Comparative chloroplast genome analysis of seven extant Citrullus species insight into genetic variation, phylogenetic relationships, and selective pressure.

Citrullus ecirrhosus, Citrullus rehmii, and Citrullus naudinianus are three important related wild species of watermelon in the genus Citrullus, and their morphological differences are clear, however, their chloroplast genome differences remain unknown. This study is the first to assemble, analyze, and publish the complete chloroplast genomes of C. ecirrhosus, C. rehmii, and C. naudinianus. A comparative analysis was then conducted among the complete chloroplast genomes of seven extant Citrullus species, and the results demonstrated that the average genome sizes of Citrullus is 157,005 bp, a total of 130-133 annotated genes were identified, including 8 rRNA, 37 tRNA and 85-88 protein-encoding genes. Their gene content, order, and genome structure were similar. However, noncoding regions were more divergent than coding regions, and rps16-trnQ was a hypervariable fragment. Thirty-four polymorphic SSRs, 1,271 SNPs and 234 INDELs were identified. Phylogenetic trees revealed a clear phylogenetic relationship of Citrullus species, and the developed molecular markers (SNPs and rps16-trnQ) could be used for taxonomy in Citrullus. Three genes (atpB, clpP1, and rpoC2) were identified to undergo selection and would promote the environmental adaptation of Citrullus.

The complete plastome sequence of Momordica cochinchinensis (Cucurbitaceae).

Momordica cochinchinensis (Lour.) Spreng. is an important medicinal plant that is used to treat various diseases in South and Southeast Asia. In this study, the complete plastome of M. cochinchinensis was sequenced and found to exhibit a total length of 158,955 bp, with a large single copy (LSC) region of 87,924 bp and a small single copy (SSC) region of 18,479 bp, as well as with two inverted repeats (IRs) that were both 26,726 bp in length. In total, 129 genes were detected, comprising 86 protein-encoding genes, 8 ribosomal RNA (rRNA) genes, and 35 transfer RNA (tRNA) genes. Furthermore, the inferred phylogenetic tree confirmed that M. cochinchinensis belongs to the genus Momordica in the Cucurbitaceae family. The research results will be used for authenticating M. cochinchinensis plant materials and for analyzing the genetic diversity and phylogenetic relationships in Momordica.

Identification of chromosome region and candidate genes for canary-yellow flesh (Cyf) locus in watermelon (Citrullus lanatus).

Genetic control of fruit flesh color in watermelon is complex, and significant knowledge gaps still exist. In the present study, we investigated the genetic basis of canary-yellow flesh color in watermelon inbred line PI 635597 using a segregating population derived from a cross between PI 635597 and another inbred line, Cream of Saskatchewan (pale yellow flesh color). We showed that a single dominant gene controls the canary-yellow flesh color for the Cyf (canary-yellow flesh) trait. Bulk segregant analysis (BSA) and fine genetic mapping narrowed down the Cyf locus to a 79.62-kb region on chromosome 6, which harbors 10 predicted genes. Sequence variation analysis in the promoter and coding regions and gene expression analysis in both parental lines and selected watermelon accessions with diverse fruit flesh colors support Cla97C06G122050 (unknown protein) and Cla97C06G122120 (pentatricopeptide repeat) as predicted candidate genes for the Cyf locus. Marker-assisted selection and sequence alignment showed that the Cyf locus could differentiate canary-yellow flesh and pale-yellow flesh. Our results indicate that the Cyf locus might be responsible for canary-yellow flesh color and carotenoid accumulation levels.

First Report of Fusarium oxysporum and F. proliferatum Causing Postharvest Corm Rot on Taro in China.

Taro (Colocasia esculenta), a perennial tuberous herb of the family Araceae, is cultivated widely in southern China. In December 2020, postharvest corm rot occurred on taro of 5 tons with approximately 70% incidence in a 18 square meter cellar in the Qingshanhu District (115°83'E, 28°76'N) of Nanchang City, Jiangxi Province, China. Infected corms had round, soft and slightly sunken lesions covered with white mycelia. The lesions gradually expanded, causing part or whole corm to become soft and shrink, and the inner corm tissue turned brown and rotten. To isolate the pathogen, a total of 30 diseased corm samples were collected. The corms were surface-disinfected by wiping them with 70% ethanol and then passing them over flame back and forth for 5 s. After epidermal tissue of the corms was removed using a sterilized scalpel, small portions of the inner tissue were transferred onto potato dextrose agar (PDA) and incubated at 25°C in the dark. A total of 27 isolates forming Fusarium-like colonies were obtained using monosporic isolation, of which 11 isolates were identified as F. oxysporum and 16 isolates were identified as F. proliferatum based on the colony characteristics and conidial morphology (Leslie and Summerell, 2006). Colonies of F. oxysporum isolates produced dense whitish to light purple mycelia with dark red pigments. Macroconidia were sickle-shaped, straight to slightly curved, 3-5 septa, measuring 25.6 to 45.8 × 3.3 to 6.1 µm. Microconidia were hyaline, oval or ellipsoid, aseptate, and measured 5.2 to 11.8 × 2.2 to 3.5 µm. Chlamydospores were round, 3.5 to 7.6 µm in diameter. Colonies of F. proliferatum isolates were whitish with abundant aerial mycelia and orange pigments. Numerous oval unicellular microconidia were 4.5 to 11.8 × 1.9 to 4.2 µm, and sparse falcate macroconidia with 3-4 septa were 19.4 to 39.2 × 1.9 to 5.2 µm in size. No chlamydospores were observed. Genomic DNA of two representative isolates (F. oxysporum isolate YTU1 and F. proliferatum isolate YTH1) was extracted, and the internal transcribed spacer (ITS) region and translation elongation factor 1-α (TEF1-α) gene were amplified and sequenced using primers ITS1/ITS4 and EF-1H/EF-2T (White et al., 1990; Zhang et al., 2014) respectively. Using BLAST analysis, the ITS sequences of isolates YTU1 (506 bp) and YTH1 (508 bp) exhibited 100% homology with F. oxysporum (MN633363) and F. proliferatum (MT534188), respectively, and the TEF1-α sequences of YTU1 (712 bp) and YTH1 (703 bp) shared 100% homology with F. oxysporum (MN507110) and F. proliferatum (MK952799), respectively. Sequences were deposited in GenBank with the Accession Nos. MZ157124 and MZ310443 for ITS, and MZ383814 and MZ383815 for TEF1-α. The pathogenicity of each isolate was determined on six healthy taro corms. All the taro corms were surface-disinfected with 70% alcohol and two locations from each corm were inoculated. One location was inoculated with 20 µl of conidial suspension (1×105 conidia/ml) and the other was inoculated with sterilized water as a control. All corms were incubated in a growth chamber at 25℃ and 95% relative humidity in the dark. After 15 days, all inoculated corms developed brown rot symptoms, while the non-inoculated control corms remained symptomless. The original isolates were successfully reisolated from all symptomatic corms and identified by sequencing, fulfilling Koch's postulates. F. oxysporum has been reported causing postharvest corm rot of taro in Bogor, Japan, and British Solomon Islands (Widodo et al., 2011). However, to our knowledge, this is the first report of F. oxysporum causing postharvest corm rot of taro in China and F. proliferatum causing postharvest corm rot of taro in the world. The disease poses a potential threat to taro production and should be timely assessed and properly managed.

Complete chloroplast genome sequences of three aroideae species (Araceae): lights into selective pressure, marker development and phylogenetic relationships.

BACKGROUND: Colocasia gigantea, Caladium bicolor and Xanthosoma sagittifolium are three worldwide famous ornamental and/or vegetable plants in the Araceae family, these species in the subfamily Aroideae are phylogenetically perplexing due to shared interspecific morphological traits and variation. RESULT: This study, for the first time ever, assembled and analyzed complete chloroplast genomes of C. gigantea, C. bicolor and X. sagittifolium with genome sizes of 165,906 bp, 153,149 bp and 165,169 bp in length, respectively. The genomes were composed of conserved quadripartite circular structures with a total of 131 annotated genes, including 8 rRNA, 37 tRNA and 86 protein-coding genes. A comparison within Aroideae showed seven protein-coding genes (accD, ndhF, ndhK, rbcL, rpoC1, rpoC2 and matK) linked to environmental adaptation. Phylogenetic analysis confirmed a close relationship of C. gigantea with C. esculenta and S. colocasiifolia, and the C. bicolor with X. sagittifolium. Furthermore, three DNA barcodes (atpH-atpI + psaC-ndhE, atpH-atpI + trnS-trnG, atpH-atpI + psaC-ndhE + trnS-trnG) harbored highly variable regions to distinguish species in Aroideae subfamily. CONCLUSION: These results would be beneficial for species identification, phylogenetic relationship, genetic diversity, and potential of germplasm resources in Aroideae.

Genome-wide analysis of valine-glutamine motif-containing proteins related to abiotic stress response in cucumber (Cucumis sativus L.).

BACKGROUND: Cucumber (Cucumis sativus L.) is one of the most important economic crops and is susceptible to various abiotic stresses. The valine-glutamine (VQ) motif-containing proteins are plant-specific proteins with a conserved "FxxhVQxhTG" amino acid sequence that regulates plant growth and development. However, little is known about the function of VQ proteins in cucumber. RESULTS: In this study, a total of 32 CsVQ proteins from cucumber were confirmed and characterized using comprehensive genome-wide analysis, and they all contain a conserved motif with 10 variations. Phylogenetic tree analysis revealed that these CsVQ proteins were classified into nine groups by comparing the CsVQ proteins with those of Arabidopsis thaliana, melon and rice. CsVQ genes were distributed on seven chromosomes. Most of these genes were predicted to be localized in the nucleus. In addition, cis-elements in response to different stresses and hormones were observed in the promoters of the CsVQ genes. A network of CsVQ proteins interacting with WRKY transcription factors (CsWRKYs) was proposed. Moreover, the transcripts of CsVQ gene were spatio-temporal specific and were induced by abiotic adversities. CsVQ4, CsVQ6, CsVQ16-2, CsVQ19, CsVQ24, CsVQ30, CsVQ32, CsVQ33, and CsVQ34 were expressed in the range of organs and tissues at higher levels and could respond to multiple hormones and different stresses, indicating that these genes were involved in the response to stimuli. CONCLUSIONS: Together, our results reveal novel VQ resistance gene resources, and provide critical information on CsVQ genes and their encoded proteins, which supplies important genetic basis for VQ resistance breeding of cucumber plants.

The complete chloroplast genome sequence of the Cucurbita ficifolia Bouché (Cucurbitaceae).

Cucurbita ficifolia Bouché is an important germplasm resource used for rootstock and hypoglycemic food in Cucurbitaceae. The complete chloroplast genome sequence of C. ficifolia has been determined in this study. The total genome size is 157,533 bp in length and contains a pair of inverted repeats (IRs) of 25,639 bp, which were separated by large single copy (LSC) and small single copy (SSC) of 88,112 bp and 18,143 bp, respectively. A total of 130 genes were predicted including 86 protein-coding genes, eight rRNA genes and 36 tRNA genes. Further, Maximum-likelihood phylogenetic analysis revealed that C. ficifolia is a base clade of genus Cucurbita and closer to Cucurbita maxima. The chloroplast genome of C. ficifolia would promote the germplasm exploration, phylogenetic relationships, and molecular biology researches in Cucurbita.

Uncovering the genetic diversity of yams (Dioscorea spp.) in China by combining phenotypic trait and molecular marker analyses.

Yam is an important edible tuber and root plant worldwide; China as one of the native places of yams has many diverse local resources. The goal of this study was to clarify the genetic diversity of the commonly cultivated yam landraces and the genetic relationship between the main yam species in China. In this study, 26 phenotypic traits of 112 yam accessions from 21 provinces in China were evaluated, and 24 simple sequence repeat (SSR) and 29 sequence-related amplified polymorphism (SRAP) markers were used for the genetic diversity analysis. Phenotypic traits revealed that Dioscorea opposita had the highest genetic diversity, followed by D. alata, D. persimilis, D. fordii, and D. esculenta. Among the 26 phenotypic traits, the Shannon diversity indexes of leaf shape, petiole color, and stem color were high, and the range in the variation of tuber-related traits in the underground part was higher than that in the aboveground part. All accessions were divided into six groups by phenotypic trait clustering, which was also supported by principal component analysis (PCA). Molecular marker analysis showed that SSR and SRAP markers had good amplification effects and could effectively and accurately evaluate the genetic variation of yam. The unweighted pair-group method with arithmetic means analysis based on SSR-SRAP marker data showed that the 112 accessions were also divided into six groups, similar to the phenotypic trait results. The results of PCA and population structure analysis based on SSR-SRAP data also produced similar results. In addition, the analysis of the origin and genetic relationship of yam indicated that the species D. opposita may have originated from China. These results demonstrate the genetic diversity and distinctness among the widely cultivated species of Chinese yam and provide a theoretical reference for the classification, breeding, germplasm innovation, utilization, and variety protection of Chinese yam resources.

Comparative analysis of nuclear, chloroplast, and mitochondrial genomes of watermelon and melon provides evidence of gene transfer.

During plant evolution, there is genetic communication between organelle and nuclear genomes. A comparative analysis was performed on the organelle and nuclear genomes of the watermelon and melon. In the watermelon, chloroplast-derived sequences accounted for 7.6% of the total length of the mitochondrial genome. In the melon, chloroplast-derived sequences accounted for approximately 2.73% of the total mitochondrial genome. In watermelon and melon, the chloroplast-derived small-fragment sequences are either a subset of large-fragment sequences or appeared multiple times in the mitochondrial genome, indicating that these fragments may have undergone multiple independent migration integrations or emerged in the mitochondrial genome after migration, replication, and reorganization. There was no evidence of migration from the mitochondria to chloroplast genome. A sequence with a total length of about 73 kb (47%) in the watermelon chloroplast genome was homologous to a sequence of about 313 kb in the nuclear genome. About 33% of sequences in the watermelon mitochondrial genome was homologous with a 260 kb sequence in the nuclear genome. A sequence with a total length of about 38 kb (25%) in the melon chloroplast genome was homologous with 461 sequences in the nuclear genome, with a total length of about 301 kb. A 3.4 Mb sequence in the nuclear genome was homologous with a melon mitochondrial sequence. These results indicate that, during the evolution of watermelon and melon, a large amount of genetic material was exchanged between the nuclear genome and the two organelle genomes in the cytoplasm.

The complete chloroplast genome sequence of the Dioscorea persimilis Prain et Burkill (Dioscoreaceae).

Dioscorea persimilis belongs to Dioscorea genus, which is considered as one of the most popular food and traditional folk medicine in China. The complete chloroplast genome of D. persimilis was determined in this study. The total genome size was 153,219 bp in length, containing a pair of inverted repeats (IRs) of 25,477 bp, which were separated by large single copy (LSC) and small single copy (SSC) of 83,448 bp and 18,817 bp, respectively. The GC content is 37.01%. A total of 129 genes were predicted including 84 protein-coding genes, eight rRNA genes and 37 tRNA genes. Phylogenetic tree analysis of 24 species in the genus Dioscorea indicated that D. persimilis was closer to Chinese yam, but has remote phylogenetic relationship with Guinea yam.

The complete chloroplast genome sequence of the Pueraria lobata (Willd.) Ohwi (Leguminosae).

Pueraria lobata (Willd.) Ohwi is an essential traditional oriental medicine with therapeutic effects. In this study, we assembled the complete chloroplast genome of P. lobata. The total genome size was 153,442 bp in length, containing a large single-copy (LSC) region of 84,162 bp, a small single-copy (SSC) of 17,998 bp, and a pair of inverted repeats (IRs) of 25,641 bp, and possessing 35.41% GC content. In addition, the whole chloroplast genome encodes a total of 129 genes, including 84 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Phylogenetic tree analysis of 48 species in the family Papilionoideae of Leguminosae indicated that P. lobata was belong to Papilionoideae and closely related to the genus, Pachyrhizus, Vigna and Phaseolus.

The complete chloroplast genome sequence of the Dioscorea esculenta (Lour.) Burkill (Dioscoreaceae).

Dioscorea esculenta (Lour.) Burkill is an essential tuber crop with pharmacological effects in the family Dioscoreaceae. The complete chloroplast genome of D. esculenta was determined in this study. The total genome size is 153, 437 bp in length and demonstrates a typical quadripartite structure containing a large single copy (LSC, 83,628 bp) and a small single copy (SSC, 18,893 bp), separated by a pair of inverted repeats (IRa, IRb) of 25,458 bp. The GC content of the complete chloroplast genome sequence is 37.07%. A total of 131 genes were predicted including 86 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Phylogenetic tree analysis of 25 species belonging to the genus Dioscorea indicated that D. esculenta and D. sansibarensis were clustered into one branch.

Population structure and genetic diversity of watermelon (Citrullus lanatus) based on SNP of chloroplast genome.

Citrullus amarus (citronmelon) is an important crop with resistance to many diseases. The chloroplast genome is important in studying the genetic evolution of plants. The C. amarus chloroplast genome was first reported in this study using a novel assembly method based on whole genome sequencing. We identified 82 SNP sites in chloroplast genome with 313 watermelon materials. The 82 SNPs could effectively divide the natural watermelon population into four groups: C. lanatus subsp. lanatus, C. lanatus subsp. mucosospermus, C. lanatus subsp. vulgaris (ecologically from the Americas) and C. lanatus subsp. vulgaris (ecologically from Asia), with decreasing genetic diversity (π) (6.6 × 10-5, 2.4 × 10-5, 9.8 × 10-6 and 5.41 × 10-6, respectively). The single fruit weight, soluble solids, fruit color and 1000-seed weight of C. lanatus subsp. lanatus were significantly different from those of the other three groups. These results indicate that the complete chloroplast genome can be used in studying population genetics of watermelon, which is helpful for classification among intra species subgroups and identification of core germplasm resources.

Resequencing of 297 melon accessions reveals the genomic history of improvement and loci related to fruit traits in melon.

Domestication and improvement are two important stages in crop evolution. Melon (Cucumis melo L.) is an important vegetable crop with wide phenotypic diversity in many horticultural traits, especially fruit size, flesh thickness and aroma, which are likely the results of long-term extensive selection during its evolution. However, selective signals in domestication and improvement stages for these remarkable variations remain unclear. We resequenced 297 wild, landrace and improved melon accessions and obtained 2 045 412 high-quality SNPs. Population structure and genetic diversity analyses revealed independent and two-step selections in two subspecies of melon: ssp. melo and ssp. agrestis during melon breeding. We detected 233 (~18.35 Mbp) and 159 (~17.71 Mbp) novel potential selective signals during the improvement stage in ssp. agrestis and spp. melo, respectively. Two alcohol acyltransferase genes (CmAATs) unique to the melon genome compared with other cucurbit crops may have undergone stronger selection in ssp. agrestis for the characteristic aroma as compared with other cucurbits. Genome-wide association analysis identified eight fruit size and seven flesh thickness signals overlapping with selective sweeps. Compared with thin-skinned ssp. agrestis, thick-skinned ssp. melo has undergone a stronger selection for thicker flesh. In most melon accessions, CmCLV3 has pleiotropic effects on carpel number and fruit shape. Findings from this study provide novel insights into melon crop evolution, and new tools to advance melon breeding.

The complete chloroplast genome sequence of the Canna edulis Ker Gawl. (Cannaceae).

Canna edulis Ker Gawl. is an essential traditional tuber crop used for fresh consumption and to isolate starch in some tropical and semitropical regions. The complete chloroplast genome sequence of C. edulis has been determined in this study. The total genome size is 164,650 bp in length and contains a pair of inverted repeats (IRs) of 27,278 bp, which were separated by large single-copy (LSC) and small single-copy (SSC) of 91,421 bp and 18,673 bp, respectively. A total of 131 genes were predicted including 86 protein-coding genes, 8 rRNA genes and 37 tRNA genes. Further, maximum-likelihood phylogenetic analysis revealed that C. edulis belongs to Cannaceae in Zingiberales. The chloroplast genome of C. edulis is first complete genome sequence in Cannaceae and would play a significant role in the development of molecular markers in plant phylogenetic and population genetic studies.

Complete sequence of mitochondrial genome of Cucumis melo L.

Cucumis melo L. is one of the most important fruit-type vegetables in the world. This genome is divided into a main loop and two small loops. The length of the main loop is 2,709,526 bp, and the two small loops are 149,555 bp and 47,592 bp long, respectively. There are 88 coding genes in the melon mitochondrial genome, including 40 protein-coding genes (which accounted for about 1.23% of the whole genome), 8 rRNAs, and 40 tRNAs. The total length of rRNAs and tRNAs spans 0.31% of the total genome sequence. Among the 88 mitochondrial coding genes, only 5 tRNAs were located into the second largest circular DNA molecule. The complete mitogenome sequence provided herein would help understand C. melo evolution.

Identification of SNP loci and candidate genes related to four important fatty acid composition in Brassica napus using genome wide association study.

Rapeseed oil (canola, Brassica napus L.) is an important healthy vegetable oil throughout the world, the nutritional and economical value of which largely depends on its seed fatty acid composition. In this study, based on 201,187 SNP markers developed from the SLAF-seq (specific locus amplified fragment sequencing), a genome wide association study of four important fatty acid content traits (erucic acid, oleic acid, linoleic acid and linolenic acid) in a panel of 300 inbred lines of rapeseed in two environments (JXAU and JXRIS) was carried out. A total of 148 SNP loci significantly associated with these traits were detected by MLM model analysis respectively, and 30 SNP loci on A08 and C03 chromosomes were detected in three traits of erucic acid, oleic acid and linoleic acid contents simultaneously. Furthermore, 108 highly favorable alleles for increasing oleic acid and linoleic acid content, also for decreasing erucic acid content simultaneously were observed. By a basic local alignment search tool (BLAST) search with in a distance of 100 Kb around these significantly SNP-trait associations, we identified 20 orthologs of the functional candidate genes related to fatty acid biosynthesis, including the known vital fatty acid biosynthesis genes of BnaA.FAE1 and BnaC. FAE1 on the A08 and C03 chromosomes, and other potential candidate genes involving in the fatty acid biosynthesis pathway, such as the orthologs genes of FAD2, LACS09, KCS17, CER4, TT16 and ACBP5. This study lays a basis for uncovering the genetic variations and the improvement of fatty acid composition in B. napus.

The complete chloroplast genome sequence of the Siraitia Grosvenorii (Cucurbitaceae).

Siraitia grosvenorii is a famous Chinese plant used in traditional food and medicine with pharmacological effects. The complete chloroplast genome sequence of S. grosvenorii has been determined in this study. The total genome size is 158,834 bp in length and contains a pair of inverted repeats (IRs) of 26,288 bp, which were separated by large single-copy (LSC) and small single-copy (SSC) of 87,702 bp and 18,556 bp length, respectively. A total of 131 genes were predicted including 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis showed that S. grosvenorii belongs to the family Cucurbitaceae. The complete chloroplast genome of S. grosvenorii would play a significant role in the development of molecular markers in plant phylogenetic and population genetic studies.

The complete chloroplast genome sequence of the Cucurbita pepo L. (Cucurbitaceae).

Cucurbita pepo is an important economic plant cultivated widely in the world. The complete chloroplast genome sequence of C. pepo is reported here. The genome is 157,343 bp in length and exhibits a typical quadripartite structure of the large (LSC, 87,970 bp) and small (SSC, 18,167 bp) single-copy regions, separated by a pair of inverted repeats (IRs, 25,603 bp). A total of 131 genes were predicted including 85 protein-coding genes, eight rRNA genes and 38 tRNA genes. Further, phylogenetic analysis showed that C. pepo were closely related to other species in the family Cucurbitaceae. The complete chloroplast genome of C. pepo would be taken as a useful molecular tool for species discrimination, taxonomy, and phylogenetic relationships in the family Cucurbitaceae.

Comparative transcriptome analysis of two contrasting watermelon genotypes during fruit development and ripening.

BACKGROUND: Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is an economically important crop with an attractive ripe fruit that has colorful flesh. Fruit ripening is a complex, genetically programmed process. RESULTS: In this study, a comparative transcriptome analysis was performed to identify the regulators and pathways that are involved in the fruit ripening of pale-yellow-flesh cultivated watermelon (COS) and red-flesh cultivated watermelon (LSW177). We first identified 797 novel genes to extend the available reference gene set. Second, 3958 genes in COS and 3503 genes in LSW177 showed at least two-fold variation in expression, and a large number of these differentially expressed genes (DEGs) during fruit ripening were related to carotenoid biosynthesis, plant hormone pathways, and sugar and cell wall metabolism. Third, we noted a correlation between ripening-associated transcripts and metabolites and the key function of these metabolic pathways during fruit ripening. CONCLUSION: The results revealed several ripening-associated actions and provide novel insights into the molecular mechanisms underlying the regulation of watermelon fruit ripening.