Nitrate transporters and peptide transporters

In higher plants, two types of nitrate transporters, NRT1 and NRT2, have been identified. In Arabidopsis, there are 53 NRT1 genes and 7 NRT2 genes. NRT2 are high-affinity nitrate transporters, while most members of the NRT1 family are low-affinity nitrate transporters. The exception is CHL1 (AtNRT1.1), which is a dual-affinity nitrate transporter, its mode of action being switched by phosphorylation and dephosphorylation of threonine 101. Two of the NRT1 genes, CHL1 and AtNRT1.2, and two of the NRT2 genes, AtNRT2.1 and AtNRT2.2, are known to be involved in nitrate uptake. In addition, AtNRT1.4 is required for petiole nitrate storage. On the other hand, some members of the NRT1 family are dipeptide transporters, called PTRs, which transport a broad spectrum of di/tripeptides. In barley, HvPTR1, expressed in the plasma membrane of scutellar epithelial cells, is involved in mobilizing peptides, produced by hydrolysis of endosperm storage protein, to the developing embryo. In higher plants, there is another family of peptide transporters, called oligopeptide transporters (OPTs), which transport tetra/pentapeptides. In addition, some OPTs transport GSH, GSSH, GSH conjugates, phytochelatins, and metals.     

Chloroplast genome aberration in micropropagation-derived albino <Emphasis Type="Italic">Bambusa edulis</Emphasis> mutants, <Emphasis Type="Italic">ab1</Emphasis> and <Emphasis Type="Italic">ab2</Emphasis>

Two albino mutants (ab1 and ab2) have been derived from long-term shoot proliferation of Bambusa edulis. Based on transmission electronic microscopy data, the chloroplasts of these mutants were abnormal. To study the mutation of gene regulation in the aberrant chloroplasts, we designed 19 pairs of chloroplast-encoded gene primers for genomic and RT-PCR. Only putative NAD(P)H-quinone oxidoreductase chain 4L (ndhE; DQ908943) and ribosomal protein S7 (rps7; DQ908931) were conserved in both the mutant and wild-type plants. The deletions in the chloroplast genome of these two mutants were different: nine genes were deleted in the chloroplast genomic aberration in ab1 and 11 genes in ab2. The chloroplast genes, NAD(P)H-quinone oxidoreductase chain 4 (ndhD; DQ908944), chloroplast 50S ribosomal protein L14 (rpl14; DQ908934), and ATP synthase beta chain (atpB; DQ908948) were abnormal in both mutants. The gene expressions of 18 of these 20 genes were correlated with their DNA copy number. The two exceptions were: ATP synthase CF0 A chain (atpI; DQ908946), whose expression in both mutants was not reduced even though the copy number was reduced; ribosomal protein S19 (rps19; DQ908949), whose expression was reduced or it was not expressed at all even though there was no difference in genomic copy number between the wild-type and mutant plants. The genomic PCR results showed that chloroplast genome aberrations do occur in multiple shoot proliferation, and this phenomenon may be involved in the generation of albino mutants.     

A role for synaptic inputs at distal dendrites: instructive signals for hippocampal long-term plasticity

Synaptic potentials originating at distal dendritic locations are severely attenuated when they reach the soma and, thus, are poor at driving somatic spikes. Nonetheless, distal inputs convey essential information, suggesting that such inputs may be important for compartmentalized dendritic signaling. Here we report a new plasticity rule in which stimulation of distal perforant path inputs to hippocampal CA1 pyramidal neurons induces long-term potentiation at the CA1 proximal Schaffer collateral synapses when the two inputs are paired at a precise interval. This subthreshold form of heterosynaptic plasticity occurs in the absence of somatic spiking but requires activation of both NMDA receptors and IP(3) receptor-dependent release of Ca(2+) from internal stores. Our results suggest that direct sensory information arriving at distal CA1 synapses through the perforant path provide compartmentalized, instructive signals that assess the saliency of mnemonic information propagated through the hippocampal circuit to proximal synapses.     

Uptake, allocation and signaling of nitrate

Plants need to acquire nitrogen (N) efficiently from the soil for growth. Nitrate is one of the major N sources for higher plants. Therefore, nitrate uptake and allocation are key factors in efficient N utilization. Membrane-bound transporters are required for nitrate uptake from the soil and for the inter- and intracellular movement of nitrate inside the plants. Four gene families, nitrate transporter 1/peptide transporter (NRT1/PTR), NRT2, chloride channel (CLC), and slow anion channel-associated 1 homolog 3 (SLAC1/SLAH), are involved in nitrate uptake, allocation, and storage in higher plants. Recent studies of these transporters or channels have provided new insights into the molecular mechanisms of nitrate uptake and allocation. Interestingly, several of these transporters also play versatile roles in nitrate sensing, plant development, pathogen defense, and/or stress response.     

ERK1/2-mediated phosphorylation of small hepatitis delta antigen at serine 177 enhances hepatitis delta virus antigenomic RNA replication

The small hepatitis delta virus (HDV) antigen (SHDAg) plays an essential role in HDV RNA double-rolling-circle replication. Several posttranslational modifications (PTMs) of HDAgs, including phosphorylation, acetylation, and methylation, have been characterized. Among the PTMs, the serine 177 residue of SHDAg is a phosphorylation site, and its mutation preferentially abolishes HDV RNA replication from antigenomic RNA to genomic RNA. Using coimmunoprecipitation analysis, the cellular kinases extracellular signal-related kinases 1 and 2 (ERK1/2) are found to be associated with the Flag-tagged SHDAg mutant (Ser-177 replaced with Cys-177). In an in vitro kinase assay, serine 177 of SHDAg was phosphorylated directly by either Flag-ERK1 or Flag-ERK2. Activation of endogenous ERK1/2 by a constitutively active MEK1 (hemagglutinin-AcMEK1) increased phosphorylation of SHDAg at Ser-177; this phosphorylation was confirmed by immunoblotting using an antibody against phosphorylated S177 and mass spectrometric analysis. Interestingly, we found an increase in the HDV replication from antigenomic RNA to genomic RNA but not in that from genomic RNA to antigenomic RNA. The Ser-177 residue was critical for SHDAg interaction with RNA polymerase II (RNAPII), the enzyme proposed to regulate antigenomic RNA replication. These results demonstrate the role of ERK1/2-mediated Ser-177 phosphorylation in modulating HDV antigenomic RNA replication, possibly through RNAPII regulation. The results may shed light on the mechanisms of HDV RNA replication.     

Curcumin induces apoptosis through an ornithine decarboxylase-dependent pathway in human promyelocytic leukemia HL-60 cells

Curcumin, a well-known dietary pigment derived from the food flavoring turmeric (Curcuma longa) exhibits anti-proliferative, anti-inflammatory, and anti-oxidative activities. Recently, studies have shown that a chemopreventive effect of curcumin could be due to the hyperproduction of reactive oxygen species (ROS) inducing apoptosis in tumor cells. In our previous studies, ornithine decarboxylase (ODC) overexpression prevented tumor necrosis factor alpha (TNF-alpha)- and methotrexate-induced apoptosis via reduction of ROS. Furthermore, ODC is the rate-limiting enzyme in polyamine biosynthesis and a target for chemoprevention. In this study, we found that enzyme activity and protein expression of ODC were reduced during curcumin treatment. Overexpression of ODC in human promyelocytic leukemia HL-60 parental cells could reduce curcumin-induced apoptosis, which leads to loss of mitochondrial membrane potential (Deltapsi(m)), through reducing intracellular ROS. Moreover, ODC overexpression prevented cytochrome c release and the activation of caspase-9 and caspase-3 following curcumin treatment. These results demonstrate that curcumin-induced apoptosis occurs through a mechanism of down-regulating ODC and along a ROS-dependent mitochondria-mediated pathway.     

Effect of cultivation conditions on spore production from Bacillus amyloliquefaciens B128 and its antagonism to Botrytis elliptica

Aims:  To maximize spore production by Bacillus amyloliquefaciens B128, and its antagonism to the fungal pathogen Botrytis elliptica B061. Methods and Results:  In the 5-l stirred-tank bioreactor (STR), with the 0·5 vvm aeration rate, an agitation rate of 200 rev min⁻¹ significantly enhanced the spore yield compared to the same in 300 rev min⁻¹ cultivations. In a 20-l airlift bioreactor (ALR) the maximal spore production was further increased with a controlled aeration rate of 2·5 vvm operated in a 24-mesh net-draft tube mode, and no pH control cultivation. This spore yield in the 20-l ALR was five- and eightfold higher; in addition the cultivation period was 19 h shorter, compared to that obtained from shaker flask and in the 5-l STR cultivations respectively. Conclusions:  Although culture conditions are still to be optimized, by using an ALR with net-draft tube, a scaling up from shaker flasks and STR to ALR of spore production by the strain B128 is technically feasible. Significance and Impact of the Study:  The spore yields obtained using bioreactors were much higher than those previously reported. The freshly produced spore preparations from the B128 strain significantly antagonized the grey mould pathogen B. elliptica.     

cAMP/PKA regulates osteogenesis, adipogenesis and ratio of RANKL/OPG mRNA expression in mesenchymal stem cells by suppressing leptin

Background

Mesenchymal stem cells (MSCs) are a pluripotent cell type that can differentiate into adipocytes, osteoblasts and other cells. The reciprocal relationship between adipogenesis and osteogenesis was previously demonstrated; however, the mechanisms remain largely unknown.

Methods and Findings

We report that activation of PKA by 3-isobutyl-1 methyl xanthine (IBMX) and forskolin enhances adipogenesis, the gene expression of PPARγ2 and LPL, and downregulates the gene expression of Runx2 and osteopontin, markers of osteogenesis. PKA activation also decreases the ratio of Receptor Activator of the NF-κB Ligand to Osteoprotegerin (RANKL/OPG) gene expression – the key factors of osteoclastogenesis. All these effects are mediated by the cAMP/PKA/CREB pathway by suppressing leptin, and may contribute to PKA stimulators-induced in vivo bone loss in developing zebrafish.

Conclusions

Using MSCs, the center of a newly proposed bone metabolic unit, we identified cAMP/PKA signaling, one of the many signaling pathways that regulate bone homeostasis via controlling cyto-differentiation of MSCs and altering RANKL/OPG gene expression.     

Evaluation of Asteraceae Plants for Control of Meloidogyne incognita

Of the 56 species and 43 genera of Asteraceae tested, 9 were highly resistant or immune to Meloidogyne incognita and did not form root galls. Twenty-six species and six cultivars had 25% or fewer roots galled and were considered moderately resistant to M. incognita. Pre-planting Cosmos bipinnatus (F190), Gaillardia pulchella, Tagetes erecta, Tithonia diversifolia, or Zinnia elegans (F645) reduced root galling and M. incognita J2 in and around Ipomoea reptans. Amendment of soils with roots, stems, or leaves of G. pulchella was effective in controlling M. incognita on I. reptans. Tissue extracts of G. pulchella were lethal to various plant-parasitic nematodes but were innocuous to free-living nematodes. Root exudates of G. pulchella were lethal to J2 of M. incognita and were inhibitory to the hatch of eggs at the concentration of 250 ppm or higher. Gaillardia pulchella could be used to manage M. incognita as a rotation crop, a co-planted crop, or a soil amendment for control of root-knot nematode.