Purple-fleshed sweet potato (PFSP) is an important food crop, as it is a rich source of nutrients and anthocyanin pigments. Drought has become a major threat to sustainable sweetpotato production, resulting in huge yield losses. Therefore, the present study was conducted to identify drought stress-responsive genes using next-generation (NGS) and third-generation sequencing (TGS) techniques. Five cDNA libraries were constructed from seedling leaf segments treated with a 30% solution of polyethylene glycol (PEG-6000) for 0, 1, 6, 12, and 48 h for second-generation sequencing. Leaf samples taken from upper third of sweet potato seedlings after 1, 6, 12, and 48 h of drought stress were used for the construction of cDNA libraries for third-generation sequencing; however, leaf samples from untreated plants were collected as controls. A total of 184,259,679 clean reads were obtained using second and third-generation sequencing and then assembled into 17,508 unigenes with an average length of 1,783 base pairs. Out of 17,508 unigenes, 642 (3.6%) unigenes failed to hit any homologs in any databases, which might be considered novel genes. A total of 2, 920, 1578, and 2,418 up-regulated unigenes and 3,834, 2,131, and 3,337 down-regulated unigenes from 1 h, 6 h, 12 h, and 48 h library were identified, respectively in drought stress versus control. In addition, after 6, 12, and 48 h of drought stress, 540 up-regulated unigenes, 486 down-regulated unigenes and 414 significantly differentially expressed unigenes were detected. It was found that several gene families including Basic Helix-loop-helix (bHLH), basic leucine zipper (bZIP), Cystein2/Histidine2 (C2H2), C3H, Ethylene-responsive transcription factor (ERF), Homo domain-leucine zipper (HD-ZIP), MYB, NAC (NAM, ATAF1/2, and CUC2), Thiol specific antioxidant and WRKY showed responses to drought stress. In total, 17,472 simple sequence repeats and 510,617 single nucleotide polymorphisms were identified based on transcriptome sequencing of the PFSP. About 96.55% of the obtained sequences are not available online in sweet potato genomics resources. Therefore, it will enrich annotated sweet potato gene sequences and enhance understanding of the mechanisms of drought tolerance through genetic manipulation. Moreover, it represents a sequence resource for genetic and genomic studies of sweet potato.

Polyphenols and polysaccharides are very important natural products with special physicochemical properties and extensive biological activities. Recently, polyphenol-polysaccharide conjugates have been synthesized to overcome the limitations of polysaccharides and broaden their application range. Grafted copolymers are produced through chemical coupling, enzyme-mediated, and free radical-mediated methods, among which the free radical-induced grafting reaction is the most cost-effective, ecofriendly, safe, and plausible approach. Here, we review the grafting reactions of polysaccharides mediated by free radicals with various bioactive polyphenols, such as gallic acid (GA), ferulic acid (FA), and catechins. A detailed introduction of the methods and their mechanisms for free radical-mediated grafting is given. Structural characterization methods of the graft products, including thin-layer chromatography (TLC), ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) analysis, and X-ray diffraction (XRD) are introduced. Furthermore, the biological properties of polyphenol-polysaccharide conjugates are also presented, including antioxidant, antibacterial, antidiabetic, and neuroprotection activities, etc. Moreover, the potential applications of polyphenol-polysaccharide conjugates are described. Finally, the challenges and research prospects of graft products are summarized.

Background: Purple-fleshed sweetpotato (PFSP) is one of the most important crops in the word which helps to bridge the food gap and contribute to solve the malnutrition problem especially in developing countries. Salt stress is seriously limiting its production and distribution. Due to lacking of reference genome, transcriptome sequencing is offering a rapid approach for crop improvement with promising agronomic traits and stress adaptability. Results: Five cDNA libraries were prepared from the third true leaf of hexaploid sweetpotato at seedlings stage (Xuzi-8 cultivar) treated with 200 mM NaCl for 0, 1, 6, 12, 48 h. Using second and third generation technology, Illumina sequencing generated 170,344,392 clean high-quality long reads that were assembled into 15,998 unigenes with an average length 2178 base pair and 96.55% of these unigenes were functionally annotated in the NR protein database. A number of 537 unigenes failed to hit any homologs which may be considered as novel genes. The current results indicated that sweetpotato plants behavior during the first hour of salt stress was different than the other three time points. Furthermore, expression profiling analysis identified 4, 479, 281, 508 significantly expressed unigenes in salt stress treated samples at the different time points including 1, 6, 12, 48 h, respectively as compared to control. In addition, there were 4, 1202, 764 and 2195 transcription factors differentially regulated DEGs by salt stress at different time points including 1, 6, 12, 48 h of salt stress. Validation experiment was done using 6 randomly selected unigenes and the results was in agree with the DEG results. Protein kinases include many genes which were found to play a vital role in phosphorylation process and act as a signal transductor/ receptor proteins in membranes. These findings suggest that salt stress tolerance in hexaploid sweetpotato plants may be mainly affected by TFs, PKs, Protein Detox and hormones related genes which contribute to enhance salt tolerance. Conclusion: These transcriptome sequencing data of hexaploid sweetpotato under salt stress conditions can provide a valuable resource for sweetpotato breeding research and focus on novel insights into hexaploid sweetpotato responses to salt stress. In addition, it offers new candidate genes or markers that can be used as a guide to the future studies attempting to breed salt tolerance sweetpotato cultivars.

To examine the effects of different solvents on the molecular weight, yield, chemical composition, and bioactivity of pectins, four RG-I type pectins were separately extracted from sweet potato residue (SPR) using hot water extraction (HWSP), sodium hydroxide extraction (SHSP), hydrochloric acid extraction (HASP), and chelating agents (CASP). The results showed that the four pectin samples comprised GalUA, Gal, Rha, Ara, Glc, GlcUA, Man, and Xyl components. Among these components, GalA content was the highest in all four pectins. SHSP exhibited relatively higher yield (3.16 %, w/w). Additionally, SHSP exhibited a lower molecular weight (44.49 kDa) and the largest proportion of the RG-I region (75.42 %) compared with other extraction methods. On the contrary, HASP showed relatively lower yield (2.14 %, w/w), and its corresponding prepared pectin had relatively high molecular weight (69.81 kDa) and the minimum range of RG-I region (46.87 %) compared with HWSP, SHSP, and CASP. The anti-inflammation effect of the four SPR pectin samples was investigated using in vitro experiments. Results showed that all of SPR pectin significantly inhibited the levels of IL-1β, IL-6, and TNF-α in lipopolysaccharide (LPS)-treated iBMDM macrophage cells. The preliminary structure-activity relationship between pectin structure and anti-inflammatory activity was also analyzed. SPR pectin can be developed as a potential bioactive ingredient for applications in the food and medicine industries.