Fruit characteristics of sweet watermelon are largely the result of human selection. Here we report an improved watermelon reference genome and whole-genome resequencing of 414 accessions representing all extant species in the Citrullus genus. Population genomic analyses reveal the evolutionary history of Citrullus, suggesting independent evolutions in Citrullus amarus and the lineage containing Citrullus lanatus and Citrullus mucosospermus. Our findings indicate that different loci affecting watermelon fruit size have been under selection during speciation, domestication and improvement. A non-bitter allele, arising in the progenitor of sweet watermelon, is largely fixed in C. lanatus. Selection for flesh sweetness started in the progenitor of C. lanatus and continues through modern breeding on loci controlling raffinose catabolism and sugar transport. Fruit flesh coloration and sugar accumulation might have co-evolved through shared genetic components including a sugar transporter gene. This study provides valuable genomic resources and sheds light on watermelon speciation and breeding history.

The delivery of therapeutic peptides and proteins is often challenged by a short half-life, and thus the need for frequent injections that limit efficacy, reduce patient compliance and increase treatment cost. Here, we demonstrate that a single subcutaneous injection of site-specific (C-terminal) conjugates of exendin-4 (exendin) — a therapeutic peptide that is clinically used to treat type 2 diabetes — and poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) with precisely controlled molecular weights lowered blood glucose for up to 120 h in fed mice. Most notably, we show that an exendin-C-POEGMA conjugate with an average of 9 side-chain ethylene glycol (EG) repeats exhibits significantly lower reactivity towards patient-derived anti-poly(ethylene glycol) (PEG) antibodies than two FDA-approved PEGylated drugs, and that reducing the side-chain length to 3 EG repeats completely eliminates PEG antigenicity without compromising in vivo efficacy. Our findings establish the site-specific conjugation of POEGMA as a next-generation PEGylation technology for improving the pharmacological performance of traditional PEGylated drugs, whose safety and efficacy are hindered by pre-existing anti-PEG antibodies in patients.

The primary purpose of grafting vegetables worldwide has been to provide resistance to soilborne diseases. The potential loss of methyl bromide as a soil fumigant combined with pathogen resistance to commonly used pesticides will make resistance to soilborne pathogens even more important in the future. The major disease problems addressed by grafting include fusarium wilt, bacterial wilt, verticillium wilt, monosporascus root rot, and nematodes. Grafting has also been shown in some instances to increase tolerance to foliar fungal diseases, viruses, and insects. If the area devoted to grafting increases in the future, there will likely be a shift in the soil microbial environment that could lead to the development of new diseases or changes in the pathogen population of current diseases. This shift in pathogen populations could lead to the development of new diseases or the re-emergence of previously controlled diseases. Although grafting has been demonstrated to control many common diseases, the ultimate success will likely depend on how well we monitor for changes in pathogen populations and other unexpected consequences.

A 159 bp deletion in ClFS1 gene encoding IQD protein is responsible for fruit shape in watermelon. Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is known for its rich diversity in fruit size and shape. Fruit shape has been one of the major objectives of watermelon breeding. However, the candidate genes and the underlying genetic mechanism for such an important trait in watermelon are unknown. In this study, we identified a locus on chromosome 3 of watermelon genome controlling fruit shape. Segregation analysis in F and BC populations derived from a cross between two inbred lines "Duan125" (elongate fruit) and "Zhengzhouzigua" (spherical fruit) suggests that fruit shape of watermelon is controlled by a single locus and elongate fruit (OO) is incompletely dominant to spherical fruit (oo) with the heterozygote (Oo) being oval fruit. GWAS profiles among 315 accessions identified a major locus designated on watermelon chromosome 3, which was confirmed by BSA-seq mapping in the F population. The candidate gene was mapped to a region 46 kb on chromosome 3. There were only four genes present in the corresponding region in the reference genome. Four candidate genes were sequenced in this region, revealing that the CDS of Cla011257 had a 159 bp deletion which resulted in the omission of 53 amino acids in elongate watermelon. An indel marker was derived from the 159 bp deletion to test the F population and 105 watermelon accessions. The results showed that Cla011257 cosegregated with watermelon fruit shape. In addition, the Cla011257 expression was the highest at ovary formation stage. The predicted protein of the Cla011257 gene fitted in IQD protein family which was reported to have association with cell arrays and Ca-CaM signaling modules. Clear understanding of the genes facilitating the fruit shape along with marker association selection will be an effective way to develop new cultivars.

We report a new methodology for the synthesis of polymer-drug conjugates from “compound”—all in one—prodrug monomers that consist of a cyclic polymerizable group that is appended to a drug through a cleavable linker. We show that organocatalyzed ring-opening polymerization can polymerize these monomers into well-defined polymer prodrugs that are designed to self-assemble into nanoparticles and release drug in response to a physiologically relevant stimulus. This method is compatible with structurally diverse drugs and allows different drugs to be copolymerized with quantitative conversion of the monomers. The drug loading can be controlled by adjusting the monomer(s) to initiator feed ratio and drug release can be encoded into the polymer by the choice of linker. Initiating these monomers from a polyethylene glycol macroinitiator yields amphiphilic diblock copolymers that spontaneously self-assemble into micelles with a long plasma circulation, which is useful for systemic therapy.

The organoleptic qualities of watermelon fruit are defined by the sugar and organic acid contents, which undergo considerable variations during development and maturation. The molecular mechanisms underlying these variations remain unclear. In this study, we used transcriptome profiles to investigate the coexpression patterns of gene networks associated with sugar and organic acid metabolism. We identified 3 gene networks/modules containing 2443 genes highly correlated with sugars and organic acids. Within these modules, based on intramodular significance and Reverse Transcription Quantitative polymerase chain reaction (RT-qPCR), we identified 7 genes involved in the metabolism of sugars and organic acids. Among these genes, Cla97C01G000640, Cla97C05G087120 and Cla97C01G018840 (r2 = 0.83 with glucose content) were identified as sugar transporters (SWEET, EDR6 and STP) and Cla97C03G064990 (r2= 0.92 with sucrose content) was identified as a sucrose synthase from information available for other crops. Similarly, Cla97C07G128420, Cla97C03G068240 and Cla97C01G008870, having strong correlations with malic (r2 = 0.75) and citric acid (r2 = 0.85), were annotated as malate and citrate transporters (ALMT7, CS, and ICDH). The expression profiles of these 7 genes in diverse watermelon genotypes revealed consistent patterns of expression variation in various types of watermelon. These findings add significantly to our existing knowledge of sugar and organic acid metabolism in watermelon.

Watermelon (Citrullus lanatus L.) is an important horticultural crop that is grown worldwide and has a high economic value. To dissect the loci associated with important horticultural traits and to analyze the genetic and genomic information of this species, a high-density genetic map was constructed based on whole-genome resequencing (WGR), a powerful high-resolution method for single-nucleotide polymorphism (SNP) marker development, genetic map construction, and gene mapping. Resequencing of both parental lines and 126 recombinant inbred lines (RIL) resulted in the detection of 178,762 single-nucleotide polymorphism (SNP) markers in the parental lines at a sequencing depth greater than four-fold. Additionally, 2132 recombination bin markers comprising 103,029 SNP markers were mapped onto 11 linkage groups (LGs). Substantially more SNP markers were mapped to the genetic map compared with other recent studies. The total length of the linkage map was 1508.94 cM, with an average distance of 0.74 cM between adjacent bin markers. Based on this genetic map, one locus for fruit bitterness, one locus for rind color, and one locus for seed coat color with high LOD scores (58.361, 18.353, 26.852) were identified on chromosome 1, chromosome 8, and chromosome 3, respectively. These prominent loci were identified in a region of 6.16 Mb, 2.07 Mb, and 0.37 Mb, respectively. On the basis of current research, the high-density map and mapping results will provide a valuable tool for identifying candidate genes, map-based gene cloning, comparative mapping, and marker-assisted selection (MAS) in watermelon breeding.

Apoptosis has been widely reported to be involved in the pathogenesis associated with spinal cord injury (SCI). Recently, autophagy has also been implicated in various neuronal damage models. However, the role of autophagy in SCI is still controversial and its interrelationship with apoptosis remains unclear. Here, we used an in vitro SCI model to observe a time-dependent induction of autophagy and apoptosis. Mechanical injury induced autophagy markers such as LC3 lipidation, LC3II/LC3I conversion, and Beclin-1 expression. Injured neurons showed decreased cell viability and increased apoptosis. To elucidate the effect of autophagy on apoptosis, the mechanically-injured neurons were treated with the mTOR inhibitor rapamycin and 3-methyl adenine (3-MA), which are known to regulate autophagy positively and negatively, respectively. Rapamycin-treated neurons showed the highest level of cell viability and lowest level of apoptosis among the injured neurons and those treated with 3-MA showed the reciprocal effect. Notably, rapamycin-treated neurons exhibited slightly reduced Bax expression and significantly increased Bcl-2 expression. Furthermore, by plasmid transfection, we showed that Beclin-1-overexpressing neuronal cells responded to mechanical injury with greater LC3II/LC3I conversion and cell viability, lower levels of apoptosis, higher Bcl-2 expression, and unaltered Bax expression as compared to vector control cells. Beclin-1-knockdown neurons showed almost the opposite effects. Taken together, our results suggest that autophagy may serve as a protection against apoptosis in mechanically-injured spinal cord neurons. Targeting mTOR and/or enhancing Beclin-1 expression might be alternative therapeutic strategies for SCI.