Prolonged Cold Of Winter Research Articles

Transcriptome and epigenome analyses of vernalization in Arabidopsis thaliana.

Vernalization accelerates flowering after prolonged winter cold. Transcriptional and epigenetic changes are known to be involved in the regulation of the vernalization response. Despite intensive applications of next-generation sequencing in diverse aspects of plant research, genome-wide transcriptome and epigenome profiling during the vernalization response has not been conducted. In this work, to our knowledge, we present the first comprehensive analyses of transcriptomic and epigenomic dynamics during the vernalization process in Arabidopsis thaliana. Six major clusters of genes exhibiting distinctive features were identified. Temporary changes in histone H3K4me3 levels were observed that likely coordinate photosynthesis and prevent oxidative damage during cold exposure. In addition, vernalization induced a stable accumulation of H3K27me3 over genes encoding many development-related transcription factors, which resulted in either inhibition of transcription or a bivalent status of the genes. Lastly, FLC-like and VIN3-like genes were identified that appear to be novel components of the vernalization pathway.

Vernalization and Floral Transition in Autumn Drive Winter Annual Life History in Oilseed Rape.

SummaryPlants with winter annual life history germinate in summer or autumn and require a period of prolonged winter cold to initiate flowering, known as vernalization. In the Brassicaceae, the requirement for vernalization is conferred by high expression of orthologs of the FLOWERING LOCUS C (FLC) gene, the expression of which is known to be silenced by prolonged exposure to winter-like temperatures [1]. Based on a wealth of vernalization experiments, typically carried out in the range of 5°C–10°C, we would expect field environments during winter to induce flowering in crops with winter annual life history. Here, we show that, in the case of winter oilseed rape, expression of multiple FLC orthologs declines not during winter but predominantly during October when the average air temperature is 10°C–15°C. We further demonstrate that plants proceed through the floral transition in early November and overwinter as inflorescence meristems, which complete floral development in spring. To validate the importance of pre-winter temperatures in flowering time control, we artificially simulated climate warming in field trial plots in October. We found that increasing the temperature by 5°C in October results in raised FLC expression and delays the floral transition by 3 weeks but only has a mild effect on flowering date the following spring. Our work shows that winter annuals overwinter as a floral bud in a manner that resembles perennials and highlights the importance of studying signaling events in the field for understanding how plants transition to flowering under real environmental conditions.

Vulnerability to prolonged cold: a case study of the Zeravshan Valley of Tajikistan

Tajikistan like other mountainous nations in Central Asia faces the dual problem of poverty and exposure to multiple natural hazards such as mass wasting, flooding, and prolonged cold. In this case study, semi-structured interviews were conducted with 31 rural Tajik households in order to characterize their vulnerability and adaptation to prolonged winter cold. The household interviews were supplemented with interviews with village leaders, doctors, and school staff. Key interview themes regarding the road network were then compared with GIS road network analysis of the region. Results suggested that the area is highly vulnerable to the impacts of prolonged cold, which could ultimately be made worse through the unsustainable land-use practices, especially for agricultural and biofuel resources. The combination of unreliable sources of income and lower accessibility to markets in winter results in less ability of the residents of these rural villages to mitigate the impacts of prolonged cold. Analysis of the road network using GIS provided additional evidence for the influence of accessibility on vulnerability to prolonged cold.

Tuning growth cycles of Brassica crops via natural antisense transcripts of BrFLC.

Several oilseed and vegetable crops of Brassica are biennials that require a prolonged winter cold for flowering, a process called vernalization. FLOWERING LOCUS C (FLC) is a central repressor of flowering. Here, we report that the overexpression of natural antisense transcripts (NATs) of Brassica rapa FLC (BrFLC) greatly shortens plant growth cycles. In rapid-, medium- and slow-cycling crop types, there are four copies of the BrFLC genes, which show extensive variation in sequences and expression levels. In Bre, a biennial crop type that requires vernalization, five NATs derived from the BrFLC2 locus are rapidly induced under cold conditions, while all four BrFLC genes are gradually down-regulated. The transgenic Bre lines overexpressing a long NAT of BrFLC2 do not require vernalization, resulting in a gradient of shortened growth cycles. Among them, a subset of lines both flower and set seeds as early as Yellow sarson, an annual crop type in which all four BrFLC genes have non-sense mutations and are nonfunctional in flowering repression. Our results demonstrate that the growth cycles of biennial crops of Brassica can be altered by changing the expression levels of BrFLC2 NATs. Thus, BrFLC2 NATs and their transgenic lines are useful for the genetic manipulation of crop growth cycles.

Cross generation plasticity in cold hardiness is associated with diapause, but not the non-diapause developmental pathway, in the blowfly, Calliphora vicina

Predicting insect responses to global climate change involves understanding cross-generation effects of temperature. The majority of temperate insects overwinter in a state of diapause, a pre-emptive response to winter conditions associated with increased cold hardiness. Diapause is often induced following maternal adult detection of an environmental cue signifying the onset of winter, whilst diapause is initiated in a subsequent life stage and/or generation. Continued global warming will expose adults to higher late-autumn temperatures, whilst diapause life stages will still experience prolonged winter cold. The cross-generation effect of temperature was investigated by acclimating adult Calliphora vicina to present-day (15°C) and future (20°C) late-autumn conditions and assessing cold-hardiness in diapause (D15 and D20) and non-diapause (ND15 and ND20) progeny. A cross-generation plasticity in cold hardiness was associated with D but not ND larvae. D15 larvae exhibited an enhanced ability to suppress internal freezing (supercooling point=-18.9±0.9°C) compared with D20 (-15.3±0.8°C), and displayed a greater tolerance of prolonged exposure to -4°C (LT50=26.0±1.0 and 11.4±1.1 days, respectively) and -8°C (5.1±1.1 and 3.0±1.1 days, respectively). These changes were associated with a reduced glucose content in D15 (2.4±0.3 g mg(-1)) compared with D20 (3.0±0.3 g mg(-1)) larvae. In conclusion, C. vicina adults exposed to warmer autumn conditions during diapause induction will produce larvae with a reduced cold hardiness capacity, which could negatively impact winter survival. Given that maternal regulation of diapause is common among temperate insects, this could be a widespread phenomenon.

Memory of prolonged Winter cold inhibits flowering and increases long-day leaf number in the chrysanthemum cultivar ‘Nagano Queen’

SummaryChrysanthemum (Chrysanthemum morifolium Ramat.) is a short-day plant; however, flowering is eventually initiated under non-inductive long-day or night-break conditions. When using Summer-to-Autumn-flowering cultivars, such flowering is undesirable for stable horticultural production, particularly for Summer cropping, because of the short length of the cut flower, the formation of a crown bud, and the development of a branched spray of flowers. Under non-inductive conditions, flowering depends on the number of leaves that form below the terminal flower bud (i.e., the long-day leaf number). Long-day leaf numbers varied among cultivars in this study. ‘Nagano Queen’ showed a seasonal change in long-day leaf number, being high in Spring and decreasing in Summer. In addition, rooted cuttings under night-break conditions initiated very early flowering. Here, we show how exposure to prolonged Winter cold influenced long-day leaf number, and its inhibitory effect on flowering. Cold pre-treatments inhibited flower initiation under subsequent short-day conditions, with noticeable genetic variation among cultivars. For instance, flower initiation in ‘Nagano Queen’ was strongly inhibited in Spring, but the inhibition decreased in Summer. This result indicated that the inhibitory effect of Winter cold caused a delay in Spring flowering, which gradually declined from Spring to Summer. Exposure to prolonged Winter cold also inhibited flower initiation under long-day and night-break conditions, and increased long-day leaf number in Spring. These results indicate that this seasonal change in the inhibitory effect of Winter cold influences long-day leaf number in ‘Nagano Queen’.

The low temperature response pathways for cold acclimation and vernalization are independent

Vernalization is the promotion of flowering in response to the prolonged cold of winter. To survive sub-zero winter temperatures, plants must first acclimate to low, non-freezing temperatures (cold acclimation). Induction of VERNALIZATION INSENSITIVE 3 (VIN3), the first gene in the vernalization pathway, is initiated within the same time frame as the induction of genes in the cold acclimation pathway raising the question of whether there are common elements in the signal transduction pathways that activate these two responses to cold. We show that none of the signalling components required for cold acclimation, including the 'master regulator'INDUCTION OF CBF EXPRESSION1 (ICE1) or HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (HOS1), which has been described as a link between cold acclimation and vernalization, play a role in VIN3 induction. We also show that the hormone abscisic acid (ABA) does not modulate VIN3 induction, consistent with earlier reports that ABA signalling plays no role in the vernalization response. The cold acclimation pathway is activated at 12 °C, at which temperature there is no induction of VIN3 expression. Taken together, our data demonstrate that the responses to low temperatures leading to cold acclimation and vernalization are controlled by distinct signalling pathways.

Crystal Structures of the Clock Protein EA4 from the Silkworm Bombyx mori

Many insects pass the winter in an arrested developmental stage called diapause, either as eggs, as pupae, or even as adults. Exposure to the prolonged cold of winter is required to permit awakening from diapause in the spring. In the diapause eggs of the silkworm Bombyx mori, a metalloglycoprotein, esterase A4 (EA4), has been suggested to serve as a cold-duration clock because its characteristic ATPase activity is transiently elevated at the end of the necessary cold period. This timer property of EA4 is known to start with the dissociation of an inhibitory peptide (called “peptidyl inhibitory needle”) under cold conditions, but its time-measuring mechanism is completely unknown. Here we present the crystal structures and functional properties of EA4 with and without glycosylation. We show that EA4 is a homodimeric ATPase, with each subunit consisting of a copper–zinc superoxide dismutase fold. There is an additional short N-terminal region that is capable of binding one more copper ion, suggesting a timer mechanism in which this ion is involved. The sugar chain appears to reinforce the binding of peptidyl inhibitory needle, which may in turn stabilize the initial conformation of the N-terminal domain, explaining the requirement for glycosylation and for the peptide to set the clock.

The PHD Finger Protein VRN5 Functions in the Epigenetic Silencing of Arabidopsis FLC

Vernalization, the acceleration of flowering by the prolonged cold of winter, ensures that plants flower in favorable spring conditions. During vernalization in Arabidopsis, cold temperatures repress FLOWERING LOCUS C (FLC) expression in a mechanism involving VERNALIZATION INSENSITIVE 3 (VIN3), and this repression is epigenetically maintained by a Polycomb-like chromatin regulation involving VERNALIZATION 2 (VRN2), a Su(z)12 homolog, VERNALIZATION 1 (VRN1), and LIKE-HETEROCHROMATIN PROTEIN 1. In order to further elaborate how cold repression triggers epigenetic silencing, we have targeted mutations that result in FLC misexpression both at the end of the prolonged cold and after subsequent development. This identified VERNALIZATION 5 (VRN5), a PHD finger protein and homolog of VIN3. Our results suggest that during the prolonged cold, VRN5 and VIN3 form a heterodimer necessary for establishing the vernalization-induced chromatin modifications, histone deacetylation, and H3 lysine 27 trimethylation required for the epigenetic silencing of FLC. Double mutant and FLC misexpression analyses reveal additional VRN5 functions, both FLC-dependent and -independent, and indicate a spatial complexity to FLC epigenetic silencing with VRN5 acting as a common component in multiple pathways.

Molecular genetic studies of the memory of winter

Many plant species have evolved the ability to flower in the proper season by sensing environmental cues. The prolonged cold of winter is one such cue that certain plants use to acquire competence to flower the following spring. For example, biennials and winter annuals become established in one growing season and often flower quickly in the early spring of the following year to complete their life cycles. The process by which exposure to prolonged cold establishes competence to flower is known as vernalization. Many studies, starting with the classic work of Lang and Melchers, have shown that the vernalized state can be stable; i.e. after exposure to cold has ended, competence to flower, in certain species, can persist for many months and throughout many cell divisions in the shoot apical meristem. Thus, plants can exhibit a 'memory of winter' and vernalization can result in an epigenetic switch in the classic sense of the term: a change that is stable in the absence of the inducing signal. The nature of this epigenetic switch in Arabidopsis thaliana is discussed here.

REMEMBERING WINTER: Toward a Molecular Understanding of Vernalization

Exposure to the prolonged cold of winter is an important environmental cue that favors flowering in the spring in many types of plants. The process by which exposure to cold promotes flowering is known as vernalization. In Arabidopsis and certain cereals, the block to flowering in plants that have not been vernalized is due to the expression of flowering repressors. The promotion of flowering is due to the cold-mediated suppression of these repressors. Recent work has demonstrated that covalent modifications of histones in the chromatin of target loci are part of the molecular mechanism by which certain repressors are silenced during vernalization.

Vernalization in Arabidopsis thaliana is mediated by the PHD finger protein VIN3.

In biennials and winter annuals, flowering is typically blocked in the first growing season. Exposure to the prolonged cold of winter, through a process called vernalization, is required to alleviate this block and permit flowering in the second growing season. In winter-annual types of Arabidopsis thaliana, a flowering repressor, FLOWERING LOCUS C (FLC), is expressed at levels that inhibit flowering in the first growing season. Vernalization promotes flowering by causing a repression of FLC that is mitotically stable after return to warm growing conditions. Here we identify a gene with a function in the measurement of the duration of cold exposure and in the establishment of the vernalized state. We show that this silencing involves changes in the modification of histones in FLC chromatin.