Expression analysis of proline metabolism-related genes from halophyte Arabis stelleri under osmotic stress conditions

CIPK11: a calcineurin B-like protein-interacting protein kinase from Nitraria tangutorum, confers tolerance to salt and drought in Arabidopsis

BACKGROUND

The CIPKs are a group of plant-specific Ser/Thr protein kinases acting in response to calcium signaling, which plays an important role in the physiological and developmental adaptation of plants to adverse environments. However, the functions of halophyte-derived CIPKs are still poorly understood, that limits a potential application of CIPKs from halophytes for improving the tolerance of glycophytes to abiotic stresses.

RESULTS

In this study, we characterized the NtCIPK11 gene from the halophyte Nitraria tangutorum and subsequently analyzed its role in salt and drought stress tolerance, using Arabidopsis as a transgenic model system. NtCIPK11 expression was upregulated in N. tangutorum root, stem and blade tissues after salt or drought treatment. Overexpressing NtCIPK11 in Arabidopsis improved seed germination on medium containing different levels of NaCl. Moreover, the transgenic plants grew more vigorously under salt stress and developed longer roots under salt or drought conditions than the WT plants. Furthermore, NtCIPK11 overexpression altered the transcription of genes encoding key enzymes involved in proline metabolism in Arabidopsis exposed to salinity, however, which genes showed a relatively weak expression in the transgenic Arabidopsis undergoing mannitol treatment, a situation that mimics drought stress. Besides, the proline significantly accumulated in NtCIPK11-overexpressing plants compared with WT under NaCl treatment, but that was not observed in the transgenic plants under drought stress caused by mannitol application.

CONCLUSIONS

We conclude that NtCIPK11 promotes plant growth and mitigates damage associated with salt stress by regulating the expression of genes controlling proline accumulation. These results extend our understanding on the function of halophyte-derived CIPK genes and suggest that NtCIPK11 can serve as a candidate gene for improving the salt and drought tolerance of glycophytes through genetic engineering.

Proline metabolism and molecular cloning of AmP5CS in the mangrove Avicennia marina under heat stress

Proline is one of the most important compatible osmolyte in cells, which accumulates in response to various stresses, including salt, water deficit, heavy metal, pathogen infection and extreme temperature. In this study, a growth chamber was employed to simulate heat environment for Avicennia marina seedlings. We detected some physiological indices in the leaves of A. marina at 40 °C, including the activity of delta-1-pyrroline-5-carboxylate synthase (P5CS), the content of free proline and soluble protein, transpiration rate and membrane permeability, and discussed the relationship between these five indices and heat resistant ability. And then a P5CS gene was cloned from A. marina using homologous cloning and rapid amplification of cDNA ends methods. It was designated as AmP5CS, encoding a protein that contained a feedback inhibition site of proline, proA, proB, conserved Leu zipper, GSA-DH domain and other functional domains of P5CS protein in high plants. Expression analysis of AmP5CS gene indicated it was involved in heat stress response. It is the first time that P5CS from A. marina has been cloned and the findings laid the foundation of figuring out heat resistant mechanisms and relieving heat damage, which is significant during global warming.

Modulation of Energy Metabolism Is Important for Low-Oxygen Stress Adaptation in Brassicaceae Species

Low-oxygen stress, mainly caused by soil flooding, is a serious abiotic stress affecting crop productivity worldwide. To understand the mechanisms of low-oxygen stress responses and adaptation of plants, we characterized and compared low-oxygen responses in six species with different accessions of the Brassicaceae family. Based on the growth and survival responses to submergence or low-oxygen condition, these accessions could be divided into three groups: (i) Highly tolerant species (Rorippa islandica and Arabis stelleri); (ii) moderately tolerant species (Arabidopsis thaliana [esk-1, Ler, Ws and Col-0 ecotype]); and (iii) intolerant species (Thlaspi arvense, Thellungiella salsuginea [Shandong and Yukon ecotype], and Thellungiella parvula). Gene expression profiling using Operon Arabidopsis microarray was carried out with RNA from roots of A. thaliana (Col-0), A. stelleri, R. islandica, and T. salsuginea (Shandong) treated with low-oxygen stress (0.1% O2/99.9% N2) for 0, 1, 3, 8, 24, and 72 h. We performed a comparative analysis of the gene expression profiles using the gene set enrichment analysis (GSEA) method. Our comparative analysis suggested that under low-oxygen stress each species distinctively reconfigures the energy metabolic pathways including sucrose-starch metabolism, glycolysis, fermentation and nitrogen metabolism, tricarboxylic acid flow, and fatty acid degradation via beta oxidation and glyoxylate cycle. In A. thaliana, a moderately tolerant species, the dynamical reconfiguration of energy metabolisms occurred in the early time points of low-oxygen treatment, but the energy reconfiguration in the late time points was not as dynamic as in the early time points. Highly tolerant A. stelleri appeared to have high photosynthesis capacity that could produce more O2 and in turn additional ATP energy to cope with energy depletion caused by low-oxygen stress. R. islandica seemed to retain some ATP energy produced by anaerobic energy metabolism during a prolonged period of low-oxygen conditions. Intolerant T. salsuginea did not show significant changes in the expression of genes involved in anaerobic energy metabolisms. These results indicate that plants developed different energy metabolisms to cope with the energy crisis caused by low-oxygen stress.

Identification of the antioxidant defense genes which may provide enhanced salt tolerance in Oryza sativa L

Antioxidative mechanisms are important to protect cells from the hazardous effects of reactive oxygen species (ROS). Salt stress is one of the environmental stress factors that leads to accumulation of ROS at toxic levels. In this study, we analyzed the responses of two rice (Oryza sativa L.) cultivars against NaCl stress at enzymatic and transcriptional levels. In 14 day-old-seedlings, different antioxidant enzyme activities were observed. These findings were also supported by transcriptional analyses of the responsible genes. According to the results, Cyt-APX, CAT A, Cyt-GR1 and proline metabolism-related genes were differentially expressed between two rice varieties under different salt concentrations. Their regulational differences cause different salt sensitivities of the varieties. By this study, we provided an insight into understanding of the correlation between antioxidant defence genes and ROS enzymes under salt stress.

Regulation of proline biosynthesis and resistance to drought stress in two barley (Hordeum vulgare L.) genotypes of different origin

Drought is considered the main abiotic stress factor that inhibits growth of crop plants (including barley), limiting yield in many regions worldwide. Predicted climate changes show that in future the frequency and intensity of drought events will rise, so crops that are resistant to this stress are in demand. One of the adaptive metabolic responses to drought is the accumulation of proline. The aim of this study was to examine the effect of 10-day drought on tissue dehydration and proline biosynthesis in leaves as well as in roots of barley genotypes of different origin: the Syrian breeding line Cam/B1/CI and the German cultivar Maresi. The involvement of Δ¹ pyrroline-5-carboxylate synthetase (P5CS), the expression of the P5CS gene and ABA in proline synthesis under drought were also studied. Finally, we examined the resistance of tested genotypes to applied drought using chlorophyll fluorescence parameters and above-ground dry matter accumulation. Drought caused a gradual decrease of water content and an increase of proline and ABA content in roots and leaves of both genotypes. A statistically significant positive correlation between proline accumulation and activity of P5CS was also revealed. The skyrocketing increase of P5CS activity and proline accumulation was proceeded by transcriptional up-regulation of P5CS. The relationships between changes in P5CS expression, P5CS activity and ABA content show that the latter compound is involved in drought-induced proline synthesis at the transcription and enzyme activity level. The examined barley genotypes were equally resistant to applied moderate drought stress regardless of the differences in the level of proline accumulated.

Evolution of proline biosynthesis: enzymology, bioinformatics, genetics, and transcriptional regulation

Proline is not only an essential component of proteins but it also has important roles in adaptation to osmotic and dehydration stresses, redox control, and apoptosis. Here, we review pathways of proline biosynthesis in the three domains of life. Pathway reconstruction from genome data for hundreds of eubacterial and dozens of archaeal and eukaryotic organisms revealed evolutionary conservation and variations of this pathway across different taxa. In the most prevalent pathway of proline synthesis, glutamate is phosphorylated to γ-glutamyl phosphate by γ-glutamyl kinase, reduced to γ-glutamyl semialdehyde by γ-glutamyl phosphate reductase, cyclized spontaneously to Δ(1)-pyrroline-5-carboxylate and reduced to proline by Δ(1)-pyrroline-5-carboxylate reductase. In higher plants and animals the first two steps are catalysed by a bi-functional Δ(1) -pyrroline-5-carboxylate synthase. Alternative pathways of proline formation use the initial steps of the arginine biosynthetic pathway to ornithine, which can be converted to Δ(1)-pyrroline-5-carboxylate by ornithine aminotransferase and then reduced to proline or converted directly to proline by ornithine cyclodeaminase. In some organisms, the latter pathways contribute to or could be fully responsible for the synthesis of proline. The conservation of proline biosynthetic enzymes and significance of specific residues for catalytic activity and allosteric regulation are analysed on the basis of protein structural data, multiple sequence alignments, and mutant studies, providing novel insights into proline biosynthesis in organisms. We also discuss the transcriptional control of the proline biosynthetic genes in bacteria and plants.

60 years of development of the journal of integrative plant biology

In celebration of JIPB's 60(th) anniversary, this paper summarizes and reviews the development process of the journal. To start, we offer our heartfelt thanks to JIPB's pioneer Editors-in-Chief who helped get the journal off the ground and make it successful. Academic achievement is the soul of academic journals, and this paper summarizes JIPB's course of academic development by analyzing it in four stages: the first two stages are mostly qualitative analyses, and the latter two stages are dedicated to quantitative analyses. Most-cited papers were statistically analyzed. Improvements in editing, publication, distribution and online accessibility--which are detailed in this paper--contribute to JIPB's sustainable development. In addition, JIPB's evaluation index and awards are provided with accompanying pictures. At the end of the paper, JIPB's milestones are listed chronologically. We believe that JIPB's development, from a national journal to an international one, parallels the development of the Chinese plant sciences.

Tobacco leaves and roots differ in the expression of proline metabolism-related genes in the course of drought stress and subsequent recovery

In plants, members of gene families differ in function and mode of regulation. Fine-tuning of the expression of individual genes helps plants to cope with a variable environment. Genes encoding proline dehydrogenase (PDH), the key enzyme in proline degradation, and the proline biosynthetic enzyme, Δ(1)-pyrroline-5-carboxylate synthetase (P5CS), play an important role in responses to osmotic and drought stresses. We compared the expression patterns of three PDH and two putative P5CS genes during drought stress progression and subsequent recovery. Whereas the NtPDH1 gene was affected little by dehydration or rehydration, the NtPDH2 gene responded rapidly to both conditions, and was down-regulated under drought. The CIG1 gene, encoding cytokinin-inducible PDH, exhibited an intermediate transcription pattern. Whereas P5CS B was not affected by the stress conditions, the P5CS A gene was highly up-regulated during drought stress. CIG1 and NtPDH1 transcription was not activated, and P5CS A was only partially reduced in leaves within 24-h after rehydration, a re-watering period sufficient for large physiological changes to occur. The lack of activation of tobacco PDH genes and incomplete reduction of the P5CS A gene in leaves within 24-h of rehydration may reflect the need for the protection of plants to potential subsequent stresses. The data indicate that recovery is a specific physiological process following different patterns in leaves and roots.