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Background: Rootstocks can improve the chilling tolerance of grafted cucumbers, but their effectiveness varies. Rootstocks with strong de-blooming capacity may result in lower chilling tolerance of grafted cucumbers compared to those with weak de-blooming capacity, while also reducing the silicon absorption. However, it remains unclear whether this reduction in chilling tolerance is due to differences in rootstock genotypes or the reduction in silicon absorption., Results: The chilling tolerance of cucumber seedlings was improved by using rootstocks and silicon nutrition. Rootstocks had a more significant effect than silicon nutrition, and the weak de-blooming rootstock 'Yunnan figleaf gourd' was superior to the strong de-blooming rootstock 'Huangchenggen No. 2'. Compared to self-rooted cucumber, twelve miRNAs were regulated by two rootstocks, including seven identical miRNAs (novel-mir23, novel-mir26, novel-mir30, novel-mir37, novel-mir46, miR395a and miR398a-3p) and five different miRNAs (novel-mir32, novel-mir38, novel-mir65, novel-mir78 and miR397a). Notably, four of these miRNAs (novel-mir38, novel-mir65, novel-mir78 and miR397a) were only identified in 'Yunnan figleaf gourd'-grafted cucumbers. Furthermore, six miRNAs (miR168a-5p, miR390a-5p, novel-mir26, novel-mir55, novel-mir67 and novel-mir70) were found to be responsive to exogenous silicon. Target gene prediction for 20 miRNAs resulted in 520 genes. Functional analysis of these target genes showed that 'Yunnan figleaf gourd' improves the chilling tolerance of cucumber by regulating laccase synthesis and sulfate metabolism, while 'Huangchenggen No. 2' and exogenous silicon reduced chilling stress damage to cucumber by regulating ROS scavenging and protein protection, respectively., Conclusion: Among the identified miRNAs, novel-mir46 and miR398a-3p were found in cucumbers in response to chilling stress and two types of rootstocks. However, no identical miRNAs were identified in response to chilling stress and silicon. In addition, the differential expression of novel-mir38, novel-mir65, novel-mir78 and miR397a may be one of the important reasons for the differences in chilling tolerance of grafted cucumbers caused by two types of rootstocks., (© 2023. The Author(s).)

With the increasing reliance on intensive arable agriculture, analysis of the problems associated with continuous cropping has become a global research focus. Here, high-throughput sequencing and nontargeted metabolomics were used to evaluate the responses of soil microbial community structure and soil metabolic function to continuous cucumber cultivation (from 1 to 18 years of continuous cultivation) in greenhouses. Continuous cucumber cropping resulted in increased soil nutrient concentrations, but decreased concentrations of available nutrients. The abundance of several bacterial genera associated with nutrient cycling, such as Bacillus and Sphingomonas, was reduced by continuous cucumber cultivation. The abundance of several beneficial fungal genera, including pathogen antagonists (e.g. Chaetomium, Mortierella, Aspergillus, and Penicillium), were found to gradually decrease in response to the increased duration of continuous cropping. 3-amino-2-naphthoic acid and L-valine increased initially and then decreased as the cropping continued, which were related to fatty acid metabolism and amino acid biosynthesis. We also confirmed a close association between microbial community structure and soil metabolites. This study linked the changes in microbial community structure and metabolites in the rhizosphere soil and provided new insights into soil-microbial interactions in continuous cucumber culture systems., (© The Author(s) 2022. Published by Oxford University Press on behalf of FEMS.)

Fruit shape, an important agronomic trait of cucumber ( Cucumis sativus L.), is tightly controlled by a series of genes such as CsSUN , a homologue of SlSUN that is responsible for the tomato ( Solanum lycopersicum ) fruit shape via the modulation of cell division. However, the direct genetic evidence about the CsSUN -mediated regulation of fruit shape is still scarce, limiting our mechanistic understanding of the biological functions of CsSUN . Here, we introduced CsSUN into the round-fruited tomato inbred line 'SN1' (wild type, WT) via the Agrobacterium tumefaciens -mediated method. The high and constitutive expression of CsSUN was revealed by real-time PCR in all the tested tissues of the transgenic plants, especially in the fruits and ovaries. Phenotypic analyses showed that the ectopic expression of CsSUN increased fruit length while it decreased fruit diameter, thus leading to the enhanced fruit shape index in the transgenic tomato lines relative to the WT. Additionally, the reduction in the seed size and seed-setting rate and the stimulation of seed germination were observed in the CsSUN -expressed tomato. A histological survey demonstrated that the elongated fruits were mainly derived from the significant increasing of the longitudinal cell number, which compensated for the negative effects of decreased cell area in the central columellae. These observations are different from action mode of SlSUN , thus shedding new insights into the SUN -mediated regulation of fruit shape.

Cucumber ( Cucumis sativus L.) is an economically important vegetable crop with the unique growth habit and typical trailing shoot architecture of Cucurbitaceae. Elucidating the regulatory mechanisms of growth and development is significant for improving quality and productivity in cucumber. Here we isolated a spontaneous cucumber mutant organ development defective 1 ( odd1 ) with multiple morphological changes including root, plant stature, stem, leaf, male and female flowers, as well as fruit. Anatomical and cytological analyses demonstrated that both cell size and number decreased, and the shoot apical meristem (SAM) was smaller in odd1 compared with WT. Pollen vigor and germination assays and cross tests revealed that odd1 is female sterile, which may be caused by the absence of ovules. Genetic analysis showed that odd1 is a recessive single gene mutant. Using the MutMap strategy, the odd1 gene was found to be located on chromosome 5. Integrated profiling of transcriptome and proteome indicated that the different expression genes related to hormones and SAM maintenance might be the reason for the phenotypic changes of odd1 . These results expanded the insight into the molecular regulation of organ growth and development and provided a comprehensive reference map for further studies in cucumber.

Fulvic acid (FA) participates in the regulation of drought stress tolerance in plants, but the underlying mechanisms remain unclear. We carried out an experiment with cucumber cultivar 'Jinyou 35' as the test material and the polyethylene glycol (PEG-6000) being used to simulate drought stress. The concentration effect of FA on drought alleviation of cucumber as well as the effect of FA on photosynthetic enzymes activities, chloroplast ultrastructure, fluorescence parameters, water use efficiency, yield and quality of cucumber plants were studied through spraying FA with different concentrations (0, 100, 300, 500, 700 and 900 mg·L -1 ). The results showed that FA with different concentrations significantly promoted the relative water content and leaf area and decreased drought injure index as well as the electrolyte leakage and malondialdehyde (MDA) content, compared with the control (0 mg·L -1 ) under drought stress. The mitigative effect of FA increased first and then decreased with the increases of FA concentration, with 700 mg·L -1 FA showing the best effect. FA significantly enhanced the chlorophyll content, Rubiasco and Rubisco activase (RCA) activities and gene expression, net photosynthesis ( P n ), maximal photochemical efficiency of PSⅡin darkness, actual photochemical efficiency, absorbed light energy per unit area, captured light energy per unit area, quantum yield of electron transport and PSⅠ activity, decreased the increase of K point and maintained chloroplast ultrastructure. The experiment in solar-greenhouse showed that FA obviously increased water use efficiency, promoted dry matter accumulation as well as the contents of Vc, soluble sugar, soluble protein and free amino acid, and decreased tannin content. Our results suggested that FA could improve the yield and quality of cucumber in solar greenhouse under drought stress.

Cucumber is an economically important crop cultivated worldwide. Gibberellins (GAs) play important roles in the development of lateral roots (LRs), which are critical for plant stress tolerance and productivity. Therefore, it is of great importance for cucumber production to study the role of GAs in LR development. Here, the results showed that GAs regulated cucumber LR development in a concentration-dependent manner. Treatment with 1, 10, 50 and 100 μM GA 3 significantly increased secondary root length, tertiary root number and length. Of these, 50 μM GA 3 treatment had strong effects on increasing root dry weight and the root/shoot dry weight ratio. Pairwise comparisons identified 417 down-regulated genes enriched for GA metabolism-related processes and 447 up-regulated genes enriched for cell wall metabolism-related processes in GA 3 -treated roots. A total of 3523 non-redundant DEGs were identified in our RNA-Seq data through pairwise comparisons and linear factorial modeling. Of these, most of the genes involved in auxin and cell wall metabolisms were up-regulated in GA 3 -treated roots. Our findings not only shed light on LR regulation mediated by GA but also offer an important resource for functional studies of candidate genes putatively involved in the regulation of LR development in cucumber and other crops., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Root rot caused by Fusarium solani is one of the most common fungal diseases in cucumber ( Cucumis sativus ). Proanthocyanidins (PAs) are known to play important roles in inhibiting the growth of phytopathogens. In addition, CsMYB60 is a known positive regulator of flavonol and PA biosynthesis in cucumber. However, it remains unclear that whether PAs can inhibit the growth of F. solani and whether CsMYB60 serves as a target gene for increasing resistance to phytopathogens in cucumber. In this study, we demonstrated that PAs (or their building block, catechin) could increase the resistance of cucumber seedlings to F. solani both in vitro and in vivo. The addition of catechins, or crude leaf extracts treated with different concentrations of catechins in culture medium, could significantly inhibit the hyphal growth of F. solani . On the other hand, cucumber seedlings treated with catechins showed higher resistance to F. solani than the seedlings of control group. Moreover, transgenic cucumber seedlings overexpressing CsMYB60 , with the observed accumulation of PAs, were more resistant to F. solani than the nontransgenic siblings. Therefore, our results suggest that PAs (or catechin) can serve as a biological control agent to protect cucumber plants from the infection of F. solani . More importantly, CsMYB60 holds great promise as a target gene to confer disease resistance during the molecular breeding in cucumber.

Long-term continuous cropping is a common practice in facility vegetable production, which has an adverse effect on cucumber yield and quality. Soil fungi are of great significance for creating a normal soil ecological environment. However, the impact of continuous cropping on cucumber quality and soil fungal community has yet to be understood. In this study, we evaluated the effects of continuous cropping on cucumber using high-throughput sequencing technology. The results showed that the extension of continuous cropping would increase nitrate and total acidity of cucumber, while the contents of vitamin C (VC), soluble sugar, and protein were decreased. The increase of continuous cropping duration also reduced the fungal diversity of the cucumber soil. For example, the activity of three dominant fungal phylums, Ascomycota, Aphelidiomycota, and Basidiomycota, decreased with the extension of planting years. The relative abundance of the two fungi species (Remersonia&#95;thermophila, Mortierella&#95;oligospora) was negatively correlated with the contents of available phosphorus and available potassium (P < 0.05). Redundancy analysis (RDA) found that soil electrical conductivity (EC), available phosphorus (AP), and pH accounted for the top three major factors of fungal community structure changes. The soil fungal community was changed during the continuous cucumber cultivation, which might be the result of the combined cultivation period of cucumber and excessive application of chemical fertilizers (nitrogen fertilizer, phosphate fertilizer, etc.). Our study provides a theoretical basis for the understanding of the impact of continuous cropping in cucumber facilities.

Main Conclusion: We discovered a potential defense pathway of cucumber to downy mildew. The signaling that activates the pathways of ROS and lignin accumulation may play an important role in the defense response. Many resistance genes were identified by transcriptome analysis. Downy mildew (DM), caused by Pseudoperonospora cubensis, is one of the most destructive diseases and causes severe yield losses of cucumber. However, the genes and pathways involved in regulating DM resistance were still poorly understood. In our study, we observed that the highly sensitive inbred line 53 (IL53) exhibited more severe disease symptoms than the highly resistant inbred line 51 (IL51) under P. cubensis infection. Furthermore, lignin, limiting the germination and extension of P. cubensis, and H 2 O 2 , as a signaling molecule during the resistant process, were both shown to increase, indicating that the signaling that activates these pathways might be responsible for the resistance divergence between IL51 and IL53. Transcriptome analysis, using the resistant and susceptible pools in F 2 populations with IL51 and IL53 as parents, showed that a series of differentially expressed genes was involved in multiple functions of defense response: pathogen-associated molecular pattern recognition, signal transduction, reactive oxygen species and lignin accumulation, and transcription regulators. Combining physiological data with transcriptomes, we predicted a potential molecular mechanism of cucumber resistance to DM. Our research provided a foundation for further studies on the mechanism of cucumber resistance to DM.

Salicylic acid (SA) and hydrogen sulfide (H 2 S) have been proved to be multifunctional signal molecules to participate in the response of plants to abiotic stresses. However, it is still unclear whether there is interaction between SA and H 2 S in response to chilling intensity of cucumber seedlings. Here, we found SA was sensitive to chilling intensity. Under normal condition, NaHS (H 2 S donor) or removing endogenous H 2 S with hypotaurine (HT, a specific scavenger of H 2 S) and DL-propargylglycine (PAG, a specific inhibitor of H 2 S) has no effect on endogenous SA level; however, SA induced endogenous H 2 S content and activated the activities and mRNA level of L-/D-cysteine desulfhydrase (L-/D-CD), and inhibiting endogenous SA with paclobutrazol (PAC) or 2-aminoindan-2-phosphonic acid (AIP) blocked this effect, implying H 2 S may play a role after SA signal. Further studies showed that both SA and NaHS notably alleviated chilling injury, which was evidenced by lower electrolyte leakage (EL), MDA content, and ROS accumulation, compared with H 2 O treatment. Of note, SA and H 2 S improved the activities and mRNA level of antioxidant enzymes (SOD, POD, CAT, APX, and GR) as well as the contents of AsA and GSH. Additionally, the chilling-response genes (ICE, CBF1, and COR) were obviously upregulated by exogenous SA and NaHS. However, the positive effect of SA on chilling tolerance was inhibited by HT, whereas PAC or AIP did not affect NaHS-induced chilling tolerance. Taken together, the data reveals that H 2 S acts as a downstream signal of SA-induced chilling tolerance of cucumber via modulating antioxidant system and chilling-response genes.

Cucumber (Cucumis sativus) is one of the most widely cultivated vegetable crops in the world, and its yield is often reduced due to the infection of Botrytis cinerea (B. cinerea), which causes a serious disease. However, few genes involved in the response to B. cinerea have been identified in cucumber. In this study, we identified that CsWRKY10 plays a key role in the cucumber resistance to B. cinerea because that the overexpression of CsWRKY10 significantly increased the susceptibility to B. cinerea in cucumber. After the pathogen infection, the enzyme activities of catalase, superoxide dismutase and peroxidase in transgenic plants were affected, resulting in the decrease in reactive oxygen species (ROS) contents. In addition, the light microscopic images showed that overexpression of CsWRKY10 promoted the spore germination and mycelia elongation of B. cinerea in cucumber. Importantly, after B. cinerea infection, the contents of jasmonic acid (JA) are decreased, and the expression levels of JA- and salicylic acid- related defence genes significantly changed in transgenic plants. In contrast, overexpression of CsWRKY10 enhanced resistance to Corynespora cassiicola in cucumber. Collectively, this study indicated that CsWRKY10 negatively regulates the resistance of cucumber to B. cinerea by reducing the ROS contents and inhibiting the JA-mediated resistance signalling pathway, but strengthens resistance to Corynespora cassiicola., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: Cucumber (Cucumis sativus L.) is an economically important vegetable crop species. However, it is susceptible to various abiotic and biotic stresses. WRKY transcription factors play important roles in plant growth and development, particularly in the plant response to biotic and abiotic stresses. However, little is known about the expression pattern of WRKY genes under different stresses in cucumber., Results: In the present study, an analysis of the new assembly of the cucumber genome (v3.0) allowed the identification of 61 cucumber WRKY genes. Phylogenetic and synteny analyses were performed using related species to investigate the evolution of the cucumber WRKY genes. The 61 CsWRKYs were classified into three main groups, within which the gene structure and motif compositions were conserved. Tissue expression profiles of the WRKY genes demonstrated that 24 CsWRKY genes showed constitutive expression (FPKM > 1 in all samples), and some WRKY genes showed organ-specific expression, suggesting that these WRKYs might be important for plant growth and organ development in cucumber. Importantly, analysis of the CsWRKY gene expression patterns revealed that five CsWRKY genes strongly responded to both salt and heat stresses, 12 genes were observed to be expressed in response to infection from downy mildew and powdery mildew, and three CsWRKY genes simultaneously responded to all treatments analysed. Some CsWRKY genes were observed to be induced/repressed at different times after abiotic or biotic stress treatment, demonstrating that cucumber WRKY genes might play different roles during different stress responses and that their expression patterns vary in response to stresses., Conclusions: Sixty-one WRKY genes were identified in cucumber, and insight into their classification, evolution, and expression patterns was gained in this study. Responses to different abiotic and biotic stresses in cucumber were also investigated. Our results provide a better understanding of the function of CsWRKY genes in improving abiotic and biotic stress resistance in cucumber.

Cucumber fruit shape, a significant agronomic trait, is controlled by quantitative trait loci (QTLs). Feasibility of chromosome segment substitution lines (CSSLs) is well demonstrated to map QTLs, especially the minor-effect ones. To detect and identify QTLs with CSSLs can provide new insights into the underlying mechanisms regarding cucumber fruit shape. In the present study, 71 CSSLs were built from a population of backcross progeny (BC 4 F 2 ) by using RNS7 (a round-fruit cucumber) as the recurrent parent and CNS21 (a long-stick-fruit cucumber) as the donor parent in order to globally detect QTLs for cucumber fruit shape. With the aid of 114 InDel markers covering the whole cucumber genome, 21 QTLs were detected for fruit shape-related traits including ovary length, ovary diameter, ovary shape index, immature fruit length, immature fruit diameter, immature fruit shape index, mature fruit length, mature fruit diameter and mature fruit shape index, and 4 QTLs for other traits including fruit ground and flesh color, and seed size were detected as well. Together our results provide important resources for the subsequent theoretical and applied researches on cucumber fruit shape and other traits.

Background: The basic/helix-loop-helix (bHLH) transcription factor family exists in all three eukaryotic kingdoms as important participants in biological growth and development. To date, the comprehensive genomic and functional analyses of bHLH genes has not been reported in cucumber (Cucumis sativus L.)., Results: Here, a total of 142 bHLH genes were identified and classified into 32 subfamilies according to the conserved motifs, phylogenetic analysis and gene structures in cucumber. The sequences of CsbHLH proteins were highly conserved based on the results of multiple sequence alignment analyses. The chromosomal distribution, synteny analysis, and gene duplications of these 142 CsbHLHs were further analysed. Many elements related to stress responsiveness and plant hormones were present in the promoter regions of CsbHLH genes based on a cis-element analysis. By comparing the phylogeny of cucumber and Arabidopsis bHLH proteins, we found that cucumber bHLH proteins were clustered into different functional clades of Arabidopsis bHLH proteins. The expression analysis of selected CsbHLHs under abiotic stresses (NaCl, ABA and low-temperature treatments) identified five CsbHLH genes that could simultaneously respond to the three abiotic stresses. Tissue-specific expression profiles of these five genes were also analysed. In addition, 35S:CsbHLH041 enhanced the tolerance to salt and ABA in transgenic Arabidopsis and in cucumber seedlings, suggesting CsbHLH041 is an important regulator in response to abiotic stresses. Lastly, the functional interoperability network among the CsbHLH proteins was analysed., Conclusion: This study provided a good foundation for further research into the functions and regulatory mechanisms of CsbHLH proteins and identified candidate genes for stress resistance in cucumber.

To elucidate the mechanism of bloom formation on fruit surface of cucumber, we investigated silicon absorption and bloom formation on fruit surface of cucumber with 'Shannong No. 5' (Cucumis sativus) as scion, 'Yunnan figleaf gourd' (Cucurbita ficifolia, weak de-blooming ability) and 'Huangchenggen No. 2' (C. moschata, strong de-blooming ability) as rootstocks in solar greenhouse at winter-spring and autumn-winter growing seasons. Experimental conditions inclu-ded: T 1 with temperature 28 ℃/18 ℃ (day/night), relative humidity 55%/65%, photosynthetic photon flux density 600 μmol·m -2 ·s -1 , and T 2 with temperature 22 ℃/12 ℃ (day/night), relative humidity 85%/95%, photosynthetic photon flux density 300 μmol·m -2 ·s -1 . We examined environmental effects on silicon absorption and expression of silicon transporter genes in. The amount of bloom on cucumber fruit surface at winter-spring growing season dramatically increased compared with autumn-winter season. 'Yunnan figleaf gourd' grafted cucumber was more heavily affected by the cultivation season than self-rooted and 'Huangchenggen No. 2' grafted cucumber. In the same cultivation season, 'Yunnan figleaf gourd' grafted cucumber had the highest amount of bloom on fruit surface and silicon content, while own-rooted and 'Huangchenggen No. 2' grafted cucumber had the medium and least amount of bloom and silicon content. Silicon content in each organ and expression of silicon transporter genes in cucumber leaves and roots under T 1 environment were significantly increased compared with T 2 . 'Yunnan figleaf gourd' grafted cucumber had the highest contents of silicon in each organ and expression of silicon transporter genes in leaves in the same environment, followed by own-rooted and 'Huangchenggen No. 2' grafted cucumber. In conclusion, environmental conditions affect absorption and allocation of silicon in cucumber plants, with conseuqnece on bloom formation on fruit surface. Suitable environmental conditions, including temperature, humidity and light, are beneficial to reduce the bloom formation on cucumber fruit surface. High temperature, strong light, and low humidity will increase bloom amount on cucumber fruit. Rootstocks have significant effects on silicon absorption and fruit bloom formation of grafted cucumber.

The effects of CO 2 enrichment on water balance and nitrogen (N) assimilation in cucumber (Cucumis sativus L. cv. Jinyou No.35) seedlings under salt stress were investigated. Two-way randomized block design was used: the main treatment consisted of two [CO 2 ] levels, ambient and enriched (400 and 800 ± 40 μmol mol -1 , respectively), and the minor treatment consisted on two salinity treatment levels, 0 and 80 mmol L -1 NaCl. The results showed that, under the experimental conditions, enriched [CO 2 ] and salt stress significantly inhibited the N assimilation process in cucumber leaves; however, enriched [CO 2 ] had no effect on the nitrate (NO 3 - ) reduction or ammonium (NH 4 + ) assimilation of leaves under salt stress, inhibiting only the transamination. Moreover, enriched [CO 2 ] increased the plasma membrane H + -ATPase activity, vacuolar membrane H + -ATPase activity and root hydraulic conductivity under salt stress, thereby increasing the ion selective absorption and water absorption capacity. To a certain extent, enriched [CO 2 ] promoted the accumulation of K + in plants, which significantly reduced the Na + /K + ratio; moreover, the enrichment ultimately improved the water state conditions and helped to maintain the ion balance in plants under stress, ensuring normal enzymatic activity., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Oxybenzone (OBZ), an active ingredient in most sunscreens, was recently shown to be toxic to humans, corals and other animals. This study is the first to demonstrate that OBZ can significantly inhibit photosynthesis and respiration in the leaves of a higher plant, cucumber. An OBZ suspension content as low as 0.228 mg/L obviously inhibited the photosynthesis and respiration of cucumber. OBZ instantly inhibits the electron transport of chloroplasts and mitochondria in cucumber leaves. Probit analysis demonstrated that the effective content for 20% inhibition of photosynthetic electron transport was 11.7 mg/L (95% confidence level). The inhibition of photosynthesis and respiration restricts carbohydrate synthesis and ATP regeneration, respectively, limiting the energy available for metabolic processes including the synthesis of vital organic macromolecules such as proteins and nucleic acids in plant cells. The inhibition of photosynthesis also enhanced the excess excitation energy in chloroplasts, resulting in overproduction of reactive oxygen species (ROS), and the inhibition of respiration aggravated this process. ROS accumulation adversely affects the structure and function of proteins, DNA and membrane lipids in plant cells, interfering with normal metabolism and even leading to plant death. Therefore, reducing the use of OBZ is important for protecting global ecological security., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The cucumber (Cucumis sativus L.), an economically important vegetable crop, is often infected by Pseudoperonospora cubensis (P. cubensis), which results in inhibited growth and reduced yield. WRKY transcription factors (TFs) play critical roles in plant disease resistance. However, little is known about the function of WRKY TFs in cucumber downy mildew resistance. In this study, we reported that CsWRKY50, a cucumber WRKY subgroup Ⅱc TF localized in the nucleus, plays an important role in cucumber defense responses to downy mildew. In addition, several putative cis-acting elements involved in abiotic stress responsiveness were also identified in the CsWRKY50 promoter. Expression analysis revealed that CsWRKY50 can be induced by P. cubensis infection, abiotic stress and diverse signaling molecules. The overexpression of CsWRKY50 in cucumber enhanced the resistance of the plant to the fungal pathogen P. cubensis. In addition, less ROS accumulated in 35S:CsWRKY50 transgenic plants infected by the pathogen due to the higher expression levels of antioxidant enzymes. Importantly, after P. cubensis infection, the transcript levels of several hormone-related defense genes were also upregulated in transgenic plants, including SA- and JA-responsive genes and SA-synthesis genes. Collectively, our results indicate that CsWRKY50 positively regulates cucumber disease resistance to P. cubensis via multiple signaling pathways., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Spine colour is an important fruit quality trait that influences the commercial value of cucumber (Cucumis sativus). However, little is known about the metabolites and the regulatory mechanisms of their biosynthesis in black spine varieties. In this study, we determined that the pigments of black spines are flavonoids, including flavonols and proanthocyanidins (PAs). We identified CsMYB60 as the best candidate for the previously identified B (Black spine) locus. Expression levels of CsMYB60 and the key genes involved in flavonoid biosynthesis were higher in black-spine inbred lines than that in white-spine lines at different developmental stages. The insertion of a Mutator-like element (CsMULE) in the second intron of CsMYB60 decreased its expression in a white-spine line. Transient overexpression assays indicated that CsMYB60 is a key regulatory gene and Cs4CL is a key structural gene in the pigmentation of black spines. In addition, the DNA methylation level in the CsMYB60 promoter was much lower in the black-spine line compared with white-spine line. The CsMULE insert may decrease the expression level of CsMYB60, causing hindered synthesis of flavonols and PAs in cucumber fruit spines.

Elevated atmospheric CO 2 alleviates moderate to severe drought stresses at physiological level in cucumber. To investigate the underlying metabolic mechanisms, cucumber seedlings were treated with two [CO 2 ] and three water treatments combinations, and their leaves were analyzed using a non-targeted metabolomics approach. The results showed that elevated [CO 2 ] changed 79 differential metabolites which were mainly associated with alanine, aspartate and glutamate metabolism; arginine and proline metabolism; TCA cycle; and glycerophospholipid metabolism under moderate drought stress. Moreover, elevated [CO 2 ] promoted the accumulation of secondary metabolites; including isoferulic acid, m-coumaric acid and salicyluric acid. Under severe drought stress, elevated [CO 2 ] changed 26 differential metabolites which mainly involved in alanine, aspartate and glutamate metabolism; pyruvate metabolism; arginine and proline metabolism; glyoxylate and dicarboxylate metabolism; cysteine and methionine metabolism; starch and sucrose metabolism; glycolysis or gluconeogenesis; and pyrimidine metabolism. In addition, elevated [CO 2 ] accumulated carbohydrates, 1,2,3-trihydroxybenzene, pyrocatechol, glutamate, and l-gulonolactone, to allow adaption to severe drought. In conclusion, the metabolites and metabolic pathways associated with the alleviation of drought stresses by elevated [CO 2 ] were different according to the level of drought stress. Our results may provide a theoretical basis for CO 2 fertilization and application of exogenous metabolites to enhance drought tolerance of cucumber., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Cucumber ( Cucumis sativus L.) is an important vegetable crop worldwide and gibberellins (GAs) play important roles in the regulation of cucumber developmental and growth processes. GA oxidases (GAoxs), which are encoded by different gene subfamilies, are particularly important in regulating bioactive GA levels by catalyzing the later steps in the biosynthetic pathway. Although GAoxs are critical enzymes in GA synthesis pathway, little is known about GAox genes in cucumber, in particular about their evolutionary relationships, expression profiles and biological function. In this study, we identified 17 GAox genes in cucumber genome and classified them into five subfamilies based on a phylogenetic tree, gene structures, and conserved motifs. Synteny analysis indicated that the tandem duplication or segmental duplication events played a minor role in the expansion of cucumber GA2ox , GA3ox and GA7ox gene families. Comparative syntenic analysis combined with phylogenetic analysis provided deep insight into the phylogenetic relationships of CsGAox genes and suggested that protein homology CsGAox are closer to AtGAox than OsGAox. In addition, candidate transcription factors BBR/BPC (BARLEY B RECOMBINANT/BASIC PENTACYSTEINE) and GRAS (GIBBERELLIC ACID-INSENSITIVE, REPRESSOR of GAI, and SCARECROW) which may directly bind promoters of CsGAox genes were predicted. Expression profiles derived from transcriptome data indicated that some CsGAox genes, especially CsGA20ox1 , are highly expressed in seedling roots and were down-regulated under GA₃ treatment. Ectopic over-expression of CsGA20ox1 in Arabidopsis significantly increased primary root length and lateral root number. Taken together, comprehensive analysis of CsGAoxs would provide a basis for understanding the evolution and function of the CsGAox family.

The effects of 0.2 μmol·L -1 exogenous 2,4-epibrassinolide (EBR) on the growth and reactive oxygen species metabolism of cucumber seedlings ('Jinyan 4' cucumber) under salt-alkaline stress (30 mmol·L -1 NaHCO 3 ) were examined by hydroponics method. The results showed that NaHCO 3 stress significantly induced production of O 2 -· and accumulation of H 2 O 2 in leaves and roots, resulting in the increases of MDA content and electrolyte leakage. Under NaHCO 3 stress, activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, dehydroascorbatereductase, monodehydrodroascorbate reductase, and glutathione reductase as well as contents of ascorbic acid and glutathione were firstly increased and then decreased with progress of stress time. Exogenous EBR application significantly increased the activities of antioxidant enzymes and contents of antioxidants as well as the ratio of AsA/DHA (dehydroascorbic acid) and GSH/GSSG (L-glutathione oxidized) in leaves and roots of cucumber under NaHCO 3 stress. Such changes improved the redox hemostasis in plants, reduced the level of reactive oxygen species, and alleviated the membrane lipid peroxidation. Together, they increased the alkaline tolerance of cucumber seedlings.

Nitric oxide (NO) is a signal molecule that can mediate a wide range of physiological processes against cadmium (Cd) toxicity in plants. However, little information can be used to reveal the global and systematic mitigative mechanism of NO in improving Cd stress tolerance of cucumber plants. In the present study, we used Isobaric Tag for Relative and Absolute Quantification (iTRAQ) analysis to identify 1691 proteins, which can be used to determine the role of NO in regulating the molecular changes of proteome in cucumber leaves exposed to Cd stress. Several dysregulated key proteins indicated that Cd-induced physiological deterioration of cucumber leaves were mainly involved in metabolic process, cellular process, response to stimulus and so on. Metabolic pathway analysis indicated that several Cd-disruptive pathways were markedly reversed by NO treatments, including Cd transport and localization, photosynthesis, chlorophyll metabolism, redox homeostasis, glutathione-mediated Cd detoxification and Ca 2+ signaling transduction. Taken together, this iTRAQ analysis provides more comprehensive insights into the physiological and molecular mechanisms of NO against Cd toxicity in cucumber plants., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Using split plot and then-split plot design, effects of water-nitrogen coupling on photosynthesis and ultrastructure of cucumber (Cucumis sativus) (Jinyou No.35) under CO 2 enrichment were investigated. The main plot had two CO 2 concentrations: ambient CO 2 concentration (400 μmol·mol -1 , A) and doubled CO 2 concentration (800±20 μmol·mol -1 , E). The split plot had two treatments: no drought stress (95% of field capacity, W) and drought stress (75% of field capacity, D). The then-split plot contained low nitrogen treatment (450 kg·hm -2 , N 1 ) and high nitrogen treatment (900 kg·hm -2 , N 2 ). The results showed that under the condition of drought and high nitrogen, increasing CO 2 enhanced the cucumber plant height, and no matter what kinds of water treatment, CO 2 enrichment increased the leaf area significantly under high nitrogen. Under the condition of normal irrigation, the photosynthetic rate, stomatal conductance and transpiration rate of high nitrogen treatment were higher than low nitrogen treatment, while it was under the drought condition. Elevated CO 2 enhanced the water use efficiency of cucumber leaf which increased with increasing nitrogen application rate. Under drought stress, cucumber adaxial surface porosity density was increased, and the CO 2 enrichment and high nitrogen significantly reduced the stomatal density. Increasing nitrogen application improved the number of chloroplast, and reduced that of starch grains. Drought stress decreased the number of chloroplast, but tended to promote the number of starch grains. Drought stress increased the chloroplast length and width, and the size of the starch grains, while high nitrogen reduced the length and width of the chloroplast and starch grains. CO 2 enrichment and high nitrogen increased grana thickness and layers (except ADN 2 ), and the slice layer of EDN 2 was significantly higher than that of ADN 2 . In conclusion, CO 2 enrichment and suitable water and nitrogen could promote the development of chloroplast thylakoid membrane system, significantly increase the thickness of grana and the number of grana lamella, and effectively improve the chloroplast structure of cucumber, which would benefit the photosynthesis of cucumber plants and ability to utilize CO 2 and water and nitrogen.

Taking 'Xintaimici' and 'Jinyou 1' as experimental cucumber cultivars, this paper studied the effects of watering purified humic acid (PHA) at different levels (0, 50, 100, 150, 200 mg·L -1 ) on growth and nutrient absorption of cucumber seedlings under low nitrogen stress (1 mmol·L -1 NO 3 - ) in sand culture pots. The results showed that, under low N condition, PHA could significantly increase the total root length, root surface area, root tip number and root volume of cucumber seedlings, and promote plant height, stem diameter and leaf area. Proline and soluble sugar contents in cucumber leaves were significantly increased by PHA. The absorption of N, P, K, Ca, Mg, Fe in cucumber seedlings was promoted. According to the response of the two cucumber cultivars to PHA under low N stress, some traits of two cultivars showed different sensitivity to PHA level. The comprehensive analysis of the above results inferred that the PHA level from 100 mg·L -1 to 150 mg·L -1 could significantly enhance the growth and nutrient absorption of cucumber seedlings.

'Jinyan No. 4'cucumber was used as experimental material. The growth of cucumber radicles treated with different concentrations of p-hydroxybenzoic acid (0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 mmol·L -1 ) was investigated firstly, and 10 mmol·L -1 p-hydroxybenzoic acid was chosen for the further experiment. To investigate if melatonin alleviate p-hydroxybenzoic acid stress on cucumber radical elongation, 0, 1, 10, 25, 50, 75 and 100 μmol·L -1 melatonin were used to pretreat cucumber seeds for 24 h before 10 mmol·L -1 p-hydroxybenzoic acid treatment. The results suggested that exogenous melatonin could alleviate the radicle growth inhibition induced by p-hydroxybenzoic acid, and 75 μmol·L -1 melatonin showed the best effect. The growth of cucumber radical was significantly inhibited with an increase in p-hydroxybenzoic acid concentration, which was accompanied with lower activity of amylase. The melatonin pretreatment could significantly increase the activities of amylase and antioxidant enzymes in cucumber seeds resulting in lower accumulation of O 2 -· , H 2 O 2 and MDA. Exogenous melatonin effectively reduced the PHBA stress on cucumber germination, which might be due to its function in decreasing oxidative stress and promoting starch catabolism.

Nitric oxide (NO) and auxin (indole-3-acetic acid; IAA) play vital roles in regulating plants tolerance to abiotic stresses. This study showed that both NO and IAA could induce cucumber plants tolerance to sodic alkaline stress, which depended on their roles in regulating reactive oxygen species (ROS) scavenging, antioxidative enzymes activities, Na(+) accumulation and protecting photosystems II (PSII) from damage. In addition, IAA has significant effect on NO accumulation in cucumber root, which could be responsible for IAA-induced sodic alkaline stress tolerance. Further investigation indicated that the function of IAA could be abolished by NO scavenger (cPTIO). On the contrary, IAA transport inhibitor (NPA) showed no significant effects on abolishing the function of NO. Based on these results, it could be concluded that NO is an essential downstream signal for IAA-induced cucumber tolerance to sodic alkaline stress., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)