Zhiwei Qin

Cucumber (Cucumis sativus L.) is a globally significant vegetable crop, and its fruit quality remains a major focus of research. The hollow-heart trait, characterized by internal cracks or cavities, severely compromises both the commercial value and edible quality of cucumber fruit. In this study, a six-generation segregating population (P₁, P₂, F₁, F₂, BC₁P₁, BC₁P₂) was developed from the parental lines “JZ6-1-2” and “D0432-3-4”. BSA-seq was employed to map candidate genomic regions associated with the hollow-heart trait to chromosomes 2, 3, and 7. Subsequently, a major QTL for the trait was delineated on chromosome 7, spanning a region containing 98 genes. Comparative RNA-seq between the parental lines identified 2141 differentially expressed genes. The integration of QTL mapping and RNA-seq data revealed 11 candidate genes residing within the key QTL interval. Through further validation via qRT-PCR, gene sequence comparison, and gene annotation, Csa7G039280 was identified as a promising candidate gene regulating hollow-heart formation, potentially via the lignin biosynthesis pathway. The identification of these candidate regions and genes provides critical information for molecular breeding aimed at developing non-hollow-heart cucumber varieties, thereby enhancing the understanding of the genetic regulatory mechanisms underlying this economically important trait.

Auxin serves as an essential regulator of the expression of many different genes in plants, thereby regulating growth and development. The specific functional roles of members of the SAUR (small auxin-up RNA) auxin early response gene family in the development of cucumber plants, however, remain to be fully clarified. Here, 62 SAUR family genes were identified, followed by their classification into 7 groups that included several functionally associated cis-regulatory elements. Phylogenetic tree and chromosomal location-based analyses revealed a high degree of homology between two cucumber gene clusters and other plants in the Cucurbitaceae family. These findings, together with the results of an RNA-seq analysis, revealed high levels of CsSAUR31 expression within the root and male flower tissues. Plants overexpressing CsSAUR31 exhibited longer roots and hypocotyls. Together, these results provide a basis for further efforts to explore the roles that SAUR genes play in cucumber plants, while also expanding the pool of available genetic resources to guide research focused on plant growth and development.

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.

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). 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. 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.

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.

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. 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. 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.

Overexpression of CsERF025 induces fruit bending by promoting the production of ethylene.

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. 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. 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.