Transcriptome profiling reveals the occurrence mechanism of bisexual flowers in melon (Cucumis melo L.).

Most cultivated melons are andromonoecies in which male flowers arose both in main stem and lateral branches but bisexual flowers only emerged from the leaf axils of lateral branches. However, bisexual flowers emerged in leaf axils of main stem after ethephon treatment. Therefore, the mechanism regulating the occurrence of bisexual flowers were investigated by performing transcriptome analysis in two comparison sets: shoot apex of main stem (MA) versus that of lateral branches (LA), and shoot apex of main stem after ethephon treatment (Eth) versus control (Cont). KEGG results showed that genes involved in "plant hormone signal transduction", "MAPK signaling pathway" and "carbon metabolism" were significantly upregulated both in LA and Eth. Further, details of DEGs involved in ethylene signaling pathway were surveyed and six genes were co-upregulated in two comparison sets. Among these, CmERF1, downstream in ethylene signaling pathway, showed the most significantly difference and expressed higher in bisexual buds than that in male buds. Furthermore, fifteen DEGs were found to contain GCC box or CRT/DRE cis-element for CmERF1 in their putative promoter region, and these DEGs involved in several plant hormones signaling pathway, camalexin synthesis, carbon metabolism and plant pathogen interaction.

Differential Effects of Aquaponic Production System on Melon (Cucumis melo L.) Fruit Quality.

We investigated the effect on melon fruits of "fish water" alone or in combination with a supplement of synthetic fertilizers in a nutrient solution or foliar application of Ca(NO3)2. These treatments were compared with a traditional soilless system with synthetic fertilizers and no reuse of the nutrient solution. The results show that the treatments with recirculation of fish water and with the foliar supplement yielded fruits of greater weight and size but with reduced lightness and lower concentrations of proteins, NO3-, K+, and total amino acids. The supply of synthetic nutrients to the roots or leaves caused a reduction in the sugar concentrations and the antioxidant activity of these fruits. The use of fish water (alone or with an amendment) increased spermine and putrescine with respect to the traditional soilless crop management. The results for these bioactive compounds in melons should be considered for maintenance of health with age.

Compound repair effect of carbon dots and Fe2+ on iron deficiency in Cucumis melon L.

Iron-deficiency is one of the most widespread micronutrient deficiency faced by plants, and proper iron supplementation is essential for the growth of crops and for people to obtain iron from food. In order to explore new methods of iron supplementation, we studied the repair effect of CDs on iron-deficient (Cucumis melo L.) muskmelon. Iron-deficient muskmelons were treated with different concentrations of Fe2+, CDs and their complexes. The results showed that CDs significantly increased the iron transport rate and it is noteworthy that 75 mg/L CDs increased the iron transport rate of 0.7 mg/L Fe2+ by 134%. The compound treatment reduced the oxidative stress caused by iron deficiency, such as the CAT activity in the leaves of the compound treatment group was 10%-50% lower than that of the iron supplementation alone. Fluorescent imaging results of melon proved that CDs entered into the muskmelon seedlings. In combination with the above results and the adsorption of CDs, we speculated that the way CDs promoted iron absorption and transport was most likely to combine with Fe2+ and co-transport in melon, which changed the content of reactive oxygen species and other free radicals, thus causing changes of physiological state of melon. This study confirmed that CDs had a positive effect on the iron deficiency of muskmelon, and improved the growth of muskmelon under the condition of iron deficiency, which has a certain reference value for further optimization of iron supplementation solution.

Postharvest gaseous ozone treatment enhances quality parameters and delays softening in cantaloupe melon during storage at 6 °C.

BACKGROUND: A trial was conducted to evaluate the effect of postharvest gaseous ozone (O3 ) treatment on quality parameters and cell wall enzymes of cantaloupe melon cv. Caldeo during storage at 6 °C for 13 days. Fruits were kept in cold storage and treated with 0.15 ppm gaseous O3 during the day and 0.3 ppm overnight; control fruits (CK) were stored in normal atmosphere. RESULTS: Firmness was higher and ethylene concentration significantly lower in O3 fruits compared with CK fruits. During storage, microbial counts were lower in both O3 and CK fruits; from day 9, O3 fruits showed a significant decrease in mesophilic aerobes. Additionally, total carotenoids had a tendency to be higher, with no significant differences between CK and O3 fruits. The same trend was observed for ascorbic acid, colour, total soluble solids content and acidity. Finally, O3 treatment reduced the activities of cell wall enzymes α-arabinopyranosidase, ß-galactopyranosidase and polygalacturonase starting from day 3 of storage. Pectin methyl esterase activity did not seem to be affected by O3 treatment. CONCLUSION: Gaseous O3 treatment during cold storage was effective in decreasing ethylene production and delaying fruit softening in cantaloupe melon by extending quality maintenance. © 2017 Society of Chemical Industry.

Diversity in expression of phosphorus (P) responsive genes in Cucumis melo L.

BACKGROUND: Phosphorus (P) is a major limiting nutrient for plant growth in many soils. Studies in model species have identified genes involved in plant adaptations to low soil P availability. However, little information is available on the genetic bases of these adaptations in vegetable crops. In this respect, sequence data for melon now makes it possible to identify melon orthologues of candidate P responsive genes, and the expression of these genes can be used to explain the diversity in the root system adaptation to low P availability, recently observed in this species. METHODOLOGY AND FINDINGS: Transcriptional responses to P starvation were studied in nine diverse melon accessions by comparing the expression of eight candidate genes (Cm-PAP10.1, Cm-PAP10.2, Cm-RNS1, Cm-PPCK1, Cm-transferase, Cm-SQD1, Cm-DGD1 and Cm-SPX2) under P replete and P starved conditions. Differences among melon accessions were observed in response to P starvation, including differences in plant morphology, P uptake, P use efficiency (PUE) and gene expression. All studied genes were up regulated under P starvation conditions. Differences in the expression of genes involved in P mobilization and remobilization (Cm-PAP10.1, Cm-PAP10.2 and Cm-RNS1) under P starvation conditions explained part of the differences in P uptake and PUE among melon accessions. The levels of expression of the other studied genes were diverse among melon accessions, but contributed less to the phenotypical response of the accessions. CONCLUSIONS: This is the first time that these genes have been described in the context of P starvation responses in melon. There exists significant diversity in gene expression levels and P use efficiency among melon accessions as well as significant correlations between gene expression levels and phenotypical measurements.

Overexpression of the downward leaf curling (DLC) gene from melon changes leaf morphology by controlling cell size and shape in Arabidopsis leaves.

A plant-specific gene was cloned from melon fruit. This gene was named downward leaf curling (CmDLC) based on the phenotype of transgenic Arabidopsis plants overexpressing the gene. This expression level of this gene was especially upregulated during melon fruit enlargement. Overexpression of CmDLC in Arabidopsis resulted in dwarfism and narrow, epinastically curled leaves. These phenotypes were found to be caused by a reduction in cell number and cell size on the adaxial and abaxial sides of the epidermis, with a greater reduction on the abaxial side of the leaves. These phenotypic characteristics, combined with the more wavy morphology of epidermal cells in overexpression lines, indicate that CmDLC overexpression affects cell elongation and cell morphology. To investigate intracellular protein localization, a CmDLC-GFP fusion protein was made and expressed in onion epidermal cells. This protein was observed to be preferentially localized close to the cell membrane. Thus, we report here a new plant-specific gene that is localized to the cell membrane and that controls leaf cell number, size and morphology.

Molecular characterization and expression studies during melon fruit development and ripening of L-galactono-1,4-lactone dehydrogenase.

The last step of ascorbic acid (AA) biosynthesis is catalysed by the enzyme L-galactono-1,4-lactone dehydrogenase (GalLDH, EC 1.3.2.3), located on the inner mitochondrial membrane. The enzyme converts L-galactono-1,4-lactone to ascorbic acid (AA). In this work, the cloning and characterization of a GalLDH full-length cDNA from melon (Cucumis melo L.) are described. Melon genomic DNA Southern analysis indicated that CmGalLDH was encoded by a single gene. CmGalLDH mRNA accumulation was detected in all tissues studied, but differentially expressed during fruit development and seed germination. It is hypothesized that induction of CmGalLDH gene expression in ripening melon fruit contributes to parallel increases in the AA content and so playing a role in the oxidative ripening process. Higher CmGalLDH message abundance in light-grown seedlings compared with those raised in the dark suggests that CmGalLDH expression is regulated by light. Finally, various stresses and growth regulators resulted in no significant change in steady state levels of CmGalLDH mRNA in 20-d-old melon seedlings. To the authors' knowledge, this is the first report of GalLDH transcript induction in seed germination and differential gene expression during fruit ripening.