Molecular characterization of a cucumber nitrate reductase (CsNR) gene under NO3 − stress

Transcription strategies related to photosynthesis and nitrogen metabolism of wheat in response to nitrogen deficiency

BACKGROUND

Agricultural yield is closely associated with nitrogen application. Thus, reducing the application of nitrogen without affecting agricultural production remains a challenging task. To understand the metabolic, physiological, and morphological response of wheat (Triticum aestivum) to nitrogen deficiency, it is crucial to identify the genes involved in the activated signaling pathways.

RESULTS

We conducted a hydroponic experiment using a complete nutrient solution (N1) and a nutrient solution without nitrogen (N0). Wheat plants under nitrogen-deficient conditions (NDC) showed decreased crop height, leaf area, root volume, photosynthetic rate, crop weight, and increased root length, root surface area, root/shoot ratio. It indicates that nitrogen deficiency altered the phenotype of wheat plants. Furthermore, we performed a comprehensive analysis of the phenotype, transcriptome, GO pathways, and KEGG pathways of DEGs identified in wheat grown under NDC. It showed up-regulation of Exp (24), and Nrt (9) gene family members, which increased the nitrogen absorption and down-regulation of Pet (3), Psb (8), Nar (3), and Nir (1) gene family members hampered photosynthesis and nitrogen metabolism.

CONCLUSIONS

We identified 48 candidate genes that were involved in improved photosynthesis and nitrogen metabolism in wheat plants grown under NDC. These genes may serve as molecular markers for genetic breeding of crops.

Cucumber Phospholipase D alpha gene overexpression in tobacco enhanced drought stress tolerance by regulating stomatal closure and lipid peroxidation

BACKGROUND

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. Both PLD and PA play key roles in plant growth, development, and cellular processes. PLD was suggested to mediate the regulation of stomatal movements by abscisic acid (ABA) as a response to water deficit. In this research, we characterized the roles of the cucumber phospholipase D alpha gene (CsPLDα, GenBank accession number EF363796) in the growth and tolerance of transgenic tobacco (Nicotiana tabacum) to drought stress.

RESULTS

The CsPLDα overexpression in tobacco lines correlated with the ABA synthesis and metabolism, regulated the rapid stomatal closure in drought stress, and reduced the water loss. The NtNCED1 expression levels in the transgenic lines and wild type (WT) were sharply up-regulated after 16 days of drought stress compared with those before treatment, and the expression level in the transgenic lines was significantly higher than that in the WT. The NtAOG expression level evidently improved after 8 and 16 days compared with that at 0 day of treatment and was significantly lower in the transgenic lines than in the WT. The ABA content in the transgenic lines was significantly higher than that in the WT. The CsPLDα overexpression could increase the osmolyte content and reduce the ion leakage. The proline, soluble sugar, and soluble protein contents significantly increased. By contrast, the electrolytic leakage and malondialdehyde accumulation in leaves significantly decreased. The shoot and root fresh and dry weights of the overexpression lines significantly increased. These results indicated that a significant correlation between CsPLDα overexpression and improved resistance to water deficit.

CONCLUSIONS

The plants with overexpressed CsPLDα exhibited lower water loss, higher leaf relative water content, and heavier fresh and dry matter accumulation than the WT. We proposed that CsPLDα was involved in the ABA-dependent pathway in mediating the stomatal closure and preventing the elevation of intracellular solute potential.

Effects of melatonin on seedling growth, mineral nutrition, and nitrogen metabolism in cucumber under nitrate stress

In China, excessive use of nitrogen fertilizers in glasshouses leads to nitrate accumulations in soil and plants, which then limits productivity. Melatonin, an evolutionarily highly conserved molecule, has a wide range of functions in plants. We analyzed the effects of melatonin pretreatment on the growth, mineral nutrition, and nitrogen metabolism in cucumber (Cucumis sativus L. "Jin You No. 1") when seedlings were exposed to nitrate stress. An application of 0.1 mmol/L melatonin significantly improved the growth of plants and reduced their susceptibility to damage due to high nitrate levels (0.6 mol/L) during the ensuing period of stress treatment. Although excess nitrate led to an increase in the concentrations of nitrogen, potassium, and calcium, as well as a decrease in levels of phosphorus and magnesium, exogenous melatonin generally had the opposite effect except for a further rise in calcium concentrations. Pretreatment also significantly reduced the accumulations of nitrate nitrogen and ammonium nitrogen and enhanced the activities of enzymes involved in nitrogen metabolism. Expression of Cs-NR and Cs-GOGAT, two genes that function in that metabolism, was greatly down-regulated when plants were exposed to 0.6 mol/L nitrate, but was up-regulated in plants that had received the 0.1 mmol/L melatonin pretreatment. Our results are the first evidence that melatonin has an important role in modulating the composition of mineral elements and nitrogen metabolism, thereby alleviating the inhibitory effect on growth normally associated with nitrate stress.

Mining, identification and function analysis of microRNAs and target genes in peanut (Arachis hypogaea L.)

In the present investigation, a total of 60 conserved peanut (Arachis hypogaea L.) microRNA (miRNA) sequences, belonging to 16 families, were identified using bioinformatics methods. There were 392 target gene sequences, identified from 58 miRNAs with Target-align software and BLASTx analyses. Gene Ontology (GO) functional analysis suggested that these target genes were involved in mediating peanut growth and development, signal transduction and stress resistance. There were 55 miRNA sequences, verified employing a poly (A) tailing test, with a success rate of up to 91.67%. Twenty peanut target gene sequences were randomly selected, and the 5' rapid amplification of the cDNA ends (5'-RACE) method were used to validate the cleavage sites of these target genes. Of these, 14 (70%) peanut miRNA targets were verified by means of gel electrophoresis, cloning and sequencing. Furthermore, functional analysis and homologous sequence retrieval were conducted for target gene sequences, and 26 target genes were chosen as the objects for stress resistance experimental study. Real-time fluorescence quantitative PCR (qRT-PCR) technology was applied to measure the expression level of resistance-associated miRNAs and their target genes in peanut exposed to Aspergillus flavus (A. flavus) infection and drought stress, respectively. In consequence, 5 groups of miRNAs & targets were found accorded with the mode of miRNA negatively controlling the expression of target genes. This study, preliminarily determined the biological functions of some resistance-associated miRNAs and their target genes in peanut.

Overexpression of Cucumber Phospholipase D alpha Gene (CsPLDα) in Tobacco Enhanced Salinity Stress Tolerance by Regulating Na+-K+ Balance and Lipid Peroxidation

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. In this research, we characterized the roles of the cucumber phospholipase D alpha gene (PLDα, GenBank accession number EF363796) in growth and tolerance to short- and long-term salt stress in transgenic tobacco (Nicotiana tabacum). Fresh and dry weights of roots, PLD activity and content, mitogen activated protein kinase (MAPK) gene expression, Na⁺-K⁺ homeostasis, expression of genes encoding ion exchange, reactive oxygen species (ROS) metabolism and osmotic adjustment substances were investigated in wild type (WT) and CsPLDα-overexpression tobacco lines grown under short- and long-term high salt (250 mM) stress. Under short-term stress (5 h), in both overexpression lines, the PA content, and the expression levels of MAPK and several genes related to ion exchange (NtNHX1, NtNKT1, NtHAK1, NtNHA1, NtVAG1), were promoted by high PLD activity. Meanwhile, the Na⁺/K⁺ ratio decreased. Under long-term stress (16 days), ROS scavenging systems (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase activities) in leaves of transgenic lines were more active than those in WT plants. Meanwhile, the contents of proline, soluble sugar, and soluble protein significantly increased. In contrast, the contents of O₂^•- and H₂O₂, the electrolytic leakage and the accumulation of malondialdehyde in leaves significantly decreased. The root fresh and dry weights of the overexpression lines increased significantly. Na⁺-K⁺ homeostasis had the same trend as under the short-term treatment. These findings suggested that CsPLDα-produced PA can activate the downstream signals' adaptive response to alleviate the damage of salt stress, and the main strategies for adaptation to salt stress are the accumulation of osmoprotective compounds, maintaining Na⁺-K⁺ homeostasis and the scavenging of ROS, which function in the osmotic balancing and structural stabilization of membranes.

Spinach 14-3-3 protein interacts with the plasma membrane H(+)-ATPase and nitrate reductase in response to excess nitrate stress

To investigate the function of 14-3-3 protein in response to excess nitrate stress, a 14-3-3 protein, designated as So14-3-3, was isolated from spinach. Phylogenetic analysis demonstrated that So14-3-3 belongs to non-ε group of 14-3-3 superfamily. Real time-quantitative RT-PCR and western blot analysis showed that So14-3-3 was induced by excess nitrate stress in spinach roots and leaves. After nitrate treatment, the phosphorylated H(+)-ATPase and nitrate reductase (NR) increased and decreased respectively. Co-Immunoprecipitation (Co-IP) suggested that the interaction of So14-3-3 with the phosphorylated H(+)-ATPase enhanced, but reduced with phosphorylated NR in spinach roots after nitrate treatment. Besides, 5 proteins interacted with So14-3-3 were found by Co-IP and LC-MS/MS analysis. So14-3-3 overexpressing transgenic tobacco plants showed enhanced tolerance to nitrate treatment at the germination and young seedlings stage. The transgenic plants showed longer root length, lower malondialdehyde (MDA), H2O2, protein carbonyl contents, relatively higher soluble sugar and protein contents, than the WT plants after nitrate treatment. The phosphorylation levels of H(+)-ATPase in transgenic plants were higher than the WT plants after nitrate treatment, whereas NR were lower. Additionally, in transgenic plants, the interaction of So14-3-3 with phosphorylated H(+)-ATPase and NR increased and decreased more than the WT plants under nitrate stress, leading to higher H(+)-ATPase and NR activities in transgenic plants. These data suggested that So14-3-3 might be involved in nitrate stress response by interacting with H(+)-ATPase and NR.

Nitrate reductase-mediated NO production enhances Cd accumulation in Panax notoginseng roots by affecting root cell wall properties

Panax notoginseng (Burk) F. H. Chen is a traditional medicinal herb in China. However, the high capacity of its roots to accumulate cadmium (Cd) poses a potential risk to human health. Although there is some evidence for the involvement of nitric oxide (NO) in mediating Cd toxicity, the origin of Cd-induced NO and its function in plant responses to Cd remain unknown. In this study, we examined NO synthesis and its role in Cd accumulation in P. notoginseng roots. Cd-induced NO production was significantly decreased by application of the nitrate reductase inhibitor tungstate but not the nitric oxide synthase inhibitor L-NAME (N(G)-methyl-l-arginine acetate), indicating that nitrate reductase is the major contributor to Cd-induced NO production in P. notoginseng roots. Under conditions of Cd stress, sodium nitroprusside (SNP, an NO donor) increased Cd accumulation in root cell walls but decreased Cd translocation to the shoot. In contrast, the NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and tungstate both significantly decreased NO-increased Cd retention in root cell walls. The amounts of hemicellulose 1 and pectin, together with pectin methylesterase activity, were increased with the addition of SNP but were decreased by cPTIO and tungstate. Furthermore, increases or decreases in hemicellulose 1 and pectin contents as well as pectin methylesterase activity fit well with the increased or decreased retention of Cd in the cell walls of P. notoginseng roots. The results suggest that nitrate reductase-mediated NO production enhances Cd retention in P. notoginseng roots by modulating the properties of the cell wall.

The functions of a cucumber phospholipase D alpha gene (CsPLDα) in growth and tolerance to hyperosmotic stress

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. In this research, a qRT-PCR analysis indicated that the expression of a cucumber phospholipase D alpha gene (CsPLDα) was induced by salt and drought stresses in the roots and leaves. To further study the roles of CsPLDα in regulating plant tolerance to salt, polyethylene glycol (PEG) and abscisic acid (ABA) stresses, transgenic tobacco plants constitutively overexpressing CsPLDα were produced. A qRT-PCR analysis showed that the CsPLDα transcript levels were high in transgenic tobacco lines, whereas no expression was found in wild type (WT) tobacco, indicating that CsPLDα was successfully transferred into the tobacco genome and overexpressed. Under normal conditions for 30 d, seeds of transgenic lines germinated neatly, and the seedlings were robust and bigger than WT plants. When treated with different concentrations of NaCl, PEG and ABA, germination rates and seedling sizes of the transgenic lines were significantly greater than WT. In addition, the germination times for transgenic lines were also remarkably shorter. Further studies indicated that transgenic lines had longer primary roots and more biomass accumulation than WT plants. The water loss in transgenic lines was also much lower than in WT. These findings suggest that the CsPLDα overexpression positively regulates plant tolerance to hyperosmotic stresses, and that CsPLDα is involved in the ABA regulation of stomatal closure and the alleviation of ABA inhibition on seed germination and seedling growth.

Genome-wide identification and characterization of R2R3MYB family in Cucumis sativus

BACKGROUND

The R2R3MYB proteins comprise one of the largest families of transcription factors in plants. Although genome-wide analysis of this family has been carried out in some species, little is known about R2R3MYB genes in cucumber (Cucumis sativus L.).

PRINCIPAL FINDINGS

This study has identified 55 R2R3MYB genes in the latest cucumber genome and the CsR2R3MYB family contained the smallest number of identified genes compared to other species that have been studied due to the absence of recent gene duplication events. These results were also supported by genome distribution and gene duplication analysis. Phylogenetic analysis showed that they could be classified into 11 subgroups. The evolutionary relationships and the intron-exon organizations that showed similarities with Arabidopsis, Vitis and Glycine R2R3MYB proteins were also analyzed and suggested strong gene conservation but also the expansions of particular functional genes during the evolution of the plant species. In addition, we found that 8 out of 55 (∼14.54%) cucumber R2R3MYB genes underwent alternative splicing events, producing a variety of transcripts from a single gene, which illustrated the extremely high complexity of transcriptome regulation. Tissue-specific expression profiles showed that 50 cucumber R2R3MYB genes were expressed in at least one of the tissues and the other 5 genes showed very low expression in all tissues tested, which suggested that cucumber R2R3MYB genes took part in many cellular processes. The transcript abundance level analysis during abiotic conditions (NaCl, ABA and low temperature treatments) identified a group of R2R3MYB genes that responded to one or more treatments.

CONCLUSIONS

This study has produced a comparative genomics analysis of the cucumber R2R3MYB gene family and has provided the first steps towards the selection of CsR2R3MYB genes for cloning and functional dissection that can be used in further studies to uncover their roles in cucumber growth and development.

BcNRT1, a plasma membrane-localized nitrate transporter from non-heading Chinese cabbage

A nitrate transporter, BcNRT1, was isolated from non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) cultivar 'Suzhouqing'. The full-length cDNA was obtained using the rapid amplification of cDNA ends technique and contains an open reading frame of 1,770 bp that predicts a protein of 589 acid residues that possesses 12 putative transmembrane domains. Using the GUS marker gene driven by the BcNRT1 promoter, we found BcNRT1 expression to be concentrated in primary and lateral root tips and in shoots of transgenic Arabidopsis plants. The YFP fused to BcNRT1 and transformed into cabbage protoplasts indicated that BcNRT1 was localized to the plasma membrane. The expression of BcNRT1 in roots was induced by exposure to 25 mM nitrate, and the BcNRT1 cRNA heterologously expressed in Xenopus laevis oocytes showed nitrate conductance when nitrate was included in the medium. Moreover, mutant chl1-5 plants harboring 35S::BcNRT1 showed sensitivity to chlorate treatment and exhibited restored nitrate uptake. In conclusion, the results indicate that BcNRT1 functions as a low affinity nitrate transporter in non-heading Chinese cabbage.