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Background: Wax gourd [Benincasa hispida (Thunb) Cogn. (2n = 2x = 24)] is an economically important vegetable crop of genus Benincasa in the Cucurbitaceae family. Fruit is the main consumption organ of wax gourd. The mature fruit cuticular wax (MFCW) is an important trait in breeding programs, which is also of evolutionary significance in wax gourd. However, the genetic architecture of this valuable trait remains unrevealed. Results: In this study, genetic analysis revealed that the inheritance of MFCW was controlled by a single gene, with MFCW dominant over non-MFCW, and the gene was primarily named as BhWAX. Genome-wide association study (GWAS) highlighted a 1.1 Mb interval on chromosome 9 associated with MFCW in wax gourd germplasm resources. Traditional fine genetic mapping delimited BhWAX to a 0.5 Mb region containing 12 genes. Based on the gene annotation, expression analysis and co-segregation analysis, Bhi09G001428 that encodes a membrane bound O-acyltransferase (MBOAT) was proposed as the candidate gene for BhWAX. Moreover, it was demonstrated that the efficiency of a cleaved amplified polymorphic sequences (CAPS) marker in the determination of MFCW in wax gourd reached 80%. Conclusions: In closing, the study identified the candidate gene controlling MFCW and provided an efficient molecular marker for the trait in wax gourd for the first time, which will not only be beneficial for functional validation of the gene and marker-assisted breeding of wax gourd, but also lay a foundation for analysis of its evolutionary meaning among cucurbits. [ABSTRACT FROM AUTHOR]

(1) Background: Wax gourd is an economically important vegetable crop in many tropical and sub-tropical countries in Asia. Fruit color is an important fruit quality trait, but the genetic, biochemical basis and regulatory network of fruit color variation in wax gourd are rarely studied. (2) Methods: In this study, two wax gourd inbred lines with different pericarp colors were used as materials to conduct joint metabolomic and transcriptomic analyses on mature fruit pericarp: B214 with yellow and B227 with dark green color. (3) Results: It was found that the chlorophyll content in the pericarp of B214 was significantly lower than that of B227, consistent with the down-regulation of several genes involved in the chlorophyll biosynthesis pathway, including hemA, hemB, hemC, hemF, chlH, chlI, chlM, POR, and CAO. The 229 metabolites showed differential accumulation levels between B214 and B227, and 4 anthocyanins, 5 flavanones, 25 flavones, 25 flavone C-glycosides, 12 flavonols, and 3 isoflavones were identified. In particular, cyanidin 3-O-glucoside, an anthocyanin contributing to the coloration of dark color, showed higher accumulation in B227 than in B214, probably due to the higher expression of genes of F3′H and glucosyl transferases (GTs) in B227. Transcription factors such as MYBs and bHLHs showed differential expressions between the two lines including bHLH14, a homolog of Arabidopsis AtbHLH14 that had significantly higher expression in B227 than in B214. bHLH14 was located in a region where the pericarp color (pc) locus was mapped, suggesting it may be a candidate gene for the pc locus. (4) Conclusions: This work supports the association of chlorophyll and flavonoid synthesis in wax gourd fruit color variation and also provides a good foundation for understanding the regulatory network for wax gourd coloration. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are endogenous single-stranded non-coding small RNAs of 20–24 nucleotides and play important roles in many plant biological and metabolic processes. Wax gourd is an important vegetable of Cucurbitacea family, with great economic and medicinal value. Although miRNAs have been extensively studied in model plant species, less is known in wax gourd (Benincasa hispida). In this study, in order to identify miRNAs in wax groud, five independent small RNA libraries were constructed using leaf, root, stem, flower, and fruit of B227. Based on high-throughput Illumina deep sequencing. In total, 422 known and 409 novel miRNAs were identified from five libraries. Comparative analysis revealed that many miRNAs were differentially expressed among different tissues, indicating tissue-specific expression of some miRNAs. qRT-PCR verified the reliability of small RNA sequencing results. Furthermore, miRNAs with similar expression patterns among five tissues were clustered into the same profile, among which many miRNAs were found with relatively high expression in the fruit of wax gourd. MiR164-x had the highest expression in fruit than in other tissues and many NAC transcription factors were predicted as its target genes. We propose that miR164 might regulate fruit development by forming miR164-NAC module in wax gourd. Taken together, this study provides the first global miRNAs profiling of wax gourd, and lays the foundation for understanding the regulatory roles of miRNAs in the growth and development processes of wax gourd. [ABSTRACT FROM AUTHOR]

The botanical family Cucurbitaceae includes a variety of fruit crops with global or local economic importance. How their genomes evolve and the genetic basis of diversity remain largely unexplored. In this study, we sequence the genome of the wax gourd (Benincasa hispida), which bears giant fruit up to 80 cm in length and weighing over 20 kg. Comparative analyses of six cucurbit genomes reveal that the wax gourd genome represents the most ancestral karyotype, with the predicted ancestral genome having 15 proto-chromosomes. We also resequence 146 lines of diverse germplasm and build a variation map consisting of 16 million variations. Combining population genetics and linkage mapping, we identify a number of regions/genes potentially selected during domestication and improvement, some of which likely contribute to the large fruit size in wax gourds. Our analyses of these data help to understand genome evolution and function in cucurbits. Cucurbits fruits have diverse shapes and sizes, but their genomes evolution and genetic basis of diversity are unclear. Here, the authors show that the wax gourd genome has the most ancestral karyotype among cucurbits and identify candidate genes which contribute to large fruit size by comparative and population genomics analyses. [ABSTRACT FROM AUTHOR]

Wax gourd (2n = 2 x = 24) is an important vegetable species in Cucurbitaceae . Because it can be stored for a very long period of time, it plays an important role in ensuring the annual supply and regulating off-season supply of the vegetables. However, the availability of genetic information about wax gourd is limited. This study aimed to identify the useful genetic information for wax gourd. The conserved domains of reverse transcriptase (RT) genes of Ty1- copia retrotransposons were isolated from the genome of wax gourd using degenerate oligonucleotide primers. A total of twenty eight RT sequences were obtained, which showed high heterogeneity with the similarity ranging from 47.5% to 94.3%. Sixteen (57.1%) of them were found to be defective, being disrupted by stop codons and/or frameshift mutations. These 28 sequences were divided into five subfamilies. The comparative phylogenetic analysis with other Cucurbitaceae species from GenBank database showed that most retrotransposons derived from the same genus tended to cluster together, although there were a few exceptions. These results indicate that both vertical transmission and horizontal transmission are the sources of Ty1- copia retrotransposons in wax gourd. Fluorescent in situ hybridization (FISH) with Ty1- copia retrotransposon sequences as probes revealed that this kind of retrotransposons had a dispersed genomic organization, physically distributed among all the chromosomes of wax gourd, with clusters in the heterochromatin regions. This is the first report of Ty1- copia retrotransposons in wax gourd, which would be helpful for our understanding about the organization and evolutions of wax gourd genome and also provide valuable information for our utilization of wax gourd retrotransposons. [ABSTRACT FROM AUTHOR]

• Time-course transcriptome analysis of bilateral and unilateral seeds in wax gourd. • Comparative analysis discovered transcriptomic differences between two types of seeds. • Secondary metabolite biosynthesis-related genes were highly differentially expressed between bilateral and unilateral seeds. • Lignin might play a crucial role in the formation of seed ribs and final seed shape. Wax gourd is an important vegetable crop in Cucurbitaceae. There are two shapes of wax gourd seeds, bilateral and unilateral. Bilateral seeds are more popular than unilateral seeds because they germinate faster along with a higher germination rate. Previously, we identified the seed shape determination gene YABBY4 through genetic mapping and genome-wide association study. However, the molecular mechanisms underlying seed shape differentiation remain elusive. In this study, the B214 variety containing bilateral seeds and the B227 variety containing unilateral seeds were subjected to time-course transcriptome analysis. Our results showed that genes related to secondary metabolite biosynthesis were differentially expressed between B214 and B227 seeds at all stages, and some lignin biosynthesis-related genes were highly expressed in B214 seeds at the later stages. At the early stages, genes associated with cell periphery, plasma membrane, plant hormone signal transduction, and MAPK signaling pathway were more active. Catalytic activity, biosynthetic, and metabolic process-related genes were differentially expressed at the later stages. Together, our findings dissect the transcriptomic differences between the two types of seeds and gain insights into the regulatory networks of seed shape differentiation in wax gourd. [Display omitted] [ABSTRACT FROM AUTHOR]

• The pan-genome of wax gourd aids in the discovery of more functional genes. Large-scale resequencing studies in wax gourd have generated a large data resource and mined many selection signals and candidate genes. In this study, we constructed the first pangenome of wax gourd based on resequencing data and obtained 316 Mb novel contigs containing 996 novel genes. A pan-genome-wide gene present/absent variations analysis of 25,188 genes identified 2154 genes as variable genes. Analysis of gene present/absent variations selection between wild accessions, landraces, and cultivar accessions revealed that many genes, including resistance genes, were lost during the process of domestication and improvement. The 22 resistance gene analogs identified in non-reference contigs are complementary to the 642 resistance gene analogs on the reference genome. Genome-wide association studies of gene present/absent variations with fruit weight, fruit length, fruit diameter, and fruit thickness of wax gourd identified five phenotypic-related candidate genes. Pan-genome-wide identification of NAC, WRKY and HSF gene family identified 7 novel genes. In conclusion, this study provides a more complete sequence and genes of the wax gourd genome and identifies new selected genes as well as phenotypically related candidate genes through a series of analyses, as well as provides an abundant resource and research reference for breeding and gene function studies in the wax gourd. [ABSTRACT FROM AUTHOR]