Cucurbitaceae Species Research Articles

Genome-Wide Identification of Two-Component System Genes in Cucurbitaceae Crops and Expression Profiling Analyses in Cucumber.

Cucumber and watermelon, which belong to Cucurbitaceae family, are economically important cultivated crops worldwide. However, these crops are vulnerable to various adverse environments. Two-component system (TCS), consisting of histidine kinases (HKs), phosphotransfers (HPs), and response regulator proteins (RRs), plays important roles in various plant developmental processes and signaling transduction in responses to a wide range of biotic and abiotic stresses. No systematic investigation has been conducted on TCS genes in Cucurbitaceae species. Based on the completion of the cucumber and watermelon genome draft, we identified 46 and 49 TCS genes in cucumber and watermelon, respectively. The cucumber TCS members included 18 HK(L)s, 7 HPs, and 21 RRs, whereas the watermelon TCS system consisted of 19 HK(L)s, 6 HPs, and 24 RRs. The sequences and domains of TCS members from these two species were highly conserved. Gene duplication events occurred rarely, which might have resulted from the absence of recent whole-genome duplication event in these two Cucurbitaceae crops. Numerous stress- and hormone-responsive cis-elements were detected in the putative promoter regions of the cucumber TCS genes. Meanwhile, quantitative real-time PCR indicated that most of the TCS genes in cucumber were specifically or preferentially expressed in certain tissues or organs, especially in the early developing fruit. Some TCS genes exhibited diverse patterns of gene expression in response to abiotic stresses as well as exogenous trans-zeatin (ZT) and abscisic acid (ABA) treatment, suggesting that TCS genes might play significant roles in responses to various abiotic stresses and hormones in Cucurbitaceae crops.

Nutritional Analysis of Selected Cucurbitaceae Species

The global consumption of conventional feed resources is presently close to production, therefore the need to search for alternative cum additional feed ingredients become imperative. Cucurbitaceae are flowering plants that occur in the tropical and sub-tropical vegetation, primarily in rainforest, vine thickets and sparsely vegetated rocky outcrops. This study explored the nutritional potential of the seeds of six selected Cucurbitaceae species: Cucurbita pepo, Cucumeropsis manii, Luffa cylindrica, Lagenaria scicereria, Adenopus breviflorus and Citrullus lanatus as feed resource. Pods of the six Cucurbitaceae species were from major markets across various parts of Oyo State, Nigeria. Results from the proximate analysis of the seeds revealed that there were significant (p<0.05) differences among the samples in all the parameters (moisture content, crude fibre, ash, protein, carbohydrate and fat) considered. Lagenaria sicereria recorded the highest values in crude protein, fat and ash content of 27.80%, 48.75% and 4.25% respectively while it had the least percentage moisture content (7.30%). Percentage carbohydrate content was highest in Luffa cylindrica (22.20%). Cucurbitaceae species could serve as an alternative feed stuff in animal nutrition when supplemented with other materials.

Comparative anatomy of tendril and fruit stalk in Curcubitaceae Juss. from Nigeria

Comparative anatomy of the fruit stalk and tendril of nine (9) species representing 8 genera of Cucurbits from Nigeria has been carried out to complement the existing taxonomic data on the family. Fresh plant materials from representative members of the genera Zehneria, Luffa, Momordica, Coccinnia, Telfairia, Cucurbita, Lagenaria and Cucumis collected from the wild during field trips to various parts of Nigeria were used for this study. The specimens were wax embedded, sectioned, stained and photographed with Leitz Diaplan photomicroscope fitted with Leica WILD MPS 52 camera. The findings of this study showed that there are similarities and variations in the shape, number and size of vascular bundles, nature of epidermis, layers and nature of sclerenchymatuous, chllenchymatuous and chlorenchymatuous cells in the fruit stalk and tendril could be used to delimit the species of Cucurbitaceae in Nigeria. The variation in number and layers of these tissues among the species studied include vascular bundles (4 – 22 in fruit stalk, 4 – 10 in tendril), sclerenchymatuous cells (1 -8 layers in both tendril and fruit stalk), chlorenchymatuous cells (1 – 8 layers in both tendril and fruit stalk) and collenchymatuous cells (1 – 6 layers in friut stalks, 2 – 6 layers in tendrils). Druses and prismatic crystals were observed among the species and the taxonomic implications of these features are discussed and represent the first report on the anatomy of fruit stalk of these cucurbits from Nigeria. © 2015 International Formulae Group. All rights reserved. Keywords: Anatomy, Cucurbitaceae, fruit stalk, Parenchyma, Sclerenchyma, tendril

YUCCA type auxin biosynthesis genes encoding flavin monooxygenases in melon: Genome-wide identification and developmental expression analysis

Auxin, the first plant hormone identified more than 80years ago, is critical for nearly all aspects of plant life. As its diverse action and signaling in plants, auxin biosynthesis also has manifold facets. Recently, a simple two-step pathway of auxin biosynthesis called the TAA/YUC pathway has been proposed to be the main source of IAA in plants. Melon, a global crop, holds a key position in the Cucurbitaceae family for its high economic value and as a model to study biologically relevant characters. Here, we identified the YUCCA (YUC) family in this model of genetic system for Cucurbitaceae species. The genome of melon contains at least 9 loci for YUC-like FMOs and 7 members of the family have been successfully isolated in this study. Quantitative RT-PCR analysis shows that CmYUCs are differentially expressed in nearly all melon young organs. All seven CmYUCs were found to be expressed in certain stage(s) of melon fruits. Of the family, CmYUC6 and CmYUC11 are quite noticeable due to their high expression in seeds and mesocarp of fruits, respectively. In sum, this work supports that the TAA/YUC pathway to IAA may have a role in melon fruit development.

Differential heterochromatin distribution, flow cytometric genome size and meiotic behavior of chromosomes in three Cucurbitaceae species

Basic cytogenetic investigation of economically important members of Cucurbitaceae is a prerequisite to understand their genetic architecture. The study reports detailed chromosome morphometric analyses with fluorescence banding technique, differential distribution of heterochromatin, flow cytometric nuclear DNA contents and meiotic behavior of the native populations of Benincasa hispida, Luffa cylindrica and Trichosanthes dioica in India. In spite of frequent vegetative propagation, different populations of these cultivated cucurbits show regular genetic processes evident from stable chromosome counts, nuclear DNA sizes, ploidy levels and regular meiotic behavior. Distal CMA+ve signals have been scored in two pairs of chromosomes in B. hispida and four pairs of chromosomes in L. cylindrica, representing the GC rich heterochromatic portions in genomes. The presence of terminal DAPI+ve bands in the chromosomes of male and female populations of T. dioica indicates the predominance of AT rich heterochromatin. In addition to DAPI bands, terminal CMA+ve bands in the female plants of T. dioica depict the chromosomal signs of sexual differentiation in this species. The existence of rod bivalent in meiosis of male plants facilitates further approach to characterize the genetics of chromosomal evolution since gross similarity in genome size and karyotypic features of male and female plants advocates genic control of sexual dimorphism in T. dioica.

Resurgence of Pseudoperonospora cubensis: The Causal Agent of Cucurbit Downy Mildew.

The downy mildew pathogen, Pseudoperonospora cubensis, which infects plant species in the family Cucurbitaceae, has undergone major changes during the last decade. Disease severity and epidemics are far more destructive than previously reported, and new genotypes, races, pathotypes, and mating types of the pathogen have been discovered in populations from around the globe as a result of the resurgence of the disease. Consequently, disease control through host plant resistance and fungicide applications has become more complex. This resurgence of P. cubensis offers challenges to scientists in many research areas including pathogen biology, epidemiology and dispersal, population structure and population genetics, host preference, host-pathogen interactions and gene expression, genetic host plant resistance, inheritance of host and fungicide resistance, and chemical disease control. This review serves to summarize the current status of this major pathogen and to guide future management and research efforts within this pathosystem.

PRODUCTION OF PUMPKIN POWDER AND IT'S UTILIZATION IN BAKERY PRODUCTS DEVELOPMENT: A REVIEW

Pumpkin covers a wide number of species of the family Cucurbitaceae, most of them with actual or potential economic value. Dehydration of pumpkin for producing pumpkin powder can be a useful technique to preserve the pumpkin and obtain new processed food products from dehydrated pumpkin. The review focused on production of pumpkin powder by various drying techniques and incorporation of pumpkin powder in various bakery products as a replacement of wheat flour and also fortification of phytochemicals . The review also focused on physico chemical analysis of the pumpkin powder and pumpkin based bakery products and sensory analysis of the pumpkin based products. The replacement level of wheat flour by pumpkin flour in various bakery products determined by various researcher also focused in this review. The researchers reported that increasing the pumpkin flour concentration had an adverse effect on sensory analysis and colour. The researcher reported that pumpkin flour with low to medium concentration was found to be more acceptable from sensory point of view and thereafter sensory score was reduced. Adding more pumpkin powder increased the level of carotene in the bakery products. Phytochemicals were increased with increasing pumpkin flower concentration in bakery products.

Extreme expansion of NBS-encoding genes in Rosaceae.

BackgroundNucleotide binding site leucine-rich repeats (NBS-LRR) genes encode a large class of disease resistance (R) proteins in plants. Extensive studies have been carried out to identify and investigate NBS-encoding gene families in many important plant species. However, no comprehensive research into NBS-encoding genes in the Rosaceae has been performed.ResultsIn this study, five whole-genome sequenced Rosaceae species, including apple, pear, peach, mei, and strawberry, were analyzed to investigate the evolutionary pattern of NBS-encoding genes and to compare them to those of three Cucurbitaceae species, cucumber, melon, and watermelon. Considerable differences in the copy number of NBS-encoding genes were observed between Cucurbitaceae and Rosaceae species. In Rosaceae species, a large number and a high proportion of NBS-encoding genes were observed in peach (437, 1.52%), mei (475, 1.51%), strawberry (346, 1.05%) and pear (617, 1.44%), and apple contained a whopping 1303 (2.05%) NBS-encoding genes, which might be the highest number of R-genes in all of these reported diploid plant. However, no more than 100 NBS-encoding genes were identified in Cucurbitaceae. Many more species-specific gene families were classified and detected with the signature of positive selection in Rosaceae species, especially in the apple genome.ConclusionsTaken together, our findings indicate that NBS-encoding genes in Rosaceae, especially in apple, have undergone extreme expansion and rapid adaptive evolution. Useful information was provided for further research on the evolutionary mode of disease resistance genes in Rosaceae crops.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0208-x) contains supplementary material, which is available to authorized users.

Partially resistant Cucurbita pepo showed late onset of the Zucchini yellow mosaic virus infection due to rapid activation of defense mechanisms as compared to susceptible cultivar.

Zucchini yellow mosaic virus (ZYMV) is an emerging viral pathogen in cucurbit-growing areas wordwide. Infection causes significant yield losses in several species of the family Cucurbitaceae. To identify proteins potentially involved with resistance toward infection by the severe ZYMV-H isolate, two Cucurbita pepo cultivars (Zelena susceptible and Jaguar partially resistant) were analyzed using a two-dimensional gel electrophoresis-based proteomic approach. Initial symptoms on leaves (clearing veins) developed 6–7 days post-inoculation (dpi) in the susceptible C. pepo cv. Zelena. In contrast, similar symptoms appeared on the leaves of partially resistant C. pepo cv. Jaguar only after 15 dpi. This finding was confirmed by immune-blot analysis which showed higher levels of viral proteins at 6 dpi in the susceptible cultivar. Leaf proteome analyses revealed 28 and 31 spots differentially abundant between cultivars at 6 and 15 dpi, respectively. The variance early in infection can be attributed to a rapid activation of proteins involved with redox homeostasis in the partially resistant cultivar. Changes in the proteome of the susceptible cultivar are related to the cytoskeleton and photosynthesis.

Genome-wide analysis and expression of the calcium-dependent protein kinase gene family in cucumber.

Calcium-dependent protein kinases (CDPKs) are multi-functional proteins that combine calcium-binding and signaling capabilities within a single gene product. Current studies have shown that the CDPKs regulate numerous growth and developmental processes and biotic and abiotic stress responses. Nonetheless, knowledge concerning the specific expression patterns and evolutionary history of the CDPK family in cucumber (Cucumis sativus L.) remains very limited. We, therefore, investigated the phylogenetic relationships and expression profiles of the 19 CDPK genes identified in the cucumber genome sequence, resolving them into four subfamilies based on a phylogenetic tree and gene structures. Tissue-specific expression profiles suggest that cucumber CDPK genes are involved in cucumber tissue development. An expression analysis based on qRT-PCR indicated that cucumber CDPK genes are extensively involved in abscisic acid, salt, cold, drought, heat, and waterlogging responses, possibly by different mechanisms. The fates of two paralogs after divergence were also investigated, suggesting subfunctionalization and neofunctionalization during evolution. These observations lay an important foundation for functional and evolutionary analyses of the CDPK gene family in cucurbitaceae species.

Characterization of Two Cucurbitaceae Species Seeds Flour and its Utilization in Biscuits Processing

The objectives of this study were to characterize and utilize the seeds flour of two species of cucurbitaceae with wheat flour for biscuits making. Cucurbitaceae species used were (Tibish) Cucumis melo agrestis and (Fagoos) Cucumis metuliferus obtained from Khartoum and Darfor, respectively, season 2011/12. The cucurbitaceae seeds were milled into flour by warring blender then proximate analysis, minerals composition and protein fractions were conducted. Biscuits were made from cucurbitaceae seeds flour and wheat flour in ratios 5:95, 10:90 and 15:85 respectively. Organolyptic quality of biscuits was investigated. Proximate analysis of the seeds flour revealed that the crude protein was 26.1 and 27.0% respectively, crude fat was 26 and 33.3%, crude fiber 24.8 and 25%, ash 2.8 and 5.3 respectively. The results proved that the two species contained height amount of minerals especially iron (7.4 mg/100 g and 5.7 mg/100). Protein fractions showed that the water- and salt-soluble proteins (albumin and globulin) of the two species of cucurbitaceae seeds flour were the ranges of (32.4, 35.1) and 26.57 to 28.7% respectively, prolamin and glutelin fractions were (10.9, 11.15) and (23.85, 19.7%), respectively. The highest spread ratio of the wheat biscuits and composite cucurbitaceae seeds flour biscuits was observed in 5%Fagoos (3.63) and the lowest in 15% Tibish (4.07). The mean quality scores for the overall acceptability was highest in 15%Tibish (7.87) and the lowest score of (4.5) was obtained by 5% Fagoos. In conclusion the results revealed that the good nutritional value of seeds flour reinforced the usefulness of cucurbitaceae seeds flour in biscuits making.

Soil Type and Growing Conditions Influence Uptake and Translocation of Organochlorine (Chlordecone) by Cucurbitaceae Species

Chlordecone (CLD), an organochlorine insecticide, and other persistent organic pollutants continue to contaminate the environment worldwide and have adverse effects on human health through food exposure. Cucurbitaceae take up weathered hydrophobic pollutants from the soil and translocate them to their shoots. As Cucurbitaceae are an important part of the diet in the French West Indies, they are among the main contributors to total dietary intake of CLD. We analyzed the contamination by CLDs (CLD and 5b-hydroCLD) of four cucurbits grown in the field and/or in the greenhouse. Different physiological (crop species) and environmental (soil type, growth conditions) variables were shown to influence uptake of the pollutant from the soil by the crop. Cucurbita species (zucchini and pumpkin) were more contaminated than Cucumis sativus (cucumber), and Sechium edule (christophine or chayote) translocated CLDs to fruits very poorly compared with cucumber and pumpkin. Greenhouse conditions and non-allophanic (nitisols and ferralsols) soils favored plant contamination more than field conditions and allophanic soils (andosols).

Characterization and chromosomal organization of Ty1-copia retrotransposons in wax gourd

Wax gourd (2n=2x=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.

Attracting mutualists and antagonists: plant trait variation explains the distribution of specialist floral herbivores and pollinators on crops and wild gourds.

• Floral traits play important roles in pollinator attraction and defense against floral herbivory. However, plants may experience trade-offs between conspicuousness to pollinators and herbivore attraction. Comparative studies provide an excellent framework to examine the role of multiple traits shaping mutualist and antagonist interactions.• To assess whether putative defensive and attractive traits predict species interactions, we grew 20 different Cucurbitaceae species and varieties in the field to measure interactions with pollinators and herbivores and in the greenhouse to assess trait variation. Cucurbits are characterized by the production of cucurbitacins, bitter nonvolatile terpenoids that are effective against generalist herbivores but can attract specialist beetles. We determined whether plant traits such as cucurbitacins predict herbivore resistance and pollinator attraction using an information-theoretic approach.• Mutualists and floral antagonists were attracted to the same cucurbit varieties once they flowered. However, rather than cucurbitacin concentration, we found that the size of the flower and volatile emissions of floral sesquiterpenoids explained both pollinator and floral herbivore visitation preference across cucurbit taxa. This pattern held across cucurbit taxa and within the Cucurbita genus.• Surprisingly, floral sesquiterpenoid volatiles, which are associated with direct defense, indirect defense, and attraction, rather than defense traits such as cucurbitacins, appeared to drive interactions with both pollinators and floral herbivores across cucurbit taxa. Identifying the relevant plant traits for attraction and deterrence is important in this economically valuable crop, particularly if pollinators and floral herbivores use the same plant traits as cues.

Tolerance of Watermelon Seedlings to Low-temperature Chilling Injury

Watermelon [Citrullus lanatus (Thunb.) Matsum. &amp; Nakai] is one of the Cucurbitaceae species and subtropical crops that exhibit chilling injury (CI) when exposed to low temperatures. Watermelon seedlings were tested for chilling tolerance using methods modified from cucumber. Three experiments were conducted using different combinations of chilling durations of 6, 12, 24, or 36 hours and chilling temperatures of 2 or 4 °C. Watermelon seedlings were more resistant to low temperatures than cucumber seedlings, so it was necessary to use long chilling durations to induce significant foliar damage. A diverse set of 16 watermelon cultigens was tested: Allsweet, Black Diamond, Chubby Gray, Charlee, Charleston Gray, Dixielee, Golden, Golden Honey, New Winter, NH Midget, Sugar Baby, Sugarlee, Sunshade, PI 189225, PI 244018, and PI 595203. Experiments were conducted in a controlled environment with a light intensity of 500 mmol·m−2·s−1 photosynthetic photon flux density (PPFD). Optimal conditions for chilling treatment were 36 hours at 4 °C or 24 hours at 2 °C. The most resistant cultigen was PI 244018, and the most susceptible cultigens were NH Midget and Golden.

Nutritional Properties of the Leaf, Seed and Pericarp of the fruit of four cucurbitaceae Species from South- East Nigeria

Nutritional Properties of the Leaf, Seed and Pericarp of the fruit of four cucurbitaceae Species from South- East Nigeria

Phylogeny of Cucurbitaceae species in Korea based on 5S rDNA non-transcribed spacer

The 5S rDNA coding region and its spacer have been successfully utilized in phylogenetic studies of plants. However, it has not been utilized in the phylogenetic analysis of Cucurbitaceae. Here, we obtained the 5S rDNA sequences of 12 Cucurbitaceae species by direct PCR or cloning. The 5S rDNA sequences ranged from 275 to 359 bp, and the coding regions of all species were 120 bp long, except for that of Cucurbita, which was 119 bp. Some genus-specific SNPs were observed in the coding regions of Cucurbita, Lagenaria, Melothria, and Tricosanthes. The GC content of the coding regions was generally higher than that of the NTS regions, and the difference in GC content between the coding and NTS regions varied among species, with Gynostemma pentaphyllum having the greatest difference of 20.3. The phylogenetic trees generated using maximum parsimony and maximum likelihood were congruent and well supported by the recently published classification of Cucurbitaceae. These results demonstrated the utility of the 5S rDNA sequence in inferring phylogenetic relationships among 12 Cucurbitaceae species, and its utility could be extended by using a greater number of species in future studies.

GENETIC ANALYSIS IN SOME Cucurbitaceae PLANTS

The present study was carried out to analysis the genetic differentiation between seven species of Cucurbitaceae by using biochemical and molecular markers. Analysis of SDS-PAGE of soluble proteins for the seven Cucurbitaceae species such as: Cucumis melo L., Citrullus lanatus L., Citrullus sativtus L., Citrullus colocynthis L., Cucumis prophetarum, Cucurbita pepo L. and Corallocarpus schempri, revealed polymorphism of 98%. Seven isozyme systems including Acp (acid phosphatase), Adh (alchol dehydrogenase), α- and β-Est (esterases), Ao (Aldehyde oxidase), Mdh (malate dehydrogenase) and Prx (peroxidase) successfully indicated genetic variability estimated as 70% polymorphism discriminating between seven Cucurbitaceae species. Six preselected RAPD primers were used in the present study to discriminating between the seven Cucurbitaceae species. RAPD markers revealed (99%) polymorphism that is considerable the highest polymorphism among seven Cucurbitaceae species and the lowest similarity (1%), ISSR markers revealed (98%) polymorphism and finally, AFLP gave (54.8%) of polymorphism with the lowest polymorphism indicating the highest similarity (46%). Based on the results and polymorphism percentages, RAPD, ISSR, SDS-PAGE of soluble proteins, isozymes and AFLP were useful molecular and biochemical tools to discriminate between the seven Cucurbitaceae species.

Frequent loss of lineages and deficient duplications accounted for low copy number of disease resistance genes in Cucurbitaceae

BackgroundThe sequenced genomes of cucumber, melon and watermelon have relatively few R-genes, with 70, 75 and 55 copies only, respectively. The mechanism for low copy number of R-genes in Cucurbitaceae genomes remains unknown.ResultsManual annotation of R-genes in the sequenced genomes of Cucurbitaceae species showed that approximately half of them are pseudogenes. Comparative analysis of R-genes showed frequent loss of R-gene loci in different Cucurbitaceae species. Phylogenetic analysis, data mining and PCR cloning using degenerate primers indicated that Cucurbitaceae has limited number of R-gene lineages (subfamilies). Comparison between R-genes from Cucurbitaceae and those from poplar and soybean suggested frequent loss of R-gene lineages in Cucurbitaceae. Furthermore, the average number of R-genes per lineage in Cucurbitaceae species is approximately 1/3 that in soybean or poplar. Therefore, both loss of lineages and deficient duplications in extant lineages accounted for the low copy number of R-genes in Cucurbitaceae. No extensive chimeras of R-genes were found in any of the sequenced Cucurbitaceae genomes. Nevertheless, one lineage of R-genes from Trichosanthes kirilowii, a wild Cucurbitaceae species, exhibits chimeric structures caused by gene conversions, and may contain a large number of distinct R-genes in natural populations.ConclusionsCucurbitaceae species have limited number of R-gene lineages and each genome harbors relatively few R-genes. The scarcity of R-genes in Cucurbitaceae species was due to frequent loss of R-gene lineages and infrequent duplications in extant lineages. The evolutionary mechanisms for large variation of copy number of R-genes in different plant species were discussed.

Genome-wide analysis of NBS-encoding disease resistance genes in Cucumis sativusand phylogenetic study of NBS-encoding genes in Cucurbitaceae crops

BackgroundPlant nucleotide-binding site (NBS)-leucine-rich repeat (LRR) proteins encoded by resistance genes play an important role in the responses of plants to various pathogens, including viruses, bacteria, fungi, and nematodes. In this study, a comprehensive analysis of NBS-encoding genes within the whole cucumber genome was performed, and the phylogenetic relationships of NBS-encoding resistance gene homologues (RGHs) belonging to six species in five genera of Cucurbitaceae crops were compared.ResultsCucumber has relatively few NBS-encoding genes. Nevertheless, cucumber maintains genes belonging to both Toll/interleukine-1 receptor (TIR) and CC (coiled-coil) families. Eight commonly conserved motifs have been established in these two families which support the grouping into TIR and CC families. Moreover, three additional conserved motifs, namely, CNBS-1, CNBS-2 and TNBS-1, have been identified in sequences from CC and TIR families. Analyses of exon/intron configurations revealed that some intron loss or gain events occurred during the structural evolution between the two families. Phylogenetic analyses revealed that gene duplication, sequence divergence, and gene loss were proposed as the major modes of evolution of NBS-encoding genes in Cucurbitaceae species. Compared with NBS-encoding sequences from the Arabidopsis thaliana genome, the remaining seven TIR familes of NBS proteins and RGHs from Cucurbitaceae species have been shown to be phylogenetically distinct from the TIR family of NBS-encoding genes in Arabidopsis, except for two subfamilies (TIR4 and TIR9). On the other hand, in the CC-NBS family, they grouped closely with the CC family of NBS-encoding genes in Arabidopsis. Thus, the NBS-encoding genes in Cucurbitaceae crops are shown to be ancient, and NBS-encoding gene expansions (especially the TIR family) may have occurred before the divergence of Cucurbitaceae and Arabidopsis.ConclusionThe results of this paper will provide a genomic framework for the further isolation of candidate disease resistance NBS-encoding genes in cucumber, and contribute to the understanding of the evolutionary mode of NBS-encoding genes in Cucurbitaceae crops.