAPK that is critical for zoosporogenesis by regulating the sporangial cleavage and pathogenicity of P.litchii, likely by regulating laccase activity.

Metabolite Differences of Polyphenols in Different Litchi Cultivars (Litchi chinensis Sonn.) Based on Extensive Targeted Metabonomics.

Litchi is an important fruit cultivated in tropical and subtropical areas with high nutritious and delicious flavor and the pulp is the main part of the fruit consumed. Previous studies found that litchi had high total phenol content and antioxidant activity, but most of them focused on the identification of single or a few phenolic components with a low throughput test, and the metabolic differences of cultivars are still unknown to a some extent. In this study we used widely targeted metabolome based on ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS/MS) to analyze the polyphenol metabolites of five different genotypes of mature litchi fruit. A total of 126 polyphenol metabolites in eight categories were identified to reveal the composition and differences of polyphenol; 15 common differential metabolites and 20 specific differential metabolites to each cultivar were found for the first time. The results infer that flavonoids, flavonols, hydroxycinnamoyls and catechins are the main polyphenol metabolites of litchi pulp. Cluster analysis showed that there were three groups of polyphenols from high to low; early maturing Feizhixiao is a kind of high polyphenol content cultivars, especially in catechins, anthocyanins, flavonols, quinic acids and hydroxycinnamoyls. The polyphenols in the flesh of mature litchi are rich, and there are significant differences among cultivars; there was a level of correlation between the contents of phenolics and the maturity of litchi cultivars; the content of phenolics in early maturing litchi cultivars appeared higher than those of mid- to late-maturing cultivars. This experiment will provide significant reference information for cultivation, breeding, processing and consumption.

Effects of hydrogen water treatment on antioxidant system of litchi fruit during the pericarp browning.

Litchi fruit were exposed to 0.7 PPM hydrogen water (HW) before storage at 25 ± 1 â„ƒ. HW treatment delayed the pericarp browning and maintained the total soluble solids (TSS) of litchi fruit. Then, a total of 25 antioxidant system-related characters were determined to evaluate the effects of HW on antioxidant system during pericarp browning. Compared with control pericarp, the pericarp of HW-treated litchi fruit exhibited higher levels of superoxide radical (O2-·) scavenging activity, glutathione (GSH), monodehydroascorbate reductase (MDHAR), polyphenol oxidase (PPO) and total flavonoids during whole storage, higher levels of hydrogen peroxide (H2O2), catalase (CAT), glutathione disulfide (GSSG), ascorbate oxidase (AAO) and total phenols only on day 1, and higher levels of ascorbate peroxidase (APX), total anthocyanin, glutathione reductase (GR) and glutathione peroxidases (GPX) at later stage of storage. Those HW-induced antioxidant system-related characters might directly or indirectly enhanced the antioxidant capacity and delayed the pericarp browning of litchi.

LcEIL2/3 are involved in fruitlet abscission via activating genes related to ethylene biosynthesis and cell wall remodeling in litchi.

Fruit crops are subject to precocious fruit abscission, during which the phytohormone ethylene (ET) acts as a major positive regulator. However, the molecular basis of ET-induced fruit abscission remains poorly understood. Here, we show that two ETHYLENE INSENSITIVE 3-like (EIL) homologs in litchi, LcEIL2 and LcEIL3, play a role in ET-activated fruitlet abscission. LcEIL2/3 were significantly upregulated in the fruit abscission zone (AZ) during the ET-induced fruitlet abscission in litchi. The presence of LcEIL2/3 in wild-type Arabidopsis and ein3 eil1 mutants can accelerate the floral organ abscission. Moreover, the electrophoretic mobility shift assay and dual luciferase reporter analysis illustrated that LcEIL2/3 directly interacted with the gene promoters to activate the expression of cell wall remodeling genes LcCEL2/8 and LcPG1/2, and ET biosynthetic genes LcACS1/4/7 and LcACO2/3. Furthermore, we showed that LcPG1/2 were expressed in the floral abscission zone of Arabidopsis, and constitutive expression of LcPG2 in Arabidopsis promoted the floral organ abscission. In conclusion, we propose that LcEIL2/3 are involved in ET-induced fruitlet abscission via controlling expression of genes related to ET biosynthesis and cell wall remodeling in litchi.

KNOX protein KNAT1 regulates fruitlet abscission in litchi by repressing ethylene biosynthetic genes.

Abscission is triggered by multiple environmental and developmental cues, including endogenous plant hormones. KNOTTED-LIKE HOMEOBOX (KNOX) transcription factors (TFs) play an important role in controlling abscission in plants. However, the underlying molecular mechanism of KNOX TFs in abscission is largely unknown. Here, we identified LcKNAT1, a KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1)-like protein from litchi, which regulates abscission by modulating ethylene biosynthesis. LcKNAT1 is expressed in the fruit abscission zone and its expression decreases during fruitlet abscission. Furthermore, the expression of the ethylene biosynthetic genes LcACS1, LcACS7, and LcACO2 increases in the fruit abscission zone, in parallel with the emission of ethylene in fruitlets. In vitro and in vivo assays revealed that LcKNAT1 inhibits the expression of LcACS/ACO genes by directly binding to their promoters. Moreover, ectopic expression of LcKNAT1 represses flower abscission in tomatoes. Transgenic plants expressing LcKNAT1 also showed consistently decreased expression of ACS/ACO genes. Collectively, these results indicate that LcKNAT1 represses abscission via the negative regulation of ethylene biosynthesis.

Postharvest application of antibrowning chemicals modulates oxidative stress and delays pericarp browning of controlled atmosphere stored litchi fruit.

Litchi fruit were treated with methionine [(0.25%) MN] and cysteine [(025%) CN] alone or in combination, and kept under 1% O2 + 5% CO2 controlled atmosphere (CA) at 5 ± 1ºC for 28 days. Among different treatments, CN was most effective to inhibit browning, than MN and CN + MN under CA conditions. Application of 0.25% CN significantly delayed browning index, reduced disease incidence, weight loss, malondialdehyde (MDA) contents, electrolyte leakage, hydrogen peroxide (H2 O2 ), superoxide anion (O2-• ) and polyphenol oxidase (PPO) and peroxidase (POD) activities with higher contents of total anthocyanins under CA-storage. In addition, 0.25% CN treatment showed higher contents of ascorbic acid, total phenolics (TPC), and 2,2-diphenyl-1-picrylhydrazyl-radical scavenging capacity and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) enzymes having maintained quality attributes. Therefore, 0.25% CN pre-treatment could be considered a promising way for managing browning, and conserving litchi fruit quality under CA-storage. PRACTICAL APPLICATIONS: Litchi fruit are highly perishable due to rapid pericarp browning having limited postharvest market potential. The browning takes place due to enzymatic reactions and phenolic oxidation. However, it can be delayed by exogenous antibrowning treatments and suitable storage environment. The delayed incidence of pericarp browning may help to maintain its quality with extended storage potential suitable for domestic and international markets. So, the outcomes of the current work may help to maintain overall quality and to extend its storage potential that would be helpful in extending its market life with maintained visual quality at domestic and international destinations.

Characterization by HPLC-ESI-MS2 of native and oxidized procyanidins from litchi (Litchi chinensis) pericarp.

Procyanidins (PCs) are polyphenols highly accumulated in litchi fruit (Litchi chinensis). Despite their bioactivity, the molecular composition of native and oxidized procyanidins is little understood. In this paper, polyphenols from litchi pericarp were extracted using two solvents (methanol and acetone). The mean degree of polymerization (mDP) of native and identification of oxidized PCs were carried out by phloroglucinolysis- and thioglycolysis-HPLC-ESI-MS/MS, respectively. About 60% of extracted polyphenols corresponded to procyanidins from litchi pericarp. Native PCs were mainly oligomeric procyanidins (mDP 4). Only (-)-epicatechin was detected as terminal and extension units in PCs. Thioglycolysis-HPLC-ESI-MS identified five oxidation markers of PCs with [M-H]-m/z 575, 593, 609, 679 and 863. Intra- and intermolecular modifications of A and B-type procyanidins were identified. The method used for the characterization of PCs from litchi pericarp allowed understanding of the structural composition of its native and oxidized tannins.

Transport of Flavanolic Monomers and Procyanidin Dimer A2 across Human Adenocarcinoma Stomach Cells (MKN-28).

It has been proven that A-type procyanidins, containing an additional ether bond, compared to B-type procyanidins are also bioavailable in vitro and in vivo. However, their bioavailability and absorption in the gastrointestinal tract remain uncertain. In this study, a model of the human adenocarcinoma stomach cell line (MKN-28) was established to explore the cellular transport of flavanolic monomers and procyanidin dimer A2, which were isolated from the litchi pericarp extract. After the integrity and permeability of the cell monolayer were ensured by measurement of the transepithelial electrical resistance and the apparent permeability coefficient for Lucifer yellow, the transportation of procyanidins A2 and B2, (-)-epicatechin (EC), and (+)-catechin (CC) was studied at pH 3.0, 5.0, or 7.0 in the apical side, with compound concentrations of 0.05 and 0.1 mg/mL based on the cytotoxicity test. High-performance liquid chromatography and liquid chromatography-mass spectrometry analyses indicated that EC, CC, and A2 were transported in the MKN-28 cell line from 30 to 180 min, while B2 showed no transport. The maximal transport efficiencies of EC, CC, and A2 were 23 ± 0.81, 13.16 ± 1.53, and 16.41 ± 1.36%, respectively, existing at 120, 180, and 120 min of transportation. Laser scanning confocal microscopy analysis presented the dynamic transmission of EC, in accordance with the result of concentration determination, suggesting that the A-type procyanidins are possibly absorbed through the stomach barrier, which is pH- and time-dependent.

Characterization of a novel litchi R2R3-MYB transcription factor that involves in anthocyanin biosynthesis and tissue acidification.

BACKGROUND: Maturation of litchi (Litchi chinensis) fruit is characterized by dramatic changes in pigments in the pericarp and flavor compounds in the aril. Among them, the biosynthesis of anthocyanins is most noticeable. Previous studies showed that LcMYB1 and LcbHLH transcription factors participated in regulating the anthocyanin biosynthesis in litchi. However, the roles of other MYB factors remain unclear. RESULTS: In this study, we cloned and characterized the function of LcMYB5, a novel R2R3-MYB identified from litchi transcriptome. Although LcMYB5 was constitutively expressed in litchi tissues and its expressions was not correlated with tissue coloration, overexpression of LcMYB5 resulted in enhanced biosynthesis of anthocyanins in tobacco and petunia concurrent with the up-regulation of their endogenous bHLHs and key structural genes in anthocyanin precursor biosynthesis. These results indicate that LcMYB5 is an R2R3 transcriptional factor regulates anthocyanin biosynthesis either by directly activating the expression of key structural genes such as DFR or by indirectly up regulating the expressions of endogenous bHLH regulators. More interestingly, the pH values in petals and leaves from transgenic lines were significant lower than those in both untransformed tobacco and petunia, indicating LcMYB5 is also associated with pH regulation. The expressions of LcMYB5 and its bHLH partner LcbHLH1 were consistent with the expression of putative tissue acidification gene LcPH1, and the changes in malic acid provided further evidence for the close relationship between LcMYB5 and tissue acidification. CONCLUSIONS: Taking together, our study indicated that LcMYB5 is involved in not only anthocyanin biosynthesis but also tissue acidification.