Vernalization Requirement Research Articles

Genetic analysis of bolting tendency in Beta vulgaris ssp. maritima

Beta vulgaris ssp. maritima is a facultative perennial species exhibits large intraspecific variation in vernalization requirement. Bolting tendency is a complex character governed by various environmental cues and multiple genetic factors. A panel of B. vulgaris ssp. maritima accessions collected from the Mediterranean costs revealed significant variations in bolting time. Three F2 populations derived from crosses between six annual beet accessions were analyzed for bolting behavior. Two F2 segregated populations, i.e., Bvm12-7 and Bvm12-8 exhibited phenotypic segregation ratios of 3: 1 early-bolting and late-bolting which is expected for dominant-recessive inheritance of a monogenic trait. Meanwhile, the phenotypic segregation ratio for earlybolting: late-bolting in the F2 population Bvm12-5 did not deviate significantly from 63: 1, indicating a polygenic inheritance of bolting tendency in Beta vulgaris ssp. maritime. Broad sense heritability for bolting tendency ranged from 0.58 to 0.74.

Identification of the VERNALIZATION 4 gene reveals the origin of spring growth habit in ancient wheats from South Asia

Wheat varieties with a winter growth habit require long exposures to low temperatures (vernalization) to accelerate flowering. Natural variation in four vernalization genes regulating this requirement has favored wheat adaptation to different environments. The first three genes (VRN1-VRN3) have been cloned and characterized before. Here we show that the fourth gene, VRN-D4, originated by the insertion of a ∼290-kb region from chromosome arm 5AL into the proximal region of chromosome arm 5DS. The inserted 5AL region includes a copy of VRN-A1 that carries distinctive mutations in its coding and regulatory regions. Three lines of evidence confirmed that this gene is VRN-D4: it cosegregated with VRN-D4 in a high-density mapping population; it was expressed earlier than other VRN1 genes in the absence of vernalization; and induced mutations in this gene resulted in delayed flowering. VRN-D4 was found in most accessions of the ancient subspecies Triticum aestivum ssp. sphaerococcum from South Asia. This subspecies showed a significant reduction of genetic diversity and increased genetic differentiation in the centromeric region of chromosome 5D, suggesting that VRN-D4 likely contributed to local adaptation and was favored by positive selection. Three adjacent SNPs in a regulatory region of the VRN-D4 first intron disrupt the binding of GLYCINE-RICH RNA-BINDING PROTEIN 2 (TaGRP2), a known repressor of VRN1 expression. The same SNPs were identified in VRN-A1 alleles previously associated with reduced vernalization requirement. These alleles can be used to modulate vernalization requirements and to develop wheat varieties better adapted to different or changing environments.

Growth, bolting and yield of garlic (Allium sativum L.) in response to clove chilling treatment

Garlic (Allium sativum L.) has been long favored as a seasoning and as a seasonal vegetable all over the world. However, the production of fresh garlic scapes and bulbs is extremely limited by the climate and region, especially the temperature and photoperiod, under natural production conditions, and the uncertainty of the vernalization characteristic of garlic has been a key restriction to the developmental regulation of bolting and bulbing. A thorough understanding of the vernalization conditions for garlic growth should improve our knowledge of the bolting and bulbing processes. This research was conducted to assess the response of the clove to chilling treatment and further demonstrate whether chilling treatment on garlic clove could substitute the vernalization requirements for garlic plant. Before planting, the cloves (cv. G064) were subjected to low temperature (5°C, 10°C, 15°C) for different durations (20 days, 40 days or 60 days) for chilling treatment. The control cloves or plants remained in the 20–22°C regime throughout. Then, the plant growth, bolting and garlic yield were evaluated during field growing. The results indicate that pre-plant chilling treatment significantly affects garlic plant growth and development, and could act as the vernalization and enable the garlic plant to bolt without undergoing chilling during plant growth. Lower temperatures and longer treatment durations significantly enhanced the leaf elongation, shortened the growth period (5°C or 60 days), promoted the rate of one-clove bulbs (5°C or 40 days), stimulated bolting and increased the bolting rate (10°C) compared with the control. However, the bolting rate and low-temperature treatment did not follow a simple linear relation, as lower temperatures (5°C) or higher temperatures (15°C) were not beneficial to garlic bolting. It was found that garlic plants subjected to a treatment of 10°C for 20/40 days or 5°C for 20 days had comparatively higher bolting rates. Nevertheless, the garlic bulb yield and mean bulb weight decreased significantly as a function of the increasing period of the chilling treatment compared with the control. The treatment of 5°C for 20 days had the greatest yield among all the treatments, second only to the control. These findings provide strong evidence for the potential cultivation of garlic of various cultivars in various climates or seasons, making off-season cultivation possible. Other researchers could use a similar methodology to shorten the period needed until harvest or even produce desirable scapes and bulbs in the warm season.

Seasonal shift in timing of vernalization as an adaptation to extreme winter.

The requirement for vernalization, a need for prolonged cold to trigger flowering, aligns reproductive development with favorable spring conditions. In Arabidopsis thaliana vernalization depends on the cold-induced epigenetic silencing of the floral repressor locus FLC. Extensive natural variation in vernalization response is associated with A. thaliana accessions collected from different geographical regions. Here, we analyse natural variation for vernalization temperature requirement in accessions, including those from the northern limit of the A. thaliana range. Vernalization required temperatures above 0°C and was still relatively effective at 14°C in all the accessions. The different accessions had characteristic vernalization temperature profiles. One Northern Swedish accession showed maximum vernalization at 8°C, both at the level of flowering time and FLC chromatin silencing. Historical temperature records predicted all accessions would vernalize in autumn in N. Sweden, a prediction we validated in field transplantation experiments. The vernalization response of the different accessions was monitored over three intervals in the field and found to match that when the average field temperature was given as a constant condition. The vernalization temperature range of 0-14°C meant all accessions fully vernalized before snowfall in N. Sweden. These findings have important implications for understanding the molecular basis of adaptation and for predicting the consequences of climate change on flowering time.

Identification and distribution of VERNALIZATION1 alleles in Chinese barley (Hordeum vulgare) germplasm

VERNALIZATION1 (VRN1) is a central regulator of the vernalization requirement, which affects the yield and geographical distribution of Triticeae crops through regulation of the flowering time. The first intron (Intron I) of VRN1 contains putative cis-elements that mediate repression of VRN1 expression. Allelic variations in Intron I are closely associated with increased VRN1 expression in vernalization-responsive accessions in the absence of vernalization. In this study, diagnostic molecular markers were developed to distinguish the main 12 known alleles, including a new allele, of barley (Hordeum vulgare) VRN1 (HvVRN1), and to investigate HvVRN1 alleles in 373 barley varieties from major agroecological regions in China. The new allele, HvVRN1-11, with a 3172-bp deletion in Intron I of HvVRN1, was identified in a Chinese barley landrace. Analysis of eight polymorphic sites flanking major variations in Intron I of HvVRN1 classified the 12 HvVRN1 alleles into five distinct groups. Compared with modern commercial barley, landraces possessed greater genetic diversity and contained the majority of HvVRN1 alleles, especially in the winter barley regions. HvVRN1 diversity in terms of allele number reduced significantly (P < 0.01) along with higher growing latitudes, but increased in accessions carrying the winter HvVRN2 allele. Wild-type HvVRN1 and the HvVRN1-8 allele showed the most widespread distribution in most regions whereas HvVRN1-1 & HvVRN1-8, and HvVRN1-5 are predominant in the Inner Mongolian Plateau spring barley region and the Northeast Plain spring barley region, respectively, with relatively higher latitudes. Compared with landraces, the frequency of HvVRN1-8 decreased while wild-type HvVRN1 increased significantly (P < 0.01) in commercial varieties. Our study classified HvVRN1 genetic diversity in a large collection of Chinese germplasm and provided a tool for identifying HvVRN1 alleles in barley breeding populations.

Simulation of the phenological development of wheat and maize at the global scale

AbstractAimTo derive location‐specific parameters that reflect the geographic differences among cultivars in vernalization requirements, sensitivity to day length (photoperiod) and temperature, which can be used to simulate the phenological development of wheat and maize at the global scale.LocationGlobal.MethodsBased on crop calendar observations and literature describing the large‐scale patterns of phenological characteristics of cultivars, we developed algorithms to compute location‐specific parameters to represent this large‐scale pattern. Vernalization requirements were related to the duration and coldness of winter, sensitivity to day length was assumed to be represented by the minimum and maximum day lengths occurring at a location, and sensitivity to temperature was related to temperature conditions during the vegetative development phase of the crop.ResultsApplication of the derived location‐specific parameters resulted in high agreement between simulated and observed lengths of the cropping period. Agreement was especially high for wheat, with mean absolute errors of less than 3 weeks. In the main maize cropping regions, cropping periods were over‐ and underestimated by 0.5–1.5 months. We also found that interannual variability in simulated wheat harvest dates was more realistic when accounting for photoperiod effects.Main conclusionsThe methodology presented here provides a good basis for modelling the phenological characteristics of cultivars at the global scale. We show that current global patterns of growing season length as described in cropping calendars can be largely reproduced by phenology models if location‐specific parameters are derived from temperature and day length indicators. Growing seasons can be modelled more accurately for wheat than for maize, especially in warm regions. Our method for computing parameters for phenology models from temperature and day length offers opportunities to improve the simulation of crop productivity by crop simulation models developed for large spatial areas and for long‐term climate impact projections that account for adaptation in the selection of varieties.

Flowering Locus C's Lessons: Conserved Chromatin Switches Underpinning Developmental Timing and Adaptation.

Analysis of how seasonal cues influence the timing of the floral transition has revealed many important principles for how epigenetic regulation can integrate a variety of environmental cues with developmental signals. The study of the pathways that necessitate overwintering in plants and their ability to respond to prolonged cold (the vernalization requirement and response pathways) has elaborated different chromatin regulatory pathways and the involvement of noncoding RNAs. The major target of these vernalization pathways in Arabidopsis (Arabidopsis thaliana) is Flowering Locus C (FLC). A relatively simple picture of FLC regulation is emerging of a few core complexes and mechanisms that antagonize each other's actions. This balance provides a fine degree of control that has nevertheless permitted evolution of a wide range of natural variation in vernalization in Arabidopsis. Similar simple routes of adaptation may underlie life history variation between species.

Genetic variation in the flowering and yield formation of timothy (Phleum pratense L.) accessions after different photoperiod and vernalization treatments.

Timothy is a perennial forage grass grown commonly in Boreal regions. This study explored the effect of vernalization and photoperiod (PP) on flowering and growth characteristics and how this related to changes in expression of three flowering related genes in accessions from different geographic origin. Large variation was found in accessions in their vernalization and PP responses. In southern accessions vernalization response or requirement was not observed, the heading date remained unchanged, and plants flowered without vernalization. On the contrary, northern types had obligatory requirement for vernalization and long PP, but the tiller elongation did not require vernalization at 16-h PP. Longer vernalization or PP treatments reduced the genotypical differences in flowering. Moreover, the vernalization saturation progressed stepwise from main tiller to lateral tillers, and this process was more synchronized in southern accessions. The expression of PpVRN1 was associated with vernalization while PpVRN3 accumulated at long PP. A crucial role for PpVRN3 in the transition to flowering was supported as in southern accession the transcript accumulated in non-vernalized plants after transfer to 16-h PP, and the apices transformed to generative stage. Differences in vernalization requirements were associated with variation in expression levels of PpVRN1 and PpVRN3, with higher expression levels in southern type. Most divergent transcript accumulation of PpMADS10 was found under different vernalization conditions. These differences between accessions can be translated into agronomic traits, such as the tiller composition of canopy, which affects the forage yield. The southern types, with minimal vernalization response, have fast re-growth ability and rapidly decreasing nutritive value, whereas northern types grow slowly and have better quality. This information can be utilized in breeding for new cultivars for longer growing seasons at high latitudes.

Genetic dissection of earliness by analysis of a recombinant chromosome substitution double haploid mapping population of bread wheat (Triticum aestivum L.) in different geographic regions

The synchronization of flowering with the time of most favorable temperatures and light has substantial effects on grain yield and quality. In bread wheat, the major developmental genes determining vernalization requirement (Vrn-1) and photoperiod response are used in breeding cultivars adapted to different latitudes and climates. Fine regulation of flowering date is provided by minor genes whose allelic variation is not well studied. Although spring cultivars Saratovskaya 29 (S29) and Yanetzkis Probat (YP) carry the same two dominant Vrn-1 alleles, YP is several days later in flowering compared to S29. The aim of the current study was to establish the chromosomal and map locations of loci determining this difference. Inter-cultivar single chromosome substitution lines S29(YP) and a set of recombinant chromosome substitution double haploid lines grown at three contrasting climatic and geographic locations in Western Siberia and Europe. The substitution line S29(YP 4D*7A) carrying the entire donor chromosome 4D and an additional fragment of chromosome 7A showed the largest delay in flowering at all sites. A quantitative trait locus (QTL) between microsatellite markers Xgwm0089 and Xgwm4736 on chromosome 4D was detected only in Europe following substantially earlier sowing. It was manifested under increasing day length, and, therefore, was regarded as a photoperiod response locus. Another QTL associated with (TG)8 or 9-(CG)3 polymorphism of the TaFTA gene on chromosome 7A was effective under both long and short days thus representing an intrinsic earliness per se gene. This knowledge could aid the fine regulation of flowering in cultivars tailored for growing in specific agro-climatic conditions.

Distribution of the Vrn-D1b allele associated with facultative growth habit in Chinese wheat accessions

Vernalization requirement in wheat is determined by allelic variation mainly at three loci, Vrn-A1, Vrn-B1 and Vrn-D1. Up to 2011 only two alleles at the Vrn-D1 locus were known. The dominant allele, now designated as Vrn-D1a, confers spring growth habit, and the other, recessive allele, vrn-D1, is associated with the winter growth habit. Recently, we found an additional dominant allele, Vrn-D1b, associated with the facultative growth habit. As facultative wheat cultivars play an important role in wheat production we screened 689 accessions from all over China, with a specific aim of determining the frequency and distribution of Vrn-D1b. The results showed that Vrn-D1a, Vrn-D1b and vrn-D1 were present in 27.3, 20.6 and 52.1 % of all accessions, respectively. Vrn-D1a was mostly distributed in the autumn sown spring wheat zone, whereas Vrn-D1b was common in the autumn sown facultative wheat zone. One cultivar (Shiluan 02-1) was heterogeneous at the Vrn-D1 locus. A comparison between the Vrn-D1b genotype and the vrn-D1 genotype from the same cultivar showed that without vernalization the Vrn-D1b genotype reached the double ridge (DR) stage 27 days earlier than the vrn-D1 genotype. Vernalization responses, expressed as a reduction in the number of days to reach the DR stage following cold treatment, at 4 °C for 20, 30 and 40 days, were 62, 67 and 75 days, respectively, for the Vrn-D1b genotype, and 74, 87 and 98 days, respectively, for the vrn-D1 genotype, confirming the effect of Vrn-D1b on facultative growth habit. Pedigree analysis indicates that the Vrn-D1b allele originated from Chinese landraces.

Evaluation of vernalization requirement in wheat inbred lines and cultivars under controlled conditions

An understanding of vernalization requirement is a prerequisite for the development of cold tolerant cultivars for high stress regions. Vernalization requirement in winter wheat (Triticum aestivum L.) has not been adequately addressed. Therefore, the objective of the present study was to understand how the vernalization dates are related to cold tolerance, phenological development and photosynthesis in four inbred lines (inbred line 1, 2, 3 and 4) and two wheat cultivars (Mironovskaya-808 and Pishtaz). These genotypes were subjected to vernalization temperature (5 C) on 30.11.2012, 17.12.2012, 09.01.2013, 13.02.2013 and 08.03.2013 as different vernalization dates. Control plants were grown under 25/20 C, day/night condition. Final leaf number was determined at intervals throughout the growth period to measure vernalization status. Number of days until heading was registered and lethal temperature (LT50) was determined. Photosynthesis rate was measured at the end of winter and flowering stages. According to the results the individual effect of genotype and vernalization date was significant on final leaf number, number of days until flowering and LT50. However, photosynthesis rate was just affected by vernalization date. In addition, interaction between vernalization date and genotype was significant on final leaf number, number of days until flowering and LT50. These results support the hypothesis that vernalization responses regulate phenological growth and affect cold tolerance through their influence on the rate of plant development.

Virus-induced gene silencing-based functional verification of six genes associated with vernalization in wheat

Vernalization requirement is an important characteristic in crop breeding. Wheat is a widely grown crop in the world that possesses enormous economic significance. To better understand the gene networks in vernalization process, we performed a high-throughput RNA sequencing analysis comparing the transcriptomes of spring and winter wheat cultivars, with and without vernalization (unpublished data). In this study, we selected six unigenes (CL14010, CL12788, CL176, Unigene 16777, CL8746 and Unigene10196) from our transcriptome analysis based on their expression differences to further characterize their function. Transient silencing of the six unigenes individually were achieved through virus-induced gene silencing (VIGS) using BSMV vector. The period from germination to spike differentiation were recorded and compared between plants underwent VIGS silencing and the control. Our result showed that VIGS of the six unigenes significantly shortened the period from seedling to double ridge (DR) stage. Resulting in SD period ranging from 59.8 ± 0.60 to 65.8 ± 0.48 days, compared to 85.0 ± 0.73 days in the control. The results indicated that these six unigenes function as suppressors in vernalization process and silence or down-regulation of these genes promoted flower development in wheat. Further characterization of these six unigenes and their function in vernalization and flowering control is needed.

Effect of timing and height of defoliation on the grain yield of barley, wheat, oats and canola in Western Australia

Winter cropping in Western Australia (WA) is dominated by spring-type cereals and canola (Brassica napus L.) with no vernalisation requirement that are sown in late autumn (late April and May). With limited earlier sowing opportunities for later maturing winter-type crops in early autumn, farmers aiming to obtain some benefit from the grazing of crops (i.e. dual-purpose) must consider the grazing potential of spring types sown in late autumn. The aim of this study was to develop grazing guidelines for spring-type crops in WA that will limit the potential for grain yield losses. In order to determine the recovery response of spring-type crops to grazing intensity and timing, 59 time-of-cutting × height-of-cutting experiments were conducted throughout the south-western region of WA in 2012. Experiments were conducted on spring types of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola and oats (Avena sativa L.). Multi-site analysis showed that treatments simulating high-intensity ‘crash’ grazing to ground level or to a height of 5 cm reduced grain yield unless conducted early in vegetative growth before reproductive stages. Treatments simulating ‘clip’ grazing by removing only the top 5–10 cm of crop foliage reduced grain yield to a lesser extent than crash grazing, and in several instances could extend the safe cutting period past hollow stem (Zadoks growth stage 30) and/or the end of July for cereals, or past mid-July for spring canola, provided the developing reproductive parts of all crops were not damaged. On average, the amounts of biomass removed by clip grazing without yield penalty were 0.4, 0.3, 0.5 and 0.3 t ha–1 for barley, wheat, oats and canola and were similar to those removed by earlier, safe crash grazing. These represent significant amounts of forage and suggest that clip grazing of spring-type crops may be an approach suited to WA cropping and grazing systems.

Studies on the flowering biology of red sorrel (Rumex acetosella) ramets from lowbush blueberry (Vaccinium angustifolium) fields in Nova Scotia, Canada

Red sorrel (Rumex acetosella L.) is a ramet-producing herbaceous creeping perennial species commonly found as a weed in commercially managed lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Flowering and seed production occur primarily in overwintering ramets of this species, indicating a potential vernalization requirement for flowering. This study was therefore initiated to examine the role of vernalization, photoperiod, and pre-vernalization stimulus on ramet flowering. Red sorrel ramets propagated from creeping roots and seeds collected from established red sorrel populations in lowbush blueberry had an obligate requirement for vernalization to flower. Ramet populations maintained under pre- and post-vernalization photoperiods of 16 h flowered following 12 weeks of vernalization at 4 ± 0.1 °C, whereas those maintained under constant 16, 14, or 8 h photoperiods without vernalization did not flower. Vernalization for 10 weeks maximized, but did not saturate, the flowering response. Pre-vernalization photoperiod affected flowering response, with increased flowering frequency observed in ramet populations exposed to decreasing, rather than constant, photoperiod prior to vernalization. This study represents the first attempt to determine the combined effects of vernalization and photoperiod on red sorrel flowering, and the results provide a benchmark for the future study of flowering and sexual reproduction in this economically important perennial weed species.

Optimising grain yield and grazing potential of crops across Australia’s high-rainfall zone: a simulation analysis. 2. Canola

Recent expansion of cropping into Australia’s high-rainfall zone (HRZ) has involved dual-purpose crops suited to long growing seasons that produce both forage and grain. Early adoption of dual-purpose cropping involved cereals; however, dual-purpose canola (Brassica napus) can provide grazing and grain and a break crop for cereals and grass-based pastures. Grain yield and grazing potential of canola (up until bud-visible stage) were simulated, using APSIM, for four canola cultivars at 13 locations across Australia’s HRZ over 50 years. The influence of sowing date (2-weekly sowing dates from early March to late June), nitrogen (N) availability at sowing (50, 150 and 250 kg N/ha), and crop density (20, 40, 60, 80 plants/m2) on forage and grain production was explored in a factorial combination with the four canola cultivars. The cultivars represented winter, winter × spring intermediate, slow spring, and fast spring cultivars, which differed in response to vernalisation and photoperiod. Overall, there was significant potential for dual-purpose use of winter and winter × spring cultivars in all regions across Australia’s HRZ. Mean simulated potential yields exceeded 4.0 t/ha at most locations, with highest mean simulated grain yields (4.5–5.0 t/ha) in southern Victoria and lower yields (3.3–4.0 t/ha) in central and northern New South Wales. Winter cultivars sown early (March–mid-April) provided most forage (&gt;2000 dry sheep equivalent (DSE) grazing days/ha) at most locations because of the extended vegetative stage linked to the high vernalisation requirement. At locations with Mediterranean climates, the low frequency (&lt;30% of years) of early sowing opportunities before mid-April limited the utility of winter cultivars. Winter × spring cultivars (not yet commercially available), which have an intermediate phenology, had a longer, more reliable sowing window, high grazing potential (up to 1800 DSE-days/ha) and high grain-yield potential. Spring cultivars provided less, but had commercially useful grazing opportunities (300–700 DSE-days/ha) and similar yields to early-sown cultivars. Significant unrealised potential for dual-purpose canola crops of winter × spring and slow spring cultivars was suggested in the south-west of Western Australia, on the Northern Tablelands and Slopes of New South Wales and in southern Queensland. The simulations emphasised the importance of early sowing, adequate N supply and sowing density to maximise grazing potential from dual-purpose crops.

Molecular-genetic mechanisms of regulation of growth habit in wheat

The vernalization requirement determines the need of plants in a prolonged period of cold treatment for transition from a vegetative to a reproductive phase. The vernalization response in wheat is controlled by the alleles of Vrn genes. A molecular structure and causes that are the basis of alternative alleles have been defined for almost all Vrn genes. Vrn1, Vrn2, and Vrn3 interact epistaticaly and form the positive feedback loop that is activated in winter wheat by the vernalization conditions. Vrn2 locus is a key element for flowering repression in winter wheat before vernalization, whereas Vrn1 mostly determines flowering time for spring varieties. In the present review, the studies of molecular mechanisms and genetic determination of pathways that regulate of growth habit (type of development) in wheat have been analyzed. The organization, structure, and functions of Vrn genes and their expression products are discussed in detail. Particular attention is paid to the structure of regulatory regions and the molecular mechanisms, which regulate of these genes’ expression. The modern view on the model reflecting interaction between Vrn genes and the environmental during vernalization has been formulated.

Analysis of VRN1 gene in triticale and common wheat genetic background

In cereals, the transition from the vegetative stage to flowering is controlled in the main by the set of vernalization genes. Within these genes the most important role is played by VRN1, which encodes a MADS-box transcription factor, regulating the transition of shoot apical meristem to the reproductive phase. The level of vernalization requirement is strongly linked to the molecular structure of this gene. In this study we analyzed molecular mechanisms regulating the vernalization requirement in triticale on the basis of comparative analysis of the VRN1 locus between triticale (×Triticosecale Witt.) and common wheat (Triticum aestivum L.) genotypes. We also estimated the influence of VRN genotype on heading time and the winter hardiness of these two species. Molecular markers developed for VRN genotype detection in common wheat were successfully applied to an analysis of triticale genomic DNA. Subsequent analysis of the amplicons nucleotide sequence confirmed full similarity of the products obtained between triticale and common wheat. All winter triticale cultivars tested contained the recessive vrn-A1 allele, whereas all spring genotypes carried the dominant Vrn-A1a allele. Molecular analysis of the Vrn-B1 gene revealed the presence of the dominant Vrn-B1b allele in only one of the triticale genotypes analyzed (Legalo). The major system of determination of the vernalization requirement in triticale was transferred from common wheat without changes and is based on an alteration in the VRN1 gene promoter sequence within the A genome.

Vernalization mediated changes in the Lolium perenne transcriptome.

Vernalization is a key requirement for the induction of flowering in perennial ryegrass (Lolium perenne L.). The transcriptome of two genotypes with contrasting vernalization requirement was studied during primary (vernalization and short day conditions) and secondary induction (higher temperature and long day conditions) using an RNA-Seq approach. This revealed transcripts with expression profiles indicative of a role in floral induction, both in the promotion and repression of flowering. We observed similarities and specific differences between the two genotypes related to cold response, carbohydrate metabolism, and photoperiod regulation. Components of the photoperiod pathway showed regulation during vernalization, pointing to possible interactions between elements of the photoperiod and vernalization pathways. The results provide a global picture of the processes ongoing during the transition from vegetative to reproductive phase of perennial ryegrass genotypes with and without a vernalization requirement.

Epigenetic reprogramming that prevents transgenerational inheritance of the vernalized state.

Reprogramming of epigenetic states in gametes and embryos is essential for correct development in plants and mammals1. In plants, the germ line arises from somatic tissues of the flower necessitating erasure of chromatin modifications accumulated at specific loci during development or in response to external stimuli. If this occurs inefficiently it can lead to epigenetic states being inherited from one generation to the next2-4. However, in most cases accumulated epigenetic modifications are efficiently erased before the next generation. An important example of epigenetic reprogramming in plants is the resetting of expression of the Arabidopsis thaliana floral repressor FLC locus. FLC is epigenetically silenced by prolonged cold in a process called vernalization. However, the locus is reactivated prior to completion of seed development to ensure a vernalization requirement every generation. In contrast to our detailed understanding of the Polycomb-mediated epigenetic silencing induced by vernalization, little is known about the mechanism involved in the re-activation of FLC. Here we show that a hypomorphic mutation in the jumonji domain protein ELF6 impaired the reactivation of FLC in reproductive tissues, leading to inheritance of a partially vernalized state. ELF6 has H3K27me3 demethylase activity and the mutation reduced this enzymatic activity in planta. Consistent with this, H3K27me3 levels at the FLC locus stayed higher and FLC expression remained lower, than in the wild type in the following generation. Our data reveal an ancient role for H3K27 demethylation in the reprogramming of epigenetic states in plant and mammalian embryos5-7.

Capturing sequence variation among flowering-time regulatory gene homologs in the allopolyploid crop species Brassica napus.

Flowering, the transition from the vegetative to the generative phase, is a decisive time point in the lifecycle of a plant. Flowering is controlled by a complex network of transcription factors, photoreceptors, enzymes and miRNAs. In recent years, several studies gave rise to the hypothesis that this network is also strongly involved in the regulation of other important lifecycle processes ranging from germination and seed development through to fundamental developmental and yield-related traits. In the allopolyploid crop species Brassica napus, (genome AACC), homoeologous copies of flowering time regulatory genes are implicated in major phenological variation within the species, however the extent and control of intraspecific and intergenomic variation among flowering-time regulators is still unclear. To investigate differences among B. napus morphotypes in relation to flowering-time gene variation, we performed targeted deep sequencing of 29 regulatory flowering-time genes in four genetically and phenologically diverse B. napus accessions. The genotype panel included a winter-type oilseed rape, a winter fodder rape, a spring-type oilseed rape (all B. napus ssp. napus) and a swede (B. napus ssp. napobrassica), which show extreme differences in winter-hardiness, vernalization requirement and flowering behavior. A broad range of genetic variation was detected in the targeted genes for the different morphotypes, including non-synonymous SNPs, copy number variation and presence-absence variation. The results suggest that this broad variation in vernalization, clock and signaling genes could be a key driver of morphological differentiation for flowering-related traits in this recent allopolyploid crop species.