ELONGATED HYPOTCOTYL5 and SPINE BASE SIZE1 together mediate light-regulated spine expansion in cucumber.

Plant trichome development is influenced by diverse developmental and environmental signals, but the molecular mechanisms involved are not well understood in most plant species. Fruit spines (trichomes) are an important trait in cucumber (Cucumis sativus L.), as they affect both fruit smoothness and commercial quality. Spine Base Size1 (CsSBS1) has been identified as essential for regulating fruit spine size in cucumber. Here, we discovered that CsSBS1 controls a season-dependent phenotype of spine base size in wild-type plants. Decreased light intensity led to reduced expression of CsSBS1 and smaller spine base size in wild-type plants, but not in the mutants with CsSBS1 deletion. Additionally, knockout of CsSBS1 resulted in smaller fruit spine base size and eliminated the light-induced expansion of spines. Overexpression of CsSBS1 increased spine base size and rescued the decrease in spine base size under low light conditions. Further analysis revealed that ELONGATED HYPOTCOTYL5 (HY5), a major transcription factor involved in light signaling pathways, directly binds to the promoter of CsSBS1 and activates its expression. Knockout of CsHY5 led to smaller fruit spine base size and abolished the light-induced expansion of spines. Taken together, our study findings have clarified a CsHY5-CsSBS1 regulatory module that mediates light-regulated spine expansion in cucumber. This finding offers a strategy for cucumber breeders to develop fruit with stable appearance quality under changing light conditions.

Construction and application of a new watermelon germplasm with the phenotype of dwarf and branchless.

Watermelon (Citrullus lanatus) is a widely cultivated cucurbitaceae crop appreciated by consumers worldwide. However, the long vine and abundant lateral branches of currently cultivated watermelon varieties hinder light simplification and mechanized cultivation, affecting plant spacing and row spacing requirements. To address this, the development of watermelon with dwarf and branchless traits has become a crucial direction for the industry. In previous studies, the genes controlling dwarf (Cldw-1) and branchless (Clbl) traits were mapped and cloned. Marker-assisted selection markers, dCAPS3 and dCAPS10, were developed for these traits, respectively. In this study, the dwarf germplasm WM102 and the branchless germplasm WCZ were crossed to obtain F1 .Further self-crossing of the F1 individuals resulted in the F2 population. Through multiple generations of self-pollination, a new watermelon germplasm DM with double mutation (dwarf and branchless) was obtained. DM exhibited stable inheritance without segregation. Moreover, DM was used as a donor parent for crossing with commercial watermelon materials, and near-isogenic lines (NILs) with the dwarf and branchless traits were developed. These NILs carry additional desirable agronomic traits and provide valuable genetic resources for future watermelon breeding programs, particularly in improving plant architecture and overall quality. The development and application of DM and NILs hold great potential for advancing the watermelon industry toward industrialization, large-scale cultivation, and enhanced plant architecture.

Sensing materials for fresh food quality deterioration measurement: a review of research progress and application in supply chain.

Fresh food are consumed in large quantities worldwide. During the supply chain, microbial growth in fresh food can lead to the production of a number of metabolites, which make food highly susceptible to spoilage and contamination. The quality of fresh food changes in terms of smell, tenderness, color and texture, which causes a decrease in freshness and consumers acceptance. Therefore, the quality monitoring of fresh food has become an essential part in the supply chain. As traditional analysis methods are highly specialized, expensive and have a small scope of application, which cannot be applied to the supply chain to realize real-time monitoring. Recently, sensing materials have received a lot of attention from researchers due to the low price, high sensitivity and high speed. However, the progress of research on sensing materials has not been critically evaluated. The study examines the progress of research in the application of sensing materials for fresh food quality monitoring. Meanwhile, indicator compounds for spoilage of fresh food are analyzed. Moreover, some suggestions for future research directions are given.

The WUSCHEL-related homeobox1 gene of cucumber regulates reproductive organ development.

The WUSCHEL-related homeobox1 (WOX1) transcription factor plays an important role in lateral growth of plant organs; however, the underlying mechanisms in the regulation of reproductive development are largely unknown. Cucumber (Cucumis sativus) has separate male and female flowers, facilitating the study of the role of WOX1 in stamen and carpel development. Here, we identified a mango fruit (mf) mutant in cucumber, which displayed multiple defects in flower growth as well as male and female sterility. Map-based cloning showed that Mf encodes a WOX1-type transcriptional regulator (CsWOX1), and that the mf mutant encodes a truncated protein lacking the conserved WUS box. Further analysis showed that elevated expression of CsWOX1 was responsible for the mutant phenotype in cucumber and Arabidopsis. Comparative transcriptome profiling revealed certain key players and CsWOX1-associated networks that regulate reproductive development. CsWOX1 directly interacts with cucumber SPOROCYTELESS (CsSPL), and many genes in the CsSPL-mediated pathway were down-regulated in plants with the mutant allele at the Mf locus. In addition, auxin distribution was affected in both male and female flowers of the mutant. Taking together, these data suggest that CsWOX1 may regulate early reproductive organ development and be involved in sporogenesis via the CsSPL-mediated pathway and/or modulate auxin signaling in cucumber.

Ethylene responsive factor ERF110 mediates ethylene-regulated transcription of a sex determination-related orthologous gene in two Cucumis species.

In plants, unisexual flowers derived from developmental sex determination form separate stamens and pistils that facilitate cross pollination. In cucumber and melon, ethylene plays a key role in sex determination. Six sex determination-related genes have been identified in ethylene biosynthesis in these Cucumis species. The interactions among these genes are thought to involve ethylene signaling; however, the underlying mechanism of regulation remains unknown. In this study, hormone treatment and qPCR assays were used to confirm expression of these sex determination-related genes in cucumber and melon is ethylene sensitive. RNA-Seq analysis subsequently helped identify the ethylene responsive factor (ERF) gene, CsERF110, related to ethylene signaling and sex determination. CsERF110 and its melon ortholog, CmERF110, shared a conserved AP2/ERF domain and showed ethylene-sensitive expression. Yeast one-hybrid and ChIP-PCR assays further indicated that CsERF110 bound to at least two sites in the promoter fragment of CsACS11, while transient transformation analysis showed that CsERF110 and CmERF110 enhance CsACS11 and CmACS11 promoter activity, respectively. Taken together, these findings suggest that CsERF110 and CmERF110 respond to ethylene signaling, mediating ethylene-regulated transcription of CsACS11 and CmACS11 in cucumber and melon, respectively. Furthermore, the mechanism involved in its regulation is thought to be conserved in these two Cucumis species.

A mutant in the CsDET2 gene leads to a systemic brassinosteriod deficiency and super compact phenotype in cucumber (Cucumis sativus L.).

KEY MESSAGE: A novel dwarf cucumber mutant, scp-2, displays a typical BR biosynthesis-deficient phenotype, which is due to a mutation in CsDET2 for a steroid 5-alpha-reductase. Brassinosteroids (BRs) are a group of plant hormones that play important roles in the development of plant architecture, and extreme dwarfism is a typical outcome of BR-deficiency. Most cucumber (Cucumis sativus L.) varieties have an indeterminate growth habit, and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems. In this study, we identified a spontaneous dwarf mutant, super compact-2 (scp-2), that also has dark green, wrinkle leaves. Genetic analyses indicated that scp-2 was different from two previously reported dwarf mutants: compact (cp) and super compact-1 (scp-1). Map-based cloning revealed that the mutant phenotype was due to two single nucleotide polymorphism and a single-base insertion in the CsDET2 gene that resulted in a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5α-reductase protein. Measurement of endogenous hormone levels indicated a reduced level of brassinolide (BL, a bioactive BR) in scp-2, and the mutant phenotype could be partially rescued by the application of epibrassinolide (EBR). In addition, scp-2 mutant seedlings exhibited dark-grown de-etiolation, and defects in cell elongation and vascular development. These data support that scp-2 is a BR biosynthesis-deficient mutant, and that the CsDET2 gene plays a key role in BR biosynthesis in cucumber. We also described the systemic BR responses and discussed the specific BR-related phenotypes in cucumber plants.

A novel allele of monoecious (m) locus is responsible for elongated fruit shape and perfect flowers in cucumber (Cucumis sativus L.).

KEY MESSAGE: A 14 bp deletion in CsACS2 gene encoding a truncated loss-of-function protein is responsible for elongated fruit shape and perfect flowers in cucumber. In cucumber (Cucumis sativus L.), sex expression and fruit shape are important components of biological and marketable yield. The association of fruit shape and sex expression is a very interesting phenomenon. The sex determination is controlled primarily by the F (female) and M (monoecy) loci. Homozygous recessive mm plants bear bisexual (perfect) flowers, and the fruits are often round shaped. CsACS2 encoding the 1-aminocyclopropane-1-carboxylic acid synthase has been shown to be the candidate gene for the m locus. We recently identified an andromonoecious cucumber line H38 that has bisexual flowers but elongated fruits. To rapidly clone this monoecious gene in H38, we developed a tri-parent mapping strategy, which took advantage of the high-density Gy14 × 9930 cucumber genetic map and the powder of bulk segregant analysis. Microsatellite markers from the Gy14 × 9930 map were used to screen two pairs of unisexual and bisexual bulks constructed from H38 × Gy14 and H38 × 9930 F2 populations. Polymorphic markers were identified and used to quickly develop a framework map and place the monoecious locus of H38 in cucumber chromosome 1. Further fine mapping allowed identification of a novel allele, m-1, at the monoecious locus to control the bisexual flower in H38, which was due to a 14 bp deletion in the third exon of the CsACS2 gene encoding a truncated loss-of-function protein of the cucumber 1-aminocyclopropane-1-carboxylic acid synthase. This new allele provides a valuable tool in understanding the molecular mechanisms of CsACS2 in the relationships of sex determination, fruit shape, and CsACS activities in cucumber.

Exogenous auxin-induced ENHANCER OF SHOOT REGENERATION 2 (ESR2) enhances femaleness of cucumber via activating CsACS2 gene.

Cucumber (Cucumis sativus L.) is a model for the study of sex differentiation in the last two decades. In cucumber, sex differentiation is mainly controlled by genetic material, but plant growth regulators can also influence or even change it. However, the effect of exogenous auxin application on cucumber sex differentiation is mostly limited in physiological level. In this study, we explored the effects of different exogenous auxin concentrations on the varieties with different mutant sex-controlling genotypes and found that there was a dosage effect of exogenous indole-3-acetic acid (IAA) on the enhancement of cucumber femaleness. Several ACC synthetase (ACS) family members could directly respond to the induction of exogenous IAA to improve endogenous ethylene synthesis, and this process can be independent on the previously identified sex-related ACC oxidase CsACO2. We further demonstrated that ENHANCER OF SHOOT REGENERATION 2 (ESR2), responding to the induction of exogenous auxin, could directly activate CsACS2 expression by combining the ERE cis-acting element regions in the promoter, and then increase endogenous ethylene content, which may induce femaleness. These findings reveal that exogenous auxin improves cucumber femaleness via inducing sex-controlling gene and promoting ethylene synthesis.

Gynoecy instability in cucumber (Cucumis sativus L.) is due to unequal crossover at the copy number variation-dependent Femaleness (F) locus.

Cucumber, Cucumis sativus is an important vegetable crop, and gynoecy has played a critical role in yield increase of hybrid cucumber production. Cucumber has a unique genetic system for gynoecious sex expression, which is determined by the copy number variation (CNV)-based, dominant, and dosage-dependent femaleness (F) locus. However, this gynoecy expression system seems unstable since monecious plants could often be found in F-dependent gynoecious cucumber inbreds. We hypothesized that gynoecy instability (gynoecy loss) may be due to unequal crossing over (UCO) during meiosis among repeat units of the CNV. In this study, using high throughput genome resequencing, fiber-FISH and genomic qPCR analyses, we first confirmed and refined the structure of the F locus, which was a CNV of a 30.2-kb tandem repeat. Gynoecious plants contained three genes: CsACS1, CsACS1G, and CsMYB, of which CsACS1G is a duplication of CsACS1 but with a recombinant distal promoter that may contribute to gynoecy sex expression. In two large populations from self-pollinated gynoecious inbred lines, 'gynoecy loss' mutants were identified with similar mutation rates (~0.12%). We show that these monecious mutants have lost CsACS1G. In addition, we identified gynoecious lines in natural populations that carry two copies of CSACS1G. We proposed a model to explain gynoecy instability in F-dependent cucumbers, which is caused by UCO among CSACS1/G units during meiosis. The findings present a convincing case that the phenotypic variation of an economically important trait is associated with the dynamic changes of copy numbers at the F locus. This work also has important implications in cucumber breeding.

WUSCHEL-related homeobox1 (WOX1) regulates vein patterning and leaf size in Cucumis sativus.

In plants, WUSCHEL-related homeobox1 (WOX1) homologs promote lamina mediolateral outgrowth. However, the downstream components linking WOX1 and lamina development remain unclear. In this study, we revealed the roles of WOX1 in palmate leaf expansion in cucumber (Cucumis sativus). A cucumber mango fruit (mf) mutant, resulting from truncation of a WOX1-type protein (CsWOX1), displayed abnormal lamina growth and defects in the development of secondary and smaller veins. CsWOX1 was expressed in the middle mesophyll and leaf margins and rescued defects of the Arabidopsis wox1 prs double mutant. Transcriptomic analysis revealed that genes involved in auxin polar transport and auxin response were highly associated with leaf development. Analysis of the cucumber mf rl (round leaf) double mutant revealed that CsWOX1 functioned in vein development via PINOID (CsPID1)-controlled auxin transport. Overexpression of CsWOX1 in cucumber (CsWOX1-OE) affected vein patterning and produced 'butterfly-shaped' leaves. CsWOX1 physically interacted with CsTCP4a, which may account for the abnormal lamina development in the mf mutant line and the smaller leaves in the CsWOX1-OE plants. Our findings demonstrated that CsWOX1 regulates cucumber leaf vein development by modulating auxin polar transport; moreover, CsWOX1 regulates leaf size by controlling CIN-TCP genes.

Gene Interactions Regulating Sex Determination in Cucurbits.

The family Cucurbitaceae includes many economically important crops, such as cucumber (Cucumis sativus), melon (Cucumis melo), watermelon (Citrullus lanatus), and zucchini (Cucurbita pepo), which share homologous gene pathways that control similar phenotypes. Sex determination is a research hotspot associated with yield and quality, and the genes involved are highly orthologous and conserved in cucurbits. In the field, six normal sex types have been categorized according to the distribution of female, male, or bisexual flowers in a given plant. To date, five orthologous genes involved in sex determination have been cloned, and their various combinations and expression patterns can explain all the identified sex types. In addition to genetic mechanisms, ethylene controls sex expression in this family. Two ethylene signaling components have been identified recently, which will help us to explore the ethylene signaling-mediated interactions among sex-related genes. This review discusses recent advances relating to the mechanism of sex determination in cucurbits and the prospects for research in this area.

A Wall-Associated Kinase Gene CaWAKL20 From Pepper Negatively Modulates Plant Thermotolerance by Reducing the Expression of ABA-Responsive Genes.

Heat stress has become a major threat to crop production due to global warming; however, the mechanisms underlying plant high-temperature sensing are not well known. In plants, the membrane-anchored receptor-like kinases (RLKs) relay environmental signals into the cytoplasm. In a previous study, we isolated a wall-associated RLK-like (WAKL) gene CaWAKL20 from pepper (Capsicum annuum L.). Here, the amino acid sequence of CaWAKL20 was characterized and found to consist of conserved domains of WAK/WAKL family, including an extracellular region containing a GUB-WAK binding domain and a degenerated EGF2-like domain; a transmembrane region; and an intercellular region with an STKc catalytic domain. Moreover, CaWAKL20 transcription was inhibited by heat stress, whereas it was induced by both ABA and H2O2 treatments. Silencing of CaWAKL20 enhanced pepper thermotolerance, while overexpression decreased Arabidopsis thermotolerance. Additionally, Arabidopsis lines overexpressing CaWAKL20 showed less sensitivity to ABA during seed germination and root growth. Finally, the survival rate of Arabidopsis seedlings under heat stress treatment was enhanced by ABA pre-treatment, while it was compromised by the overexpression of CaWAKL20. Furthermore, the heat-induced expression of several ABA-responsive genes and some key regulator genes for thermotolerance was decreased in Arabidopsis CaWAKL20-overexpression lines. These results suggest that CaWAKL20 negatively modulates plant thermotolerance by reducing the expression of ABA-responsive genes, laying a foundation for further investigation into the functional mechanisms of WAKs/WAKLs in plants undergoing environmental stresses.

Characterization of BiP Genes from Pepper (Capsicum annuum L.) and the Role of CaBiP1 in Response to Endoplasmic Reticulum and Multiple Abiotic Stresses.

Adverse environmental conditions have a detrimental impact on crop growth and development, and cause protein denaturation or misfolding. The binding protein (BiP) plays an important protective role by alleviating endoplasmic reticulum (ER) stress induced by misfolded proteins. In this study, we characterized three BiP genes (CaBiP1, CaBiP2, and CaBiP3) in pepper, an economically important vegetable and spice species. The role of CaBiP1 in plant tolerance to ER stress and adverse environmental conditions (including heat, salinity, osmotic and drought stress) were investigated. All the expected functional and signaling domains were detected in three BiP proteins, but the motifs and exon-intron distribution differed slightly in CaBiP3. CaBiP1 and CaBiP2 were constitutively expressed in all the tested tissues under both normal and stressed conditions, whereas CaBiP3 was mainly expressed following stress. Silencing of CaBiP1 reduced pepper tolerance to ER stress and various environment stresses, and was accompanied by increased H2O2 accumulation, MDA content, relative electric leakage (REL), water loss rate, and a reduction in soluble protein content and relative water content (RWC) in the leaves. Conversely, overexpression of CaBiP1 in Arabidopsis enhanced tolerance to ER stress and multiple environment stresses, as demonstrated by an increase in germination rate, root length, survival rate, RWC, the unfolded protein response (UPR) pathway, and a decrease in water loss rate. Our results suggest that CaBiP1 may contribute to plant tolerance to abiotic stresses by reducing ROS accumulation, increasing the water-retention ability, and stimulating UPR pathways and expression of stress-related genes.

The Edge Stresses and Phase Transitions for Magnetic BN Zigzag Nanoribbons.

The edge states are of particular importance to understand fundamental properties of finite two-dimensional (2D) crystals. Based on first-principles calculations, we investigated on the bare zigzag boron nitride nanoribbons (zzBNNRs) with different spin-polarized states well localized at and extended along their edges. Our calculations examined the edge stress, which is sensitively dependent on the magnetic edge states, for either B-terminated edge or N-terminated edge. Moreover, we revealed that different magnetic configurations lead to a rich spectrum of electronic behaviors at edges. Using an uniaxial tensile strain, we proposed the magnetic phase transitions and thereby obtained the metallic to half-metallic (or reverse) phase transitions at edges. It suggests zzBNNR as a promising candidate for potential applications of non-metal spintronic devices.