Search

SUMMARY: Skin color is an important trait that determines the cosmetic appearance and quality of fruits. In cucumber, the skin color ranges from white to brown in mature fruits. However, the genetic basis for this important trait remains unclear. We conducted a genome‐wide association study of natural cucumber populations, along with map‐based cloning techniques, on an F2 population resulting from a cross between Pepino (with yellow‐brown fruit skin) and Zaoer‐N (with creamy fruit skin). We identified CsMYB60 as a candidate gene responsible for skin coloration in mature cucumber fruits. In cucumber accessions with white to pale yellow skin color, a premature stop mutation (C to T) was found in the second exon region of CsMYB60, whereas light yellow cucumber accessions exhibited splicing premature termination caused by an intronic mutator‐like element insertion in CsMYB60. Transgenic CsMYB60c cucumber plants displayed a yellow‐brown skin color by promoting accumulation of flavonoids, especially hyperoside, a yellow‐colored flavonol. CsMYB60c encodes a nuclear protein that primarily acts as a transcriptional activator through its C‐terminal activation motif. RNA sequencing and DNA affinity purification sequencing assays revealed that CsMYB60c promotes skin coloration by directly binding to the YYTACCTAMYT motif in the promoter regions of flavonoid biosynthetic genes, including CsF3′H, which encodes flavonoid 3′‐hydroxylase. The findings of our study not only offer insight into the function of CsMYB60 as dominantly controlling fruit coloration, but also highlight that intronic DNA mutations can have a similar phenotypic impact as exonic mutations, which may be valuable in future cucumber breeding programs. Significance Statement: Genome‐wide association study and map‐based cloning revealed that CsMYB60 regulates mature cucumber fruit skin coloring, which is promising for cucumber breeding. Two loss‐of‐function mutations of CsMYB60 provided color variations in the natural cucumber population. [ABSTRACT FROM AUTHOR]

SUMMARY: The formation of adventitious roots (ARs) derived from hypocotyl is the most important morphological adaptation to waterlogging stress in Cucumis sativus (cucumber). Our previous study showed that cucumbers with the gene CsARN6.1, encoding an AAA ATPase domain‐containing protein, were more tolerant to waterlogging through increased AR formation. However, the apparent function of CsARN6.1 remained unknown. Here, we showed that the CsARN6.1 signal was predominantly observed throughout the cambium of hypocotyls, where de novo AR primordia are formed upon waterlogging treatment. The silencing of CsARN6.1 expression by virus‐induced gene silencing and CRISPR/Cas9 technologies adversely affects the formation of ARs under conditions of waterlogging. Waterlogging treatment significantly induced ethylene production, thus upregulating CsEIL3 expression, which encodes a putative transcription factor involved in ethylene signaling. Furthermore, yeast one‐hybrid, electrophoretic mobility assay and transient expression analyses showed that CsEIL3 binds directly to the CsARN6.1 promoter to initiate its expression. CsARN6.1 was found to interact with CsPrx5, a waterlogging‐responsive class‐III peroxidase that enhanced H2O2 production and increased AR formation. These data provide insights into understanding the molecular mechanisms of AAA ATPase domain‐containing protein and uncover a molecular mechanism that links ethylene signaling with the formation of ARs triggered by waterlogging. Significance Statement: The AAA ATPase domain‐containing protein CsARN6.1 is required for waterlogging stress tolerance, where it regulates adventitious root (AR) formation. However, the functional relevance of this gene remained unknown. Our results reveal that in cucumber, a CsEIL3‐CsARN6.1 regulatory module confers AR formation through H2O2 production, mediated by CsPrx5. [ABSTRACT FROM AUTHOR]

Podosphaera xanthii is a well-known obligate biotrophic pathogen that causes powdery mildew (PM) disease on cucurbitaceous plants and is one of the most important limiting factors for cucumber production worldwide. To better understand the avirulence effector proteins in this species that are known to be involved in host-pathogen interaction, the draft genome assembly of P. xanthii isolate YZU573 from cucumber leaves with symptoms of PM was obtained with a hybrid approach, combining nanopore long-read and llumina paired-end sequencing. The final P. xanthii YZU573 genome assembly of 152.7 Mb consists of 58 contigs, with an N50 value of 0.75 Mb and 6491 predicted protein-coding genes. The effector analysis using the whole-genome sequence information revealed a total of 87 putative effector candidates, and 65 of them had their analogs, whereas the remaining 22 were novel ones. The new P. xanthii genome provides valuable resources to better understand plant-microbe interaction in cucumber PM disease. [ABSTRACT FROM AUTHOR]

Flat stem and witches' broom phytoplasma-like symptoms in the cucumber inbred line C17 were observed in a greenhouse at Yangzhou University, China for three consecutive planting seasons; these symptoms resulted in a decreased yield. To better understand the cause of these symptoms, 16S rRNA PCR, plant hormones, mineral elements, and RNA-seq profiling were performed using symptomatic and normal stem samples. The results showed that the causal agent was classified as the Candidatus phytoplasma asteris strain, a plant pathogenic prokaryote that could not be cultured in vitro. Measurement of plant hormones showed that auxin, salicylic acid, and jasmonic acid contents were significantly increased, whereas that of ethylene's immediate biosynthetic precursor, 1-aminocyclopropane-1-carboxylic acid, was decreased in the phytoplasma-infected stems compared with the healthy stems. Furthermore, measurement of mineral element composition showed that magnesium, calcium, sodium, iron, and zinc concentrations significantly changed in the phytoplasma-infected cucumber stems compared with the uninfected stems. Comparative RNA-seq identified 253 differentially expressed genes, including 179 upregulated and 74 downregulated genes. Further analyses suggested that genes related to phenylpropanoid biosynthesis, phenylalanine metabolism, and plant hormone signal transduction contributed to phytoplasma infection. Taken together, this study presents the first in-depth assessment of disease symptoms and biochemical content of cucumber stems known to be infected with phytoplasma. [ABSTRACT FROM AUTHOR]

The cucumber is characterized by the presence of a wide range of volatile organic compounds (VOCs), which are recognized as the main responsible for its unique flavor. However, research on the types and contents of VOCs in different cucumber cultivars remains fragmentary. Here, using an automatic headspace solid-phase microextraction coupled with the gas chromatography–mass spectrometry method, the VOCs were analyzed in three representative cucumber cultivars, including YX, KX, and GX, with the best, middle, and worst flavor quality, respectively, which were selected from 30 cultivars after flavor quality evaluation. Principal component analysis revealed that the six biological replicates were grouped, indicating high reliability of the data. A total of 163 VOCs were detected. There were 28 differential VOCs in YX compared to GX, 33 differential VOCs in YX compared to KX, and 10 differential VOCs in KX compared to GX. Furthermore, K-means clustering analysis showed that 38 of the 43 no-overlapping differential VOCs were represented by the most abundant compounds detected in YX. The prevailing VOCs in YX included: hydrocarbons, aldehydes, and ketones. The data obtained in the present study extend our understanding the impact of cultivars on VOCs in cucumber and will help facilitate targeted breeding. [ABSTRACT FROM AUTHOR]

Summary: Fruit neck length (FNL) is an important quality trait in cucumber because it directly affects its market value. However, its genetic basis remains largely unknown. We identified a candidate gene for FNL in cucumber using a next‐generation sequencing‐based bulked segregant analysis in F2 populations, derived from a cross between Jin5‐508 (long necked) and YN (short necked). A quantitative trait locus (QTL) on chromosome 7, Fnl7.1, was identified through a genome‐wide comparison of single nucleotide polymorphisms between long and short FNL F2 pools, and it was confirmed by traditional QTL mapping in multiple environments. Fine genetic mapping, sequences alignment and gene expression analysis revealed that CsFnl7.1 was the most likely candidate Fnl7.1 locus, which encodes a late embryogenesis abundant protein. The increased expression of CsFnl7.1 in long‐necked Jin5‐508 may be attributed to mutations in the promoter region upstream of the gene body. The function of CsFnl7.1 in FNL control was confirmed by its overexpression in transgenic cucumbers. CsFnl7.1 regulates fruit neck development by modulating cell expansion. Probably, this is achieved through the direct protein–protein interactions between CsFnl7.1 and a dynamin‐related protein CsDRP6 and a germin‐like protein CsGLP1. Geographical distribution differences of the FNL phenotype were found among the different cucumber types. The East Asian and Eurasian cucumber accessions were highly enriched with the long‐necked and short‐necked phenotypes, respectively. A further phylogenetic analysis revealed that the Fnl7.1 locus might have originated from India. Thus, these data support that the CsFnl7.1 has an important role in increasing cucumber FNL. [ABSTRACT FROM AUTHOR]

Waterlogging is a severe environmental stress that causes severe crop productivity losses. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots (ARs) that enhance gas exchange. Little is known about the role of light and sugars in the waterlogging‐induced production of ARs. The role of these factors in AR production was therefore studied in cucumber seedlings grown in the absence or presence of waterlogging and different light conditions. The effect of photosynthesis was studied by removing the shoots of the seedlings and replacing them with exogenous applications of sucrose or stachyose. Shoot removal inhibited AR emergence and elongation. However, the exogenous application of sugars fully restored AR emergence and partially restored root elongation. The exogenous application of a synthetic auxin restored AR emergence but not AR elongation. Transcriptome profiling analysis was used to determine the effects of light on gene expression in the hypocotyls under these conditions. The levels of transcripts encoding proteins involved in auxin transport and signalling were higher in the light and following the exogenous application of sucrose and stachyose. These results show that the waterlogging‐induced emergence of ARs is regulated by the interaction between sugars and auxin, whereas AR elongation depends only on sugars alone. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots to enhance gas exchange. However, the molecular mechanisms underlying waterlogging‐induced adventitious root formation is less studied. The present results indicate that waterlogging‐induced adventitious root formation is regulated by an interaction of sugars (especially stachyose and sucrose) and auxin signalling. Sugars act as molecular signals that are mediated by auxin transport and response signalling to induce the adventitious root emergence, and as energy resources for adventitious root elongation. [ABSTRACT FROM AUTHOR]

Fusarium wilt (FW) is a very serious soil-borne disease worldwide, which usually results in huge yield losses in cucumber production. However, the inheritance and molecular mechanism of the response to FW are still unknown in cucumber (Cucumis sativus L.). In this study, two inbred cucumber lines Superina (P1) and Rijiecheng (P2) were used as the sensitive and resistant lines, respectively. A mixed major gene plus polygene inheritance model was used to analyze the resistance to FW in different generations of cucumber, namely, P1, P2, F1 (P1×P2), B1, and B2, obtained by backcrossing F1 plants with Superina (B1) or Rijiecheng (B2), and F2, obtained by self-crossing the F1 plants. After screening 18 genetic models, we chose the E-1 model, which included two pairs of additive-dominance-epistatic major genes and additive-dominance polygenes, as the optimal model for resistance to FW on the basis of fitness tests. The major effect quantitative trait locus (QTL) fw2.1 was detected in a 1.91-Mb-long region of chromosome 2 by bulked-segregant analysis. We used five insertion/deletion markers to fine-map the fw2.1 to a 0.60 Mb interval from 1,248,093 to 1,817,308 bp on chromosome 2 that contained 80 candidate genes. We also used the transcriptome data of Rijiecheng inoculated with Fusarium oxysporum f. sp. cucumerinum (Foc) to screen the candidate genes. Twelve differentially expressed genes were detected in fw2.1 , and five of them were significantly induced by FW. The expression levels of the five genes were higher in FW-resistant Rijiecheng inoculated with Foc than in the control inoculated with water. Our results will contribute to a better understanding of the genetic basis of FW resistance in cucumber, which may help in breeding FW-resistant cucumber lines in the future. [ABSTRACT FROM AUTHOR]

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1‐methylcyclopropene (1‐MCP), the auxin transport inhibitor 1‐naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin‐induced AR formation was inhibited by 1‐MCP, although ethylene‐induced AR formation was not inhibited by NPA. Both ethylene‐ and auxin‐induced AR formation were counteracted by DPI. These results indicate that auxin‐induced AR formation is dependent on ethylene, whereas ethylene‐induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene‐ and auxin‐induced AR formation in cucumber plants. In response to waterlogging, many plants develop adventitious roots (ARs) to enhance gas exchange and nutrient uptake. Auxin, ethylene, and reactive oxygen species (ROS) all take part in this process, but little is known about how they interact. In cucumber, we report that auxin‐induced AR formation is dependent on ethylene, whereas ethylene‐induced AR formation is independent of auxin. Both ethylene and auxin upregulated genes involved in ROS production, which finally lead to AR formation. These results demonstrate the importance of crosstalk among ethylene, auxin, and ROS and show that the crosstalk is generally different in different plants. [ABSTRACT FROM AUTHOR]

Summary: In plants, the formation of hypocotyl‐derived adventitious roots (ARs) is an important morphological acclimation to waterlogging stress; however, its genetic basis remains fragmentary. Here, through combined use of bulked segregant analysis‐based whole‐genome sequencing, SNP haplotyping and fine genetic mapping, we identified a candidate gene for a major‐effect QTL, ARN6.1, that was responsible for waterlogging tolerance due to increased AR formation in the cucumber line Zaoer‐N. Through multiple lines of evidence, we show that CsARN6.1 is the most possible candidate for ARN6.1 which encodes an AAA ATPase. The increased formation of ARs under waterlogging in Zaoer‐N could be attributed to a non‐synonymous SNP in the coiled‐coil domain region of this gene. CsARN6.1 increases the number of ARs via its ATPase activity. Ectopic expression of CsARN6.1 in Arabidopsis resulted in better rooting ability and lateral root development in transgenic plants. Transgenic cucumber expressing the CsARN6.1Asp allele from Zaoer‐N exhibited a significant increase in number of ARs compared with the wild type expressing the allele from Pepino under waterlogging conditions. Taken together, these data support that the AAA ATPase gene CsARN6.1 has an important role in increasing cucumber AR formation and waterlogging tolerance. [ABSTRACT FROM AUTHOR]

Cucumber is an economically important vegetable crop worldwide. Powdery mildew (PM) is one of the most severe diseases that can affect cucumber crops. There have been several research efforts to isolate PM resistance genes for breeding PM-resistant cucumber. In the present study, we used a chromosome segment substitution line, SSL508-28, which carried PM resistance genes from the donor parent, JIN5-508, through twelve generations of backcrossing with a PM-susceptible inbred line, D8. We performed whole-genome resequencing of SSL508-28 and D8 to identify single nucleotide polymorphisms (SNPs), and insertions and deletions (indels). When compared against the reference genome of the inbred cucumber line 9930, a total of 468,616 SNPs and 67,259 indels were identified in SSL508-28, and 537,352 SNPs and 91,698 indels were identified in D8. Of these, 3,014 non-synonymous SNPs and 226 frameshift indels in SSL508-28, and 3,104 non-synonymous SNPs and 251 frameshift indels in D8, were identified. Bioinformatics analysis of these variations revealed a total of 15,682 SNPs and 6,262 indels between SSL508-28 and D8, among which 120 non-synonymous SNPs and 30 frameshift indels in 94 genes were detected between SSL508-28 and D8. Finally, out of these 94 genes, five resistance genes with nucleotide-binding sites and leucine-rich repeat domains were selected for qRT-PCR analysis. This revealed an upregulation of two transcripts, Csa2M435460.1 and Csa5M579560.1, in SSL508-28. Furthermore, the results of qRT-PCR analysis of these two genes in ten PM resistant and ten PM susceptible cucumber lines showed that when exposed to PM, Csa2M435460.1 and Csa5M579560.1 exhibited a higher expression level of resistant lines than susceptible lines. This indicates that Csa2M435460.1 and Csa5M579560.1 are candidate genes for PM resistance in cucumber. In addition, the non-synonymous SNPs in Csa2M435460.1 and Csa5M579560.1, identified in SSL508-28 and D8, might be the key to high PM-resistance in SSL508-28. [ABSTRACT FROM AUTHOR]

Cucumber (Cucumis sativus L.) is an important vegetable crop worldwide, and Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. cucumerinum (Foc), severely restricts cucumber growth and yield. Accumulating lines of evidence indicate that chitinases play important roles in attacking the invading fungal pathogens through catalyzing their cell wall degradation. Here, we identified the chitinase (Chi) genes in cucumber and further screened the FW-responsive genes via a comparative transcriptome analysis and found that six common genes were predominantly expressed in roots but also significantly upregulated after Foc infection. Expression verification further conformed that Chi2 and Chi14 were obviously induced by Foc as well as by hormone treatments, compared with the controls. The purified Chi2 and Chi14 proteins significantly affected the growth of Foc in vitro, compared with the controls. Knockdown of Chi2 in cucumber by virus-induced gene silencing (VIGS) increased susceptibility to FW, compared with the Chi14-silenced and control plants, and silencing of Chi2 drastically impaired gene activation in the jasmonic acid pathway, suggesting that the Chi2 gene might play positive roles in cucumber FW defense and, therefore, can provide a gene resource for developing cucumber-FW-resistance breeding programs. [ABSTRACT FROM AUTHOR]

Fusarium wilt (FW) of cucumber (Cucumis sativus L.) caused by Fusarium oxysporum f. sp. cucumerinum (Foc) is a destructive soil-borne disease that severely decreases cucumber yield and quality worldwide. MicroRNAs (miRNAs) are small non-coding RNAs (sRNAs) that are important for regulating host immunity because they affect target gene expression. However, the specific miRNAs and the miRNA/target gene crosstalk involved in cucumber resistance to FW remain unknown. In this study, we compared sRNA-seq and RNA-seq data for cucumber cultivar 'Rijiecheng', which is resistant to FW. The integrated analysis identified FW-responsive miRNAs and their target genes. On the basis of verified expression levels, we detected two highly expressed miRNAs with down-regulated expression in response to Foc. Moreover, an analysis of 21 target genes in cucumber inoculated with Foc indicated that JRL3 (Csa2G362470), which is targeted by miR319a, and BEE1 (Csa1G024150), DAHP1 (Csa2G369040), and PERK2 (Csa4G642480), which are targeted by miR6300, are expressed at high levels, but their expression is further up-regulated after Foc inoculation. These results imply that miR319a-JRL3, miR6300-BEE1, miR6300-DAHP1 and miR6300-PERK2 regulate cucumber defenses against FW, and provide the gene resources that may be useful for breeding programs focused on developing new cucumber varieties with enhanced resistance to FW. [ABSTRACT FROM AUTHOR]

Fusarium wilt (FW) in cucumber (Cucumis sativus L.), caused by Fusarium oxysporum f. sp. cucumerinum (Foc), poses a major threat to cucumber growth and productivity. However, lack of available natural resistance resources for FW restricts the breeding of resistant cultivars via conventional approaches. Susceptibility (S) genes in susceptible host plants facilitate infection by the pathogen and contribute to susceptibility. Loss of function of these S genes might provide broad-spectrum and durable disease resistance. Here, we screened S genes via comparative proteomic analysis between cucumber cultivars Rijiecheng and Superina, which exhibited resistance and high -susceptibility to FW, respectively. We identified 210 and 243 differentially regulated proteins (DRPs) in the Rijiecheng and Superina, respectively, and further found that 32 DRPs were predominantly expressed in Superina and significantly up-regulated after Foc inoculation. Expression verification found that TMEM115 (CsaV3_5G025750), encoding a transmembrane protein, TET8 (CsaV3_2G007840), encoding function as a tetraspanin, TPS10 (CsaV3_2G017980) encoding a terpene synthase, and MGT2 (CsaV3_7G006660), encoding a glycosyltransferase, were significantly induced in both cultivars after Foc infection but were induced to a higher expression level in Superina. These candidate genes might act as negative regulators of FW resistance in cucumber and provide effective FW-susceptibility gene resources for improving cucumber FW resistance through breeding programs. [ABSTRACT FROM AUTHOR]

• Spermidine (0.5 mmol/L) significantly promoted the fruit development of weakly parthenocarpic cucumber;. • Methylglyoxal-bis(ornithhydrazone) (Spermidine inhibitor) significantly inhibited the fruit development of parthenocarpic cucumber;. • Spermidine-induced parthenocarpic fruit formation is dependent on sugars and photosynthates accumulation in fruits. Parthenocarpic fruit formation is one of the most important traits which determines the production of cucumber. For improving the parthenocarpy, some kind of plant growth regulators were applied. However, the effect of spermidine (spd) on parthenocarpic fruit formation is unknown. In the presented study, 4 cucumber lines with different parthenocarpic ability were treated with spd to identify its role in parthenocarpy fruit formation. The results indicated that 0.25–1 mmol/L spd efficiently induced parthenocarpic fruit induction. The fruit development of YN (non-parthenocarpy line) was significantly enhanced by 1 mmol/L spd, while the fruit development of EP-6 (parthenocarpy line) was significantly inhibited by spd inhibitor MGBG (methylglyoxal-bis(guanylhydrazone)). The mechanism of spd-induced parthenocarpy was further identified by 14C isotope labeling technique. In comparison with non-pollinated fruit of YN, the sugar contents in spd-treated YN and non-pollinated EP-6 were higher. The spd enhanced output of 14C photosynthates from source leaf and accumulation in fruit of YN, while MGBG inhibited these processes in EP-6. In addition, the 14C photosynthates were mainly accumulated in the pulp of fruits. These results indicate that spd-induced parthenocarpic fruit formation is dependent on sugars and photosynthates accumulation in fruits. [ABSTRACT FROM AUTHOR]

Summary: A cold-tolerant line (NY-1) and a cold-sensitive cultivar (Jinyan 4) of cucumber (Cucumis sativus) were treated with temperatures of 28°C/22°C or 28°C/12°C (day/night) in a 10-h photoperiod. Carbohydrates and related enzymes were assayed from 0 to 4h after the start of the dark period. Compared to the normal night temperature (22°C, control), sucrose, stachyose and galactinol increased in mature leaves under cold-night treatment (12°C) while sucrose, glucose and fructose in fruits remained unchanged. In peduncles, where stachyose is catabolized to sucrose after long-distance transport, cold nights simultaneously induced a significant increase of stachyose (substrate) and a decrease of sucrose (product), indicating that the metabolic step from stachyose to sucrose in peduncles is crucial to translocation inhibition in cold nights. This decrease was more pronounced in the cold-sensitive cultivar. Similar growth rates of fruits on one-fruit and two-fruit plants under cold-night treatment further confirmed that it is sink activity rather than source supply that is limiting the source–sink translocation. No significant genotypic differences in enzyme activities involved in the stachyose–sucrose conversion, including alkaline α-galactosidase, acid α-galactosidase, galactokinase, uridine diphosphate (UDP)-galactose pyrophosphorylase, UDP–glucose-4′-epimerase and sucrose synthase, were observed when assayed in an adenosine triphosphate (ATP)-rich in vitro environment. However, the ATP concentration was much higher in peduncles of the cold-tolerant line, indicating that a limiting ATP supply may be partially responsible for the stronger inhibition of the stachyose–sucrose pathway observed in the cold-sensitive cultivar (Jinyan 4). [Copyright &y& Elsevier]

In protected vegetable fields, plant growth regulators are often used to improve cucumber fruit growth. However, the effects of plant growth regulators on the appearance and nutritional quality of cucumber ( Cucumis sativus L.) remain largely unknown. In the present study, 100 mg/L N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), naphthaleneacetic acid (NAA) or gibberellin A4+A7 (GA 4+7 ) was applied to the female cucumber flowers 1 day before anthesis and at anthesis. The CPPU, NAA and GA 4+7 treatments resulted in parthenocarpic fruits with similar weights, sizes and shapes as the pollinated fruits. NAA treatment did not affect the appearance and nutritional characteristics of cucumber at harvest and after storage. CPPU treatment increased the flesh firmness at harvest but decreased phenolic acid and vitamin C contents after storage. GA 4+7 treatment decreased the flesh firmness but increased total flavonoids and protein content after storage. [ABSTRACT FROM AUTHOR]

Cucumber varieties with shortend internodes require less space than regular vining varieties, thus have great significance for germplasm improvement. Here, we found a novel spontaneous cucumber mutant si107 that exhibited short intenodes (si), smaller leaves, fruits, and seeds. The decrease in longitudinal cell length led to the shortened internodes of si107. The genetic analysis revealed a single recessive gene si-2 that was responsible for the mutation. Through multiple lines of evidence, we demonstrated that CsSI is the possible candidate gene for si-2 , which encodes an ERECTA leucine-rich repeat receptor-like kinase. The shortened internode in si107 is attributed to a 2-bp deletion in the protein kinase domain region of this gene. The expression of CsSI was higher in the internodes, petioles, and fruit peels of si107 than in the wild type (WT). The transcriptome analysis between the si107 mutant and WT indicated that differentially expressed genes were significantly enriched in the plant hormone signal transduction pathway, in which auxin signal genes comprised the largest group, and all were downregulated in si107. Phytohormone quantitation confirmed that endogenous auxin levels in the stems of si107 were decreased. Our results provide new insights into the molecular mechanisms underlying the internode length control in cucumber. • We identified a novel short internode mutant, si107, in cucumber. • The shortened internodes in si107 is attributed to a 2-bp deletion in the ERECTA-like receptor kinase gene CsSI. • CsSI regulates cucumber internode length through auxin signaling pathway. [ABSTRACT FROM AUTHOR]

Abstract: A population of BC7 near-isogenic cucumber line (NIL210) was made from a cross between the powdery mildew susceptible cultivar (D8) and resistant cultivar (JIN5-508) in order to get powdery mildew resistance genes in cucumber. In this study, suppression subtractive hybridizations (SSHs) were applied to identify differential expressed genes between NIL210 and D8. 166 differentially expressed ESTs were identified from two SSH cDNA libraries including constitutively expressed resistant and susceptible factors. Most of the classified genes belong to four pathogenesis-related categories: ‘disease/defense’, ‘signal transduction’, ‘transcription’ and ‘transporter’, which altogether accounted for 46–53% of the genes classified. Some candidate powdery mildew resistant genes were also identified, such as GT053536 (TIR-NBS-LRR protein) and GT053570 (phenylalanine ammonia-lyase 2). These results will contribute to the better understanding of molecular mechanisms underlying powdery mildew resistance in cucumber. [ABSTRACT FROM AUTHOR]

• Endogenous carbohydrates levels affect the parthenocarpic fruit set of cucumber. • Exogenous sugars induced parthenocarpic fruit initiation. • Sugars enhance parthenocarpic fruit set through auxin and cytokinin signaling. Parthenocarpy is an important agricultural trait that determines the yield of cucumber. The role of sugars in parthenocarpic fruit formation is unknown. Therefore, we investigated these factors by using one highly parthenocarpic line DDX and one weakly parthenocarpic line ZK. To identify the possible effect of photosynthesis on parthenocarpy, leaf of ZK and DDX were covered for limiting the synthesis of carbohydrates. Leaf covering inhibited parthenocarpic fruit initiation and growth. Sugars (sucrose, fructose and glucose) contents in CPPU-induced, pollinated fruit of ZK and non-pollinated fruit of DDX were higher than those in non-pollinated fruit of ZK. The exogenous application of sugars (especially fructose and sucrose) significantly induced the parthenocarpic fruit set and growth. Transcriptomes of fruits treated with and without exogenously applied sugars showed that genes involved in auxin signaling and cytokinin signaling were more strongly expressed in the treated fruits. Auxin responsive gene IAA14 , and cytokinin responsive genes encoding histidine-containing phosphotransfer protein 4 and two-component response regulator 17 were upregulated in sugar-induced parthenocarpic fruits. These results show that parthenocarpic fruit formation is regulated by the interplay among sugars and the plant hormones auxin and cytokinin. [ABSTRACT FROM AUTHOR]

• Cytokinin and gibberellic acid concentrations were positive correlated with parthenocarpy in cucumber. • Cytokinin, auxin and GA4 + 7 could induce the parthenocarpic fruit set in cucumber. • Cytokinin- and auxin-related genes contribute to high parthenocarpic fruit formation in cucumber. Parthenocarpy (fruit development without pollination) is an important agricultural trait, which determines the production of horticultural crops like tomato, eggplant and cucumber. Parthenocarpy ability varies widely among cucumber lines. To better understand the genetic regulators underlying this variation, hormone and transcriptome profiles and the expressions of hormone-related genes in non-pollinated fruit of a highly parthenocarpic line DDX and a weakly parthenocarpic line ZK were compared at 1 day after anthesis. The cytokinin and gibberellic acid contents were higher in DDX than in ZK, while the abscisic acid content was less. Exogenous application of cytokinins, auxin and gibberellic acid 4 + 7 successfully induced the parthenocarpic fruit set of ZK. The transcript levels of several cytokinin biosynthesis genes (CsCYP735A1 , CsCYP735A2 and CsLOG1), cytokinin-responsive genes (CsRR8/9b, CsRR8/9d, CsRR8/9e and CsRR16/17) and auxin signal transduction genes (Aux/IAAs) were greater in DDX than in ZK, while the level of an abscisic acid receptor (CsPYR1) was lower. These results suggest that high expression levels of cytokinin- and auxin-related genes in DDX contribute to its high parthenocarpy ability. [ABSTRACT FROM AUTHOR]