Arabidopsis thaliana eIF4E1 and eIF(iso)4E Participate in Cold Response and Promote Translation of Some Stress-Related mRNAs.

Plant defense and adaptation to adverse environmental conditions rely on gene expression control, such as mRNA transcription, processing, stability, and translation. Sudden temperature changes are common in the era of global warming; thus, understanding plant acclimation responses at the molecular level becomes imperative. mRNA translation initiation regulation has a pivotal role in achieving the synthesis of the appropriate battery of proteins needed to cope with temperature stress. In this study, we analyzed the role of translation initiation factors belonging to the eIF4E family in Arabidopsis acclimation to cold temperatures and freezing tolerance. Using knockout (KO) and overexpressing mutants of AteIF4E1 or AteIF(iso)4E, we found that AteIF4E1 but not AteIF(iso)4E overexpressing lines displayed enhanced tolerance to freezing without previous acclimation at 4°C. However, KO mutant lines, eif(iso)4e-1 and eif4e1-KO, were more sensitive to the stress. Cold acclimation in wild-type plants was accompanied by increased levels of eIF4E1 and eIF(iso)4E transcript levels, polysomes (P) enrichment, and shifts of these factors from translationally non-active to active fractions. Transcripts, previously found as candidates for eIF(iso)4E or eIF4E1 selective translation, changed their distribution in both P and total RNA in the presence of cold. Some of these transcripts changed their polysomal distribution in the mutant and one eIF4E1 overexpressing line. According to this, we propose a role of eIF4E1 and eIF(iso)4E in cold acclimation and freezing tolerance by regulating the expression of stress-related genes.

MPK6 Kinase Regulates Plasma Membrane H+-ATPase Activity in Cold Acclimation.

Cold and freezing stresses severely affect plant growth, development, and survival rate. Some plant species have evolved a process known as cold acclimation, in which plants exposed to temperatures above 0 °C trigger biochemical and physiological changes to survive freezing. During this response, several signaling events are mediated by transducers, such as mitogen activated protein kinase (MAPK) cascades. Plasma membrane H+-ATPase is a key enzyme for the plant cell life under regular and stress conditions. Using wild type and mpk3 and mpk6 knock out mutants in Arabidopsis thaliana, we explored the transcriptional, translational, and 14-3-3 protein regulation of the plasma membrane H+-ATPase activity under the acclimation process. The kinetic analysis revealed a differential profiling of the H+-ATPase activity depending on the presence or absence of MPK3 or MPK6 under non-acclimated or acclimated conditions. Negative regulation of the plasma membrane H+-ATPase activity was found to be exerted by MPK3 in non-acclimated conditions and by MPK6 in acclimated conditions, describing a novel form of regulation of this master ATPase. The MPK6 regulation involved changes in plasma membrane fluidity. Moreover, our results indicated that MPK6 is a critical regulator in the process of cold acclimation that leads to freezing tolerance and further survival.

Acclimation to cold stress reduces injury from low temperature and bispyribac-sodium on rice.

BACKGROUND: In subtropical areas, early planting exposes rice seedlings to cold stress, impairing seedling growth and making them more vulnerable to other stresses including herbicide injury. The objectives of this work were: to evaluate the effect of cold stress on bispyribac-sodium selectivity in rice; to determine the mechanisms of cold tolerance in sensitive ('Epagri 109') and tolerant ('IRGA 424') rice cultivars; and to ascertain that cold acclimatization influences bispyribac-sodium selectivity in rice. RESULTS: Prolonged cold stress caused high lipid peroxidation, increased rice injury, and stunted growth. Short-term acclimation with cold stress reduced rice injury with bispyribac-sodium. Total phenols were upregulated in rice exposed to cold stress. Prolonged cold stress increased the superoxide dismutase and catalase activity in IRGA 424. Antioxidant activity was higher in the cold-tolerant than in the cold-sensitive cultivar. Only catalase activity was responsive to bispyribac-sodium. OsRAN2, OsGSTL2, and CYP72A21 were upregulated by cold and herbicide stress in both cultivars. OsGSTL2 was upregulated more in IRGA 424 than in Epagri 109. OsFAD8 was upregulated in cold-sensitive rice exposed to short-duration cold stress but was not responsive to bispyribac-sodium. CONCLUSION: Cold stress reduces bispyribac-sodium selectivity in rice. Short-term acclimation to cold stress reduces the effect of cold stress and enhances bispyribac-sodium selectivity. The tolerance of rice (IRGA 424) to cold stress is due to differential induction of protection genes CYP72A21 and OsGSTL2 associated with herbicide metabolism, together with the accumulation of total phenols and higher activity of antioxidant enzymes.

Dormant but Active: Chilling Accumulation Modulates the Epigenome and Transcriptome of Prunus avium During Bud Dormancy.

Temperate deciduous fruit tree species like sweet cherry (Prunus avium) require long periods of low temperatures to trigger dormancy release and flowering. In addition to sequence-based genetic diversity, epigenetic variation may contribute to different chilling requirements among varieties. For the low chill variety 'Royal Dawn' and high chill variety 'Kordia', we studied the methylome of floral buds during chilling accumulation using MethylC-seq to identify differentially methylated regions (DMRs) during chilling hours (CH) accumulation, followed by transcriptome analysis to correlate changes in gene expression with DNA methylation. We found that during chilling accumulation, DNA methylation increased from 173 CH in 'Royal Dawn' and 443 CH in 'Kordia' and was mostly associated with the CHH context. In addition, transcriptional changes were observed from 443 CH in 'Kordia' with 1,210 differentially expressed genes, increasing to 4,292 genes at 1,295 CH. While 'Royal Dawn' showed approximately 5,000 genes differentially expressed at 348 CH and 516 CH, showing a reprogramming that was specific for each genotype. From conserved upregulated genes that overlapped with hypomethylated regions and downregulated genes that overlapped with hypermethylated regions in both varieties, we identified genes related to cold-sensing, cold-signaling, oxidation-reduction process, metabolism of phenylpropanoids and lipids, and a MADS-box SVP-like gene. As a complementary analysis, we used conserved and non-conserved DEGs that presented a negative correlation between DNA methylations and mRNA levels across all chilling conditions, obtaining Gene Ontology (GO) categories related to abiotic stress, metabolism, and oxidative stress. Altogether, this data indicates that changes in DNA methylation precedes transcript changes and may occur as an early response to low temperatures to increase the cold tolerance in the endodormancy period, contributing with the first methylome information about the effect of environmental cues over two different genotypes of sweet cherry.

Effect of in vitro cold acclimation of Deschampsia antarctica on the accumulation of proteins with antifreeze activity.

Deschampsia antarctica has managed to colonize the maritime Antarctic. One of the main factors associated with its tolerance to low temperatures is the presence of apoplastic proteins with antifreeze activity. This work focuses on the effect of cold acclimation of D. antarctica on the accumulation of apoplastic proteins with antifreeze activity. Antifreeze proteins present in apoplastic extracts were purified by ice affinity purification, and their identity was determined by protein sequencing. D. antarctica plants were subjected to 22 days of cold acclimation at 4 °C. The highest content of apoplastic proteins with antifreeze activity was obtained at between 12 and 16 days of acclimation. Protein sequencing allowed their identification with >95% probability. Percentage coverage was 74% with D. antarctica ice recrystallization inhibition protein 1 (DaIRIP1) and 55% with DaIRIP3. Cold acclimation of D. antarctica improved the yield of apoplastic proteins, and resulted in an increase in the antifreeze activity of apoplastic extracts. An in silico analysis suggested that the fluctuations presented by the three-dimensional structures of DaIRIPs help to explain the presence of certain DaIRIPs in apoplastic extracts under the cold acclimation conditions evaluated.

Genome-wide expression of low temperature response genes in Rosa hybrida L.

Plants respond to low temperature stress during cold acclimation, a complex process involving changes in physiological and biochemical modifications. The rose serves as a good model to investigate low temperature responses in perennial ornamentals. In this study, a heterologous apple microarray is used to investigate genome-wide expression profiles in Rosa hybrida subjected to low temperature dark treatment. Transcriptome profiles are determined in floral buds at 0h, 2h, and 12h of low temperature treatment (4 °C). It is observed that a total of 134 transcripts are up-regulated and 169 transcripts are down-regulated in response to low temperature. Interestingly, a total of eight up-regulated genes, including those coding for two cytochrome P450 proteins, two ankyrin repeat family proteins, two metal ion binding proteins, and two zinc finger protein-related transcription factors, along with a single down-regulated gene, coding for a dynamin-like protein, are detected. Transcript profiles of 12 genes known to be involved in cold stress response are also validated using qRT-PCR. Furthermore, expression patterns of the AP2/ERF gene family of transcription factors are investigated in both floral buds and leaves. Overall, AP2/ERFs genes are more rapidly induced in leaves than in floral buds. Moreover, differential expression of several AP2/ERF genes are detected earlier in vegetative rather than in reproductive tissues. These findings highlight important roles of various low temperature response genes in mediating cold acclimation, thereby allowing roses to adapt to low temperatures, but without adversely affecting flower bud development and subsequent flowering, while vegetative tissues undergo early adaptation to low temperatures.

The cost of avoiding freezing in stems: trade-off between xylem resistance to cavitation and supercooling capacity in woody plants.

Stems and leaves of Olea europaea L. (olive) avoid freezing damage by substantial supercooling during the winter season. Physiological changes during acclimation to low temperatures were studied in five olive cultivars. Water relations and hydraulic traits, ice nucleation temperature (INT) and temperatures resulting in 50% damage (LT50) were determined. All cultivars showed a gradual decrease in INT and LT50 from the dry and warm summer to the wet and cold winter in Patagonia, Argentina. During acclimation to low temperatures there was an increase in leaf cell wall rigidity and stomatal conductance (gs), as well as a decrease in leaf apoplastic water content, leaf water potential (Ψ), sap flow and stem hydraulic conductivity (ks). More negative Ψ as a consequence of high gs and detrimental effects of low temperatures on root activity resulted in a substantial loss of ks due to embolism formation. Seasonal stem INT decrease from summer to winter was directly related to the xylem resistance to cavitation, determined by the loss of ks across cultivars. Thus the loss of freezable water in xylem vessels by embolisms increased stem supercooling capacity and delayed ice propagation from stems to the leaves. For the first time, a trade-off between xylem resistance to cavitation and stem and leaf supercooling capacity was observed in plants that avoid extracellular freezing by permanent supercooling. The substantial loss of hydraulic function in olive cultivar stems by embolism formation with their high repair costs are compensated by avoiding plant damage at very low subzero temperatures.

Developmental thermal plasticity among Drosophila melanogaster populations.

Many biotic and abiotic variables influence the dispersal and distribution of organisms. Temperature has a major role in determining these patterns because it changes daily, seasonally and spatially, and these fluctuations have a significant impact on an organism's behaviour and fitness. Most ecologically relevant phenotypes that are adaptive are also complex and thus they are influenced by many underlying loci that interact with the environment. In this study, we quantified the degree of thermal phenotypic plasticity within and among populations by measuring chill-coma recovery times of lines reared from egg to adult at two different environmental temperatures. We used sixty genotypes from six natural populations of Drosophila melanogaster sampled along a latitudinal gradient in South America. We found significant variation in thermal plasticity both within and among populations. All populations exhibit a cold acclimation response, with flies reared at lower temperatures having increased resistance to cold. We tested a series of environmental parameters against the variation in population mean thermal plasticity and discovered the mean thermal plasticity was significantly correlated with altitude of origin of the population. Pairing our data with previous experiments on viability fitness assays in the same populations in fixed and variable environments suggests an adaptive role of this thermal plasticity in variable laboratory environments. Altogether, these data demonstrate abundant variation in adaptive thermal plasticity within and among populations.

Cold acclimation increases mitochondrial oxidative capacity without inducing mitochondrial uncoupling in goldfish white skeletal muscle.

Goldfish have been used for cold acclimation studies, which have focused on changes in glycolytic and oxidative enzymes or alterations in lipid composition in skeletal muscle. Here we examine the effects of cold acclimation on the functional properties of isolated mitochondria and permeabilized fibers from goldfish white skeletal muscle, focusing on understanding the types of changes that occur in the mitochondrial respiratory states. We observed that cold acclimation promoted a significant increase in the mitochondrial oxygen consumption rates. Western blot analysis showed that UCP3 was raised by ∼1.5-fold in cold-acclimated muscle mitochondria. Similarly, we also evidenced a rise in the adenine nucleotide translocase content in cold-acclimated muscle mitochondria compared to warm-acclimated mitochondria (0.96±0.05 vs 0.68±0.02 nmol carboxyatractyloside mg(-1) protein). This was followed by a 2-fold increment in the citrate synthase activity, which suggests a higher mitochondrial content in cold-acclimated goldfish. Even with higher levels of UCP3 and ANT, the effects of activator (palmitate) and inhibitors (carboxyatractyloside and GDP) on mitochondrial parameters were similar in both warm- and cold-acclimated goldfish. Thus, we propose that cold acclimation in goldfish promotes an increase in functional oxidative capacity, with higher mitochondrial content without changes in the mitochondrial uncoupling pathways.

Cold resistance in plants: a mystery unresolved

Herbaceous temperate plants are capable of developing freezing tolerance when they are exposed to low nonfreezing temperatures. Acquired freezing tolerance involves extensive reprogramming of gene expression and metabolism. Recent full-genome transcript profiling studies, in combination with mutational and transgenic plant analyses, have provided a snapshot of the complex transcriptional network that operates under cold stress. The changes in expression of hundreds of genes in response to cold temperatures are followed by increases in the levels of hundreds of metabolites, some of which are known to have protective effects against the damaging effects of cold stress. Genetic analysis has revealed important roles for cellular metabolic signals, and for RNA splicing, export and secondary structure unwinding, in regulating cold-responsive gene expression and chilling and freezing tolerance. These results along with many of the others summarized here further our understanding of the basic mechanisms that plants have evolved to survive freezing temperatures. In addition, the findings have potential practical applications, as freezing temperatures are a major factor limiting the geographical locations suitable for growing crop and horticultural plants and periodically account for significant losses in plant productivity. Although, great progress has been made in the field but lacunae still remain since it appears that the cold resistance is more complex than perceived and involves more than one pathway.