Vernalization Requirement Research Articles

小麦冬性强弱评价体系的建立

建立一个比较准确的小麦冬性评价体系,对小麦种质研究评价、引种及应对自然灾害都具有重要应用价值,对小麦生态型的解释具有一定的理论意义。以12个冬性强弱不同的小麦品种为材料,经过两年重复试验,在自然春化与人工春化条件下,对与春化有关的成穗数等4个形态指标进行调查,对人工春化条件下5月份播种的小麦生长锥进行观察。经过对成穗数进行聚类分析,将12个冬小麦品种划分为弱冬性、冬性、强冬性3类。另外,结合不同春化条件下小麦成穗数差异的显著性分析结果及相关指标的标准化数据进行分析,结果表明:(1)根据幼苗习性对小麦冬性进行划分的方式存在一定缺陷,划分结果存在误差。自然春化条件下进行冬性划分具有一定的合理性,但由于受到多种外界因素影响,对相邻类型的划分效果不理想。(2)茎蘖数、小穗数、千粒重等指标存在一定的交叉现象,不适于进行冬性评价。人工春化处理下,小麦的成穗数与生长锥形态可以准确评价小麦冬性的强弱。;Winter wheat varieties require an extended low temperature period to initiate or accelerate the flowering process (vernalization). Spring wheat varieties do not have the vernalization requirement, and they would be exposed to a high risk of cold injury if sowed in low temperature. Correct evaluation of the winterness is the prerequisite to study and utilization of wheat germplasm, wheat production, and minimizing the cold injury. It also has certain theoretical significance when explaining the ecotype of wheat. Therefore, it's of great importance to build an accurate method to evaluate vernalization characteristic of different wheat varieties. To address this issue, we investigated the growth characters of 12 wheat varieties under natural or artificial vernalization conditions, and proposed two reliable standards to evaluate the winterness of wheat.<br> Twelve varieties, including Shannong8355, Jimai20, Jimai22, Shangnong14, Shannong15, Taishan008, Shannong664, Jimai19, Shannong16, Zimai12, Yannong19 and Shannong2413, were sowed every month from October to the following February. They experienced the winter and acquired vernalization naturally. For comparison, these twelve varieties were sowed every month from March to May after an artificial low temperature treatment was appllied from March to May next year. The temperature of artificial vernalization was set to 3℃, and the durations were 0d, 10d, 20d, 30d, 40d, 50d, and 60d, respectively. The experiment was repeated twice in two years.<br> The characters related to vernalization, such as number of spikes, spikelets and stem tillers, and thousand seed weight, were investigated. The datasets obtained from wheat that have been naturally or artificially vernalized were statistically compared. In addition, the growth cones of vernalized wheat planted in May were dissected and checked on the 20th day after emergence.<br> The data was normalized first, followed by variance test and cluster analysis. The results showed, that the character of number of stem tillers, spikelets and thousand seed weight, were overlapping among different kinds of cultivars under natural and artificial vernalization, therefore the indexes above are not suitable to evaluate the strength of winterness of wheat. Neither can the number of wheat spikes under condition of natural vernalization, because it was affected by many factors, such as planting time and seeding rate. By contrast, the number of wheat spikes, under artificial vernalization that the effect of natural low temperature was eliminated, can serve as a good indicator to evaluate the strength of winterness. In addition, the shape of growth cone, which grows up about 20 days after emergence, is another indicator as good as the numbers of spikes.<br> Based on the cluster analysis of the numbers of spikes under the conditions of artificial vernalization, the twelve wheat varieties surveyed here were divided into three categories, namely weak winterness, winterness and strong winterness. Shannong8355, Jimai20, Jimai22 and Shangnong14 belonged to weak winterness cultivars. Shannong15, Taishan008, Shannong664 and Jimai19 were winterness cultivars, and the strong winterness cultivars included Shannong16, Zimai12, Yannong19 and Shannong2413. This result is largely consistent with that obtained from observation of morphology characteristics, but the former gives more accurate evaluation for some varieties.<br> As a conclusion, the number of spikes and shape of growth cone under artificial vernalization are two indicators of wheat winterness. When using this method, to avoid influence of natural low temperature, the daily maximum temperature should be higher than 12℃ at sowing stage. Meanwhile, the days of daily minimum temperature below 3℃ should be less than 4 days after planting. For evaluating vernalization characteristic of wheat in Shandong province, the temperature in April is suitable to sow after different time of artificial low temperature treatment. In other area, optimum planting date can be determined to satisfy the above temperature requirements.

The continental-oceanic climatic gradient impose clinal variation in vernalization response in Arabidopsis thaliana

Flowering time is a major determinant of plant reproductive success and adaptation to local climatic conditions. Vernalization, i.e. a prolonged period of low temperature, is one of the processes controlling flowering time. This study investigates vernalization responses in natural populations of Arabidopsis thaliana from higher latitudes and their significance for local adaptation. Twenty-seven A. thaliana populations were collected across latitudinal (59–68°N) and altitudinal gradients (2–850m a.s.l.) in Norway, and the populations were screened for responses to 5 different vernalization treatments. These populations represent the northernmost limit of the species distribution worldwide. Variations in vernalization sensitivity and vernalization saturation were tested for relationships with altitude, distance from the ocean and climatic factors associated with the site of origin. The results showed that these traits were associated with both altitude and distance from the ocean. Populations originating from higher altitudes and inland locations were more sensitive and required less time to saturate their vernalization requirement than populations from lower altitudes at coastal locations. Analyses among inland populations revealed higher contribution of distance from the ocean than altitude to the variation in vernalization responses. These results indicate that the continental-oceanic climatic gradient generate clinal variation in adaptive traits.

Analysis of proteome and frost tolerance in chromosome 5A and 5B reciprocal substitution lines between two winter wheats during long‐term cold acclimation

Dynamics of cold tolerance and crown proteome composition has been analysed in a set of two winter wheat cultivars Mironovskaya 808 and Bezostaya 1 and four reciprocal substitution lines with interchanged chromosomes 5A and 5B during a long-term cold-acclimation (CA) treatment. Proteome analysis has revealed 298 differently abundant spots during experiment. Most of them (260) were changed due to CA process and only 52 spots displayed differences between genotypes. Two hundred and seven protein spots were successfully identified by tandem mass spectrometry. Comparison of samples before and after vernalization fulfillment by a combination of ANOVA and Student' T-test displayed ten differentially abundant protein spots (e.g. chopper chaperones). However, differences in the accumulation of these spots did not reflect differences in vernalization requirement of genotypes. Therefore, our results indicate that vernalization process has not influenced total proteome of CA wheat crowns. A few protein spots (14 spots; e.g. malate dehydrogenase) revealed differential accumulation levels between the individual genotypes or their groups possessing chromosome 5A or 5B from Mironovskaya 808 versus Bezostaya 1. The study has shown the effect of chromosome 5A on physiological traits and also proteome in winter wheat. Putative candidate protein markers for cold tolerance in wheat are discussed.

Simulation of environmental and genotypic variations of final leaf number and anthesis date for wheat

The rate of organ emergence and the duration of developmental phases are key components of plant fitness to its environment. Here, we describe a hybrid genetic algorithm for the estimation of the parameters of complex non-linear simulation models that we used to estimate the varietal parameters of a well-evaluated ecophysiological model (Sirius) of wheat phenology. The aim of this study was to analyze the correlations between the varietal parameters of Sirius and to determine the minimum number of parameters that need to be estimated in order to accurately simulate the effect of the genotype and environment on wheat anthesis date. A panel of 16 bread wheat cultivars was grown under controlled conditions with different vernalization and daylength treatments and in a field nursery with different sowing dates in order to characterize their vernalization and photoperiodic requirements and earliness per se. These cultivars were also grown in the field in two consecutive growing seasons in France and in the UK along a 800km latitude transect, where the dynamics of leaf appearance and anthesis date were determined. Variation in both final leaf number and anthesis date in response to the environment and the genotype was predicted with a mean error of 0.55 leaves and 3.94d, respectively, after estimation of only three of the seven varietal parameters of Sirius: the phyllochron, the response of vernalization rate to temperature, and the daylength response of leaf production. Among them, the phyllochron was reasonably well estimated and showed a positive association with earliness per se (Spearman's coefficient of rank correlation=0.59). This study showed that the number of varietal parameters in Sirius was overestimated and that considering only three varietal parameters reduced the correlations between the parameters and the root mean square error of prediction for final leaf number and anthesis date. We conclude that a phenomenogical model of wheat development can be used to estimate key phenological parameters that are difficult to determine in the field; offering the possibility to conduct large-scale quantitative genetic studies to understand better the genetic control of flowering time in cereals.

Adaptation of barley to mild winters: a role for PPDH2.

BackgroundUnderstanding the adaptation of cereals to environmental conditions is one of the key areas in which plant science can contribute to tackling challenges presented by climate change. Temperature and day length are the main environmental regulators of flowering and drivers of adaptation in temperate cereals. The major genes that control flowering time in barley in response to environmental cues are VRNH1, VRNH2, VRNH3, PPDH1, and PPDH2 (candidate gene HvFT3). These genes from the vernalization and photoperiod pathways show complex interactions to promote flowering that are still not understood fully. In particular, PPDH2 function is assumed to be limited to the ability of a short photoperiod to promote flowering. Evidence from the fields of biodiversity, ecogeography, agronomy, and molecular genetics was combined to obtain a more complete overview of the potential role of PPDH2 in environmental adaptation in barley.ResultsThe dominant PPDH2 allele is represented widely in spring barley cultivars but is found only occasionally in modern winter cultivars that have strong vernalization requirements. However, old landraces from the Iberian Peninsula, which also have a vernalization requirement, possess this allele at a much higher frequency than modern winter barley cultivars. Under field conditions in which the vernalization requirement of winter cultivars is not satisfied, the dominant PPDH2 allele promotes flowering, even under increasing photoperiods above 12 h. This hypothesis was supported by expression analysis of vernalization-responsive genotypes. When the dominant allele of PPDH2 was expressed, this was associated with enhanced levels of VRNH1 and VRNH3 expression. Expression of these two genes is needed for the induction of flowering. Therefore, both in the field and under controlled conditions, PPDH2 has an effect of promotion of flowering.ConclusionsThe dominant, ancestral, allele of PPDH2 is prevalent in southern European barley germplasm. The presence of the dominant allele is associated with early expression of VRNH1 and early flowering. We propose that PPDH2 promotes flowering of winter cultivars under all non-inductive conditions, i.e. under short days or long days in plants that have not satisfied their vernalization requirement. This mechanism is indicated to be a component of an adaptation syndrome of barley to Mediterranean conditions.

Comparative sequence analysis of VRN1 alleles of Lolium perenne with the co-linear regions in barley, wheat, and rice

Vernalization, a period of low temperature to induce transition from vegetative to reproductive state, is an important environmental stimulus for many cool season grasses. A key gene in the vernalization pathway in grasses is the VRN1 gene. The objective of this study was to identify causative polymorphism(s) at the VRN1 locus in perennial ryegrass (Lolium perenne) for variation in vernalization requirement. Two allelic Bacterial Artificial Chromosome clones of the VRN1 locus from the two genotypes Veyo and Falster with contrasting vernalization requirements were identified, sequenced, and characterized. Analysis of the allelic sequences identified an 8.6-kb deletion in the first intron of the VRN1 gene in the Veyo genotype which has low vernalization requirement. This deletion was in a divergent recurrent selection experiment confirmed to be associated with genotypes with low vernalization requirement. The region surrounding the VRN1 locus in perennial ryegrass showed microcolinearity to the corresponding region on chromosome 3 in Oryza sativa with conserved gene order and orientation, while the micro-colinearity to the corresponding region in Triticum monococcum was less conserved. Our study indicates that the first intron of the VRN1 gene, and in particular the identified 8.6kb region, is an important regulatory region for vernalization response in perennial ryegrass.

Genome-wide association analysis to identify chromosomal regions determining components of earliness in wheat

The modification of flowering date is considered an important way to escape the current or future climatic constraints that affect wheat crops. A better understanding of its genetic bases would enable a more efficient and rapid modification through breeding. The objective of this study was to identify chromosomal regions associated with earliness in wheat. A 227-wheat core collection chosen to be highly contrasted for earliness was characterized for heading date. Experiments were conducted in controlled conditions and in the field for 3 years to break down earliness in the component traits: photoperiod sensitivity, vernalization requirement and narrow-sense earliness. Whole-genome association mapping was carried out using 760 molecular markers and taking into account the five ancestral group structure. We identified 62 markers individually associated to earliness components corresponding to 33 chromosomal regions. In addition, we identified 15 other significant markers and seven more regions by testing marker pair interactions. Co-localizations were observed with the Ppd-1, Vrn-1 and Rht-1 candidate genes. Using an independent set of lines to validate the model built for heading date, we were able to explain 34% of the variation using the structure and the significant markers. Results were compared with already published data using bi-parental populations giving an insight into the genetic architecture of flowering time in wheat.

Domestication bottlenecks limit genetic diversity and constrain adaptation in narrow-leafed lupin (Lupinus angustifolius L.)

In contrast to most widespread broad-acre crops, the narrow-leafed lupin (Lupinus angustifolius L.) was domesticated very recently, in breeding programmes isolated in both space and time. Whereas domestication was initiated in Central Europe in the early twentieth century, the crop was subsequently industrialized in Australia, which now dominates world production. To investigate the ramifications of these bottlenecks, the genetic diversity of wild (n = 1,248) and domesticated populations (n = 95) was characterized using diversity arrays technology, and adaptation studied using G × E trials (n = 31) comprising all Australian cultivars released from 1967 to 2004 (n = 23). Principal coordinates analysis demonstrates extremely limited genetic diversity in European and Australian breeding material compared to wild stocks. AMMI analysis indicates that G × E interaction is a minor, albeit significant effect, dominated by strong responses to local, Western Australian (WA) optima. Over time Australian cultivars have become increasingly responsive to warm, intermediate rainfall environments in the northern WA grainbelt, but much less so to cool vegetative phase eastern environments, which have considerably more yield potential. G × E interaction is well explained by phenology, and its interaction with seasonal climate, as a result of varying vernalization responses. Yield differences are minimized when vegetative phase temperatures fully satisfy the vernalization requirement (typical of eastern Australia), and maximized when they do not (typical of WA). In breeding for WA optima, the vernalization response has been eliminated and there has been strong selection for terminal drought avoidance through early phenology, which limits yield potential in longer season eastern environments. Conversely, vernalization-responsive cultivars are more yield-responsive in the east, where low temperatures moderately extend the vegetative phase. The confounding of phenology and vernalization response limits adaptation in narrow-leafed lupin, isolates breeding programmes, and should be eliminated by widening the flowering time range in a vernalization-unresponsive background. Concomitantly, breeding strategies that will widen the genetic base of the breeding pool in an ongoing manner should be initiated.

Diversity in the Response to Low Temperature in Representative Barley Genotypes Cultivated in Europe

ABSTRACTBarley (Hordeum vulgare L.) production in many regions is constrained by low temperatures. Numerous screening methods have been proposed for studies of freezing tolerance (FT) and winter hardiness (WH). Here, we compared the response to low temperature of 54 barley genotypes released in Europe. Major components of WH were analyzed in field and growth chamber experiments under different hardening and freezing conditions. Phenotype screening of freezing injury (lethal temperature for 50% of the plants [LT50], plant survival, and chlorophyll fluorescence) and indirect evaluations (molecular‐marker‐based analysis of vernalization requirement) were used. The maximum quantum yield of the photosystem II photochemistry measured as the variable (Fv) to maximal (Fm) fluorescence ratio (Fv:Fm) analysis was confirmed as a reliable method of screening genetic diversity for FT in plants at early growth stages. Variability for FT was also found after shorter acclimation at optimal (3/1°C day/night) or suboptimal (12/7°C day/night) hardening temperatures. High levels of FT and WH were found in both winter and facultative growth habits. Facultative genotypes were more responsive to early hardening than spring or winter types. Some of them coped best with frost in both laboratory and field experiments. The most tolerant winter genotypes coped best with prolonged exposure to low temperature in the field experiments. A conservative estimation of the role of FT in WH implies that at least 50% of WH was associated with the level of FT. A combined analysis using physiological and molecular tools is proposed for phenotyping WH in large populations.

Variation in the Vernalization Response of a Geographically Diverse Collection of Timothy Genotypes

ABSTRACTTimothy (Phleum pratense L.) has earlier been characterized as a long‐day plant, which neither requires vernalization to induce flowering nor shows a vernalization response. Variation in flowering time of timothy has thus been ascribed to differences in critical photoperiods. We studied vernalization response in a geographically diverse collection of timothy and found that vernalization accelerates heading in all 38 genotypes included in this study. In addition, considerable variation in vernalization response, ranging from 711 to &gt;1400 growing degree days, was observed between genotypes, and a vernalization requirement to induce flowering was indicated for five genotypes of Nordic origin. While heading time, irrespective of vernalization treatment, was found to be correlated to geographic origin of genotypes, a strong vernalization response was identified in genotypes of different geographic origin. Genotypes of non‐Nordic origin with a strong vernalization response were either di‐ or tetraploid, whereas respective Nordic genotypes were hexaploid. The ploidy level in relation to vernalization response is discussed. This study clearly demonstrates the presence of considerable genetic variation for vernalization response within timothy, and future studies will elucidate the underlying causative genetic variation.

The quantitative response of wheat vernalization to environmental variables indicates that vernalization is not a response to cold temperature

The initiation of flowering is a crucial trait that allows temperate plants to flower in the favourable conditions of spring. The timing of flowering initiation is governed by two main mechanisms: vernalization that defines a plant's requirement for a prolonged exposure to cold temperatures; and photoperiod sensitivity defining the need for long days to initiate floral transition. Genetic variability in both vernalization and photoperiod sensitivity largely explains the adaptability of cultivated crop plants such as bread wheat (Triticum aestivum L.) to a wide range of climatic conditions. The major genes controlling wheat vernalization (VRN1, VRN2, and VRN3) and photoperiod sensitivity (PPD1) have been identified, and knowledge of their interactions at the molecular level is growing. However, the quantitative effects of temperature and photoperiod on these genes remain poorly understood. Here it is shown that the distinction between the temperature effects on organ appearance rate and on vernalization sensu stricto is crucial for understanding the quantitative effects of the environmental signal on wheat flowering. By submitting near isogenic lines of wheat differing in their allelic composition at the VRN1 locus to various temperature and photoperiod treatments, it is shown that, at the whole-plant level, the vernalization process has a positive response to temperature with complex interactions with photoperiod. In addition, the phenotypic variation associated with the presence of different spring homoeoalleles of VRN1 is not induced by a residual vernalization requirement. The results demonstrate that a precise definition of vernalization is necessary to understand and model temperature and photoperiod effects on wheat flowering. It is suggested that this definition should be used as the basis for gene expression studies and assessment of functioning of the wheat flowering gene network, including an explicit account of the quantitative effect of environmental variables.

Flowering time variation in oilseed rape (Brassica napus L.) is associated with allelic variation in the FRIGIDA homologue BnaA.FRI.a

Oilseed rape (Brassica napus L.) is a major oil crop which is grown worldwide. Adaptation to different environments and regional climatic conditions involves variation in the regulation of flowering time. Winter types have a strong vernalization requirement whereas semi-winter and spring types have a low vernalization requirement or flower without exposure to cold, respectively. In Arabidopsis thaliana, FRIGIDA (FRI) is a key regulator which inhibits floral transition through activation of FLOWERING LOCUS C (FLC), a central repressor of flowering which controls vernalization requirement and response. Here, four FRI homologues in B. napus were identified by BAC library screening and PCR-based cloning. While all homologues are expressed, two genes were found to be differentially expressed in aerial plant organs. One of these, BnaA.FRI.a, was mapped to a region on chromosome A03 which co-localizes with a major flowering time quantitative trait locus in multiple environments in a doubled-haploid mapping population. Association analysis of BnaA.FRI.a revealed that six SNPs, including at least one at a putative functional site, and one haplotype block, respectively, are associated with flowering time variation in 248 accessions, with flowering times differing by 13–19 d between extreme haplotypes. The results from both linkage analysis and association mapping indicate that BnaA.FRI.a is a major determinant of flowering time in oilseed rape, and suggest further that this gene also contributes to the differentiation between growth types. The putative functional polymorphisms identified here may facilitate adaptation of this crop to specific environments through marker-assisted breeding.

A new multiplex PCR test for the determination of Vrn-B1 alleles in bread wheat (Triticum aestivum L.)

Winter wheat requires vernalization, a long exposure to low but non-freezing temperatures, to promote reproductive development. The vernalization requirement in bread wheat (Triticum aestivum L.) is mainly controlled by the Vrn-1 genes that are located on chromosomes 5A, 5B and 5D. Dominant alleles confer spring habit and are epistatic to the recessive winter alleles which means that spring varieties carry at least one dominant allele. To date, two dominant and one recessive Vrn-B1 alleles have been described. Vrn-B1a (formerly designated as Vrn-B1) differs from the winter vrn-B1 allele by a large deletion in intron 1. Vrn-B1b has an additional small deletion and is probably derived from Vrn-B1a. The novel allele described here and designated as Vrn-B1c also has a large deletion within intron 1 but with different breakpoints from Vrn-B1a or b, and sequence duplication, showing that this is an independently derived spring allele. By combining an exon 1 primer with previously published PCR primers it was possible to develop a multiplex PCR that distinguished all four alleles simultaneously. The multiplex PCR was validated by testing 320 winter wheat and 137 spring wheat varieties. This demonstrated that the novel Vrn-B1c allele was present in 25 spring varieties of diverse origin, showing this allele to be widely distributed.

An examination of synchrony between insect emergence and flowering in Rocky Mountain meadows

One possible effect of climate change is the generation of a mismatch in the seasonal timing of interacting organisms, owing to species-specific shifts in phenology. Despite concerns that plants and pollinators might be at risk of such decoupling, there have been few attempts to test this hypothesis using detailed phenological data on insect emergence and flowering at the same localities. In particular, there are few data sets on pollinator flight seasons that are independent of flowering phenology, because pollinators are typically collected at flowers. To address this problem, we established standardized nesting habitat (trap nests) for solitary bees and wasps at sites along an elevational gradient in the Rocky Mountains, and monitored emergence during three growing seasons. We also recorded air temperatures and flowering phenology at each site. Using a reciprocal transplant experiment with nesting bees, we confirmed that local environmental conditions are the primary determinants of emergence phenology. We were then able to develop phenology models to describe timing of pollinator emergence or flowering, across all sites and years, as a function of accumulated degree-days. Although phenology of both plants and insects is well described by thermal models, the best models for insects suggest generally higher threshold temperatures for development or diapause termination than those required for plants. In addition, degree-day requirements for most species, both plants and insects, were lower in locations with longer winters, indicating either a chilling or vernalization requirement that is more completely fulfilled at colder sites, or a critical photoperiod before which degree-day accumulation does not contribute to development. Overall, these results suggest that phenology of plants and trap-nesting bees and wasps is regulated in similar ways by temperature, but that plants are more likely than insects to advance phenology in response to springtime warming. We discuss the implications of these results for plants and pollinators, and suggest that phenological decoupling alone is unlikely to threaten population persistence for most species in our study area.

Deciphering the genetics of flowering time by an association study on candidate genes in bread wheat (Triticum aestivum L.)

Earliness is very important for the adaptation of wheat to environmental conditions and the achievement of high grain yield. A detailed knowledge of key genetic components of the life cycle would enable an easier control by the breeders. The objective of the study was to investigate the effect of candidate genes on flowering time. Using a collection of hexaploid wheat composed of 235 lines from diverse geographical origins, we conducted an association study for six candidate genes for flowering time and its components (vernalization sensitivity and earliness per se). The effect on the variation of earliness components of polymorphisms within the copies of each gene was tested in ANOVA models accounting for the underlying genetic structure. The collection was structured in five groups that minimized the residual covariance. Vernalization requirement and lateness tend to increase according to the mean latitude of each group. Heading date for an autumnal sowing was mainly determined by the earliness per se. Except for the Constans (CO) gene orthologous of the barley HvCO3, all gene polymorphisms had a significant impact on earliness components. The three traits used to quantify vernalization requirement were primarily associated with polymorphisms at Vrn-1 and then at Vrn-3 and Luminidependens (LD) genes. We found a good correspondence between spring/winter types and genotypes at the three homeologous copies of Vrn-1. Earliness per se was mainly explained by polymorphisms at Vrn-3 and to a lesser extent at Vrn-1, Hd-1 and Gigantea (GI) genes. Vernalization requirement and earliness as a function of geographical origin, as well as the possible role of the breeding practices in the geographical distribution of the alleles and the hypothetical adaptive value of the candidate genes, are discussed.

Wheat flowering repressor VRN2 and promoter CO2 compete for interactions with NUCLEAR FACTOR-Y complexes.

The transition from vegetative to reproductive development in the temperate cereals is mainly regulated by seasonal cues including vernalization (determined mainly by VRN1 and VRN2 genes) and photoperiod (determined mainly by PPD1 and CO2 genes). The wheat VRN3 gene, which is similar to Arabidopsis FT, plays a central role in the integration of the competing signals from these two pathways. Under long days, VRN3 transcription is down-regulated by VRN2, a unique flowering repressor in cereals, and up-regulated by CO2. Overexpression of VRN3 overcomes VRN2 repression and promotes VRN1 transcription and flowering initiation. Using yeast two- and three-hybrid assays we show here that the CCT domains present in VRN2 and CO2 proteins interact with the same subset of eight NF-Y proteins, and that these CCT proteins compete with NF-YA for interactions with NF-YB proteins. We have confirmed all these interactions in vitro, and the interactions between VRN2 and two of the three NF-YB proteins were further confirmed in planta. In addition, we show that mutations in the CCT domain of VRN2 that eliminate the vernalization requirement in winter wheat also reduce the strength of the interactions between VRN2 and NF-Y proteins, and the ability of VRN2 to compete with CO2. Taken together, our results suggest that the interactions between CCT and NF-Y proteins play an important role in the integration of the vernalization and photoperiod seasonal signals, and provide a flexible combinatorial system to integrate multiple developmental and environmental signals in the regulation of flowering initiation in the temperate cereals.

Low temperature and oxidative stress in cereals

Low temperature stress results in significant yield losses in cereals. Cereals of subtropical origin like maize and rice are severely damaged at temperatures below 10°C and are killed at subzero temperatures. This stress effect is called chilling. In contrast, cereals originating from the temperate zone (wheat, barley, rye and oat) may survive short periods even between −10 and −20°C, depending on the species and varieties, so they are freezing-tolerant to various extents. For the winter type of these cereals a gradual decrease in temperature up to −4°C results in cold acclimation, which increases their freezing tolerance. In addition, it fulfils their vernalization requirement, which is necessary for the correct timing of the vegetative to generative transition. During both chilling and freezing, oxidative stress is induced. Although the accumulation of high concentrations of reactive oxygen species may be lethal, a moderate increase in their level may activate various defence mechanisms. In this review the role of reactive oxygen species, antioxidants, carbohydrates, free amino acids, polyamines and hormones in the response to low temperature stress in cereals will be described. The effect of light and the use of the model plantBrachypodium distachyonL. to reveal the biochemical and molecular biological background of this response will also be discussed.

Major-Effect Alleles at Relatively Few Loci Underlie Distinct Vernalization and Flowering Variation in Arabidopsis Accessions

We have explored the genetic basis of variation in vernalization requirement and response in Arabidopsis accessions, selected on the basis of their phenotypic distinctiveness. Phenotyping of F2 populations in different environments, plus fine mapping, indicated possible causative genes. Our data support the identification of FRI and FLC as candidates for the major-effect QTL underlying variation in vernalization response, and identify a weak FLC allele, caused by a Mutator-like transposon, contributing to flowering time variation in two N. American accessions. They also reveal a number of additional QTL that contribute to flowering time variation after saturating vernalization. One of these was the result of expression variation at the FT locus. Overall, our data suggest that distinct phenotypic variation in the vernalization and flowering response of Arabidopsis accessions is accounted for by variation that has arisen independently at relatively few major-effect loci.

Juvenility and flowering of Brunonia australis (Goodeniaceae) and Calandrinia sp. (Portulacaceae) in relation to vernalization and daylength

The time at which plants are transferred to floral inductive conditions affects the onset of flowering and plant morphology, due to juvenility. Plants of Brunonia australis and Calandrinia sp. were used to investigate whether Australian native ephemeral species show a distinct juvenile phase that can be extended to increase vegetative growth and flowering. The juvenile phase was quantified by transferring seedlings from less inductive (short day and 30/20°C) to inductive (vernalization or long day) conditions at six different plant ages ranging from 4 to 35 d after seed germination. An increase in days to first visible floral bud and leaf number were used to signify the end of juvenility. Brunonia australis was receptive to floral inductive long day conditions about 18-22 d after seed germination, whereas plants aged 4-35 d appeared vernalization sensitive. Overall, transferring plants of B. australis from short to long day conditions reduced the time to anthesis compared with vernalization or constant short day conditions. Calandrinia sp. showed a facultative requirement for vernalization and an insensitive phase was not detected. Floral bud and branch production increased favourably as plant age at time of transfer to inductive conditions increased. Younger plants showed the shortest crop production time. Both species can perceive the vernalization floral stimulus from a very young age, whereas the photoperiodic stimulus is perceived by B. australis after a period of vegetative growth. However, extending the juvenile phase can promote foliage development and enhance flower production of both species.

Genetic and physiological analysis of biennialism in Hyoscyamus niger

A genetic and physiological study of biennialism in the diploid selfer Hyoscyamus niger (black henbane), an obligate long-day plant, is described. Three annual and two biennial accessions that were homozygous for their respective growth habits were selected. The early-flowering trait of two annual accessions was dominant over the late-flowering trait of the third annual accession. The late-flowering annual accession, but not the early-flowering ones, responded to vernalization. Two biennial accessions remained vegetative after more than 1 year in soil and thus had an obligate vernalization requirement. Crosses between annual and biennial accessions showed that biennialism was conferred through a single dominant gene. However, plants containing only one copy of this dominant gene were transformed from biennials into very late-flowering winter-annual plants that responded more rapidly to vernalization than biennials. Taken together, these results indicated that there were allelic differences in photoperiod-specific flowering time genes and that biennialism was a dose-dependent trait with incomplete dominance. Models for flowering time regulation in henbane involving photoperiod-, vernalization-, and most likely gibberellin-specific pathways are discussed.