The Cucurbita genus contains several economically important species in the Cucurbitaceae family. Here, we report high-quality genome sequences of C. maxima and C. moschata and provide evidence supporting an allotetraploidization event in Cucurbita. We are able to partition the genome into two homoeologous subgenomes based on different genetic distances to melon, cucumber, and watermelon in the Benincaseae tribe. We estimate that the two diploid progenitors successively diverged from Benincaseae around 31 and 26 million years ago (Mya), respectively, and the allotetraploidization happened at some point between 26 Mya and 3 Mya, the estimated date when C. maxima and C. moschata diverged. The subgenomes have largely maintained the chromosome structures of their diploid progenitors. Such long-term karyotype stability after polyploidization has not been commonly observed in plant polyploids. The two subgenomes have retained similar numbers of genes, and neither subgenome is globally dominant in gene expression. Allele-specific expression analysis in the C. maxima × C. moschata interspecific F hybrid and their two parents indicates the predominance of trans-regulatory effects underlying expression divergence of the parents, and detects transgressive gene expression changes in the hybrid correlated with heterosis in important agronomic traits. Our study provides insights into polyploid genome evolution and valuable resources for genetic improvement of cucurbit crops.

BackgroundPumpkin (Cucurbita maxima Duch.) is an economically important crop belonging to the Cucurbitaceae family. However, very few genomic and genetic resources are available for this species. As part of our ongoing efforts to sequence the pumpkin genome, high-density genetic map is essential for anchoring and orienting the assembled scaffolds. In addition, a saturated genetic map can facilitate quantitative trait locus (QTL) mapping.ResultsA set of 186 F2 plants derived from the cross of pumpkin inbred lines Rimu and SQ026 were genotyped using the genotyping-by-sequencing approach. Using the SNPs we identified, a high-density genetic map containing 458 bin-markers was constructed, spanning a total genetic distance of 2,566.8 cM across the 20 linkage groups of C. maxima with a mean marker density of 5.60 cM. Using this map we were able to anchor 58 assembled scaffolds that covered about 194.5 Mb (71.7 %) of the 271.4 Mb assembled pumpkin genome, of which 44 (183.0 Mb; 67.4 %) were oriented. Furthermore, the high-density genetic map was used to identify genomic regions highly associated with an important agronomic trait, dwarf vine. Three QTLs on linkage groups (LGs) 1, 3 and 4, respectively, were recovered. One QTL, qCmB2, which was located in an interval of 0.42 Mb on LG 3, explained 21.4 % phenotypic variations. Within qCmB2, one gene, Cma_004516, encoding the gibberellin (GA) 20-oxidase in the GA biosynthesis pathway, had a 1249-bp deletion in its promoter in bush type lines, and its expression level was significantly increased during the vine growth and higher in vine type lines than bush type lines, supporting Cma_004516 as a possible candidate gene controlling vine growth in pumpkin.ConclusionsA high-density pumpkin genetic map was constructed, which was used to successfully anchor and orient the assembled genome scaffolds, and to identify QTLs highly associated with pumpkin vine length. The map provided a valuable resource for gene cloning and marker assisted breeding in pumpkin and other related species. The identified vine length QTLs would help to dissect the underlying molecular basis regulating pumpkin vine growth.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2312-8) contains supplementary material, which is available to authorized users.

Two nanostructured proton-containing δ-MnO2 (H-δ-MnO2) materials were synthesized through proton exchange for K-containing δ-MnO2 (K-δ-MnO2) nanosheets and nanoparticles prepared by the hydrothermal homogeneous precipitation method and solid-state reaction.

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Highly effective Fe 3 O 4 /Mn 3 O 4 /reduced graphene oxide (rGO) hybrids were synthesized as a heterogeneous catalyst for the degradation of organic dyes in the aqueous solution using sulfate radicalbased advanced oxidation processes. The physicochemical properties of the composite were characterized 10 by several techniques, such as X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmelt-Teller (BET). The effects of different parameters on the catalytic activity of Fe 3 O 4 /Mn 3 O 4 /rGO, including initial Methylene Blue (MB) concentration, peroxymonosulfate (PMS) concentration, catalyst dosage, pH value, and temperature, were assessed. Typically, 98.8% removal of 50 15 mg/L of MB and 68.3% reduction of TOC could be achieved in 30 min under the conditions: temperature 25 °C, 100 mg/L of catalyst, and PMS dosage 0.3 g/L, showing a significant enhancement of the catalyst in the degradation of organic pollutants in aqueous solution Compared with Fe 3 O 4 /rGO and Mn 3 O 4 /rGO. The catalyst exhibited high stability and good reusability according to three successive repeated reactions. Based on the radical experiments, the catalytic activity of Fe 3 O 4 /Mn 3 O 4 /rGO hybrids for degradation of 20 MB is closely related with the amount of the sulfate and hydroxyl radicals generated from PMS. The excellent catalytic performance of the Fe 3 O 4 /Mn 3 O 4 /rGO is mainly attributed to the synergistic effects of Fe 3 O 4 , Mn 3 O 4 , rGO, and Oxone. 65 supporting metal and metal oxides attributed to its high electrical conductivities, unique mechanical strength, and large specific surface areas 10,11 . It has been found that graphene can This journal is © The Royal Society of Chemistry [year] conditions: catalyst = 100 mg/L, PMS dose = 0.3 g/L, initial MB concentration = 50 mg/L. pH=7.0, T = 25 °C) Fig. 6 MB degradation in the Fe3O4/Mn3O4/rGO/PMS system: the effect of initial MB concentration (a), the effect of catalyst dosage (b), the effect of PMS dosage (c), and the effect of initial pH value (d). (Except for the investigated parameter, other parameters fixed on: catalyst = 100 mg/L, Oxone dose = 0.3 g/L, initial MB concentration = 50 mg/L, pH=7.0, and T = 25 °C) 60The effect of reaction temperature on MB degradation was also investigated and the results were shown in Fig. 7. A general trend