Environmental and genetic effects on flowering differences between northern and southern populations of Arabidopsis lyrata (Brassicaceae)

Arabidopsis lyrata (Brassicaceae) is a close outcrossing relative of A. thaliana. We examine flowering time variation of northern and southern A. lyrata populations in controlled environmental conditions, in a common garden experiment with A. thaliana, and in the field. Southern populations of A. lyrata flowered earlier than northern ones in all environmental conditions. Individuals from southern populations were more likely to flower in short days (14 h light) than northern ones, and all populations had a higher probability of flowering and flowered more rapidly in long days (20 h). The interaction of population and day length significantly affected flowering probability, and flowering time in one of two comparisons. The common garden experiment demonstrated differences between populations in the response to seed cold treatment, but growth chamber experiments showed no vernalization effect after 4 wk of rosette cold treatment. In a field population in Norway, a high proportion of the plants flowered in each year of the study. The plants progressed to flowering more rapidly in the field and common garden than in the growth chamber. The genetic basis of these flowering time differences here can be further studied using A. thaliana genetic tools.     

Ecological genetics of vernalization response in Bromus tectorum L. (Poaceae)

BACKGROUND AND AIMS: Bromus tectorum (cheatgrass or downy brome) is an exotic annual grass that is dominant over large areas of former shrubland in western North America. To flower in time for seed production in early summer, B. tectorum plants generally require vernalization at winter temperatures, either as imbibed seeds or as established seedlings. METHODS: Variation in response to increasing periods of vernalization as seeds or seedlings for progeny of ten full-sib families from each of four B. tectorum populations from contrasting habitats was studied. KEY RESULTS: As vernalization was increased from 0 to 10 weeks, the proportion of plants flowering within 20 weeks increased, weeks to initiation of flowering decreased, and seed yield per plant increased, regardless of whether plants were vernalized as seeds or seedlings. Most of the variation was accounted for by differences among populations. Plants of the warm desert population flowered promptly even without vernalization, while those of the cold desert, foothill and montane populations showed incremental changes in response variables as a function of vernalization period. Populations differed in among-family variance, with the warm desert population generally showing the least variance and the cold desert population the most. Variation among populations and among families within populations decreased as vernalization period increased, whereas the non-genetic component of variance showed no such pattern. CONCLUSIONS: Variation in vernalization response was found to be adaptively significant and apparently represents the result of contrasting selection regimes on a range of founder genotypes.     

Evidence of genetic change in the flowering phenology of sea beets along a latitudinal cline within two decades

Sea beets grown from seeds collected in 1989 and 2009 along the coasts of France and adjacent regions were compared for flowering date under controlled conditions. Seeds from both collection years were sown simultaneously and cultivated under the same glasshouse conditions. Date of flowering onset and year of first flowering were recorded. There was an overall northward shift in flowering time of about 0.35° latitude (i.e. 39 km) over the 20‐year period. The southern portion of the latitudinal gradient – that is, from 44.7°N to 47.28°N – flowered significantly later by a mean of 1.78 days, equivalent to a 43.2‐km northward shift of phenotypes. In the northern latitudes between 48.6°N and 52°N, flowering date was significantly earlier by a mean of 4.04 days, corresponding to a mean northward shift of 104.9 km, and this shift was apparently due to a diminished requirement of exposure to cold temperatures (i.e. vernalization), for which we found direct and indirect evidence. As all plants were grown from seed under identical conditions, we conclude that genetic changes occurred in the sensitivity to environmental cues that mediate the onset of flowering in both the northern and the southern latitudes of the gradient. Microevolution and gene flow may have contributed to this change. There was no significant change in the frequency of plants that flowered without vernalization. The lack of vernalization requirement may be associated with environmental instability rather than with climate conditions.     

Expression analysis of vernalization and day-length response genes in barley (Hordeum vulgare L.) indicates that VRNH2 is a repressor of PPDH2 (HvFT3) under long days

The response to vernalization and the expression of genes associated with responses to vernalization (VRNH1, VRNH2, and VRNH3) and photoperiod (PPDH1 and PPDH2) were analysed in four barley (Hordeum vulgare L.) lines: 'Alexis' (spring), 'Plaisant' (winter), SBCC058, and SBCC106 (Spanish inbred lines), grown under conditions of vernalization and short days (VSD) or no vernalization and long days (NVLD). The four genotypes differ in VRNH1. Their growth habits and responses to vernalization correlated with the level of expression of VRNH1 and the length of intron 1. 'Alexis' and 'Plaisant' behaved as expected. SBCC058 and SBCC106 showed an intermediate growth habit and flowered relatively late in the absence of vernalization. VRNH1 expression was induced by cold for all genotypes. Under VSD, VRNH1 expression was detected in the SBCC genotypes later than in 'Alexis' but earlier than in 'Plaisant'. VRNH2 was repressed under short days while VRNH1 expression increased in parallel. VRNH3 was detected only in 'Alexis' under NVLD, whereas it was not expressed in plants with the active allele of VRNH2 (SBCC058 and 'Plaisant'). Under VSD, PPDH2 was expressed in 'Alexis', SBCC058, and SBCC106, but it was only expressed weakly in 'Alexis' under NVLD. Further analysis of PPDH2 expression in two barley doubled haploid populations revealed that, under long days, HvFT3 and VRNH2 expression levels were related inversely. The timing of VRNH2 expression under a long photoperiod suggests that this gene might be involved in repression of PPDH2 and, indirectly, in the regulation of flowering time through an interaction with the day-length pathway.     

Effects of photo and thermo cycles on flowering time in barley: a genetical phenomics approach

The effects of synchronous photo (16 h daylength) and thermo (2 degrees C daily fluctuation) cycles on flowering time were compared with constant light and temperature treatments using two barley mapping populations derived from the facultative cultivar 'Dicktoo'. The 'Dicktoo'x'Morex' (spring) population (DM) segregates for functional differences in alleles of candidate genes for VRN-H1, VRN-H3, PPD-H1, and PPD-H2. The first two loci are associated with the vernalization response and the latter two with photoperiod sensitivity. The 'Dicktoo'x'Kompolti korai' (winter) population (DK) has a known functional polymorphism only at VRN-H2, a locus associated with vernalization sensitivity. Flowering time in both populations was accelerated when there was no fluctuating factor in the environment and was delayed to the greatest extent with the application of synchronous photo and thermo cycles. Alleles at VRN-H1, VRN-H2, PPD-H1, and PPD-H2--and their interactions--were found to be significant determinants of the increase/decrease in days to flower. Under synchronous photo and thermo cycles, plants with the Dicktoo (recessive) VRN-H1 allele flowered significantly later than those with the Kompolti korai (recessive) or Morex (dominant) VRN-H1 alleles. The Dicktoo VRN-H1 allele, together with the late-flowering allele at PPD-H1 and PPD-H2, led to the greatest delay. The application of synchronous photo and thermo cycles changed the epistatic interaction between VRN-H2 and VRN-H1: plants with Dicktoo type VRN-H1 flowered late, regardless of the allele phase at VRN-H2. Our results are novel in demonstrating the large effects of minor variations in environmental signals on flowering time: for example, a 2 degrees C thermo cycle caused a delay in flowering time of 70 d as compared to a constant temperature.     

Verschiebung der Blütezeit der Herbstzeitlose

Summary Potted Colchium plants were subjected to a temperature of 4°C±1° for 2 1/2 to 27 weeks between April and November (1959) and then planted in the garden.Some plants flowered during the fall of the same year in spite of the cold treatment; some of them even flowered during the cold treatment itself. In other plants, the fall flowering of that year was suppressed to different degrees depending on the treatment.Plants that had been exposed to at least 13 weeks of low temperature after the middle of July had some of their fall buds arrested in the development and only flowered in the following spring. Any earlier or later cold treatment was without effect on the time of flowering.Thus the normally fall flowering Colchium was forced by experimental means to flower in spring. This effect resembles the spontaneous spring flowering that is sometimes observed in nature and which has been subject to controversial interpretations.None of the plants that flowered in the spring following the experimental year continued this behavior during consecutive years. The fall flowering of the year following on the experimental year was also influenced by the time and duration of the cold treatment. This indicates that the effects of the cold treatment reached into the next generation of bulbs.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Germination and Flowering in Arabidopsis thaliana in Sterile Culture

The optimal conditions for the germination, growth, and flowering of an Indian strain of Arabidopsis thaliana were investigated in sterile culture. Seeds require a cold treatment to germinate, and the most effective temperature is 8?C for 48 hours. Germination after vernalization is promoted by red light and inhibited by far-red. Unvernalized seeds germinated after 31 days and flower buds appeared in 61 days. On verbalization and subsequent transfer to a temperature of 25?C and a light intensity of 4300 lux of fluorescent light, plants flowered in 25 days. Under 7000 lux of light rich in both blue and red region of the spectum, plants flowered in only 12 days. A minimum of five long-day photocyeles appeared to be necessary for flowering. Kinetin (10^?7M) and gibberellic acid (10^?7M, 10^?6M) accelerated flower formation. Kinetin and 2,4-D also catised specific types of callussing from different regions of the plant.     

Local adaptation primes cold‐edge populations for range expansion but not warming‐induced range shifts

According to theory, edge populations may be poised to expand species’ ranges if they are locally adapted to extreme conditions, or ill‐suited to colonise beyond‐range habitat if their offspring are genetically and competitively inferior. We tested these contrasting predictions by transplanting low‐, mid‐, and high‐elevation (edge) populations of an annual plant throughout and above its elevational distribution. Seed from poor‐quality edge habitat (one of two transects) had inferior emergence, but edge seeds also had adaptive phenology (both transects). High‐elevation plants flowered earlier, required less heat accumulation to mature seed, and so achieved higher lifetime fitness at and above the range edge. Experimental warming improved fitness above the range, but eliminated the advantage of local cold‐edge populations, supporting recent models in which cold‐adapted edge populations do not facilitate warming‐induced range shifts. The highest above‐range fitness was achieved by a ‘super edge phenotype’ from a neighbouring mountain, suggesting key adaptations exist regionally even if absent from local edge populations.     

Rapid evolution of phenology during range expansion with recent climate change

Although climate warming is expected to make habitat beyond species’ current cold range edge suitable for future colonization, this new habitat may present an array of biotic or abiotic conditions not experienced within the current range. Species’ ability to shift their range with climate change may therefore depend on how populations evolve in response to such novel environmental conditions. However, due to the recent nature of thus far observed range expansions, the role of rapid adaptation during climate change migration is only beginning to be understood. Here, we evaluated evolution during the recent native range expansion of the annual plant Dittrichia graveolens, which is spreading northward in Europe from the Mediterranean region. We examined genetically based differentiation between core and edge populations in their phenology, a trait that is likely under selection with shorter growing seasons and greater seasonality at northern latitudes. In parallel common garden experiments at range edges in Switzerland and the Netherlands, we grew plants from Dutch, Swiss, and central and southern French populations. Population genetic analysis following RAD‐sequencing of these populations supported the hypothesized central France origins of the Swiss and Dutch range edge populations. We found that in both common gardens, northern plants flowered up to 4 weeks earlier than southern plants. This differentiation in phenology extended from the core of the range to the Netherlands, a region only reached from central France over approximately the last 50 years. Fitness decreased as plants flowered later, supporting the hypothesized benefits of earlier flowering at the range edge. Our results suggest that native range expanding populations can rapidly adapt to novel environmental conditions in the expanded range, potentially promoting their ability to spread.     

Flowering Responses of Contrasting Ecotypes of Poa annua and their Putative Ancestors Poa infirma andPoa supina

Flowering responses of two Australian and six Norwegian populationsof Poa annua and their putative ancestors P. infirma and P.supina were studied in controlled environments. The two Australianpopulations originating from suburban parks in Canberra hadopposite daylength flowering responses across the range of temperaturestested (9–21 °C), one being a quantitative short-day(SD) plant with no response to vernalization, the other a quantitativelong-day (LD) plant with a quantitative vernalization requirement(winter annual type). Variation in earliness of flowering withinthe former population was shown to be genetically determined,and testing of selfed progenies indicated that the populationis an aggregate of several largely homozygous lines with divergentflowering responses. Two lowland populations from southern Norwaywere both quantitative LD plants with no vernalization response,while two alpine snowbed populations from southern Norway andtwo high-latitude, subarctic populations from northern Norwaywere quantitative SD plants with an obligatory plant vernalizationor SD requirement for flowering. Two populations of P. supinaexhibited the same flowering responses as the alpine and high-latitudepopulations of P. annua with an obligatory plant vernalizationor SD requirement for flowering. A combination of SD and lowtemperature (9–12 °C) for 8–10 weeks was optimalfor induction and inflorescence initiation. On the other hand,P. infirma was found to be an early-flowering quantitative SDplant which flowered freely across the range of temperatures(9–21 °C) as a typical summer annual. The experimentsdemonstrate that virtually any kind of photoperiodic and vernalizationresponses can be found among populations of P. annua. Theseversatile flowering responses reflect the contrasting floweringresponses of P. supina and P. infirma, and add strong supportto the hypothesis that P. annua has originated from these species.Copyright 2001 Annals of Botany Company Adaptation, evolution, flowering, Poa annua, P. infirma, P. supina, photoperiod, vernalization     

Population age structure and reproductive behavior of the monocarpic perennial Heracleum mantegazzianum (Apiaceae) in its native and invaded distribution ranges

Many invasive species are benign in their native region-are there interactions between their key traits and the new habitats that explain invasion success? The giant perennial herb Heracleum mantegazzianum is a problematic invader in Europe and is also naturalized in North America. We compared its population structure and reproductive behavior in the native (W. Caucasus) and invaded (Czech Republic) areas in managed (pastures) and unmanaged sites. The age structure of the populations and age at flowering were analyzed using herb-chronology, a method based on counting annual rings in the secondary xylem of roots. The species was strictly monocarpic; most plants in unmanaged sites in the invaded range flowered in the third and fourth yr (maximum 12 yr). In unmanaged habitats, plants from the native range flowered later than those from the invaded range. In both ranges, flowering was delayed in managed sites where the population density was higher and most plants flowered around the fifth year. Reproductive output of individual plants was neither related to population density nor to age at flowering. More favorable climatic conditions in the invaded region, together with increased chances for dispersal in a densely colonized central Europe, seemed to allow the massive invasion.     

Role of gibberellins in stem elongation and flowering in radish

The relationship among gibberellins, CCC, vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA₃ had no additional effect. Gibberellin A₃ (60 μg total) was not able to induce flowering in nonvernalized plants grown on 8-hour days, but it did increase the percentage of nonvernalized plants that flowered under long days from 60 to 100.

Gibberellin content of vernalized seedlings increased within the first 24 hours after seedlings were transferred to the greenhouse. Content reached a peak in the first 4 days after transfer and thereafter remained constant. Essentially no gibberellin was found in 2 day-old non-vernalized (control) seedlings of comparable size to the vernalized ones. Gibberellin content in the controls reached a peak on the fourth day of growth in the greenhouse; thereafter, it decreased steadily.

Bolting was inhibited slightly by CCC when applied during vernalization; it was almost completely inhibited when CCC was applied after seed vernalization. Extraction experiments revealed that CCC actually reduced the gibberellin content when applied during or after vernalization. The dwarfing agent, however, had essentially no effect on flowering. We concluded that gibberellins likely play a direct role in bolting of `Miyashige-sofuto' radish, but probably are not directly functional in initiating flowering.

     

Life-history variation in agricultural and wild populations of Erucastrum nasturtiifolium (Brassicaceae)

In the present study we relate the variability in life-history traits (such as flowering time and lifespan) of the herbaceous biennial–perennial Erucastrum nasturtiifolium (Brassicaceae) to habitat type. We studied plant populations from arable fields and from eroded mountain habitats, such as badlands and rocky slopes. Collection sites ranged from low basin to sub-alpine regions in the NE Iberian Peninsula. Plants were grown under common garden conditions to evaluate genetic variation among and within populations. Plants were also subjected to a resource gradient to detect genetic variation in phenotypic plasticity. The populations exhibited differentiation across a number of life-history traits (mainly flowering time and lifespan) and morphological traits related to growth (basal stem diameter, plant height and number of branches). This suggests that life-history differences among populations are genetically based. Moreover, our results show that variation in flowering time and lifespan are affected by habitat type independent of other abiotic factors such as altitude or continentality. Thus, populations from arable fields started flowering in their first year and displayed annual cycles, whereas those from wild habitats generally flowered in their second year and showed biennial or even perennial cycles. Intra-population differences in flowering time were observed in only one population, and were related to nutrient availability. We suggest that early-flowering and shorter lifespan populations of E. nasturtiifolium may have been selected from late-flowering and longer lifespan populations as part of a selective process ensuring survival and future offspring amidst unpredictable and frequently disturbed environments such as exist in many agricultural habitats.     

Vernalization sensitivity in Arabidopsis thaliana (Brassicaceae): the effects of latitude and FLC variation

Latitudinal variation in climate is predicted to select for latitudinal differentiation in sensitivity to the environmental cues that signal plants to flower at the appropriate time for a given climate. In Arabidopsis thaliana, flowering is promoted by exposure to cold temperatures (vernalization), and several vernalization pathway loci are known. To test whether natural variation in vernalization sensitivity could account for a previously observed latitudinal cline in flowering time in A. thaliana, we exposed 21 European accessions to 0, 10, 20, or 30 d of vernalization and observed leaf number at flowering under short days in a growth chamber. We observed a significant latitudinal cline in vernalization sensitivity: southern accessions were more sensitive to vernalization than northern accessions. In addition, accessions that were late flowering in the absence of vernalization were more sensitive to vernalization cues. Allelic variation at the flowering time regulatory gene FLC was not associated with mean vernalization sensitivity, but one allele class exhibited greater variance in vernalization sensitivity.     

Natural variation of barley vernalization requirements: implication of quantitative variation of winter growth habit as an adaptive trait in East Asia

In many temperate plant species, prolonged cold treatment, known as vernalization, is one of the most critical steps in the transition from the vegetative to the reproductive stage. In contrast to recent advances in understanding the molecular basis of vernalization in Arabidopsis non-vernalization mutants or the spring growth habits of cereal crops such as wheat and barley, natural variations in winter growth habits and their geographic distribution are poorly understood. We analyzed varietal variation and the geographic distribution of the degree of vernalization requirements in germplasms of domesticated barley and wild barley collections. We found a biased geographic distribution of vernalization requirements in domesticated barley: Western regions were strongly associated with a higher degree of spring growth habits, and the extreme winter growth habits were localized to Far Eastern regions including China, Korea and Japan. Both wild accessions and domesticated landraces, the regions of distribution of which overlapped each other, mainly belonged to the moderate class of winter growth habit. As a result of quantitative evaluations performed in this study, we provide evidence that the variation in the degree of winter growth habit in recombinant inbred lines was controlled by quantitative trait loci including three vernalization genes (VRN1, VRN2 and VRN3) that account for 37.9% of the variation in vernalization requirements, with unknown gene(s) explaining the remaining two-thirds of the variation. This evidence implied that the Far Eastern accessions might be a genetically differentiated group derived for an evolutionary reason, resulting in their greater tendency towards a winter growth habit.     

Latitudinal population differentiation in two species of Solidago (Asteraceae) introduced into Europe

Solidago altissima and S. gigantea were introduced from North America to Europe ~250 yr ago and are now considered aggressive weeds in abandoned fields and conservation areas. We studied patterns of genetic differentiation in these two species along their present latitudinal range in Europe (44-61 degrees N). Two generations of clonally propagated ramets from randomly selected genets of 24 populations of each species were grown in a common-garden experiment at latitude 47 degrees N from 1991 to 1992. Both species showed significant variation among populations in morphological and life-history characters: at this southern location, plants from northern populations were smaller and flowered earlier than plants from southern populations. The gradient of clinal variation was more pronounced in the second year of cultivation than in the first and was steeper in S. altissima than in S. gigantea. Within-population variation among genotypes was significant tot most characters in the case of S. altissima. Phenological rate (reciprocal of days to flowering) and size at maturity showed a significant negative correlation among populations bot not among genotypes within populations, indicating that genetic trade-offs may occur at one but not another infraspecific level. We suggest that the pattern of among-population variation reflects rapid adaptive population differentiation after introduction of the species to Europe.