Abiotic stresses have a negative effect on crop production, affecting both vegetative and reproductive development. Ethylene plays a relevant role in plant response to environmental stresses, but the specific contribution of ethylene biosynthesis and signalling components in the salt stress response differs between Arabidopsis and rice, the two most studied model plants. In this paper, we study the effect of three gain-of-function mutations affecting the ethylene receptors CpETR1B, CpETR1A, and CpETR2B of Cucurbita pepo on salt stress response during germination, seedling establishment, and subsequent vegetative growth of plants. The mutations all reduced ethylene sensitivity, but enhanced salt tolerance, during both germination and vegetative growth, demonstrating that the three ethylene receptors play a positive role in salt tolerance. Under salt stress, etr1b, etr1a, and etr2b germinate earlier than WT, and the root and shoot growth rates of both seedlings and plants were less affected in mutant than in WT. The enhanced salt tolerance response of the etr2b plants was associated with a reduced accumulation of Na+ in shoots and leaves, as well as with a higher accumulation of compatible solutes, including proline and total carbohydrates, and antioxidant compounds, such as anthocyanin. Many membrane monovalent cation transporters, including Na+/H+ and K+/H+ exchangers (NHXs), K+ efflux antiporters (KEAs), high-affinity K+ transporters (HKTs), and K+ uptake transporters (KUPs) were also highly upregulated by salt in etr2b in comparison with WT. In aggregate, these data indicate that the enhanced salt tolerance of the mutant is led by the induction of genes that exclude Na+ in photosynthetic organs, while maintaining K+/Na+ homoeostasis and osmotic adjustment. If the salt response of etr mutants occurs via the ethylene signalling pathway, our data show that ethylene is a negative regulator of salt tolerance during germination and vegetative growth. Nevertheless, the higher upregulation of genes involved in Ca2+ signalling (CpCRCK2A and CpCRCK2B) and ABA biosynthesis (CpNCED3A and CpNCED3B) in etr2b leaves under salt stress likely indicates that the function of ethylene receptors in salt stress response in C. pepo can be mediated by Ca2+ and ABA signalling pathways.

A methanesulfonate-generated mutant has been identified in Cucurbita pepo that alters sex determination. The mutation converts female into hermaphrodite flowers and disrupts the growth rate and maturation of petals and carpels, delaying female flower opening, and promoting the growth rate of ovaries and the parthenocarpic development of the fruit. Whole-genome resequencing allowed identification of the causal mutation of the phenotypes as a missense mutation in the coding region of CpACO1A, which encodes for a type I ACO enzyme that shares a high identity with Cucumis sativus CsACO3 and Cucumis melo CmACO1. The so-called aco1a reduced ACO1 activity and ethylene production in the different organs where the gene is expressed, and reduced ethylene sensitivity in flowers. Other sex-determining genes, such as CpACO2B, CpACS11A, and CpACS27A, were differentially expressed in the mutant, indicating that ethylene provided by CpACO1A but also the transcriptional regulation of CpACO1A, CpACO2B, CpACS11A, and CpACS27A are responsible for determining the fate of the floral meristem toward a female flower, promoting the development of carpels and arresting the development of stamens. The positive regulation of ethylene on petal maturation and flower opening can be mediated by inducing the biosynthesis of JA, while its negative control on ovary growth and fruit set could be mediated by its repressive effect on IAA biosynthesis.

Tomato leaf curl New Delhi virus is an emerging whitefly-borne species of begomovirus in Mediterranean regions that poses a severe threat to cucurbit crops of the genus Cucurbita. Until now, only two sources of resistance have been identified in Cucurbita spp., these being PI604506 (cv. Large Cheese) and PI381814 (Indian landrace), both of C. moschata. The resistance of cv. Large Cheese is conferred by a single recessive gene located on chromosome 8. The objective of the present investigation was to screen for tomato leaf curl New Delhi virus (ToLCNDV) resistance among 105 accessions drawn from five species of Cucurbita and, if high resistance was found in any of them, determine the mode of inheritance. Screening was conducted using whitefly-mediated inoculation on all 105 accessions. The accessions showing some resistance were further screened by mechanical inoculation as well as by quantitative PCR-based diagnostics. The results showed that, overall, the accessions of C. pepo and C. maxima were the most susceptible, those of C. argyrosperma and C. ecuadorensis intermediate, and those of C. moschata most resistant to ToLCNDV. Only one accession of C. moschata, BSUAL-252, originating from Japan, was highly resistant to ToLCNDV, showing no symptoms after either method of inoculation, and absence of virus accumulation. Upon crossing BSUAL-252 with a susceptible accession of C. moschata, BSUAL-265, the resistance was observed to be conferred by a single dominant gene. This gene is not linked to the genomic region on chromosome 8 where the locus of the previously identified recessive gene for ToLCNDV resistance resides.

their role in flower development and sex determination, but also by the impact of the SNPs and indels differentially detected in the two sequenced bulks.

Pomegranate (Punica granatum L.) is a common edible fruit. Its juice can be used as a source of antioxidative compounds, primarily polyphenols and vitamin C, in addition to other vitamins and minerals. Nevertheless, little is still known about how the enzymatic machinery, mainly that related to oxidative metabolism, is influenced by the genotype and the environmental and climate conditions where pomegranate plants grow. In this work, seeds and juices from two pomegranate varieties (Valenciana and Mollar) grown in two different Spanish locations were assayed. Both varieties showed clear differences in their respective polypeptide profiles. The analysis of the isoenzymatic superoxide dismutase (SOD) activity pattern displayed one Mn-SOD and five CuZn-SODs (I–V) whose abundances depended on the variety. Furthermore, by immunoblot assays, at least one additional Fe-SOD with a subunit size of about 23 kDa was also detected in both varieties. Besides this, the presence of the H2O2-scavenging peroxisomal catalase in seeds and juice indicates that an active metabolism of reactive oxygen species (ROS) takes place in this fruit, but the two pomegranate varieties showed opposite activity profiles. The activities of the main NADPH-regenerating enzymes, including glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphlogluconate dehydrogenase (6PGDH), NADP-dependent isocitrate dehydrogenase (NADP-ICDH), and NADP-dependent malic enzyme (NADP-ME), were studied in the same plant materials, and they behaved differently depending on the genotype. Finally, our data demonstrate the presence of two specific enzymes of the peroxisomal glyoxylate cycle, malate synthase (MS) and isocitrate lyase (ICL). These enzymes participate in oilseeds by channeling the lipid catabolism to the carbohydrate synthesis for further use in seed germination and early seedling growth. The results obtained in this work indicate that a similar mechanism to that reported in oilseeds may also operate in pomegranate.