Betaine Improves Freezing Tolerance in Wheat

The accumulation of the osmolyte betaine was found to be correlatedwith the development of freezing tolerance (FT) of two wheatcultivars where it increases by about three fold during thecold acclimation period. Exogenous betaine application resultedin a large increase in total osmolality mostly due to betaineaccumulation. Plants that accumulated betaine are more tolerantto freezing stress since a four day exposure to 250 mM betaineresulted in a LT₅₀ of –8°C (in spring wheat Glenlea)and –9°C (in winter wheat Fredrick) compared to –3°C(Glenlea) and –4°C (Fredrick) for control non-exposedplants. Betaine treatment (250 mM) during cold acclimation increasedFT in an additive manner since the LT₅₀ reached –14°C(Glenlea) and –22°C (Fredrick) compared to –8°C(Glenlea) and –16°C (Fredrick) for plants that arecold acclimated in the absence of betaine. These results showthat betaine treatment can improve FT by more than 5°C inboth non-acclimated and cold-acclimated plants. The betainetreatment resulted in the induction of a subset of low temperatureresponsive genes, such as the wcor410, and wcor413, that arealso induced by salinity or drought stresses. In addition tothese genetic responses, betaine treatment was also able toimprove the tolerance to photoin-hibition of PSII and the steady-stateyield of electron transport over PSII in a manner that mimickedcold-acclimated plants. These data also suggest that betaineimproves FT by eliciting some of the genetic and physiologicalresponses associated with cold acclimation. (Received April 23, 1998; Accepted September 4, 1998)     

Active RNA Silencing at Low Temperature Indicates Distinct Pathways for Antisense-Mediated Gene-Silencing in Potato

Previously, it was shown that low temperature (≤ 15 °C) inhibits RNA silencing-mediated defence by the control of siRNA generation. In contrast, we have found nine antisense potato lines out of 24 in which RNA silencing was not inhibited at low temperature. In these lines, the extent of endogenous repression varied in leaves and was found to be different in roots and tubers. In order to address the contribution of gene dosage and repetitive structure of the transgene loci to the temperature dependence/independence of antisense-mediated gene-silencing DNA gel blot analysis was performed. Interestingly, none of the studied features correlated with the observed silencing effect. In addition, the insertion of vector backbone sequences into the potato genome did not influence the temperature dependence. RNA-directed DNA methylation was detected in the majority of antisense lines, however, it was also independent of the type of RNA silencing. Thus, it is feasible that chromosomal flanking sequences or the chromatin structure surrounding the insertion determine which silencing pathway is activated.     

Enhanced Tolerance to Ascochyta Blight in Chickpea Plants via Low Temperature Acclimation

Russian Journal of Plant Physiology - Low temperature (LT) and Ascochyta blight are two major stresses in chickpea (Cicer arietinum L.) cultivation. After exposure to LT treatments (acclimation,...     

Distinct Innate Immunity Pathways to Activation and Tolerance in Subgroups of Chronic Lymphocytic Leukemia with Distinct Immunoglobulin Receptors

Subgroups of patients with chronic lymphocytic leukemia (CLL) have distinct expression profiles of Toll-like receptor (TLR) pathway–associated genes. To test the hypothesis that signaling through innate immunity receptors may influence the behavior of the malignant clone, we investigated the functional response triggered by the stimulation of TLRs and NOD2 in 67 CLL cases assigned to different subgroups on the basis of immunoglobulin heavy variable (IGHV ) gene usage, IGHV gene mutational status or B-cell receptor (BcR) stereotypy. Differences in the induction of costimulatory molecules and/or apoptosis were observed in mutated versus unmutated CLL. Different responses were also identified in subsets with stereotyped BcRs, underscoring the idea that “subset-biased” innate immunity responses may occur independently of mutational status. Additionally, differential modulation of kinase activities was induced by TLR stimulation of different CLL subgroups, revealing a TLR7-tolerant state for cases belonging to stereotyped subset #4. The distinct patterns of TLR/NOD2 functional activity in cells from CLL subgroups defined by the molecular features of the clonotypic BcRs might prove relevant for elucidating the immune mechanisms underlying CLL natural history and for defining subgroups of patients who might benefit from treatment with specific TLR ligands.     

Anti-CD154 mAb and Rapamycin Induce T Regulatory Cell Mediated Tolerance in Rat-to-Mouse Islet Transplantation

Background

Anti-CD154 (MR1) monoclonal antibody (mAb) and rapamycin (RAPA) treatment both improve survival of rat-to-mouse islet xenograft. The present study investigated the effect of combined RAPA/MR1 treatment on rat-to-mouse islet xenograft survival and analyzed the role of CD4⁺CD25⁺Foxp3⁺ T regulatory cells (Treg) in the induction and maintenance of the ensuing tolerance.

Methodology/Principal Findings

C57BL/6 mice were treated with MR1/RAPA and received additional monoclonal anti-IL2 mAb or anti CD25 mAb either early (0–28 d) or late (100–128 d) post-transplantation. Treg were characterised in the blood, spleen, draining lymph nodes and within the graft of tolerant and rejecting mice by flow cytometry and immunohistochemistry. Fourteen days of RAPA/MR1 combination therapy allowed indefinite islet graft survival in >80% of the mice. Additional administration of anti-IL-2 mAb or depleting anti-CD25 mAb at the time of transplantation resulted in rejection (100% and 89% respectively), whereas administration at 100 days post transplantation lead to lower rejection rates (25% and 40% respectively). Tolerant mice showed an increase of Treg within the graft and in draining lymph nodes early post transplantation, whereas 100 days post transplantation no significant increase of Treg was observed. Rejecting mice showed a transient increase of Treg in the xenograft and secondary lymphoid organs, which disappeared within 7 days after rejection.

Conclusions/Significances

These results suggest a critical role for Treg in the induction phase of tolerance early after islet xenotransplantation. These encouraging data support the need of developing further Treg therapy for overcoming the species barrier in xenotransplantation.     

Changes in the Translatable RNA Population during Abscisic Acid Induce Freezing Tolerance in Bromegrass Suspension Culture

Abscisic acid (ABA) has been shown to increase freezing toleranceof bromegrass (Bromus in-ermis Leyss cv. Manchar) cell suspensioncultures from a LT₅₀ (the temperature at which 50% cells werekilled) of –7 to – 30?C in 5 days at 23?C. Our objectivewas to study the qualitative changes in the translatable RNApopulation during ABA induced frost tolernace. In vitro translationproducts of poly(A)⁺ RNA isolated from bromegrass cells withor without 75 µM ABA treatment for various periods oftime were separated by 2D-PAGE and visualized by fluorography.SDS soluble proteins from the same treatments were also separatedby 20-PAGE. After 5 days treatment, at least 22 new or increasedabundance SDS soluble polypeptides were observed. From fluorographs,29 novel or increased abundance in vitro translation productscould be detected. The pattern of changes between ABA inducedSDS-soluble proteins and translation products from the 2D gelswere similar. A time course study (0–7 days) showed that17 of the 29 translation products were detected after 1 dayABA treatment, and at least 14 were present after 1 h. Coldtreatment (+4?C) induced fewer changes in the pool of translatableRNA than with ABA treatment. Three translation products inducedby cold appear to be similar to 3 of the ABA induced translationproducts. The majority of the ABA inducible translatable RNAsappeared at 10 µM or higher which coincides with the inductionof freezing tolerance. Many of these ABA inducible RNAs persisted7 days after ABA was removed from the media and correspondinglythe LT₅₀ (–17?C) was still well above the control level(–17?C). The results suggest that ABA alters the poolof translatable RNAs during induction of freezing tolerancein bromegrass suspension culture cells. ¹Oregon Agricultural Experiment Station Technical Paper No.9256. (Received August 3, 1990; Accepted October 18, 1990)     

Cold-Induced Freezing Tolerance in Arabidopsis

Changes in the physiology of plant leaves are correlated with enhanced freezing tolerance and include accumulation of compatible solutes, changes in membrane composition and behavior, and altered gene expression. Some of these changes are required for enhanced freezing tolerance, whereas others are merely consequences of low temperature. In this study we demonstrated that a combination of cold and light is required for enhanced freezing tolerance in Arabidopsis leaves, and this combination is associated with the accumulation of soluble sugars and proline. Sugar accumulation was evident within 2 h after a shift to low temperature, which preceded measured changes in freezing tolerance. In contrast, significant freezing tolerance was attained before the accumulation of proline or major changes in the percentage of dry weight were detected. Many mRNAs also rapidly accumulated in response to low temperature. All of the cold-induced mRNAs that we examined accumulated at low temperature even in the absence of light, when there was no enhancement of freezing tolerance. Thus, the accumulation of these mRNAs is insufficient for cold-induced freezing tolerance.     

Low Temperature Tolerance of Pacu, Piaractus mesopotamicus

Pacu, Piaractus mesopotamicus (=Colossoma mitrei), is a South American warm water fish species found in the temperature range of 15–35°C. The culture of a warm water species in temperate regions demands knowledge on its temperature requirements. Pacu introduction into the Israeli fish culture system is being considered. Temperature range in the region is 8–33°C, thus the minimum winter water temperatures might be a limiting factor. To determine what is the minimum temperature pacu would tolerate, and hence which overwintering operations in warm-temperate regions are required for this warm water species, low temperature tolerance tests in the laboratory and observations in the field were carried out. Laboratory experiments reducing temperature by 1–3°C per day were carried out with fish of 150–200g, about the size pacu reach after one culture season. The field observations compared survival of two-year-old pacu of 1.3kg mean weight overwintered in outdoors and in greenhouse ponds. For one-year-old fish 7.5°C was found to be the lower temperature tolerance limit. Two-year-old fish withstand short exposures to this temperature rather well and their lower tolerance limit might be lower. This indicates that in warm-temperate regions pacu should survive in outdoors ponds. In this case some loss of weight should be expected, and suspension of feeding when temperature drops below 16–18°C is recommended to avoid wasting feed that the fish will not consume anyway. To be in the safe side, inflow of the warmest available water into the ponds is recommended if maximum water temperature drops to 10°C or below. Overwintering in greenhouses or other heated facilities would be recommended if an exceptionally cold winter is expected and for regions with lower winter minimum temperatures.     

ABA与植物的耐盐性

文章介绍近年来ABA与植物耐盐性的研究进展。     

Maintenance of Membrane Fluidity during Development of Freezing Tolerance of Winter Wheat Seedlings

Fluidity of membrane lipids of shoot and root tissue and of chloroplasts from young wheat seedlings of contrasting freezing tolerance was investigated by measuring the motion and order parameters after spin labeling. A striking similarity was observed in membrane lipid fluidity of the five cultivars grown at 22 C. After cold hardening by growth at 2 C, a small change in membrane lipid fluidity was observed, but this was not correlated with the development of freezing tolerance, and there was no alteration in the transition temperature of membrane lipids. The results show that neither changes in membrane lipid fluidity nor transition temperature are a necessary feature of cold acclimation in wheat.     

Low Temperature-Induced Decrease in trans-Delta-Hexadecenoic Acid Content Is Correlated with Freezing Tolerance in Cereals

The effect of growth at 5°C on the trans-Δ³-hexadecenoic acid content of phosphatidyl(d)glycerol was examined in a total of eight cultivars of rye (Secale cereale L.) and what (Triticum aestivum L.) of varying freezing tolerance. In these monocots, low temperature growth caused decreases in the trans-Δ³-hexadecenoic acid content of between 0 and 74% with concomitant increases in the palmitic acid content of phosphatidyl(d)glycerol. These trends were observed for whole leaf extracts as well as isolated thylakoids. The low growth temperature-induced decrease in the trans-Δ³-hexadecenoic acid content was shown to be a linear function (r² = 0.954) of freezing tolerance in these cultivars. Of the six cold tolerant dicotyledonous species examined, only Brassica and Arabidopsis thaliana L. cv Columbia exhibited a 42% and 65% decrease, respectively, in trans-Δ³-hexadecenoic acid content. Thus, the relationship between the change in trans-Δ³-hexadecenoic acid content of phosphatidyl(d)glycerol and freezing tolerance cannot be considered a general one for all cold tolerant plant species. However, species which exhibited a low growth temperature-induced decrease in trans-Δ³-hexadecenoic acid also exhibited a concomitant shift in the in vitro organization of the light harvesting complex II from a predominantly oligomeric form to the monomeric form. We conclude that the proposed role of phosphatidyl(d)glycerol in modulating the organization of light harvesting complex II as a function of growth temperature manifests itself to varying degrees in different plant species. A possible physiological role for this phenomenon with respect to low temperature acclimation and freezing tolerance in cereals is discussed.     

Ras Signals to the Cell Cycle Machinery via Multiple Pathways To Induce Anchorage-Independent Growth

Several specific cell cycle activities are dependent on cell-substratum adhesion in nontransformed cells, and the ability of the Ras oncoprotein to induce anchorage-independent growth is linked to its ability to abrogate this adhesion requirement. Ras signals via multiple downstream effector proteins, a synergistic combination of which may be required for the highly altered phenotype of fully transformed cells. We describe here studies on cell cycle regulation of anchorage-independent growth that utilize Ras effector loop mutants in NIH 3T3 and Rat 6 cells. Stable expression of activated H-Ras (12V) induced soft agar colony formation by both cell types, but each of three effector loop mutants (12V,35S, 12V,37G, and 12V,40C) was defective in producing this response. Expression of all three possible pairwise combinations of these mutants synergized to induce anchorage-independent growth of NIH 3T3 cells, but only the 12V,35S-12V,37G and 12V,37G-12V,40C combinations were complementary in Rat 6 cells. Each individual effector loop mutant partially relieved adhesion dependence of pRB phosphorylation, cyclin E-dependent kinase activity, and expression of cyclin A in NIH 3T3, but not Rat 6, cells. The pairwise combinations of effector loop mutants that were synergistic in producing anchorage-independent growth in Rat 6 cells also led to synergistic abrogation of the adhesion requirement for these cell cycle activities. The relationship between complementation in producing anchorage-independent growth and enhancement of cell cycle activities was not as clear in NIH 3T3 cells that expressed pairs of mutants, implying the existence of either thresholds for these activities or additional requirements in the induction of anchorage-independent growth. Ectopic expression of cyclin D1, E, or A synergized with individual effector loop mutants to induce soft agar colony formation in NIH 3T3 cells, cyclin A being particularly effective. Taken together, these data indicate that Ras utilizes multiple pathways to signal to the cell cycle machinery and that these pathways synergize to supplant the adhesion requirements of specific cell cycle events, leading to anchorage-independent growth.     

Halotolerant Plant Growth-Promoting Rhizobacteria Induce Salinity Tolerance in Wheat by Enhancing the Expression of SOS Genes

Journal of Plant Growth Regulation - Soil salinity is one of the main yield-limiting factors in various crops. Under different environmental stresses, many rhizobacteria have demonstrated...     

Low-Temperature Effects on Photosynthesis and Correlation with Freezing Tolerance in Spring and Winter Cultivars of Wheat and Rye

Winter cultivars of rye (Secale cereale L., cv Musketeer) and wheat (Triticum aestivum L. cvs Kharkov and Monopol), but not a spring cultivar of wheat (Glenlea), grown at cold-hardening temperatures showed, at high irradiances, a higher proportion of oxidized to reduced primary, stable quinone receptor (QA) than did the same cultivars grown under nonhardening conditions. In addition, there was a positive correlation between the effects of low-growth temperature on this increased proportion of oxidized QA, and a concomitant increase in the capacity for photosynthesis, and LT50, the temperature at which 50% of the seedlings are killed, in cultivars showing different freezing tolerances. This suggests that low-temperature modulation of the photosynthetic apparatus may be an important factor during the induction of freezing resistance in cereals. Finally, the control of photosystem II photochemistry by nonphotochemical quenching of excitation energy was identical for nonhardened and cold-hardened winter rye. However, examination of measuring temperature effects per se revealed that, irrespective of growth temperature, nonphotochemical quenching exerted a stronger control on photosystem II photochemistry at 10[deg] C rather than at 20[deg] C.     

Synthesis of Freezing Tolerance Proteins in Leaves, Crown, and Roots during Cold Acclimation of Wheat

Protein synthesis was studied in leaves, crown, and roots during cold hardening of freezing tolerant winter wheat (Triticum aestivum L. cv Fredrick and cv Norstar) and freezing sensitive spring wheat (T. aestivum L. cv Glenlea). The steady state and newly synthesized proteins, labeled with [³⁵S]methionine, were resolved by one- and two-dimensional polyacrylamide gels. The results showed that cold hardening induced important changes in the soluble protein patterns depending upon the tissue and cultivar freezing tolerance. At least eight new proteins were induced in hardened tissues. A 200 kilodalton (kD) (isoelectric point [pl] 6.85) protein was induced concomitantly in the leaves, crown, and roots. Two proteins were specifically induced in the leaves (both 36 kD, pl 5.55 and 5.70); three in the crown with M_r 150 (pl 5.30), 45 (pl 5.75), and 44 kD (pl > 6.80); and two others in the roots with M_r 64 (pl 6.20) and 52 kD (pl 5.55). In addition, 19 other proteins were synthesized at a modified rate (increased or decreased) in the leaves, 18 in the crown and 23 in the roots. Among the proteins induced or increased in hardened tissues, some were expressed at a higher level in the freezing tolerant cultivars than in the sensitive one, indicating a correlation between the synthesis and accumulation of these proteins and the degree of freezing tolerance. These proteins, suggested to be freezing tolerance proteins, may have an important role in the cellular adaptation to freezing.     

Gut Symbionts from Distinct Hosts Exhibit Genotoxic Activity via Divergent Colibactin Biosynthesis Pathways

Secondary metabolites produced by nonribosomal peptide synthetase (NRPS) or polyketide synthase (PKS) pathways are chemical mediators of microbial interactions in diverse environments. However, little is known about their distribution, evolution, and functional roles in bacterial symbionts associated with animals. A prominent example is colibactin, a largely unknown family of secondary metabolites produced by Escherichia coli via a hybrid NRPS-PKS biosynthetic pathway that inflicts DNA damage upon eukaryotic cells and contributes to colorectal cancer and tumor formation in the mammalian gut. Thus far, homologs of this pathway have only been found in closely related Enterobacteriaceae, while a divergent variant of this gene cluster was recently discovered in a marine alphaproteobacterial Pseudovibrio strain. Herein, we sequenced the genome of Frischella perrara PEB0191, a bacterial gut symbiont of honey bees and identified a homologous colibactin biosynthetic pathway related to those found in Enterobacteriaceae. We show that the colibactin genomic island (GI) has conserved gene synteny and biosynthetic module architecture across F. perrara, Enterobacteriaceae, and the Pseudovibrio strain. Comparative metabolomics analyses of F. perrara and E. coli further reveal that these two bacteria produce related colibactin pathway-dependent metabolites. Finally, we demonstrate that F. perrara, like E. coli, causes DNA damage in eukaryotic cells in vitro in a colibactin pathway-dependent manner. Together, these results support that divergent variants of the colibactin biosynthetic pathway are widely distributed among bacterial symbionts, producing related secondary metabolites and likely endowing its producer with functional capabilities important for diverse symbiotic associations.