Comparative Genomic Analysis of PEBP Genes in Cucurbits Explores the Interactors of Cucumber CsPEBPs Related to Flowering Time.

The family of phosphatidylethanolamine-binding proteins (PEBPs) participates in various plant biological processes, mainly flowering regulation and seed germination. In cucurbit crops, several PEBP genes have been recognized to be responsible for flowering time. However, the investigation of PEBP family members across the genomes of cucurbit species has not been reported, and their conservation and divergence in structure and function remain largely unclear. Herein, PEBP genes were identified from seven cucurbit crops and were used to perform a comparative genomics analysis. The cucurbit PEBP proteins could be classified into MFT, FT, TFL, and PEBP clades, and further, the TFL clade was divided into BFT-like, CEN-like, and TFL1-like subclades. The MFT-like, FT-like, and TFL-like proteins were clearly distinguished by a critical amino acid residue at the 85th position of the Arabidopsis FT protein. In gene expression analysis, CsaPEBP1 was highly expressed in flowers, and its expression levels in females and males were 70.5 and 89.2 times higher, respectively, than those in leaves. CsaPEBP5, CsaPEBP6, and CsaPEBP7 were specifically expressed in male flowers, with expression levels 58.1, 17.3, and 15.7 times higher, respectively, than those of leaves. At least five CsaPEBP genes exhibited the highest expression during the later stages of corolla opening. Through clustering of time-series-based RNA-seq data, several potential transcription factors (TFs) interacting with four CsaPEBPs were identified during cucumber corolla opening. Because of the tandem repeats of binding sites in promoters, NF-YB (Csa4G037610) and GATA (Csa7G64580) TFs appeared to be better able to regulate the CsaPEBP2 and CsaPEBP5 genes, respectively. This study would provide helpful information for further investigating the roles of PEBP genes and their interacting TFs in growth and development processes, such as flowering time regulation in cucurbit crops.

Research progress on the role of biofilm in heavy metals adsorption-desorption characteristics of microplastics: A review.

Microplastics (MPs) have been found to be widely distributed in aquatic environments, where they will interact with toxic heavy metals and result in more serious adverse effects on the aquatic environments and organisms. However, after entering the aquatic environments, MPs are quickly covered by biofilms, which significantly modify MPs properties and relevant heavy metals adsorption-desorption characteristics In order to better understand the adsorption behavior of heavy metals on biofilm developed MPs (BMPs), we comprehensively reviewed representative studies in this area. First, we summarized the formation process of biofilms on MPs. Subsequently, we reviewed the current understanding on the influence of biofilm formation on the properties of MPs and discussed the metal adsorption-desorption characteristics of MPs affected by these changes. Finally, based on the systematic literature review, some future research needs and strategies were proposed to further understand the interactions between MPs and heavy metals.

Changes of water-soluble inorganic sulfate and nitrate during severe dust storm episodes in a coastal city of North China.

Dust storms are one of the largest sources of non-exhaust emissions in China, which can adversely affect air quality and human health during long-distance transportation. To study the influence of dust storms on aerosol particle composition, samples of fine aerosol (PM2.5) were collected before, during, and after the severe dust storm episodes in a coastal city of North China. Then the water-soluble inorganic ions in the filters were analyzed. The results showed that the chemical composition varied significantly in different sampling periods. Before the dust storm periods (Phase 1), the weather was characterized by high relative humidity. NO3- was the main water-soluble inorganic ion, accounting for about 1/3 of the total mass of PM2.5, which is very different from the situation a few years ago when sulfate was the dominant. The results indicated that the chemical composition of the atmosphere in China has changed significantly after the implementation of strict air pollution control measures. During the severe dust storm periods (within a few hours after the dust invasion, Phase 2), the proportion of Ca2+ in PM2.5 was high; the sulfate formation was limited due to adiabatic air mass affected by the cold front, and the sulfate content might be mainly from desert soil. However, a small amount of nitrate can be formed during their long-distance transportation. After the dust storm periods (Phase 3), dust plums and local polluted air mass mixed well. The proportion of secondary inorganic ions increased, and nitrate formation was still the main. The changes in the chemical composition from a few years ago during Phase 1 and the sharp changes in different water-soluble inorganic ions during different Phases should be carefully considered to evaluate their implications for air quality and human health.

A Comparative Characterization and Expression Profiling Analysis of Fructokinase and Fructokinase-like Genes: Exploring Their Roles in Cucumber Development and Chlorophyll Biosynthesis.

Fructokinase (FRK) and fructokinase-like (FLN), belonging to the phosphofructokinase B type subfamily, share substantial sequence similarity, and are crucial in various plant physiological processes. However, there is limited information regarding what functionally differentiates plant FRKs from FLNs. Here, a total of three CsFRKs and two CsFLNs were identified from the cucumber genome. Their significant difference lay in the structure of their G/AXGD motif, which existed as GAGD in CsFRKs, but as G/ASGD in CsFLNs. Comparative phylogenetic analysis classified CsFRKs and CsFLNs into five sub-branches consistent with their quite different exon/intron organizations. Both transcriptome data and RT-qPCR analyses revealed that CsFRK3 was the most active gene, with the highest expression in the majority of tissues tested. Moreover, the expression levels of two putative plastidic genes, CsFRK1 and CsFLN2, were significantly positively associated with chlorophyll accumulation in the chlorophyll-reduced cucumber mutant. Briefly, both CsFRK and CsFLN genes were involved in the development of sink tissues, especially CsFRK3. CsFRK1 and CsFLN2 were recognized as candidates in the chlorophyll biosynthesis pathway of cucumber. These results would greatly assist in further investigation on functional characterization of FRKs and FLNs, especially in the development and chlorophyll biosynthesis of cucumber.

The curvature of cucumber fruits is associated with spatial variation in auxin accumulation and expression of a YUCCA biosynthesis gene.

Fruit curving lowers the commercial value of cucumber and leads to significant economic losses. The mechanism driving the abnormal curving of cucumber is largely unknown. Through our previous work, we discovered that 2 days post-anthesis (DPA) was the key time point at which various phenotypic and genotypic characteristics of cucumber fruits are determined. Here, we analyzed the transcriptome of the concave (C1) and convex (C2) sides of curved fruits at 2 DPA by Gene Ontology (GO) enrichment and functional pathway enrichment analyses and identified auxin as a putative factor influencing fruit curvature. Changes in the curve angle in the fruits and exogenous auxin treatment analyses showed that asymmetric auxin distribution induces fruit curving. Identification of differentially expressed genes (DEGs) related to auxin and qPCR validation showed that CsYUC10b had the most significant differential expression when both sides of the curved fruits were compared. Gene functional analysis showed that the transcript levels of CsYUC10b and the auxin concentration were even on both sides of the fruit in CsYUC10b-overexpressing plants, which in turn contributed to an equal rate of growth of both sides of cucumber fruits and resulted in a straight shape of the fruits. Thus, we conclude that CsYUC10b promotes the formation of straight cucumber fruits, with possible applications in the production and breeding of cucumber.

Overexpression of CsHMGB Alleviates Phytotoxicity and Propamocarb Residues in Cucumber.

Cucumber (Cucumis sativus L.) is one of the most economically important fruits of the Cucurbitaceae family, therefore consideration of potential pesticide residues in the fruit in the context of cucumber breeding and production programs is important. Propamocarb (a pesticide commonly used to prevent downy mildew) is widely used in cucumber cultivation, but the molecular mechanism underlying the degradation and metabolism of propamocarb in cucumber is not well understood. We screened a candidate CsHMGB gene (CsaV3-5G28190) for response to propamocarb exposure using transcriptome data. The coding region of CsHMGB was 624 bp in length and encoded the conserved HMB-box region. CsHMGB expression differed significantly between the "D0351" genotype, which accumulated low levels of propamocarb, and the "D9320" genotype, which accumulated high levels of propamocarb. CsHMGB expression was positively correlated with propamocarb levels in the cucumber peel. CsHMGB expression was upregulated in the fruit peels of the "D0351" genotype following exposure to propamocarb stress for 3-120 h, but no difference was observed in expression between propamocarb treatment and control for the "D9320" genotype. For the "D0351" genotype, CsHMGB expression was higher in the fruit peels and leaves than that in female flowers; expression was moderate in the stems and fruit pulps, and weak in male flowers and roots. The CsHMGB protein was targeted to the nucleus in Arabidopsis protoplasts and in the epidermis of Nicotiana benthamiana leaves. We measured MDA, O2 -, and H2O2 levels in cucumber plants and found that they were likely to accumulate reactive oxygen species (ROS) in response to propamocarb stress. Analysis of antioxidant enzyme activity (SOD, POD, CAT, APX, GPX, GST, and GR) and the ascorbate-glutathione (AsA-GSH) system showed that the resistance of the plants was reduced and the levels of propamocarb residue was increased in CsHMGB-silenced plants in response to propamocarb stress. Conversely, overexpression of CsHMGB promoted glutathione-dependent detoxification by AsA-GSH system and improved the antioxidant potential, reduced the accumulation of ROS. Ultimately, the metabolism of propamocarb in cucumber was increased via increase in the wax levels and the stomatal conductance.

Expression and functional analysis of the propamocarb-related gene CsMAPEG in cucumber.

BACKGROUND: Propamocarb (PM) is one of the main pesticides used for controlling cucumber downy mildew. However, due to its volatility and internal absorption, PM can easily form pesticide residues on cucumber fruits that seriously endanger human health and pollute the environment. The breeding of new cucumber varieties with a low abundance of PM residues via genetic methods constitutes an effective strategy for reducing pesticide residues and improving cucumber safety and quality. To help elucidate the molecular mechanism resulting in a low PM residue abundance in cucumber, we used the cucumber cultivar 'D0351' (which has the lowest PM residue content) as the test material and identified genes related to low PM residue abundance through high-throughput tag-sequencing (Tag-Seq). RESULTS: CsMAPEG was constitutively expressed and showed both varietal and organizational differences. This gene was strongly expressed in 'D0351'. The expression levels of CsMAPEG in different cucumber tissues under PM stress were as follows: fruit>leaf>stem>root. CsMAPEG can respond to salicylic acid (SA), gibberellin (GA) and Corynespora cassiicola Wei (Cor) stress and thus plays an important regulatory role in plant responses to abiotic and biological stresses. The PM residue abundance in the fruits of CsMAPEG-overexpressing plants was lower than those found in antisense CsMAPEG plants and wild-type plants at all tested time points. The results revealed that CsMAPEG played a positive role in reducing the PM residue abundance. A CsMAPEG sense construct increased the contents of SOD, POD and GST in cucumber fruits, enhanced the degradation and metabolism of PM in cucumber, and thus effectively reduced the pesticide residue abundance in cucumber fruits. CONCLUSIONS: The expression patterns of CsMAPEG in cucumber cultivars with high and low pesticide residue abundances and a transgenic verification analysis showed that CsMAPEG can actively respond to PM stress and effectively reduce the PM residue abundance in cucumber fruits. The results of this study will help researchers further elucidate the mechanism responsible for a low PM residue abundance in cucumber and lay a foundation for the breeding of new agricultural cucumber varieties with low pesticide residue abundances.

Expression and Functional Analysis of the Propamocarb-Related Gene CsMCF in Cucumber.

Propamocarb (PM), a carbamate fungicide, can effectively control downy mildew on cucumber. However, due to the large-scale and high-dose use of this fungicide, PM residues have become a major problem in cucumber production. In this report, the cucumber cultivar "D0351" (with the lowest residual PM content) and the cucumber cultivar "D9320" (with the highest residual PM content) were used as experimental materials. The candidate gene CsMCF, which is related to a low residual PM content in cucumber, was screened by high-throughput tag-sequencing (Tag-Seq) and PM analysis, and its role in reducing PM residue in cucumber was explored. CsMCF was cloned and obtained. This gene contains an open reading frame of 1026 bp, encodes 341 amino acids and contains 3 Mito-carr domains. The encoded protein is a hydrophobic protein with 4 distinct transmembrane structures but no signal peptide cleavage sites. The subcellular localization of the protein is the cytoplasm. Evolutionary tree analysis showed that CsMCF had the highest homology to a gene from the melon Cucumis melo L. (XM_008464998.2). The core elements of the promoter include cis-acting elements, such as those related to salicylic acid (SA), jasmonic acid (JA), gibberellin (GA), and abscisic acid (ABA). Following PM treatment, CsMCF was significantly upregulated at most time points in different parts of the fruit, leaf, stem and root of "D0351," while expression was downregulated at most time points in the fruit, leaf and stem of "D9320." The order of the expression levels in different cucumber organs was as follows: fruit>leaf > stem > root. CsMCF was specifically expressed in the stems and leaves of "D0351." The PM residues in CsMCF (+)-overexpressing T0 and T1 cucumber fruits were significantly lower than those in the wild type, while the PM residues in CsMCF (-)-overexpressing T0 and T1 cucumber fruits were significantly higher. The qRT-PCR results showed that CsMCF can respond to biotic and abiotic stresses, actively respond to PM treatment and play a role in reducing PM residues in cucumber fruits.

Expression and functional analysis of the Propamocarb-related gene CsDIR16 in cucumbers.

BACKGROUND: Cucumber downy mildew is among the most important diseases that can disrupt cucumber production. Propamocarb, also known as propyl-[3-(dimethylamino)propyl]carbamate (PM), is a systemic carbamate fungicide pesticide that is widely applied in agricultural production because of its high efficiency of pathogens control, especially cucumber downy mildew. However, residual PM can remain in cucumbers after the disease has been controlled. To explore the molecular mechanisms of PM retention, cucumber cultivars 'D9320' (with the highest residual PM content) and 'D0351' (lowest residual PM content) were studied. High-throughput tag-sequencing (Tag-Seq) results showed that the CsDIR16 gene was related to PM residue, which was verified using transgenic technology. RESULTS: We investigated the activity of a dirigent cucumber protein encoded by the CsDIR16 in gene response to stress induced by PM treatment. Gene-expression levels of CsDIR16 were up-regulated in the fruits, leaves, and stems of 'D0351' plants in response to PM treatment. However, in cultivar 'D9320', CsDIR16 levels were down-regulated in the leaves and stems after PM treatment, with no statistically significant differences observed in the fruits. Induction by jasmonic acid, abscisic acid, polyethylene glycol 4000, NaCl, and Corynespora cassiicola Wei (Cor) resulted in CsDIR16 up-regulation in 'D0351' and 'D9320'. Expression after salicylic acid treatment was up-regulated in 'D0351', but was down-regulated in 'D9320'. CsDIR16 overexpression lowered PM residues, and these were more rapidly reduced in CsDIR16(+) transgenic 'D9320' plants than in wild-type 'D9320' and CsDIR16(-) transgenic plants. CONCLUSIONS: Analyses of the CsDIR16-expression patterns in the cucumber cultivars with the highest and lowest levels of PM residue, and transgenic validation indicated that CsDIR16 plays a positive role in reducing PM residues. The findings of this study help understand the regulatory mechanisms occurring in response to PM stress in cucumbers and in establishing the genetic basis for developing low-pesticide residue cucumber cultivars.

The novel ethylene-responsive factor CsERF025 affects the development of fruit bending in cucumber.

KEY MESSAGE: Overexpression of CsERF025 induces fruit bending by promoting the production of ethylene. Cucumber fruit bending critically affects cucumber quality, but the mechanism that causes fruit bending remains unclear. To better understand this mechanism, we performed transcriptome analyses on tissues from the convex (C1) and concave (C2) sides of bending and straight (S) fruit at 2 days post anthesis (DPA). We identified a total of 281 differentially expressed genes (DEGs) from both the convex and concave sides of bent fruit that showed significantly different expression profiles relative to straight fruits. Of these 281 DEGs, 196 were up-regulated (C1/S_C2/S) and 85 were down-regulated (C1/S_C2/S). Among the 196 up-regulated DEGs, the transcriptional levels of genes related to ethylene biosynthesis and signaling pathways were significantly higher in bending fruit compared with straight fruit. CsERF025 showed the largest difference in expression between bending and straight fruit. CsERF025 is an AP2/ERF gene encoding a protein that localizes to the nucleus. Overexpression of this gene increased the bending rate of cucumber fruits and increased the angle of bending. CsERF025 increased both the expression of ethylene biosynthesis-related genes and the production of ethylene. The application of exogenous 1-aminocyclopropane-l-carboxylic acid (ACC) to straight fruits from control plants promoted fruit bending. Thus, CsERF025 enhances the production of ethylene and thereby promotes fruit bending in cucumber.

Expression and functional analysis of the transcription factor-encoding Gene CsERF004 in cucumber during Pseudoperonospora cubensis and Corynespora cassiicola infection.

BACKGROUND: Cucumber downy mildew, caused by P. cubensis, is an important leaf disease that can severely affect cucumber production. In recent years, cucumber target spot, caused by C. cassiicola, has been reported in both Asia and Europe and is now considered as a major disease disrupting cucumber production. Single-disease-resistant cucumber varieties have been unable to satisfy production needs. To explore the molecular mechanisms of cucumber resistance to these two diseases, cucumber cultivars D9320 (resistant to downy mildew and target spot) and D0401 (susceptible to downy mildew and target spot) were used as experimental materials in this study. We used transcriptome sequencing technology to identify genes related to disease resistance and verified using transgenic technology. RESULTS: We screened out the cucumber resistance-related gene CsERF004 using transcriptome sequencing technology. Induction by pathogens, salicylic acid (SA), and ethylene (ET) resulted in the up-regulation of CsERF004. Three treatments, namely, inoculation with C. cassiicola alone, inoculation with P. cubensis alone, and simultaneous inoculation with both pathogens, all resulted in the significant and sustained up-regulation of CsERF004 in the resistant cultivar D9320, during the early stage of infection. In the susceptible cultivar D0401, CsERF004 expression was also significantly up-regulated at the later stage of infection but to a lesser extent and for a shorter duration than in the resistant cultivar D9320. The CsERF004 gene encodes a protein localizes to the nucleus. The over-expression of CsERF004 in the susceptible cultivar D0401 resulted in the significant up-regulation of the CsPR1 and CsPR4 genes and increased the levels of SA and ET, which enhanced the resistance of cucumber to downy mildew and target spot. CONCLUSIONS: Analyses of the CsERF004 expression pattern in disease-resistant and susceptible cucumber cultivars and transgenic validation indicate that CsERF004 confers resistance to P. cubensis and C. cassiicola. The findings of this study can help to better understanding of mechanisms of response to pathogens and in establishment the genetic basis for the development of cucumber broad-spectrum resistant cultivars.

The Influence of Suspended Solids on the Combined Toxicity of Galaxolide and Lead to Daphnia magna.

Polycyclic musks and heavy metals are often present in natural aquatic environment. The aims of this study were to evaluate the toxic effects on Daphnia magna from exposure to the polycyclic musks and the heavy metals in combination with stress from suspended solids exposure. Galaxolide and lead were used as typical pollutants. The toxic effects on D. magna decreased with addition of suspended solids within the single experiments having galaxolide after 24 and 48 h. A similar result was observed for the toxic effect of lead on the D. magna with adding suspended solids during exposure. Synergism on D. magna was found within the combined tests having galaxolide and lead during the 24 and 48 h exposure based on additive index analysis. The combined toxic effect of galaxolide and lead was significantly decreased by adding suspended solids. The results could provide useful information for the toxic risks assessments of surface aquatic systems.

Transcriptome profile analysis of floral sex determination in cucumber.

Cucumber has been widely studied as a model for floral sex determination. In this investigation, we performed genome-wide transcriptional profiling of apical tissue of a gynoecious mutant (Csg-G) and the monoecious wild-type (Csg-M) of cucumber in an attempt to isolate genes involved in sex determination, using the Solexa technology. The profiling analysis revealed numerous changes in gene expression attributable to the mutation, which resulted in the down-regulation of 600 genes and the up-regulation of 143 genes. The Solexa data were confirmed by reverse transcription polymerase chain reaction (RT-PCR) and real-time quantitative RT-PCR (qRT-PCR). Gene ontology (GO) analysis revealed that the differentially expressed genes were mainly involved in biogenesis, transport and organization of cellular component, macromolecular and cellular biosynthesis, localization, establishment of localization, translation and other processes. Furthermore, the expression of some of these genes depended upon the tissue and the developmental stage of the flowers of gynoecious mutant. The results of this study suggest two important concepts, which govern sex determination in cucumber. First, the differential expression of genes involved in plant hormone signaling pathways, such as ACS, Asr1, CsIAA2, CS-AUX1 and TLP, indicate that phytohormones and their crosstalk might play a critical role in the sex determination. Second, the regulation of some transcription factors, including EREBP-9, may also be involved in this developmental process.

[Effects of cinnamic acid on physiological characteristics of Cucumis sativus seedling].

With substrate culture, this paper studied the effects of different concentrations of cinnamic acid on the physiological characteristics of Cucumis sativus seedling. The results showed that 25 micromol.L(-1) of cinnamic acid had an inhibition effect on carotenoids, but a promotion effect on chlorophyll a and b. 50 micromol.L(-1) of this compound could significantly inhibit the photosynthetic rate, transpiration rate and root activity (P < 0.05), and this effect was getting stronger when the concentration was higher. 150 micromol cinnamic acid.L(-1) had a significant inhibition effect on chlorophyll a and b (P < 0.05). Cinnamic acid had a weak inhibition effect on root activity when its concentration was low (25-50 micromol.L(-1)), but the effect was significant when the concentration was high (100-150 micromol.L(-1)), which became stronger with the longer handling time (P < 0.05).