Phloem-localizing sulfate transporter,Sultr1;3, mediates re-distribution of sulfur from source to sink organs in Arabidopsis

For the effective recycling of nutrients, vascular plants transport pooled inorganic ions and metabolites through the sieve tube. A novel sulfate transporter gene, Sultr1;3, was identified as an essential member contributing to this process for redistribution of sulfur source in Arabidopsis. Sultr1;3 belonged to the family of high-affinity sulfate transporters, and was able to complement the yeast sulfate transporter mutant. The fusion protein of Sultr1;3 and green fluorescent protein was expressed by the Sultr1;3 promoter in transgenic plants, which revealed phloem-specific expression of Sultr1;3 in Arabidopsis. Sultr1;3-green fluorescent protein was found in the sieve element-companion cell complexes of the phloem in cotyledons and roots. Limitation of external sulfate caused accumulation of Sultr1;3 mRNA both in leaves and roots. Movement of (35)S-labeled sulfate from cotyledons to the sink organs was restricted in the T-DNA insertion mutant of Sultr1;3. These results provide evidence that Sultr1;3 transporter plays an important role in loading of sulfate to the sieve tube, initiating the source-to-sink translocation of sulfur nutrient in Arabidopsis.     

New assembled Fe-trans-1,2-bis(4-pyridyl)ethylene-NCS(NCSe) complexes - hydrogen bonded and π-π interacted structure and grid structure enclathrating ligand

Reaction of FeSO₄ · 7H₂O with trans-1,2-bis(4-pyridyl)ethylene (tvp) and NaNCS in the mixed solvent of water and ethanol gave rise to the formation of different coordination polymers. One (Fe(tvp)₂(NCS)₂(H₂O)₂) is hydrogen bonded and π-π interacted structure, while the other ([Fe(tvp)₂(NCS)₂][0.5(tvp · 2EtOH)]) is 2D grid structure, which enclathrates tvp · 2EtOH. This enclathrated tvp · 2EtOH interacts with the two 2D grid sheets to form 3D structure. The same reaction was carried out with KNCSe instead of NaNCS (Fe(tvp)₂(NCSe)₂(H₂O)₂). ⁵⁷Fe Mössbauer spectra revealed that all the present assembled complexes are in the Fe^II high-spin state. The dissociation behavior of enclathrated molecule and ligand was investigated by TG, and the resultant electronic state of iron atom was studied by ⁵⁷Fe Mössbauer spectroscopy.     

A Highlights from MBoC Selection: Inhibition of cell membrane ingression at the division site by cell walls in fission yeast

Eukaryotic cells assemble actomyosin rings during cytokinesis to function as force-generating machines to drive membrane invagination and to counteract the intracellular pressure and the cell surface tension. How the extracellular matrix affects actomyosin ring contraction has not been fully explored. While studying the Schizosaccharomyces pombe 1,3-β-glucan-synthase mutant cps1-191, which is defective in division septum synthesis and arrests with a stable actomyosin ring, we found that weakening of the extracellular glycan matrix caused the generated spheroplasts to divide under the nonpermissive condition. This nonmedial slow division was dependent on a functional actomyosin ring and vesicular trafficking, but independent of normal septum synthesis. Interestingly, the high intracellular turgor pressure appears to play a minimal role in inhibiting ring contraction in the absence of cell wall remodeling in cps1-191 mutants, as decreasing the turgor pressure alone did not enable spheroplast division. We propose that during cytokinesis, the extracellular glycan matrix restricts actomyosin ring contraction and membrane ingression, and remodeling of the extracellular components through division septum synthesis relieves the inhibition and facilitates actomyosin ring contraction.     

Spatial genet dynamics of a dwarf bamboo: Clonal expansion into shaded forest understory contributes to regeneration after an episodic die-off

The ability of clonal plants to spread horizontally and to share resources within genets has long been considered advantageous in spatially heterogeneous environments, yet our understanding of how such traits relate to its widespread success and dominance is still limited. Using a dwarf bamboo, Sasa kurilensis, that often dominates cool-temperate forest understorys, we investigated how population recovery over 20 years after an episodic die-off may be augmented by clonal expansion via rhizomes. Previous analyses on genet demography using 9-m² plots showed that more productive genets were more likely to survive, spread laterally, and replace less productive ones. In this study, we examined whether the recovery of biomass in lower light microsites, where biomass recovery was initially slower, was supported by the spread of productive genets at larger scales, from surrounding higher-light microsites. We found that the biomass recovery in lower-light plots was more supported by genets that spread clonally into the plots. Such genets that spread from outside plots produced larger culms than those that had originally germinated there. Whereas genets that contributed much to the biomass of the low-light plots spread extensively from higher-light microsites, the spatial extent of genets that originally germinated in these plots was quite limited, so that the patterns of clonal expansion appeared to be unidirectional along the light gradient. Our findings suggest that clonal expansion of productive genets from higher-light into shaded microsites may be important for S. kurilensis to proliferate across heterogeneous light environments.     

Remarkable stabilization of a psychrotrophic RNase HI by a combination of thermostabilizing mutations identified by the suppressor mutation method

Ribonuclease HI from the psychrotrophic bacterium Shewanella oneidensis MR-1 (So-RNase HI) is much less stable than Escherichia coli RNase HI (Ec-RNase HI) by 22.4 degrees C in T m and 12.5 kJ mol (-1) in Delta G(H 2O), despite their high degrees of structural and functional similarity. To examine whether the stability of So-RNase HI increases to a level similar to that of Ec-RNase HI via introduction of several mutations, the mutations that stabilize So-RNase HI were identified by the suppressor mutation method and combined. So-RNase HI and its variant with a C-terminal four-residue truncation (154-RNase HI) complemented the RNase H-dependent temperature-sensitive (ts) growth phenotype of E. coli strain MIC3001, while 153-RNase HI with a five-residue truncation could not. Analyses of the activity and stability of these truncated proteins suggest that 153-RNase HI is nonfunctional in vivo because of a great decrease in stability. Random mutagenesis of 153-RNase HI using error-prone PCR, followed by screening for the revertants, allowed us to identify six single suppressor mutations that make 153-RNase HI functional in vivo. Four of them markedly increased the stability of the wild-type protein by 3.6-6.7 degrees C in T m and 1.7-5.2 kJ mol (-1) in Delta G(H 2O). The effects of these mutations were nearly additive, and combination of these mutations increased protein stability by 18.7 degrees C in T m and 12.2 kJ mol (-1) in Delta G(H 2O). These results suggest that several residues are not optimal for the stability of So-RNase HI, and their replacement with other residues strikingly increases it to a level similar to that of the mesophilic counterpart.     

v-Crk activates the phosphoinositide 3-kinase/AKT pathway by utilizing focal adhesion kinase and H-Ras

v-Crk, an oncogene product of avian sarcoma virus CT10, efficiently transforms chicken embryo fibroblasts (CEF). We have recently reported that constitutive activation of the phosphoinositide 3-kinase (PI3K)/AKT pathway plays a critical role in the v-Crk-induced transformation of CEF. In the present study we investigated the molecular mechanism by which v-Crk activates the PI3K/AKT pathway. First, we found that v-Crk promotes the association of the p85 regulatory subunit of PI3K with focal adhesion kinase (FAK) by inducing the phosphorylation of the Y397 residue in FAK. This FAK phosphorylation needs activation of the Src family tyrosine kinase(s) for which the v-Crk SH2 domain is responsible. v-Crk was unable to activate the PI3K/AKT pathway in FAK-null cells, indicating the functional importance of FAK. In addition, we found that H-Ras is also required for the activation of the PI3K/AKT pathway. The v-Crk-induced activation of AKT was greatly enhanced by the overexpression of H-Ras or its guanine nucleotide exchange factor mSOS, which binds to the v-Crk SH3 domain, whereas a dominant-negative mutant of H-Ras almost completely suppressed this activation. Furthermore, we showed that v-Crk stimulates the interaction of H-Ras with the Ras binding domain in the PI3K p110 catalytic subunit. Our data indicated that the v-Crk-induced activation of PI3K/AKT pathway was cooperatively achieved by two distinct interactions. One is the interaction of p85 with tyrosine-phosphorylated FAK promoted by the v-Crk SH2 domain, and another is the interaction of p110 with H-Ras dictated by the v-Crk SH3 domain.     

Accumulation of maize response regulator proteins in mesophyll cells after cytokinin treatment

The maize response regulator genes ZmRR1 and ZmRR2 respond to cytokinin, and the translated products seem to be involved in nitrogen signal transduction mediated by cytokinin through the His-Asp phosphorelay. To elucidate the physiological function of the proteins, we examined the temporal and spatial distribution in maize leaves by immunochemical analysis and use of transgenic plants. ZmRR1 and ZmRR2 polypeptides could be distinctively detected by western blotting. The polypeptides accumulated in leaves within 5 h of the supply of nitrate to nitrogen-depleted maize, and the accumulation was transient. The extent of induction was larger in the leaf tip, which is rich in photosynthetically matured cells, than elsewhere. In leaves, the polypeptides accumulated mostly in mesophyll cells. Histochemical analyses of transgenic maize harboring a ZmRR1 promoter-beta-glucuronidase fusion gene also showed most of the expression to be in these cells. These results suggest that ZmRR1 and ZmRR2 are induced in mesophyll cells and function in nitrogen signal transduction mediated by cytokinin.     

Neuroprotective effects of interleukin-6 on NMDA-induced rat retinal damage

This study shows that interleukin-6 (IL-6) combined with soluble interleukin-6 receptors (sIL-6R) modulates N-methyl-D-aspartate (NMDA)-induced retinal damage. Eyes pretreated with a combined injection of IL-6 and sIL-6R had NMDA administered into the vitreous cavity. Morphometric analysis and retrograde labeling analysis found that pretreatment with either IL-6 or sIL-6R alone did not bring about any neuroprotective effect. However, pretreatment with a combined administration of IL-6 and sIL-6R induced a significant neuroprotective effect against NMDA-induced retinal damage. Apoptotic changes in the retina were assessed by the TUNEL method. The results indicated that pretreatment with IL-6 combined with sIL-6R prevents NMDA-induced apoptosis. Western blotting studies demonstrated upregulation of gp130 expression in the NMDA-injected retina. Present studies suggest that IL-6 combined with sIL-6R provides a neuroprotective effect on NMDA-induced retinal damage.     

Molecular characterization of His-Asp phosphorelay signaling factors in maize leaves: Implications of the signal divergence by cytokinin-inducible response regulators in the cytosol and the nuclei

Genes for histidyl-aspartyl (His-Asp) phosphorelay components (His-containing phosphotransfer proteins, HP, and response regulators, RR) were isolated from Zea mays L. to characterize their function in cytokinin signaling. Six type-A RRs (ZmRR1, ZmRR2, ZmRR4–ZmRR7), 3 type-B RRs (ZmRR8–ZmRR10), and 3 HPs (ZmHP1–ZmHP3) were found in leaves. All type-A RR genes expressed in leaves were up-regulated by exogenous cytokinin. Transient expression of fusion products of the signaling modules with green fluorescent protein in epidermal leaf cells suggested cytosolic and nuclear localizations of ZmHPs, whereas type-B ZmRR8 was restricted to the nucleus. Type-A RRs were localized partly to the cytosol (ZmRR1, ZmRR2, and ZmRR3) and partly to the nucleus (ZmRR4, ZmRR5, and ZmRR6). In the yeast two-hybrid assay, ZmHP1 and ZmHP3 interacted with both cytosolic ZmRR1 and nuclear type-B ZmRRs. In vitro experiments demonstrated that ZmHPs function as a phospho-donor for ZmRRs; turnover rates of the phosphorylated state were tenfold lower in ZmRR8 and ZmRR9 than in ZmRR1 and ZmRR4. These results suggest that the His-Asp phosphorelay signaling pathway might diverge into a cytosolic and a nuclear branch in leaves of maize, and that the biochemical nature of ZmRRs is different in terms of stability of the phosphorylated status.