SUMOylation Is Required for Glycine-Induced Increases in AMPA Receptor Surface Expression (ChemLTP) in Hippocampal Neurons

Multiple pathways participate in the AMPA receptor trafficking that underlies long-term potentiation (LTP) of synaptic transmission. Here we demonstrate that protein SUMOylation is required for insertion of the GluA1 AMPAR subunit following transient glycine-evoked increase in AMPA receptor surface expression (ChemLTP) in dispersed neuronal cultures. ChemLTP increases co-localisation of SUMO-1 and the SUMO conjugating enzyme Ubc9 and with PSD95 consistent with the recruitment of SUMOylated proteins to dendritic spines. In addition, we show that ChemLTP increases dendritic levels of SUMO-1 and Ubc9 mRNA. Consistent with activity dependent translocation of these mRNAs to sites near synapses, levels of the mRNA binding and dendritic transport protein CPEB are also increased by ChemLTP. Importantly, reducing the extent of substrate protein SUMOylation by overexpressing the deSUMOylating enzyme SENP-1 or inhibiting SUMOylation by expressing dominant negative Ubc9 prevent the ChemLTP-induced increase in both AMPAR surface expression and dendritic SUMO-1 mRNA. Taken together these data demonstrate that SUMOylation of synaptic protein(s) involved in AMPA receptor trafficking is necessary for activity-dependent increases in AMPAR surface expression.     

Arterial Expression of the Calcium-Sensing Receptor Is Maintained by Physiological Pulsation and Protects against Calcification

Vascular calcification (VC) is common in chronic kidney disease (CKD) and contributes to cardiovascular mortality. The calcium-sensing receptor (CaSR) is present in human artery, senses extracellular calcium and may directly modulate VC. Objective: to investigate the association between arterial cyclic strain, CaSR expression and VC. Methods and Results: human aortic smooth muscle cells (HAoSMC) were cultured under static or strained conditions, with exposure to CaSR agonists, the calcimimetic R568, and after CaSR silencing and over-expression. High extracellular calcium reduced CaSR expression and promoted osteochondrogenic transformation and calcium deposition. This was partially prevented by cyclic strain and exposure to R568. CaSR silencing enhanced calcification and osteochondrogenic transformation, whereas CaSR over-expression attenuated this procalcific response, demonstrating a central role for the CaSR in the response to cyclic strain and regulation of VC. In arterial explants from CKD patients (n = 11) and controls (n = 9), exposure to R568 did not significantly alter calcium deposition, osteochondrogenic markers or total artery calcium content. Conclusions: physiological mechanical strain is important for arterial homeostasis and may protect arteries from VC. The beneficial effects of cyclic strain may be mediated via the CaSR.     

高表达拟南芥miR396提高烟草抗旱性

MiR396是一个由21个核苷酸组成的单链非编码RNA小分子。烟草内的miR396受干旱诱导说明其可能参与烟草的干旱应答。在35S强启动子作用下我们将miR396转入到烟草体内获得高表达转基因植株,生理学测试表明高表达miR396的转基因烟草耐旱性增强,同时叶片表现出比野生型较低的失水率和较高的相对含水量,进一步分析表明转基因植株除了叶片变得更为窄小外,其气孔密度和气孔系数都比野生型降低,这些都表明miR396作为一个正调节因子参与烟草的干旱胁迫应答。     

Ectopic Expression of Riboflavin-binding Protein Gene TsRfBP Paradoxically Enhances Both Plant Growth and Drought Tolerance in Transgenic Arabidopsis thaliana

Riboflavin is the precursor of the coenzymes flavin monophosphate (FMN) and flavin adenine dinucleotide (FAD), which serve as indispensable redox cofactors in all plants. Numerous data indicate that riboflavin is involved in pathogen resistance but less data are available on abiotic stress tolerance. In this experiment, the overexpression of the riboflavin-binding protein resulted in an enhancement of vegetative growth and net photosynthetic rate, and an acceleration of floral transition in transgenic Arabidopsis thaliana REAT11 (containing less than half the normal levels of free riboflavin, FMN, and FAD) compared to wild-type Col-0 under nonstressed conditions. The effect of drought stress on the antioxidant response of Col-0 and REAT11 was compared, where 20- and 40-day-old grown plants were subjected to 10 % PEG 6000 treatment for 2 days. Stress conditions caused a significant increase in H₂O₂ accumulation, lipid peroxidation, and membrane permeability in Col-0 over that in REAT11. Greater activity levels of superoxide dismutase, ascorbate peroxidase, and glutathione reductase were observed in the leaves of REAT11 compared to those of Col-0. Significant increases in total ascorbate and glutathione content and higher ratios of ASC/DHA: (ASC and DHA are reduced and oxidized ascorbate, respectively) and GSH/GSSG: (GSH and GSSG are reduced and oxidized glutathione, respectively) were observed in the leaves of REAT11 compared to those in Col-0 under drought conditions. In addition, enhancement of free proline and soluble sugar accumulation was observed in REAT11 compared to Col-0 under stress. Our results suggest that a slight deficiency in free riboflavin can paradoxically induce both a higher vegetative growth rate and an enhanced tolerance to drought in transgenic plants. The “stress escape” hypothesis is proposed here to explain this interesting phenomenon.     

Ecotype-Specific Expression of a Flowering Mutant Phenotype in Arabidopsis thaliana

The majority of mutations that delay flowering in Arabidopsis thaliana have been identified in studies of the Landsberg erecta (Ler) ecotype. In this report we describe a gene (referred to as FLD) that, when mutated, delays flowering in the Columbia ecotype but has a minimal phenotype in the Ler genetic background. The late-flowering phenotype of fld mutants requires a non-Ler allele of another gene involved in the control of flowering time, Flowering Locus C. fld mutants retain a photoperiod response, and the flowering time of fld mutants can be reduced by cold treatment and low red/far-red light ratios.     

拟南芥CBF1与植物对低温和干旱的抗性

对冷驯化过程中基因表达差异的认识,使抗冻基因(COR)的克隆及其功能的分析成为研究冷驯化过程的主要目标。在拟南芥和其他抗冻植物中,分离了许多COR基因,这些基因对植物抗冻起着非常重要的作用。在拟南芥COR调控的研究中,发现了CBF转录因子的基因家族,其中CBF1能调控一组COR基因的表达。近年来,在冷敏植物如番茄和玉米中也发现了CBF类似基因,拟南芥CBF1基因在转基因番茄中的过量表达提高了植株的抗寒和抗旱性。这一研究结果展示了拟南芥CBF1类似基因的应用可能为冷敏植物抗寒和抗旱性的品种改良提供一条新的途径。     

SUMO E3 Ligase AtMMS21 Regulates Drought Tolerance in Arabidopsis thaliana

Post-translational modifications of proteins by small ubiquitin-like modifiers (SUMOs) play crucial roles in plant growth and development, and in stress responses. The MMS21 is a newly-identified Arabidopsis thaliana L. SUMO E3 ligase gene aside from the SIZ1, and its function requires further elucidation. Here, we show that MMS21 deficient plants display improved drought tolerance, and constitutive expression of MMS21 reduces drought tolerance. The expression of MMS21 was reduced by abscisic acid (ABA), polyethylene glycol (PEG) or drought stress. Under drought conditions, mms21 mutants showed the highest survival rate and the slowest water loss, and accumulated a higher level of free proline compared to wild-type (WT) and MMS21 over-expression plants. Stomatal aperture, seed germination and cotyledon greening analysis indicated that mms21 was hypersensitive to ABA. Molecular genetic analysis revealed that MMS21 deficiency led to elevated expression of a series of ABA-mediated stress-responsive genes, including COR15A, RD22, and P5CS1 The ABA and drought-induced stress-responsive genes, including RAB18, RD29A and RD29B, were inhibited by constitutive expression of MMS21. Moreover, ABA-induced accumulation of SUMO-protein conjugates was blocked in the mms21 mutant. We thus conclude that MMS21 plays a role in the drought stress response, likely through regulation of gene expression in an ABA-dependent pathway.     

Erythropoietin (EPO) Increases Myelin Gene Expression in CG4 Oligodendrocyte Cells through the Classical EPO Receptor

Erythropoietin (EPO) has protective effects in neurodegenerative and neuroinflammatory diseases, including in animal models of multiple sclerosis, where EPO decreases disease severity. EPO also promotes neurogenesis and is protective in models of toxic demyelination. In this study, we asked whether EPO could promote neurorepair by also inducing remyelination. In addition, we investigated whether the effect of EPO could be mediated by the classical erythropoietic EPO receptor (EPOR), since it is still questioned if EPOR is functional in nonhematopoietic cells. Using CG4 cells, a line of rat oligodendrocyte precursor cells, we found that EPO increases the expression of myelin genes (myelin oligodendrocyte glycoprotein [MOG] and myelin basic protein [MBP]). EPO had no effect in wild-type CG4 cells, which do not express EPOR, whereas it increased MOG and MBP expression in cells engineered to overexpress EPOR (CG4-EPOR). This was reflected in a marked increase in MOG protein levels, as detected by Western blot. In these cells, EPO induced by 10-fold the early growth response gene 2 (Egr2), which is required for peripheral myelination. However, Egr2 silencing with a siRNA did not reverse the effect of EPO, indicating that EPO acts through other pathways. In conclusion, EPO induces the expression of myelin genes in oligodendrocytes and this effect requires the presence of EPOR. This study demonstrates that EPOR can mediate neuroreparative effects.     

Genome-Wide Meta-Analysis for Serum Calcium Identifies Significantly Associated SNPs near the Calcium-Sensing Receptor (CASR) Gene

Calcium has a pivotal role in biological functions, and serum calcium levels have been associated with numerous disorders of bone and mineral metabolism, as well as with cardiovascular mortality. Here we report results from a genome-wide association study of serum calcium, integrating data from four independent cohorts including a total of 12,865 individuals of European and Indian Asian descent. Our meta-analysis shows that serum calcium is associated with SNPs in or near the calcium-sensing receptor (CASR) gene on 3q13. The top hit with a p-value of 6.3×10^-37 is rs1801725, a missense variant, explaining 1.26% of the variance in serum calcium. This SNP had the strongest association in individuals of European descent, while for individuals of Indian Asian descent the top hit was rs17251221 (p = 1.1×10^-21), a SNP in strong linkage disequilibrium with rs1801725. The strongest locus in CASR was shown to replicate in an independent Icelandic cohort of 4,126 individuals (p = 1.02×10^-4). This genome-wide meta-analysis shows that common CASR variants modulate serum calcium levels in the adult general population, which confirms previous results in some candidate gene studies of the CASR locus. This study highlights the key role of CASR in calcium regulation.     

Phenotypic Suppression of the Gibberellin-Insensitive Mutant (gai) of Arabidopsis

The semidominant gibberellin-insensitive (gai) mutant of Arabidopsis thaliana shows impairment in multiple responses to the plant hormone gibberellin A3, which include effects on seed germination, stem elongation, apical dominance, and rapid flowering in short days. Results presented here show that the gai mutation also interferes with development of fertile flowers in continuous light. Mu-tagenesis of the gai mutant resulted in recovery of 17 independent mutants in which the gibberellin-insensitive phenotype is partially or completely suppressed. Sixteen of the suppressor mutations act semidominantly to restore gibberellin responsiveness. One representative of this class, the gar1 mutation, could not be genetically separated from the gai locus and is proposed to cause inactivation of the gai gene. The exceptional gar2 mutation partially suppresses the gai phenotype, is completely dominant, and is not linked to the gai locus. The gar2 mutation may define a new gene involved in gibberellin signaling. A recessive allele of the spindly (SPY) locus, spy-5, was also found to partially suppress the gai mutant phenotype.     

Heterologous Expression of Two Jatropha Aquaporins Imparts Drought and Salt Tolerance and Improves Seed Viability in Transgenic Arabidopsis thaliana

Drought and high salinity are environmental conditions that cause adverse effects on the growth and productivity of crops. Aquaporins are small integral membrane proteins that belong to the family of the major intrinsic proteins (MIPs), with members in animals, plants and microbes, where they facilitate the transport of water and/or small neutral solutes thereby affecting water balance. In this study we characterized two aquaporin genes namely, plasma membrane intrinsic protein (PIP2;7) and tonoplast intrinsic protein TIP1;3 from Jatropha curcas that are localised to the plasma membrane and vacuole respectively. Transgenic Arabidopsis thaliana lines over-expressing JcPIP2;7 and JcTIP1;3 under a constitutive promoter show improved germination under high salt and mannitol compared to control seeds. These transgenic plants also show increased root length under abiotic stress conditions compared to wild type Col-0 plants. Transgenic lines exposed to drought conditions by withholding water for 20 days, were able to withstand water stress and attained normal growth after re-watering unlike control plants which could not survive. Transgenic lines also had better seed yield than control under salt stress. Importantly, seed viability of transgenic plants grown under high salt concentration was 35%-45% compared to less than 5% for control seeds obtained from plants growing under salt stress. The effect of JcPIP2;7 and JcTIP1;3 on improving germination and seed viability in drought and salinity make these important candidates for genetic manipulation of plants for growth in saline soils.     

Overexpression of a Rice Monosaccharide Transporter Gene (OsMST6) Confers Enhanced Tolerance to Drought and Salinity Stress in Arabidopsis thaliana

Plant Molecular Biology Reporter - Monosaccharide transporter (MSTs) is a large family of integral membrane proteins that plays a crucial role in cell-to-cell and long-distance distribution of...