Molecular cloning, structural analysis and mass spectrometric identification of native dioscorins of various yam species

Hormones and carbohydrates synergistically regulate the formation of swollen roots in a Chinese cabbage translocation line

The genus Brassica contains a rich diversity of species and morphological types, including leaf, root, and oil crops, all of which show substantial phenotypic variation. Both Chinese cabbage and cabbage are typical leaf-type crops with normal roots. We created translocation lines based on interspecific crosses between Chinese cabbage and cabbage and identified qdh225, which exhibited a swollen-root phenotype. The swollen root of qdh225 contained a large number of granular substances, and the formation of its irregular morphological tissue was caused by a thickening of the phloem. Transcriptomic and metabolomic data suggested that differential expression of genes encoding nine types of enzymes involved in starch and sucrose metabolism caused changes in starch synthesis and degradation in the swollen root. These genes jointly regulated sucrose and starch levels, leading to significant enrichment of starch and soluble proteins in the swollen root and a reduction in the content of soluble sugars such as d-glucose and trehalose 6-phosphate. A significant increase in auxin (IAA) and abscisic acid (ABA) contents and a decrease in gibberellin (GA) content in the swollen root likely promoted the differential expression of genes associated with hormone signal transduction, thereby regulating the development of the swollen root. Taken together, our data suggest that accumulation of IAA and ABA and reduction in GA promote swollen root formation by regulating hormone-mediated signaling, leading to a thickening of phloem, root enlargement, and substantial accumulation of starch and soluble proteins. The latter provide materials, energy, and nutrient sources for the development of swollen roots.

Accurate Identification and Quantification of Chinese Yam Powder Adulteration Using Laser-Induced Breakdown Spectroscopy

As a popular food, Chinese yam (CY) powder is widely used for healthy and commercial purposes. Detecting adulteration of CY powder has become essential. In this work, chemometric methods combined with laser-induced breakdown spectroscopy (LIBS) were developed for identification and quantification of CY powder adulteration. Pure powders (CY, rhizome of winged yam (RY) and cassava (CS)) and adulterated powders (CY adulterated with CS) were pressed into pellets to obtain LIBS spectra for identification and quantification experiments, respectively. After variable number optimization by principal component analysis and random forest (RF), the best model random forest-support vector machine (RF-SVM) decreased 48.57% of the input variables and improved the accuracy to 100% in identification. Following the better feature extraction method RF, the Gaussian process regression (GPR) method performed the best in the prediction of the adulteration rate, with a correlation coefficient of prediction (R_p²) of 0.9570 and a root-mean-square error of prediction (RMSEP) of 7.6243%. Besides, the variable importance of metal elements analyzed by RF revealed that Na and K were significant due to the high metabolic activity and maximum metal content of CY powder, respectively. These results demonstrated that chemometric methods combined with LIBS can identify and quantify CY powder adulteration accurately.

Dioscorea Alata Tuber Proteome Analysis Uncovers Differentially Regulated Growth-associated Pathways of Tuber Development

During its life cycle, the Dioscorea tuber undergoes multiple morphological and biochemical changes. To gain a better understanding of the metabolic changes associated with tuber growth, a stage-specific gel-free proteome analysis of four distinct morphological stages namely germinating tuber (S1), degrading tuber (S2), new tuber formation (S3) and tuber maturation (S4) was done and validated by principal component analysis. A comprehensive data set identifying 78.2% of the total 3,681 proteins was generated. PANTHER and KEGG MAPPER revealed both expected (carbohydrate metabolism and redox regulation) and novel biological processes (transcription factors and hormonal regulation) characteristic for each developmental stage. Higher abundance of the enzymes of ascorbate-glutathione cycle and carbohydrate metabolism was detected during tuber germination (S1) and tuber formation stages (S3) in comparison with the mature tuber. The presence of ethylene biosynthesis components during tuber formation hints toward its probable role in postharvest shelf life. The data set comprehensively describes the proteome of Dioscorea tuber and provides growth-specific markers for tuber germination (ascorbate peroxidase, monodehydroascorbate reductase, invertase) and tuber formation (sucrose synthase), which were validated by enzyme activity assays and Western blotting. The study provides information that may influence the direction of research for improving the productivity of this under-utilized and largely neglected crop.

Recovery of Yam Soluble Protein from Yam Starch Processing Wastewater

Over the past two decades, many studies have shown that the yam storage protein dioscorin, which is abundant in the wastewater of starch processing, exhibits many biological activities both in vitro and in vivo. In the present study, the acid-precipitation method was optimized using Box-Behnken design (BBD) combined with response surface methodology (RSM) for the recovery of yam soluble protein (YSP) from wastewater. The experimental yield of YSP reached 57.7%. According to relative quantitative proteomics (LC-MS/MS), the crude YSP was mainly composed of 15 dioscorin isoforms, which was further verified by anion-exchange and size-exclusion chromatography. YSP was found to be rich in glutamic acid and aspartic acid, and the eight essential acids made up approximately 33.7% of the YSP. Moreover, the YSP demonstrated antioxidant activity, including scavenging DPPH, hydroxyl and superoxide anion radicals, and the possible structure-activity relationships were discussed. These results indicated that YSP produced by acid precipitation may be used as a protein source with antioxidant properties.

Research and Development of Proteins and Peptides with Therapeutic Potential from Yam Tubers

We discuss the diverse biological activities, therapeutic potential, and clinical applications of peptides and proteins isolated from various yams species including Dioscorea opposita Thunb (Chinese yam), D alata, D japonica (Japanese yam), D pseudojaponica, D batatas (Korea yam), and D cayenensis. Yam peptides and proteins have many pharmacological activities including immunomodulatory, antioxidant, estrogen-stimulating, osteogenic, angiotensin I-converting enzyme inhibiting, carbonic anhydrase and trypsin inhibiting, chitinase, anti-insect, anti-dust mite, lectin, and anti-proliferative activities. Yam peptides and proteins have therapeutic potential for treating cardiovascular diseases, inflammatory diseases, cancers, aging disorders, menopause, and osteoporosis.

Characterization of the Dioscorin Gene Family in Dioscorea alata Reveals a Role in Tuber Development and Environmental Response

Dioscorin is one of the major soluble proteins in yam tubers. Unlike other well-known plant storage proteins, such as patatin and sporamin, dioscorin is argued for its function as storage proteins, and the molecular mechanisms underlying its expressional complexity are little understood. In this study, we isolated five dioscorin genes from Dioscorea alata L., comprising three class A (Da-dio1, -3 and -4) and two class B (Da-dio2 and -5) isoforms. Expressions of all dioscorin genes gradually decreased in mother tubers during yam sprouting and regrowth. On the other hand, all dioscorin genes accumulated transcripts progressively with tuber development in new tubers, with Da-dio5 being the most prominent isoform. In yam leaves, the expressions of Da-dio5 were up-regulated by the treatments of five phytohormones (gibberellic acid, salicylic acid, indole-3-acetic acid, abscisic acid, and ethylene), and three abiotic stresses (high-temperature, low-temperature and drought). To further elucidate the regulatory mechanisms of Da-dio5 expressions, transgenic Arabidopsis plants harboring the Da-dio5 promoter-β-glucuronidase (GUS) fusion were generated. GUS staining showed that expressions of the Da-dio5 promoter were detected mainly in the shoot apical meristem (SAM) and hypocotyls, and enhanced by the treatments of the five hormones, and the three abiotic stresses mentioned above. These results suggest diverse roles of Da-dio5 in yam sprouting, regrowth, and tuberization, as well as in response to enviromental cues.

Dioscorea alata tuber proteome analysis shows over thirty dioscorin isoforms and novel tuber proteins

In Dioscorea, dioscorin (31 kDa) is the major storage protein constituting 85% of the total tuber proteins. An integrated proteomic and biochemical approach was used to understand the physiological role of dioscorin in the two contrasting growth stages (germinating and mature tuber). HPLC analysis showed 3 fold reduction in mannitol and 12.88 and 1.24 fold increase in sucrose and maltose in the germinating tuber. A 1.8 and 3 fold increase in sucrose phosphate synthase and mannitol dehydrogenase activity respectively was observed in the germinating tuber while a 2 fold higher invertase probably lowers the sucrose accumulation in the mature tuber. SDS-PAGE and 2-D maps of the mature and germinating tubers confirmed depletion (more than 50%) of dioscorin on germination. Dioscorin was purified using ion exchange and gel filtration chromatography with 43.32 fold purification and 38.16 yield. Out of a trail of 35 spots at 31 kDa only 12 spots (identified as dioscorin isoforms) were present in the 2D gel of the purified fraction. To search for other tuber proteins besides dioscorin, the unbound fractions of DEAE column were analysed by 2DGE. DREB 1A, caffeic acid 3-O-methyltransferase and Rab-1 small GTP binding protein were identified perhaps for the first time in the Dioscorea proteome. The interactome analysis revealed these to be involved in oxidative stress, carotenoid synthesis and vesicular transport. This is perhaps the first attempt to identify tuber proteome (although limited) and to understand the physiological significance of these proteins.

Suppression of allergic reactions in ovalbumin-sensitized mice by yam storage proteins dioscorins

To study the biomedical functions of dioscorins isolated from various species of Dioscorea , we investigated their antiallergic potential using an OVA-induced allergy mouse model. All the dioscorins suppressed allergic reactions by decreasing the serum IgE and histamine levels. The serum IFN-γ and IgG2a levels increased in all the dioscorin-treated mice. The spleen cells from the dioscorin-treated mice also exhibited an up-regulation of IFN-γ secretion in response to ConA stimulation. Although dioscorins did not affect the IgG1 levels, the IL-5 levels decreased to basal levels in mice treated with dioscorins of D. alata or D. japonica and in most of the lymphoid cells of the dioscorin-treated mice in response to ConA stimulation. The decrease of IgE and histamine levels was concomitant with an increase in IFN-γ and IgG2a levels and with a decrease in IL-5 levels, suggesting that dioscorins suppressed the OVA-induced allergic reactions, possibly through modulating an imbalanced Th1/Th2 immune response.

Recombinant dioscorins of the yam storage protein expressed in Escherichia coli exhibit antioxidant and immunomodulatory activities

Dioscorins, the major storage proteins in yam tubers, exhibit biochemical and immunomodulatroy activities. To investigate the potential application of dioscorins in biomedical research, we expressed the dioscorin genes Dj-dioA3 and Dp-dioA2 from Dioscorea japonica and Dioscorea pseudojaponica, respectively, in E. coli and routinely obtained approximately 15 mg proteins per liter Escherichia coli culture (mg/L) to 30 mg/L of rDj-dioscorinA3 and 4 to 8 mg/L of rDp-dioscorinA2. Western blot analyses revealed that both recombinant dioscorins contained epitopes with similar antigenicities to those of the native dioscorins. Results from dithiothreitol (DTT) treatment followed by monobromobimane (mBBr) staining showed that both recombinant dioscorins, like the native dioscorins, contain an intramolecular disulfide bond between Cys(28) and Cys(187) residues. Circular dichroism spectroscopy findings indicated that the secondary structural contents of the recombinant dioscorins showed high similarity to those of their corresponding native dioscorins. Both recombinant dioscorins, like the native dioscorins, exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and Toll-like receptor 4 signaling activities, and stimulated the phagocytosis of E. coli by macrophage. Overall, our results indicated that substantial amounts of recombinant dioscorins can be purified easily from E. coli and that these recombinant dioscorins are appropriate for application in future investigations of the biomedical functions of dioscorins.