Cloning and Function Analysis of the CsTAU1 in Response to Salt-Alkali Stress.

To investigate the role of candidate genes for salt-alkali tolerance in cucumber (Cucumis sativus L.), this study screened CsTAU1 in the glutathione pathway from previous transcriptome data for cloning and functional analysis. Clone cucumber CsTAU1 contains one 675 bp open reading frame, containing one GST-N-Tau domain and one GST-C-Tau domain, and is expressed in cytoplasm. After successfully constructing overexpression vectors of CsTAU1 (+) and CsTAU1 (-), they were transferred into cucumber varieties 'D1909' (high salt alkali resistance) and 'D1604' (low salt alkali resistance) for salt-alkali resistance identification. It was found that under salt-alkali stress, CsTAU1 (+)-overexpressing plants showed strong resistance to salt-alkali stress, while CsTAU1 (-)-overexpressing plants showed the opposite situation. qRT-PCR analysis was performed on other glutathione pathway-related genes in CsTAU1-overexpressing plants. The expression patterns of LOC101219529 and LOC105434443 were the same as CsTAU1, and the introduction of CsTAU1 (+) increased the chlorophyll, α-Naphthylamine oxidation, glutathione S-transferase (GST), and catalase (CAT) content of cucumber. The research results provide a theoretical basis for cultivating salt-alkali-tolerant cucumber varieties.

Glutathione-dependent redox homeostasis is critical for chlorothalonil detoxification in tomato leaves.

Glutathione plays a critical role in plant growth, development and response to stress. It is a major cellular antioxidant and is involved in the detoxification of xenobiotics in many organisms, including plants. However, the role of glutathione-dependent redox homeostasis and associated molecular mechanisms regulating the antioxidant system and pesticide metabolism remains unclear. In this study, endogenous glutathione levels were manipulated by pharmacological treatments with glutathione synthesis inhibitors and oxidized glutathione. The application of oxidized glutathione enriched the cellular oxidation state, reduced the activity and transcript levels of antioxidant enzymes, upregulated the expression level of nitric oxide and Ca2+ related genes and the content, and increased the residue of chlorothalonil in tomato leaves. Further experiments confirmed that glutathione-induced redox homeostasis is critical for the reduction of pesticide residues. RNA sequencing analysis revealed that miRNA156 and miRNA169 that target transcription factor SQUAMOSA-Promoter Binding Proteins (SBP) and NUCLEAR FACTOR Y (NFY) potentially participate in glutathione-mediated pesticide degradation in tomato plants. Our study provides important clues for further dissection of pesticide degradation mechanisms via miRNAs in plants.

Exogenous γ-aminobutyric acid strengthens phenylpropanoid and nitrogen metabolism to enhance the contents of flavonoids, amino acids, and the derivatives in edamame.

γ-aminobutyric acid (GABA) has been reported to improve stress resistance in plants. Nonetheless, little is known about the effects of GABA on the nutritional quality and regulatory mechanisms of edamame. Therefore, we analyzed the flavonoid and amino acid (AA) metabolism and the effects of GABA on the nutrient content of edamame seeds through physiological and metabolomic analyses. Exogenous GABA increased endogenous GABA metabolism and GABA transaminase activity and enhanced the oxoglutarate content, which entered into nitrogen metabolism and increased the activity and expression of nitrogen metabolism-related enzymes, to accumulate AAs and bioactive peptides. Meanwhile, exogenous GABA induced the metabolism of flavonoids, including total flavonoids, anthocyanins, 6''-o-malonyglycitin, glycitin, ononin, cyanin, and ginkgetin, by increasing the activity and expression of flavonoid biosynthetic enzymes. This is the first study to reveal that GABA effectively improves the nutritional quality of edamame through the accumulation of AAs, bioactive peptides, isoflavones, anthocyanins, sugars, and organic acids.

A preliminary mapping of QTL qsg5.1 controlling seed germination in melon (Cucumis melo L.).

Melon (Cucumis melo L.) seed germination significantly affects its economic value. Cultivation of melon varieties with high germination ability and seedling vigor is beneficial in large-scale melon propagation. In this study, two melon genotypes differing in their germination ability, P5 with low and P10 with high germination ability, were used to identify the optimal seed germination conditions by evaluating different water immersion times and germination temperatures. The germination rate of the P5 and P10 parental genotypes and their segregating population, consisting of 358 F2:3 families, were evaluated for 2 years to identify their genetic basis. QTL analysis was performed on a high-density genetic map constructed using specific-locus amplified fragment sequencing (SLAF-seq). The germination rate of F1 and F2 populations treated with water immersion for 8 h at 28°C and measured at 48 h showed a normal distribution Genetic mapping carried out using the high-density genetic map revealed eight QTLs in chromosomes 2, 4, 5, 6, and 8 that control melon seed germination, of which 2020/2021-qsg5.1 was consistently significant in both years of experimentation. qsg5.1 explained 15.13% of the phenotypic variance with a LOD of 4.1. To fine map the candidate region of qsg5.1, eight cleaved amplified polymorphism sequence (CAPS) markers were used to construct a genetic map with another 421 F2 individual fruits. The major QTL qsg5.1 was located between SNP53 and SNP54 within a 55.96 Kb interval containing four genes. qRT-PCR gene expression analysis of the candidate genes showed that MELO3C031219.2 (Phosphorus transporter PHO-5) exhibited a significant difference in gene expression between the parental lines at 24, 32, and 48 h after germination, potentially being the underlying gene controlling melon seed germination. These results provide a theoretical basis for the molecular mechanisms controlling melon seed germination and can practically contribute to further improving germination to increase the propagation efficiency of commercial melon cultivars.

Glutathione Promotes Degradation and Metabolism of Residual Fungicides by Inducing UDP-Glycosyltransferase Genes in Tomato.

Reduced glutathione (GSH) is a key antioxidant, which plays a crucial role in the detoxification of xenobiotics in plants. In the present study, glutathione could reduce chlorothalonil (CHT) residues in tomatoes by inducing the expression of the UDP-glycosyltransferase (UGT) gene. In plants, UGT is an important glycosylation catalyst, which can respond to stresses in time by activating plant hormones and defense compounds. Given the importance of plant growth and development, the genome-wipe analyses of Arabidopsis and soybean samples have been carried out, though not on the tomato, which is a vital vegetable crop. In this study, we identified 143 UGT genes in the tomato that were unevenly distributed on 12 chromosomes and divided into 16 subgroups and found that a variety of plant hormones and stress response cis-elements were discovered in the promoter region of the SlUGT genes, indicating that the UGT genes were involved in several aspects of the tomato stress response. Transcriptome analysis and results of qRT-PCR showed that most SlUGT genes could be induced by CHT, and the expression of these genes was regulated by glutathione. In addition, we found that SlUGT genes could participate in plant detoxification through interaction with transcription factors. These findings further clarify the potential function of the UGT gene family in the detoxification of exogenous substances in tomatoes and provide valuable information for the future study of functional genomics of tomatoes.

Integrative analysis of different low-light-tolerant cucumber lines in response to low-light stress.

Introduction: Low light stress inhibits plant growth due to a line of physiological disruptions in plants, and is one of the major barriers to protected cucumber cultivation in northern China. Methods: To comprehensively understand the responses of cucumber seedlings to low-light stress, the low-light-tolerant line (M67) and The low-light-sensitive line (M14) were conducted for the analysis of photosynthetic phenotype, RNA sequencing (RNA-seq) and the expression level of photosynthesis-related genes in leaves under low-light stress and normal light condition (control). Results: The results showed that there was a sharp decrease in the photosynthate accumulation in the leaves of the sensitive line, M14, resulting in a large decrease in the photosynthetic rate (Pn) (with 31.99%) of leaves compared to that of the control, which may have been caused by damage to chloroplast ultrastructure or a decrease in chlorophyll (Chl) content. However, under the same low-light treatment, there was no large drop in the photosynthate accumulation and even no decrease in Pn and Chl content for the tolerant line, M67. Moreover, results of gene expression analysis showed that the expression level of genes CsPsbQ (the photosystem II oxygen-evolving enhancer protein 3 gene) and Csgamma (ATPase, F1 complex gene) in the M14 leaves decreased sharply (by 35.04% and 30.58%, respectively) compared with the levels in the M67 leaves, which decreased by 14.78% and 23.61%, respectively. The expression levels of genes involved in Chl synthesis and carbohydrate biosynthesis in the leaves of M14 decreased markedly after low-light treatment; in contrast, there were no sharp decreases or changes in leaves of M67. Discussion: Over all, the ability of cucumber to respond to low-light stress, as determined on the basis of the degree of damage in leaf structure and chloroplast ultrastructure, which corresponded to decreased gene expression levels and ATP phosphorylase activity, significantly differed between different low-light-tolerant lines, which was manifested as significant differences in photosynthetic capacity between them. Results of this study will be a reference for comprehensive insight into the physiological mechanism involved in the low-light tolerance of cucumber.

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.

Transcriptome analysis of differentially expressed genes during anther development stages on male sterility and fertility in Cucumis melo L. line.

The genic male sterility (MS) plays a major role in melon hybrids production, it could reduce the cost of pollination and increase the yield and quality. However, the molecular mechanism underlying genetic male sterility is yet poorly understood. The morphological differences of flower buds of melon were observed showed that the flower buds were tetrad when they were 1 mm stage and monocyte microspore when they were 2 mm stage. Electron microscopy showed that there was significant difference between MS lines and MF (male fertility) lines. In order to detect the global expression of the genes during the melon anther development and association with MS, 12 DEGs (differentially expressed genes) libraries were constructed from the anther of MS and MF in the bud stage with 1 and 2 mm diameter, respectively. A total of 765 DEGs expressed in anther during different developmental stage (MS 1 mm vs. MS 2 mm), 148 and 309 DEGs were found to be related to MS as compared to MF (MS 1 mm vs. MF 1 mm, and MS 2 mm vs. MF 2 mm) at a false discovery rate FDR <0.01. Among these, 10 DEGs were expressed in all the three comparisons, including transcription factor bHLH genes. Among the DEGs in RNA-seq analysis, 28 were validated by qRT-PCR. Of these, a number of genes were involved in ABC transfactor B family, cytochrome-related genes, hormone-related genes (auxin transporter, gibberellin-regulated protein), MADS-box protein genes, F-box protein genes, peroxidase-related, and Zinc finger protein genes. These genes are involved in many biological pathways, including starch and sucrose metabolism, signal transduction mechanisms and transcription factors, etc. Compared to the same developmental stage of MS and MF, the different developmental stages of MS indicated diverse gene regulation pathways involved in the anther development in MS. These results would provide novel insight into the global network to male sterility in melon.

Mapping and Preliminary Analysis of ABORTED MICROSPORES (AMS) as the Candidate Gene Underlying the Male Sterility (MS-5) Mutant in Melon (Cucumis melo L.).

Melon is an important agricultural and economic vegetable crop worldwide. The genetic male sterility mutant (ms-5) has a recessive nuclear gene that controls the male sterility germplasm. Male sterility could reduce the cost of F1 seed production in melon, but heterozygous fertile plants should be removed before pollination. In this study, bulked segregant analysis combined with specific length amplified fragment sequencing was applied to map the single nuclear male sterility recessive gene. A 30-kb candidate region on chromosome 9 located on scaffold 000048 and spanning 2,522,791 to 2,555,104 bp was identified and further confirmed by cleavage amplified polymorphic sequence markers based on parental line resequencing data and classical mapping of 252 F2 individuals. Gene prediction indicated that six annotated genes are present in the 30-kb candidate region. Quantitative RT-PCR revealed significant differences in the expression level of the LOC103498166 ABORTED MICROSPORES (AMS) gene in male-sterile lines (ms-5) and male-fertile (HM1-1) lines during the 2-mm (tetrad) and 5-mm (the first pollen mitosis) periods, and negative regulation of the AMS candidate gene transcription factor was also detected. Sequencing and cluster analysis of the AMS transcription factor revealed five single-nucleotide polymorphisms between the parental lines. The data presented herein suggest that the AMS transcription factor is a possible candidate gene for single nuclear male sterility in melon. The results of this study will help breeders to identify male-sterile and -fertile plants at seeding as marker-assisted selection methods, which would reduce the cost of seed production and improve the use of male-sterile lines in melon.