Transcriptomic profiling reveals the complex interaction between a bipartite begomovirus and a cucurbitaceous host plant.

BACKGROUND: Begomoviruses are major constraint in the production of many crops. Upon infection, begomoviruses may substantially modulate plant biological processes. While how monopartite begomoviruses interact with their plant hosts has been investigated extensively, bipartite begomoviruses-plant interactions are understudied. Moreover, as one of the major groups of hosts, cucurbitaceous plants have been seldom examined in the interaction with begomoviruses. RESULTS: We profiled the zucchini transcriptomic changes induced by a bipartite begomovirus squash leaf curl China virus (SLCCNV). We identified 2275 differentially-expressed genes (DEGs), of which 1310 were upregulated and 965 were downregulated. KEGG enrichment analysis of the DEGs revealed that many pathways related to primary and secondary metabolisms were enriched. qRT-PCR verified the transcriptional changes of twelve selected DEGs induced by SLCCNV infection. Close examination revealed that the expression levels of all the DEGs of the pathway Photosynthesis were downregulated upon SLCCNV infection. Most DEGs in the pathway Plant-pathogen interaction were upregulated, including some positive regulators of plant defenses. Moreover, the majority of DEGs in the MAPK signaling pathway-plant were upregulated. CONCLUSION: Our findings indicates that SLCCNV actively interact with its cucurbitaceous plant host by suppressing the conversion of light energy to chemical energy and inducing immune responses. Our study not only provides new insights into the interactions between begomoviruses and host plants, but also adds to our knowledge on virus-plant interactions in general.

A novel O-methyltransferase Cp4MP-OMT catalyses the final step in the biosynthesis of the volatile 1,4-dimethoxybenzene in pumpkin (Cucurbita pepo) flowers.

BACKGROUND: Floral scents play a crucial role in attracting insect pollinators. Among the compounds attractive to pollinators is 1,4-dimethoxybenzene (1,4-DMB). It is a significant contributor to the scent profile of plants from various genera, including economically important Cucurbita species. Despite its importance, the biosynthetic pathway for the formation of 1,4-DMB was not elucidated so far. RESULTS: In this study we showed the catalysis of 1,4-DMB in the presence of 4-methoxyphenol (4-MP) by protein extract from Styrian oil pumpkin (Cucurbita pepo) flowers. Based on this finding, we identified a novel O-methyltransferase gene, Cp4MP-OMT, whose expression is highly upregulated in the volatile-producing tissue of pumpkin flowers when compared to vegetative tissues. OMT activity was verified by purified recombinant Cp4MP-OMT, illustrating its ability to catalyse the methylation of 4-MP to 1,4-DMB in the presence of cofactor SAM (S-(5'-adenosyl)-L-methionine). CONCLUSIONS: Cp4MP-OMT is a novel O-methyltransferase from C. pepo, responsible for the final step in the biosynthesis of the floral scent compound 1,4-DMB. Considering the significance of 1,4-DMB in attracting insects for pollination and in the further course fruit formation, enhanced understanding of its biosynthetic pathways holds great promise for both ecological insights and advancements in plant breeding initiatives.

An miR164-resistant mutation in the transcription factor gene CpCUC2B enhances carpel arrest and ectopic boundary specification in Cucurbita pepo flower development.

The sex determination process in cucurbits involves the control of stamen or carpel development during the specification of male or female flowers from a bisexual floral meristem, a function coordinated by ethylene. A gain-of-function mutation in the miR164-binding site of CpCUC2B, ortholog of the Arabidopsis transcription factor gene CUC2, not only produced ectopic floral meristems and organs, but also suppressed the development of carpels and promoted the development of stamens. The cuc2b mutation induced the transcription of CpCUC2B in the apical shoots of plants after female flowering but repressed other CUC genes regulated by miR164, suggesting a conserved functional redundancy of these genes in the development of squash flowers. The synergistic androecious phenotype of the double mutant between cuc2b and etr2b, an ethylene-insensitive mutation that enhances the production of male flowers, demonstrated that CpCUC2B arrests the development of carpels independently of ethylene and CpWIP1B. The transcriptional regulation of CpCUC1, CpCUC2, and ethylene genes in cuc2b and ethylene mutants also confirms this conclusion. However, the epistasis of cuc2b over aco1a, a mutation that suppresses stamen arrest in female flowers, and the down-regulation of CpACS27A in cuc2b female apical shoots, indicated that CpCUC2B promotes stamen development by suppressing the late ethylene production.

Simulation of early season herbivory via mechanical damage affects flower production in pumpkin (Cucurbita pepo ssp. pepo).

BACKGROUND: Damage from insect herbivores can elicit a wide range of plant responses, including reduced or compensatory growth, altered volatile profiles, or increased production of defence compounds. Specifically, herbivory can alter floral development as plants reallocate resources towards defence and regrowth functions. For pollinator-dependent species, floral quantity and quality are critical for attracting floral visitors; thus, herbivore-induced developmental effects that alter either floral abundance or attractiveness may have critical implications for plant reproductive success. Based on past work on resource trade-offs, we hypothesize that herbivore damage-induced effects are stronger in structural floral traits that require significant resource investment (e.g., flower quantity), as plants reallocate resources towards defence and regrowth, and weaker in secondary floral traits that require less structural investment (e.g., nectar rewards). SCOPE: In this study, we simulated early-season herbivore mechanical damage in the domesticated jack-o-lantern pumpkin Cucurbita pepo ssp. pepo and measured a diverse suite of floral traits over a 60-day greenhouse experiment. KEY RESULTS: We found that mechanical damage delayed the onset of male anthesis and reduced the total quantity of flowers produced. Additionally, permutational multivariate analysis of variance (PERMANOVA) indicated that mechanical damage significantly impacts overall floral volatile profile, though not output of sesquiterpenoids, a class of compounds known to recruit specialized cucumber beetle herbivores and squash bee pollinators. CONCLUSIONS: In summary, we show that C. pepo spp. pepo reduces investment in male flower production following mechanical damage, and that floral volatiles do exhibit shifts in production, indicative of damage-induced trait plasticity. Such reductions in male flower production could reduce the relative attractiveness of damaged plants to foraging pollinators in this globally relevant cultivated species.

Map-based cloning reveals Cpgp gene encoding an APRR2 protein to regulate the green fruit peel formation in Cucurbita pepo.

Fruit peel color is a major factor that influences fruit quality and customers' demand. However, the molecular mechanisms underlying the green fruit peel color trait of Cucurbita pepo L. remain unknown. Two parental lines, RP16 and RP38, were used to study the fruit peel color trait in C. pepo. The parental line RP16 shows white peel color, whereas RP38 exhibits green peel color. 384 F2 populations were used to identify the inheritance pattern associated with green fruit and white fruit peel in Cucurbita pepo L. 293 F2 individuals were white, and 91 F2 individuals were green, resulting in a ratio of 3:1. Hence, white peel is dominant over the green fruit peel trait, and a single recessive green peel gene (Cpgp) controls the green fruit peel. The fruit chlorophyll (Chll) content decreases as fruit matures in the RP16 line. In contrast, Chll increases during the fruit growing periods on fruit peels of the RP38 line. The BSA-sequence analysis revealed the Cpgp locus on Chr5, within a 2.3 Mb region. Subsequent fine-mapping analysis, using 699 F2 plants, narrowed down this region to 23.90 kb on the same chromosome. Within this region, two annotated genes, namely Cp4.1LG05g02070 and Cp4.1LG05g02060, are present. These genes are predicted to encode a two-component Arabidopsis Pseudo-Response Regulator 2-like protein (APRR2), which may be involved in green pigmentation processes in plants. Consequently, sequence alignment and gene expression analyses at various fruit development stages supported that Cp4.1LG05g02070 may be the primary candidate gene responsible for regulating the green fruit peel color trait in Cucurbita pepo L. This study may provide a basis for further study on the basic mechanisms that control the fruit peel colors in Cucurbita spp. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-024-01492-7.

Genome-Wide Identification of the WRKY Gene Family and Functional Characterization of CpWRKY5 in Cucurbita pepo.

The WRKY gene family is crucial for regulating plant growth and development. However, the WRKY gene is rarely studied in naked kernel formation in hull-less Cucurbita pepo L. (HLCP), a natural mutant that lacks the seed coat. In this research, 76 WRKY genes were identified through bioinformatics-based methods in C. pepo, and their phylogenetics, conserved motifs, synteny, collinearity, and temporal expression during seed coat development were analyzed. The results showed that 76 CpWRKYs were identified and categorized into three main groups (I-III), with Group II further divided into five subgroups (IIa-IIe). Moreover, 31 segmental duplication events were identified in 49 CpWRKY genes. A synteny analysis revealed that C. pepo shared more collinear regions with cucumber than with melon. Furthermore, quantitative RT-PCR (qRT-PCR) results indicated the differential expression of CpWRKYs across different varieties, with notable variations in seed coat development between HLCP and CP being attributed to differences in CpWRKY5 expression. To investigate this further, CpWRKY5-overexpression tobacco plants were generated, resulting in increased lignin content and an upregulation of related genes, as confirmed by qRT-PCR. This study offers valuable insights for future functional investigations of CpWRKY genes and presents novel information for understanding the regulation mechanism of lignin synthesis.

Morphological Analyses and QTL Mapping of Mottled Leaf in Zucchini (Cucurbita pepo L.).

The mottled leaf is one of the agronomic traits of zucchini and can be applied as a marker trait in aggregation breeding. However, the genetic mechanism responsible for mottled leaf has yet to be elucidated. In the present study, we used two inbred lines (line '19': silver mottled leaf; line '113': normal leaf) as parents for the physiological and genetic analysis of mottled leaf. The synthesis and net photosynthetic rate of chlorophyll were not significantly affected in the mottled areas of leaves. However, we detected a large space between the palisade parenchyma in the leaf mottle area of line '19', which may have caused the mottled leaf phenotype. Light also plays an important role in the formation of mottled leaf, and receiving light during the early stages of leaf development is a necessary factor. Genetic analysis has previously demonstrated that mottled leaf is a quantitative trait that is controlled by multiple genes. Based on the strategy of quantitative trait locus sequencing (QTL-seq), two QTLs were identified on chromosomes 1 and 17, named CpML1.1 and CpML17.1, respectively. Two major loci were identified using R/qtl software version 1.66 under greenhouse conditions in April 2019 (2019A) and April 2020 (2020A) and under open cultivation conditions in May 2020 (2020M). The major QTL, CpML1.1, was located in a 925.2-kb interval on chromosome 1 and explained 10.51%-24.15% of the phenotypic variation. The CpML17.1 was located in a 719.7-kb interval on chromosome 17 and explained 16.25%-38.68% of the phenotypic variation. Based on gene annotation, gene sequence alignment, and qRT-PCR analysis, the Cp4.1LG01g23790 at the CpML1.1 locus encoding a protein of the TPX2 family (target protein of Xklp2) may be a candidate gene for mottled leaf in zucchini. Our findings may provide a theoretical basis for the formation of mottled leaf and provide a foundation for the fine mapping of genes associated with mottled leaf. Molecular markers closely linked to mottled leaf can be used in molecular-assisted selection for the zucchini mottled leaf breeding.

Crosstalk between Ethylene, Jasmonate and ABA in Response to Salt Stress during Germination and Early Plant Growth in Cucurbita pepo.

The crosstalk of phytohormones in the regulation of growth and development and the response of plants to environmental stresses is a cutting-edge research topic, especially in crop species. In this paper, we study the role and crosstalk between abscisic acid (ABA), ethylene (ET), and jasmonate (JA) in the control of germination and seedling growth in water or in standard nutrient solution and under salt stress (supplemented with 100-200 mM NaCl). The roles of ET and JA were studied using squash ET- and JA-deficient mutants aco1a and lox3a, respectively, while the crosstalk between ET, JA, and ABA was determined by comparing the expression of the key ABA, JA, and ET genes in wild-type (WT) and mutant genotypes under standard conditions and salt stress. Data showed that ET and JA are positive regulators of squash germination, a function that was found to be mediated by downregulating the ABA biosynthesis and signaling pathways. Under salt stress, aco1a germinated earlier than WT, while lox3a showed the same germination rate as WT, indicating that ET, but not JA, restricts squash germination under unfavorable salinity conditions, a function that was also mediated by upregulation of ABA. ET and JA were found to be negative regulators of plant growth during seedling establishment, although ET inhibits both the aerial part and the root, while JA inhibits only the root. Both aco1a and lox3a mutant roots showed increased tolerance to salt stress, a phenotype that was found to be mainly mediated by JA, although we cannot exclude that it is also mediated by ABA.

Investigation of the effects of Bacillus subtilis and Bacillus thuringiensis as Bio-agents against powdery mildew (Podosphaera xanthii) disease in zucchini (Cucurbita pepo L.).

Fungi, bacteria, and viruses cause highly devastating diseases in species of the Cucurbitaceae family. Powdery mildew, a fungal disease, is one of the most important diseases of cucurbits. The pathogen, Podosphaera xanthii, is the most common causal agent of powdery mildew disease within cucurbits. The aim of this study was to investigate the effectiveness of the combined formulations of two biological agents, B. subtilis and B. thuringiensis, in combating powdery mildew disease, which represents a significant threat to C. pepo cultivation in Kayseri, Türkiye. The efficacy of six different treatments in controlling the disease agent P. xanthii was evaluated in susceptible zucchini genotypes. It was found that full-dose bacteria dilution application, before and after powdery mildew infection, as well as three- and five-fold bacteria dilutions application significantly prevented (1-2 scale value) powdery mildew disease on infected zucchini plants than the control application. There was a decrease in vegetative growth in the control-treated crops while plant growth increased significantly in bacterial-treated crops. Also, our findings showed that combined formulations made from Bacillus subtilis (61.29e and 3.3a strains) and Bacillus thuringiensis (2B3-1 and 2B2-2 strains) significantly increased the synthesis of plant defense enzymes such as DPPH, antioxidant, proline production, total phenolic substance, and total flavonoid content. The application of B + PM resulted in the highest enzyme contents, quantified as follows: 22.91 mg AAE/g antioxidant, 2.01 mg/g KU proline, 10.03 mg GAE/g TPC, and 7.756 mg CE/g TFC. These enzymes may have played vital roles in triggering zucchini defense mechanisms, thereby significantly preventing powdery disease in the bacteria-treated crops.

First Report of Cucurbita Blossom Blight and Fruit Rot Caused by Choanephora cucurbitarum in Mexico.

In December 2022, blossom blight, abortion, and soft rot of fruits were observed on Cucurbita pepo L. var. Zucchini in Mexico under greenhouse conditions (temperatures of 10 to 32°C and relative humidity up to 90%). The disease incidence in about 50 plants analyzed was around 70% with a severity of nearly 90%. Mycelial growth on flower petals and fruit rot with brown sporangiophores was observed. Ten disinfested fruit tissues in 1% NaClO for 5 min and then rinsed twice in distilled water from the lesion edges were placed on potato dextrose agar culture medium (PDA) supplemented with acid lactic and then, the morphological characterization was carried out in V8 agar medium. After 48 h of growth at 27°C, the colonies were pale yellow with diffuse cottony mycelia that were non-septate and hyaline and produced both sporangiophores bearing sporangiola and sporangia. The sporangiola were brown, ranged from ellipsoid to ovoid, and had longitudinal striations that measured 22.7 to 40.5 (29.8) µm x 16.08 to 21.9 (14.5) µm long and wide, respectively (n=100). The sporangia were subglobose, had a diameter of 127.2 to 281.09 (201.7) µm (n=50), and contained ovoid sporangiospores that measured 26.5 to 63.1 (46.7) µm x 20.07 to 34.7 (26.3) µm long and wide, respectively (n=100) which had hyaline appendages at the ends. Based on these characteristics, the fungus was identified as Choanephora cucurbitarum (Ji-Hyun et al. 2016). For molecular identification, DNA fragments for the internal transcribed spacer (ITS) and the large subunit rRNA 28S (LSU) regions for two representative strains (CCCFMx01 and CCCFMx02) were amplified and sequenced with the primer pairs ITS1-ITS4 and NL1-LR3 (White et al. 1990; Vilgalys and Hester 1990). The ITS and LSU sequences were deposited in GenBank database (Accession numbers OQ269823-24 and OQ269827-28, respectively) for both strains. The Blast alignment showed from 99.84 to 100% identity with Choanephora cucurbitarum strains JPC1 (MH041502, MH041504), CCUB1293 (MN897836), PLR2 (OL790293), and CBS 178.76 (JN206235, MT523842). To confirm the specie identification, the evolutionary analyses were conducted from the concatenated sequences of the ITS and LSU of C. cucurbitarum and other mucoralean species with the Maximum Likelihood method and Tamura-Nei model included in the software MEGA11. The pathogenicity test was demonstrated using five surface-sterilized zucchini fruits inoculated with a sporangiospores suspension containing a concentration of 1 x 105 esp/mL on two sites per fruit (20 µL each) that previously were wounded with a sterile needle. For fruit control, 20 µL of sterile water was used. Three days after inoculation under humidity conditions at 27°C, white mycelia and sporangiola growth with a soaked lesion were observed. That fruit damage was not observed on the control fruits. C.cucurbitarum was reisolated from lesions on PDA and V8 medium which was confirmed by morphological characterization fulfilling Koch's postulates. Blossom blight, abortion, and soft rot of fruits caused by C. cucurbitarum were observed on Cucurbita pepo and C. moschata in Slovenia and Sri Lanka (Zerjav and Schroers 2019; Emmanuel et al. 2021). This pathogen has the capability to infect a wide variety of plants worldwide (Kumar et al. 2022; Ryu et al. 2022). There are no reports of C. cucurbitarum causing agricultural losses in Mexico, and this is the first report causing the disease symptoms in Cucurbita pepo in this country; however, this fungus was found in the soil of papaya-producing areas and it is considered an important plant pathogenic fungus. Therefore, strategies for their control are highly recommended to avoid spreading the disease (Cruz-Lachica et al. 2018).

First Report of Cucumber Green Mottle Mosaic Virus Infecting Zucchini (Cucurbita pepo) and Wax Gourd (Benincasa hispida) in China.

Cucumber green mottle mosaic virus (CGMMV) was first discovered in China in 2003 and caused an epidemic in 2005. In China, the virus has been reported in gourd crops including watermelons, cucumbers, melons, etc (Sui et al. 2019). In Shandong Province, China from September 2014 to 2017, approximately 30% of zucchini (Cucurbita pepo) and wax gourd (Benincasa hispida) plants in commercial cucurbit fields, the two most important cash crops, exhibited chlorosis, mosaic, and mottling symptoms suspected to be caused by a tobamovirus. To identify the causative pathogens, ten zucchini and 15 wax gourd samples were collected from the commercial cucurbit fields. Total RNA was extracted and all samples were tested using reverse transcription PCR (RT-PCR) with TobamodF/TobamodR and TobamodF2/TobamodR2 (Li et al. 2018a). Five common Cucurbitaceae viruses were also tested: cucumber mosaic virus, papaya ringspot virus, squash mosaic virus, watermelon mosaic virus, and zucchini yellow mosaic virus (Ali et al. 2012). All samples generated positive results using tobamovirus generic primers but were negative for the five common Cucurbitaceae viruses. Amplification products (880 bp) from all samples were inserted into pMD19-T and recombinant clones were selected for Sanger sequencing. The results showed that zucchini green mottle mosaic virus, CGMMV, and tobacco mosaic virus (TMV) were detected in zucchini samples. CGMMV and TMV were detected in the wax gourd samples. To confirm the presence of these viruses, RT-PCR was performed using specific primer pairs, including CGMMV-cpf/CGMMV-cpr (Chen et al. 2006), ZG-F/ZG-R (Li et al. 2018b), and TMV-CP-F/TMV-CP-R (Srivastava et al. 2015). CGMMV was detected in all samples, with four zucchini and nine wax gourds only containing CGMMV. Zucchini (n=4; CGZ1-CGZ4) and wax gourd (n=4; CGWX1-CGWX4) isolates were cloned into pMD19-T and sequenced bidirectionally. The BLASTn results confirmed the presence of CGMMV, and the sequencing results were processed using DNAMAN Version (Lynnon Biosoft, San Ramon, CA, USA) and submitted to the GenBank database (https://www.ncbi.nlm.nih.gov/). A phylogenetic tree based on the CGMMV coat protein (CP) was constructed using CGZ1-CGZ4 (OP779762-OP779765), CGWX1-CGWX4 (OP779766-OP779769), and representative CGMMV sequences from GenBank. Sequence analysis of the CP demonstrated that CGMMV-zucchini and -wax gourd isolates belonged to an independent branch of the Chinese muskmelon AH-FT197 isolate (KU175639) and had 100% identity with the AH-FT197 isolate. To confirm their infectivity, leaf sap extract of CGZ4 and CGWX4 in phosphate buffer (0.1 M, pH 7.0) was mechanically inoculated on leaves of virus-free zucchini seedlings (Cucurbita pepo cv. Zaoqingyidai, 4-leaf-stage, n = 10) or virus-free wax gourd seedlings (Benincasa hispida cv. Tiezhu 2, n = 10). Ten days after inoculation, all plants exhibited symptoms (systemic chlorosis, mosaic, and mottling) similar to those of diseased plants in the field. Control seedlings inoculated with phosphate buffer remained symptomless. RT-PCR analysis using the CGMMV-cpf/CGMMV-cpr primer confirmed that all ten zucchini or wax gourd seedlings were infected with CGMMV, and all the control plants were free from CGMMV. To the best of our knowledge, this is the first report on zucchini and wax gourd as natural hosts for CGMMV in China. CGMMV is a highly contagious seed-borne virus and further attention should be paid to its spread in cucurbit crops.

The role of alanine synthesis and nitrate-induced nitric oxide production during hypoxia stress in Cucurbita pepo nectaries.

Floral nectar is a sugary solution produced by nectaries to attract and reward pollinators. Nectar metabolites, such as sugars, are synthesized within the nectary during secretion from both pre-stored and direct phloem-derived precursors. In addition to sugars, nectars contain nitrogenous compounds such as amino acids; however, little is known about the role(s) of nitrogen (N) compounds in nectary function. In this study, we investigated N metabolism in Cucurbita pepo (squash) floral nectaries in order to understand how various N-containing compounds are produced and determine the role of N metabolism in nectar secretion. The expression and activity of key enzymes involved in primary N assimilation, including nitrate reductase (NR) and alanine aminotransferase (AlaAT), were induced during secretion in C. pepo nectaries. Alanine (Ala) accumulated to about 35% of total amino acids in nectaries and nectar during peak secretion; however, alteration of vascular nitrate supply had no impact on Ala accumulation during secretion, suggesting that nectar(y) amino acids are produced by precursors other than nitrate. In addition, nitric oxide (NO) is produced from nitrate and nitrite, at least partially by NR, in nectaries and nectar. Hypoxia-related processes are induced in nectaries during secretion, including lactic acid and ethanolic fermentation. Finally, treatments that alter nitrate supply affect levels of hypoxic metabolites, nectar volume and nectar sugar composition. The induction of N metabolism in C. pepo nectaries thus plays an important role in the synthesis and secretion of nectar sugar.

Transcriptomic and genomic analysis provides new insights in molecular and genetic processes involved in zucchini ZYMV tolerance.

BACKGROUND: Cucurbita pepo is highly susceptible to Zucchini yellow mosaic virus (ZYMV) and the resistance found in several wild species cannot be considered as complete or broad-spectrum resistance. In this study, a source of tolerance introgressed in C. pepo (381e) from C. moschata, in True French (TF) background, was investigated 12 days post-inoculation (DPI) at transcriptomic and genomic levels. RESULTS: The comparative RNA-sequencing (RNA-Seq) of TF (susceptible to ZYMV) and 381e (tolerant to ZYMV) allowed the evaluation of about 33,000 expressed transcripts and the identification of 146 differentially expressed genes (DEGs) in 381e, mainly involved in photosynthesis, transcription, cytoskeleton organization and callose synthesis. By contrast, the susceptible cultivar TF triggered oxidative processes related to response to biotic stimulus and activated key regulators of plant virus intercellular movement. In addition, the discovery of variants located in transcripts allowed the identification of two chromosome regions rich in Single Nucleotide Polymorphisms (SNPs), putatively introgressed from C. moschata, containing genes exclusively expressed in 381e. CONCLUSION: 381e transcriptome analysis confirmed a global improvement of plant fitness by reducing the virus titer and movement. Furthermore, genes implicated in ZYMV tolerance in C. moschata introgressed regions were detected. Our work provides new insight into the plant virus recovery process and a better understanding of the molecular basis of 381e tolerance.

Genome-wide identification and characterization of major latex-like protein genes responsible for crop contamination in Cucurbita pepo.

BACKGROUND: Zucchini plants (Cucurbita pepo) accumulate persistent organic pollutants (POPs) at high concentrations in their aerial parts, and major latex-like proteins (MLPs) play crucial roles in their accumulation. MLPs bind to POPs in root cells, MLP-POP complexes are then translocated into xylem vessels, and POPs are transported to the aerial parts. We previously identified three CpMLP genes (MLP-PG1, MLP-GR1, and MLP-GR3) as transporting factors for POPs; however, other studies have shown that the genomes of several plant species contain more than 10 MLP genes, thus, further MLP genes responsible for POP accumulation may have been overlooked. METHODS AND RESULTS: Here, we investigated the number of CpMLP genes by performing a hidden Markov model search against the C. pepo genome database and characterized their effects on POP accumulation by performing the expression analysis in the organs and in silico structural analysis. The C. pepo genome contained 21 CpMLP genes, and several CpMLP genes, including MLP-PG1 and MLP-GR3, were highly expressed in roots. 3D structural prediction showed that all examined CpMLPs contained a cavity with a hydrophobic region, which facilitated binding to POPs. CONCLUSIONS: The present study provides insights regarding CpMLP genes responsible for POP accumulation.

Genetic variation among pumpkin landraces based on seed qualities and molecular markers.

BACKGROUND: Germplasm identification is an essential connection linking the conservation and exploitation of crop genetic resources in several plant breeding programs. This study highlights the biochemical and molecular variations in a collection of pumpkin genotypes representing four climate zones. The information could help improve germplasm management and sustainable exploitation of the neglected genotypes. METHODS AND RESULTS: Chemical characterization and genetic diversity among nine Egyptian landraces of pumpkin (Cucurbita moschata Duchesne) were estimated using Diode Array (DDA) Near Infra-Red (NIR) technology and the Inter simple Sequence Repeat markers (ISSR). Pumpkin seeds were collected from various geographical parts of Egypt. The spectroscopic properties of pumpkin seeds were used to quantify the fat, moisture, protein, ash, fiber, and total carbohydrate contents. The ten ISSR primers generated a total number of 46 genotype-specific bands, and the total polymorphism produced in the tested landraces was 63.58%. Based on the ISSR data, the polymorphism analysis divided the nine pumpkin landraces into two main groups, two subgroups, and four sub subgroups. The most diverse pumpkin landraces were Alexandria and Sohag, with a similarity percentage of 49.6%. However, the highest calculated similarity value was 88.3% between Matruh and Gharbia. The resultant genotype-specific bands can be used as markers for future genotypic characterization of pumpkins. CONCLUSIONS: The study results could be helpful in the chemical phenotypic characterization and the parental selection and planning for future breeding programs for pumpkin improvement.

Selective Supercritical CO2 Extraction and Biocatalytic Valorization of Cucurbita pepo L. Industrial Residuals.

The valorization of biomass residuals constitutes a key aspect of circular economy and thus a major challenge for the scientific community. Among industrial wastes, plant residuals could represent an attractive source of bioactive compounds. In this context, a residue from the industrial extraction of Cucurbita pepo L. seeds, whose oil is commercialized for the treatment of genito-urinary tract pathologies, has been selected. Supercritical CO2 technology has been employed as a highly selective "green" methodology allowing the recovery of compounds without chemical degradation and limited operational costs. Free fatty acids have been collected in mild conditions while an enrichment in sterols has been selectively obtained from sc-CO2 extracts by appropriate modulation of process parameters (supercritical fluid pressure and temperature), hence demonstrating the feasibility of the technique to target added-value compounds in a selective way. Obtained fatty acids were thus converted into the corresponding ethanol carboxamide derivatives by lipase-mediated biocatalyzed reactions, while the hydroxylated derivatives of unsaturated fatty acids were obtained by stereoselective hydration reaction under reductive conditions in the presence of a selected FADH2-dependent oleate hydratase.

Impact of the microalga Dunaliella salina (Dunal) Teodoresco culture and its ß-carotene extract on the development of salt-stressed squash (Cucurbita pepo L. cv. Mabrouka).

Salinity is a major threat to crop production and global food security. Algae and their extracts containing bioactive compounds can enhance the salt tolerance of plants, including the salt-sensitive plants. The current study evaluated the efficacy of Dunaliella salina (Dunal) Teodoresco culture and/or its ß-carotene extract in improving the salt tolerance of squash (Cucurbita pepo L. cv. Mabrouka). Amendment of C. pepo with D. salina culture and/or its ß-carotene extract was more effective in alleviating the impact of moderate salinity imposed by seawater dilution of 2.5 dS m-1 than either low (0.55 dS m-1) or high (3.5 dS m-1) salinity, with a comparable effect to that of salicylic acid (SA). Plants that received a combination of D. salina culture and its ß-carotene extract showed significantly higher growth (total biomass, fruit productivity) and physiological attributes (photosynthetic pigments, nitrogen (N), phosphorus (P), and potassium (K+) contents) than those receiving either amendment alone, reaching up to 80-90% of the SA-treated plants at moderate salinity (2.5 dS m-1). The combination could enhance the antioxidant activity of moderately salt-stressed C. pepo via increasing carotenoids and phenolics contents, suggesting that this combination could enhance the adaptation of C. pepo to the moderate salinity. The present study recommends using the blooms of D. salina and its ß-carotene that is naturally secreted in situ in natural or synthetic open systems in improving the salt tolerance of C. pepo instead of using the expensive synthetic hormones. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01176-6.

Effect of added hydrocolloids on ready-to-eat courgette (Cucurbita pepo) puree ohmically treated.

The influence of two natural different hydrocolloids (apple and citrus pectin) on physical, rheological and textural parameters, bioactive compounds and antioxidant activity of the courgette (Cucurbita pepo) puree was studied. The experiment aimed the development of dysphagia-oriented food products, which need to meet special requirements as a challenge for food rheology and novel ready-to-eat products. The pectin was added in the range of 0.1-0.3%. The courgette puree was ohmically heated at 20 V/cm for 3 min. The ohmic heating was used to improve and preserve the main properties of the purees. The antioxidant activity is stimulated by the ohmic heating, the values ranging up to 58% compared with the control sample. The courgette purees with apple or citrus pectin has registered a pseudoplastic rheological behaviour. The hardness increases with 22% once with the application of the thermic treatment. FT-IR spectroscopy and confocal microscopy reveal the benefits of using the ohmic heating as a processing method for courgettes puree. The results demonstrated the importance of using ohmic heating in the obtaining of courgettes puree for people with dysphagia.

A comprehensive RNA-Seq-based gene expression atlas of the summer squash (Cucurbita pepo) provides insights into fruit morphology and ripening mechanisms.

BACKGROUND: Summer squash (Cucurbita pepo: Cucurbitaceae) are a popular horticultural crop for which there is insufficient genomic and transcriptomic information. Gene expression atlases are crucial for the identification of genes expressed in different tissues at various plant developmental stages. Here, we present the first comprehensive gene expression atlas for a summer squash cultivar, including transcripts obtained from seeds, shoots, leaf stem, young and developed leaves, male and female flowers, fruits of seven developmental stages, as well as primary and lateral roots. RESULTS: In total, 27,868 genes and 2352 novel transcripts were annotated from these 16 tissues, with over 18,000 genes common to all tissue groups. Of these, 3812 were identified as housekeeping genes, half of which assigned to known gene ontologies. Flowers, seeds, and young fruits had the largest number of specific genes, whilst intermediate-age fruits the fewest. There also were genes that were differentially expressed in the various tissues, the male flower being the tissue with the most differentially expressed genes in pair-wise comparisons with the remaining tissues, and the leaf stem the least. The largest expression change during fruit development was early on, from female flower to fruit two days after pollination. A weighted correlation network analysis performed on the global gene expression dataset assigned 25,413 genes to 24 coexpression groups, and some of these groups exhibited strong tissue specificity. CONCLUSIONS: These findings enrich our understanding about the transcriptomic events associated with summer squash development and ripening. This comprehensive gene expression atlas is expected not only to provide a global view of gene expression patterns in all major tissues in C. pepo but to also serve as a valuable resource for functional genomics and gene discovery in Cucurbitaceae.

Source:sink imbalance detected with leaf- and canopy-level spectroscopy in a field-grown crop.

The finely tuned balance between sources and sinks determines plant resource partitioning and regulates growth and development. Understanding and measuring metabolic indicators of source or sink limitation forms a vital part of global efforts to increase crop yield for future food security. We measured metabolic profiles of Cucurbita pepo (zucchini) grown in the field under carbon sink limitation and control conditions. We demonstrate that these profiles can be measured non-destructively using hyperspectral reflectance at both leaf and canopy scales. Total non-structural carbohydrates (TNC) increased 82% in sink-limited plants; leaf mass per unit area (LMA) increased 38% and free amino acids increased 22%. Partial least-squares regression (PLSR) models link these measured functional traits with reflectance data, enabling high-throughput estimation of traits comprising the sink limitation response. Leaf- and canopy-scale models for TNC had R2 values of 0.93 and 0.64 and %RMSE of 13 and 38%, respectively. For LMA, R2 values were 0.91 and 0.60 and %RMSE 7 and 14%; for free amino acids, R2 was 0.53 and 0.21 with %RMSE 20 and 26%. Remote sensing can enable accurate, rapid detection of sink limitation in the field at the leaf and canopy scale, greatly expanding our ability to understand and measure metabolic responses to stress.