The dominant white color trait of the melon fruit rind is associated with epicuticular wax accumulation.

MAIN CONCLUSION: Microscopic analyses and chemical profiling demonstrate that the white rind phenotype in melon fruit is associated with the accumulation of n-alkanes, fatty alcohols, aldehydes and wax esters. Serving as an indicator of quality, the rind (or external) color of fruit directly affects consumer choice. A fruit's color is influenced by factors such as the levels of pigments and deposited epicuticular waxes. The latter produces a white-grayish coating often referred to as "wax bloom". Previous reports have suggested that some melon (Cucumis melo L.) accessions may produce wax blooms, where a dominant white rind color trait was genetically mapped to a major locus on chromosome 7 and suggested to be inherited as a single gene named Wi. We here provide the first direct evidence of the contribution of epicuticular waxes to the dominant white rind trait in melon fruit. Our light and electron microscopy and gas chromatography-mass spectrometry (GC-MS) comparative analysis of melon accessions with white or green rinds reveals that the rind of melon fruit is rich in epicuticular waxes. These waxes are composed of various biochemical classes, including fatty acids, fatty alcohols, aldehydes, fatty amides, n-alkanes, tocopherols, triterpenoids, and wax esters. We show that the dominant white rind phenotype in melon fruit is associated with increased accumulation of n-alkanes, fatty alcohols, aldehydes and wax esters, which are linked with the deposition of crystal-like wax platelets on their surfaces. Together, this study broadens the understanding of natural variation in an important quality trait of melon fruit and promotes the future identification of the causative gene for the dominant white rind trait.

Identification of MYC genes in four Cucurbitaceae species and their roles in the response to temperature stress.

BACKGROUND: Myelocytomatosis (MYC) transcription factors are crucial mediators of the response of plants to environmental stresses through via binding to DNA regulatory regions. However, few systematic characterizations of MYC genes are available in Cucurbitaceae species. RESULTS: In this study, we identified 10, 8, 12, and 10 MYC genes in Cucumis sativus, Cucumis melo, Citrullus lanatus, and Benincasa hispida, respectively. Characterization revealed that all of the MYC proteins contain a highly conserved H4-V5-E6-E8-R9-R11-R12 sequence, which is essential for the binding of DNA regulatory regions. Evolutionary analysis enabled us to categorize 40 predicted MYC proteins from seven species into five distinct groups and revealed that the expansion of the MYC genes occurred before the divergence of monocots and dicots. The upstream promoter regions of the MYC genes contain a variety of developmental, stress, and hormone-responsive regulatory elements. The expression of cucumber MYC genes varies significantly across organs, with particularly high expression of CsaV3_3G001710 observed across all organs. Transcriptomic analysis revealed that certain cucumber MYC genes undergo specific upregulation or downregulation in response to both biotic and abiotic stressors. In particular, under temperature stress, the cucumber genes CsaV3_3G007980 and CsaV3_3G001710 were significantly upregulated. Interestingly, the homologs of these two genes in C. lanatus presented a similar expression pattern to that in C. sativus, whereas in B. hispida, they presented the opposite pattern, i.e., significant downregulation. These findings indicated that these two genes indeed respond to temperature stress but with different expression patterns, highlighting the divergent functions of homologous genes across different species. CONCLUSIONS: This study analyzed the size and composition of the MYC gene family in four Cucurbitaceae species and investigated stress-responsive expression profiles, especially under temperature stress. All the results showed that MYC genes play important roles in development and stress responses, laying a theoretical foundation for further investigations of these response mechanisms.

Multiple Localization Analysis of the Major QTL-sfw 2.2 for Controlling Single Fruit Weight Traits in Melon Based on SLAF Sequencing.

Cucumis melo is an annual dicotyledonous trailing herb. It is fruity, cool, and refreshing to eat and is widely loved by consumers worldwide. The single fruit weight is an important factor affecting the yield, and thus the income and economic benefits, of melon crops. In this study, to identify the main QTLs (quantitative trait locus) controlling the single fruit weight of melon and thereby identify candidate genes controlling this trait, specific-locus amplified fragment sequencing (SLAF) analysis was performed on the offspring of female 1244 plants crossed with male MS-5 plants. A total of 115 individual plants in the melon F2 population were analyzed to construct a genetic linkage map with a total map distance of 1383.88 cM by the group in the early stages of the project, which was divided into 12 linkage groups with a total of 10,596 SLAF markers spaced at an average genetic distance of 0.13 cM. A total of six QTLs controlling single fruit weight (sfw loci) were detected. Seven pairs of markers with polymorphisms were obtained by screening candidate intervals from the SLAF data. The primary QTL sfw2.2 was further studied in 300 F2:3 family lines grown in 2020 and 2021, respectively, a positioning sfw2.2 between the markers CY Indel 11 and CY Indel 16, between 18,568,142 and 18,704,724 on chromosome 2. This interval contained 136.58 kb and included three genes with functional annotations, MELO3C029673, MELO3C029669, and MELO3C029674. Gene expression information for different fruit development stages was obtained from 1244 and MS-5 fruits on the 15d, 25d, and 35d after pollination, and qRT-PCR (quantitative reverse transcription-PCR) indicated that the expression of the MELO3C029669 gene significantly differed between the parents during the three periods. The gene sequences between the parents of MELO3C029669 were analyzed and compared, a base mutation was found to occur in the intronic interval between the parents of the gene, from A-G. Phylogenetic evolutionary tree analysis revealed that the candidate gene MELO3C029669 is most closely related to Pisum sativum Fimbrin-5 variant 2 and most distantly related to Cucumis melo var. makuwa. Therefore, it was hypothesized that MELO3C029669 is the primary major locus controlling single fruit weight in melon. These results not only provide a theoretical basis for further studies to find genes with functions in melon single fruit weight but also lay the foundation for accelerating breakthroughs and innovations in melon breeding.

Characterization and functions of Myeloblastosis (MYB) transcription factors in cucurbit crops.

Myeloblastosis (MYB) is one of the largest family of transcription factors (TFs) in plants. It plays a key role in plant life activities, such as metabolic regulation, stress resistant, as well as helpful for plant growth and development. In China, cucurbit is an important and nutrients rich vegetable crop, which have high medicinal and socio-economic values. In this review, we discussed the structure and characterization of MYB TFs and how do regulate flower development, fruit maturity, fruit quality, and flavonoid biosynthesis. Furthermore, we highlight the effect and contribution of MYB TFs in the regulation of biotic and abiotic stress resistance. This comprehensive review will provide a new reference for the more effective application of MYB TF in quality control, stress resistance research and molecular breeding of cucurbit crops.

A matter of smell: The complex regulation of aroma production in melon.

Melon fruit flavor is one of the most valuable traits for consumers. Aroma, formed by volatile organic compounds (VOCs), is a major component of flavor but has been neglected in breeding programs because of its complex regulation. Although the genetic regulation of VOCs biosynthesis is not fully understood, several advances have been recently achieved. VOCs originate from the degradation of fatty acids, aminoacids and terpenes, and the role of newly described enzymes, transcription factors and putative regulators is here discussed. Furthermore, ethylene plays a key role in fruit aroma production in melon, triggering the conversion of green-flavored aldehydes into fruity-flavored esters. A current challenge is to understand the ethylene-independent regulation of VOCs formation. Environmental conditions and human processing can also shape the melon volatile profile, and future research should focus on studying the effect of climate change in aroma formation.

Transcriptomic Analysis of the Molecular Mechanism Potential of Grafting-Enhancing the Ability of Oriental Melon to Tolerate Low-Nitrogen Stress.

Nitrogen is the primary nutrient for plants. Low nitrogen generally affects plant growth and fruit quality. Melon, as an economic crop, is highly dependent on nitrogen. However, the response mechanism of its self-rooted and grafted seedlings to low-nitrogen stress has not been reported previously. Therefore, in this study, we analyzed the transcriptional differences between self-rooted and grafted seedlings under low-nitrogen stress using fluorescence characterization and RNA-Seq analysis. It was shown that low-nitrogen stress significantly inhibited the fluorescence characteristics of melon self-rooted seedlings. Analysis of differentially expressed genes showed that the synthesis of genes related to hormone signaling, such as auxin and brassinolide, was delayed under low-nitrogen stress. Oxidative stress response, involved in carbon and nitrogen metabolism, and secondary metabolite-related differentially expressed genes (DEGs) were significantly down-regulated. It can be seen that low-nitrogen stress causes changes in many hormonal signals in plants, and grafting can alleviate the damage caused by low-nitrogen stress on plants, ameliorate the adverse effects of nitrogen stress on plants, and help them better cope with environmental stresses.

A Transcriptomic Analysis of Bottle Gourd-Type Rootstock Roots Identifies Novel Transcription Factors Responsive to Low Root Zone Temperature Stress.

The bottle gourd [Lagenaria siceraria (Molina) Standl.] is often utilized as a rootstock for watermelon grafting. This practice effectively mitigates the challenges associated with continuous cropping obstacles in watermelon cultivation. The lower ground temperature has a direct impact on the rootstocks' root development and nutrient absorption, ultimately leading to slower growth and even the onset of yellowing. However, the mechanisms underlying the bottle gourd's regulation of root growth in response to low root zone temperature (LRT) remain elusive. Understanding the dynamic response of bottle gourd roots to LRT stress is crucial for advancing research regarding its tolerance to low temperatures. In this study, we compared the physiological traits of bottle gourd roots under control and LRT treatments; root sample transcriptomic profiles were monitored after 0 h, 48 h and 72 h of LRT treatment. LRT stress increased the malondialdehyde (MDA) content, relative electrolyte permeability and reactive oxygen species (ROS) levels, especially H2O2 and O2-. Concurrently, LRT treatment enhanced the activities of antioxidant enzymes like superoxide dismutase (SOD) and peroxidase (POD). RNA-Seq analysis revealed the presence of 2507 and 1326 differentially expressed genes (DEGs) after 48 h and 72 h of LRT treatment, respectively. Notably, 174 and 271 transcription factors (TFs) were identified as DEGs compared to the 0 h control. We utilized quantitative real-time polymerase chain reaction (qRT-PCR) to confirm the expression patterns of DEGs belonging to the WRKY, NAC, bHLH, AP2/ERF and MYB families. Collectively, our study provides a robust foundation for the functional characterization of LRT-responsive TFs in bottle gourd roots. Furthermore, these insights may contribute to the enhancement in cold tolerance in bottle gourd-type rootstocks, thereby advancing molecular breeding efforts.

Rationally Engineered Novel Glycosyltransferase UGT74DD1 from Siraitia grosvenorii Catalyzes the Generation of the Sweetener Mogroside III.

Mogrosides are natural compounds highly valued in the food sector for their exceptional sweetness. Here, we report a novel O-glycosyltransferase (UGT74DD1) from Siraitia grosvenorii that catalyzes the conversion of mogrol to mogroside IIE. Site-directed mutagenesis yielded the UGT74DD1-W351A mutant, which exhibited the new capability to transform mogroside IIE into the valuable sweetener mogroside III, but with low catalytic activity. Subsequently, using structure-guided directed evolution with combinatorial active-site saturation testing, the superior mutant M6 (W351A/Q373 K/E49H/Q335W/S278C/D17F) were obtained, which showed a 46.1-fold increase in catalytic activity compared to UGT74DD1-W351A. Molecular dynamics simulations suggested that the enhanced activity and extended substrate profiles of M6 are due to its enlarged substrate-binding pocket and strengthened enzyme-substrate hydrogen bonding interactions. Overall, we redesigned UGT74DD1, yielding mutants that catalyze the conversion of mogrol into mogroside III. This study thus broadens the toolbox of UGTs capable of catalyzing the formation of valuable polyglycoside compounds.

Research Advancements in Salt Tolerance of Cucurbitaceae: From Salt Response to Molecular Mechanisms.

Soil salinization severely limits the quality and productivity of economic crops, threatening global food security. Recent advancements have improved our understanding of how plants perceive, signal, and respond to salt stress. The discovery of the Salt Overly Sensitive (SOS) pathway has been crucial in revealing the molecular mechanisms behind plant salinity tolerance. Additionally, extensive research into various plant hormones, transcription factors, and signaling molecules has greatly enhanced our knowledge of plants' salinity tolerance mechanisms. Cucurbitaceae plants, cherished for their economic value as fruits and vegetables, display sensitivity to salt stress. Despite garnering some attention, research on the salinity tolerance of these plants remains somewhat scattered and disorganized. Consequently, this article offers a review centered on three aspects: the salt response of Cucurbitaceae under stress; physiological and biochemical responses to salt stress; and the current research status of their molecular mechanisms in economically significant crops, like cucumbers, watermelons, melon, and loofahs. Additionally, some measures to improve the salt tolerance of Cucurbitaceae crops are summarized. It aims to provide insights for the in-depth exploration of Cucurbitaceae's salt response mechanisms, uncovering the roles of salt-resistant genes and fostering the cultivation of novel varieties through molecular biology in the future.

Development of New Multi-Glycosylation Routes to Facilitate the Biosynthesis of Sweetener Mogrosides from Bitter Immature Siraitia Grosvenorii Using Engineered Escherichia coli.

Mogrosides, which have various pharmacological activities, are mainly extracted from Siraitia grosvenorii (Luo Han Guo) and are widely used as natural zero-calorie sweeteners. Unfortunately, the difficult cultivation and long maturation time of Luo Han Guo have contributed to a shortage of mogrosides. To overcome this obstacle, we developed a highly efficient biosynthetic method using engineered Escherichia coli to synthesize sweet mogrosides from bitter mogrosides. Three UDP-glycosyltransferase (UGT) genes with primary/branched glycosylation catalytic activity at the C3/C24 sites of mogrosides were screened and tested. Mutant M3, which could catalyze the glycosylation of nine types of mogrosides, was obtained through enhanced catalytic activity. This improvement in ß-(1,6)-glycosidic bond formation was achieved through single nucleotide polymorphisms and direct evolution, guided by 3D structural analysis. A new multienzyme system combining three UGTs and UDP-glucose (UDPG) regeneration was developed to avoid the use of expensive UDPG. Finally, the content of sweet mogrosides in the immature Luo Han Guo extract increased significantly from 57% to 95%. This study not only established a new multienzyme system for the highly efficient production of sweet mogrosides from immature Luo Han Guo but also provided a guideline for the high-value utilization of rich bitter mogrosides from agricultural waste and residues.

Melon CmRLCK VII-8 kinase genes CmRLCK27, CmRLCK30 and CmRLCK34 modulate resistance against bacterial and fungal diseases in Arabidopsis.

Receptor-like cytoplasmic kinases (RLCKs) represent a distinct class of receptor-like kinases crucial for various aspects of plant biology, including growth, development, and stress responses. This study delves into the characterization of RLCK VII-8 members within cucurbits, particularly in melon, examining both structural features and the phylogenetic relationships of these genes/proteins. The investigation extends to their potential involvement in disease resistance by employing ectopic overexpression in Arabidopsis. The promoters of CmRLCK VII-8 genes harbor multiple phytohormone- and stress-responsive cis-acting elements, with the majority (excluding CmRLCK39) displaying upregulated expression in response to defense hormones and fungal infection. Subcellular localization studies reveal that CmRLCK VII-8 proteins predominantly reside on the plasma membrane, with CmRLCK29 and CmRLCK30 exhibiting additional nuclear distribution. Notably, Arabidopsis plants overexpressing CmRLCK30 manifest dwarfing and delayed flowering phenotypes. Overexpression of CmRLCK27, CmRLCK30, and CmRLCK34 in Arabidopsis imparts enhanced resistance against Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000, concomitant with the strengthened expression of defense genes and reactive oxygen species accumulation. The CmRLCK VII-8 members actively participate in chitin- and flg22-triggered immune responses. Furthermore, CmRLCK30 interacts with CmMAPKKK1 and CmARFGAP, adding a layer of complexity to the regulatory network. In summary, this functional characterization underscores the regulatory roles of CmRLCK27, CmRLCK30, and CmRLCK34 in immune responses by influencing pathogen-induced defense gene expression and ROS accumulation.

Genome-wide characterization and functional analysis of the melon TGA gene family in disease resistance through ectopic overexpression in Arabidopsis thaliana.

TGA-binding (TGA) transcription factors, characterized by the basic region/leucine zipper motif (bZIP), have been recognized as pivotal regulators in plant growth, development, and stress responses through their binding to the as-1 element. In this study, the TGA gene families in melon, watermelon, cucumber, pumpkin, and zucchini were comprehensively characterized, encompassing analyses of gene/protein structures, phylogenetic relationships, gene duplication events, and cis-acting elements in gene promoters. Upon transient expression in Nicotiana benthamiana, the melon CmTGAs, with typical bZIP and DOG1 domains, were observed to localize within the nucleus. Biochemical investigation revealed specific interactions between CmTGA2/3/5/8/9 and CmNPR3 or CmNPR4. The CmTGA genes exhibited differential expression patterns in melon plants in response to different hormones like salicylic acid, methyl jasmonate, and ethylene, as well as a fungal pathogen, Stagonosporopsis cucurbitacearum that causes gummy stem blight in melon. The overexpression of CmTGA3, CmTGA8, and CmTGA9 in Arabidopsis plants resulted in the upregulation of AtPR1 and AtPR5 expression, thereby imparting enhanced resistance to Pseudomonas syringae pv. Tomato DC3000. In contrast, the overexpression of CmTGA7 or CmTGA9 resulted in a compromised resistance to Botrytis cinerea, coinciding with a concomitant reduction in the expression levels of AtPDF1.2 and AtMYC2 following infection with B. cinerea. These findings shed light on the important roles of specific CmTGA genes in plant immunity, suggesting that genetic manipulation of these genes could be a promising avenue for enhancing plant immune responses.

Root suberization in the response mechanism of melon to autotoxicity.

Continuous cropping obstacles poses significant challenges for melon cultivation, with autotoxicity being a primary inducer. Suberization of cells or tissues is a vital mechanism for plant stress response. Our study aimed to elucidate the potential mechanism of root suberization in melon's response to autotoxicity. Cinnamic acid was used to simulate autotoxicity. Results showed that autotoxicity worsened the root morphology and activity of seedlings. Significant reductions were observed in root length, diameter, surface area, volume and fork number compared to the control in the later stage of treatment, with a decrease ranging from 20% to 50%. The decrease in root activity ranged from 16.74% to 29.31%. Root suberization intensified, and peripheral suberin deposition became more prominent. Autotoxicity inhibited phenylalanineammonia-lyase activity, the decrease was 50% at 16 h. The effect of autotoxicity on cinnamylalcohol dehydrogenase and cinnamate 4-hydroxylase activity showed an initial increase followed by inhibition, resulting in reductions of 34.23% and 44.84% at 24 h, respectively. The peroxidase activity only significantly increased at 24 h, with an increase of 372%. Sixty-three differentially expressed genes (DEGs) associated with root suberization were identified, with KCS, HCT, and CYP family showing the highest gene abundance. GO annotated DEGs into nine categories, mainly related to binding and catalytic activity. DEGs were enriched in 27 KEGG pathways, particularly those involved in keratin, corkene, and wax biosynthesis. Seven proteins, including C4H, were centrally positioned within the protein interaction network. These findings provide insights for improving stress resistance in melons and breeding stress-tolerant varieties.

CmPIF8-CmERF27-CmACS10-mediated ethylene biosynthesis modulates red light-induced powdery mildew resistance in oriental melon.

Powdery mildew is a serious fungal disease in protected melon cultivation that affects the growth, development and production of melon plants. Previous studies have shown that red light can improve oriental melon seedlings resistance to powdery mildew. Here, after inoculation with Podosphaera xanthii, an obligate fungal pathogen eliciting powdery mildew, we found that red light pretreatment increased ethylene production and this improved the resistance of melon seedlings to powdery mildew, and the ethylene biosynthesis gene CmACS10 played an important role in this process. By analysing the CmACS10 promoter, screening yeast one-hybrid library, it was found that CmERF27 positively regulated the expression of CmACS10, increased powdery mildew resistance and interacted with PHYTOCHROME INTERACTING FACTOR8 (CmPIF8) at the protein level to participate in the regulation of ethylene biosynthesis to respond to the red light-induced resistance to P. xanthii, Furthermore, CmPIF8 also directly targeted the promoter of CmACS10, negatively participated in this process. In summary, this study revealed the specific mechanism by which the CmPIF8-CmERF27-CmACS10 module regulates red light-induced ethylene biosynthesis to resist P. xanthii infection, elucidate the interaction between light and plant hormones under biological stress, provide a reference and genetic resources for breeding of disease-resistant melon plants.

A deletion in FLS2 and its expansion after domestication caused global dissemination of melon cultivars defective in flagellin recognition.

FLAGELLIN SENSING 2 (FLS2) encodes a pattern recognition receptor that perceives bacterial flagellin. While putative FLS2 orthologs are broadly conserved in plants, their functional characterization remains limited. Here, we report the identification of orthologs in cucumber (Cucumis sativus) and melon (C. melo), named CsFLS2 and CmFLS2, respectively. Homology searching identified CsFLS2, and virus-induced gene silencing (VIGS) demonstrated that CsFLS2 is required for flg22-triggered ROS generation. Interestingly, genome re-sequencing of melon cv. Lennon and subsequent genomic PCR revealed that Lennon has two CmFLS2 haplotypes, haplotype I encoding full-length CmFLS2 and haplotype II encoding a truncated form. We show that VIGS-mediated knockdown of CmFLS2 haplotype I resulted in a significant reduction in both flg22-triggered ROS generation and immunity to a bacterial pathogen in melon cv. Lennon. Remarkably, genomic PCR of CmFLS2 revealed that 68% of tested commercial melon cultivars possess only CmFLS2 haplotype II: these cultivars thus lack functional CmFLS2. To explore evolutionary aspects of CmFLS2 haplotype II occurrence, we genotyped the CmFLS2 locus in 142 melon accessions by genomic PCR and analyzed 437 released sequences. The results suggest that CmFLS2 haplotype II is derived from C. melo subsp. melo. Furthermore, we suggest that the proportion of CmFLS2 haplotype II increased among the improved melo group compared with the primitive melo group. Collectively, these findings suggest that the deleted FLS2 locus generated in the primitive melo subspecies expanded after domestication, resulting in the spread of commercial melon cultivars defective in flagellin recognition, which is critical for bacterial immunity.

The ethylene-responsive transcription factor ERF024 is a novel regulator of climacteric fruit ripening in melon.

Fruit ripening is an essential developmental stage in Angiosperms triggered by hormonal signals such as ethylene, a major player in climacteric ripening. Melon is a unique crop showing both climacteric and non-climacteric cultivars, offering an ideal model for dissecting the genetic mechanisms underpinning this process. The major quantitative trait locus ETHQV8.1 was previously identified as a key regulator of melon fruit ripening. Here, we narrowed down ETHQV8.1 to a precise genomic region containing a single gene, the transcription factor CmERF024. Functional validation using CRISPR/Cas9 knock-out plants unequivocally identified CmERF024 as the causal gene governing ETHQV8.1. The erf024 mutants exhibited suppression of ethylene production, leading to a significant delay and attenuation of fruit ripening. Integrative multi-omic analyses encompassing RNA-seq, DAP-seq, and DNase-seq revealed the association of CmERF024 with chromatin accessibility and gene expression dynamics throughout fruit ripening. Our data suggest CmERF024 as a novel regulator of climacteric fruit ripening in melon.

A wild melon reference genome provides novel insights into the domestication of a key gene responsible for melon fruit acidity.

KEY MESSAGE: A wild melon reference genome elucidates the genomic basis of fruit acidity domestication. Structural variants (SVs) have been reported to impose major effects on agronomic traits, representing a significant contributor to crop domestication. However, the landscape of SVs between wild and cultivated melons is elusive and how SVs have contributed to melon domestication remains largely unexplored. Here, we report a 379-Mb chromosome-scale genome of a wild progenitor melon accession "P84", with a contig N50 of 14.9 Mb. Genome comparison identifies 10,589 SVs between P84 and four cultivated melons with 6937 not characterized in previously analysis of 25 melon genome sequences. Furthermore, the population-scale genotyping of these SVs was determined in 1175 accessions, and 18 GWAS signals including fruit acidity, fruit length, fruit weight, fruit color and sex determination were detected. Based on these genotyped SVs, we identified 3317 highly diverged SVs between wild and cultivated melons, which could be the potential SVs associated with domestication-related traits. Furthermore, we identify novel SVs affecting fruit acidity and proposed the diverged evolutionary trajectories of CmPH, a key regulator of melon fruit acidity, during domestication and selection of different populations. These results will offer valuable resources for genomic studies and genetic improvement in melon.

Genome-wide identification of SAMS gene family in Cucurbitaceae and the role of ClSAMS1 in watermelon tolerance to abiotic stress.

S-Adenosyl-L-methionine (SAM) is widely involved in plant growth, development, and abiotic stress response. SAM synthetase (SAMS) is the key enzyme that catalyzes the synthesis of SAM from methionine and ATP. However, the SAMS gene family has not been identified and their functions have not been characterized in most Cucurbitaceae plants. Here, a total of 30 SAMS genes were identified in nine Cucurbitaceae species and they were categorized into 3 subfamilies. Physicochemical properties and gene structure analysis showed that the SAMS protein members are tightly conserved. Further analysis of the cis-regulatory elements (CREs) of SAMS genes' promoter implied their potential roles in stress tolerance. To further understand the molecular functions of SAMS genes, watermelon SAMSs (ClSAMSs) were chosen to analyze the expression patterns in different tissues and under various abiotic stress and hormone responses. Among the investigated genes, ClSAMS1 expression was observed in all tissues and found to be up-regulated by abiotic stresses including salt, cold and drought treatments as well as exogenous hormone treatments including ETH, SA, MeJA and ABA. Furthermore, knockdown of ClSAMS1 via virus-induced gene silencing (VIGS) decreased SAM contents in watermelon seedings. The pTRSV2-ClSAMS1 plants showed reduced susceptibility to drought, cold and NaCl stress, indicating a positive role of ClSAMS1 in abiotic stresses tolerance. Those results provided candidate SAMS genes to regulate plant resistance against abiotic stresses in Cucurbitaceae plants.

Post-harvest quality of melon accessions subjected to salinity.

The objective was to evaluate the behavior of melon genotypes (Cucumis melo L.) in the physical, chemical and biochemical quality of melon fruits as a function of electrical conductivity irrigation water levels (ECw). The experimental design adopted was randomized blocks in a 5 x 3 factorial scheme with five replications. The first factor was represented by five salinity levels (0.5, 1.5, 3.0, 4.5, and 6.0 dS m-1) and the second factor by accessions A35, and A24, and the hybrid Sancho. The physical, chemical and biochemical variables showed a reduction in production, with smaller fruits, with less weight, smaller cavity, with increased pulp thickness for Sancho. Vitamin C and yellow flavonoids increased indicating antioxidant power against ROS. The genotypes showed similar post-harvest behavior, however, the hybrid Sancho stood out over the others, possibly because it is an improved material. Accession A24 presented physiological and biochemical responses that classify it as intolerant.