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See detailThe FLC-dependent vernalization pathway in Sinapis alba.
D'Aloia, Maria ULg; Tocquin, Pierre ULg; Périlleux, Claire ULg

in Comparative Biochemistry and Physiology. Part A, Physiology (2006), 143A

In many plants, flowering is promoted by a long exposure to cold, a process known as ‘vernalisation’. In Arabidopsis, the vernalisation pathway was shown to promote flowering via the repression of the ... [more ▼]

In many plants, flowering is promoted by a long exposure to cold, a process known as ‘vernalisation’. In Arabidopsis, the vernalisation pathway was shown to promote flowering via the repression of the FLOWERING LOCUS C (FLC) gene, which encodes a repressor of flowering. As far as we know, the genetical control of flowering is conserved among Brassicaceae, and we reported elsewhere cloning of flowering times genes of the photoperiodic pathway in Sinapis alba, based on sequence similarity with Arabidopsis. However, little is known about vernalisation in Sinapis. We therefore undertook a physiological and molecular study of this process. Plants of Sinapis were grown in non inductive short days and vernalised at 7°C, at the seedling stage. Vernalisation was found to accelerate flowering and an increasing effect was observed for vernalisation treatments longer than 2 weeks. We cloned an FLC-like sequence (SaFLC) by screening a cDNA library, and used it as a probe to perform expression analyses. We observed that SaFLC was almost completely repressed after 1 week of vernalisation, but repression was stable only after 2 weeks, which is consistent with the fact that 2-week is the minimal duration of vernalisation that promotes flowering. Hence the molecular mechanisms of vernalisation seem to be conserved in Sinapis and Arabidopsis. [less ▲]

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See detailLes messagers de la floraison
Périlleux, Claire ULg

Conference given outside the academic context (2005)

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See detailPartenariat F.N.P.S.M.S. - ULg - Rapport d'activité ULg 2004
Périlleux, Claire ULg; Hustin, Cécile; Van Kerkhoven, Fabrizio

Report (2005)

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See detailA physiological overview of the genetics of flowering time control.
Bernier, Georges ULg; Périlleux, Claire ULg

in Plant Biotechnology Journal (2005), 3(1), 3-16

Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as 'primary', but ... [more ▼]

Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as 'primary', but clearly interfere with, or can even be substituted by, less predictable factors. All plant parts participate in the sensing of these interacting factors. In the case of floral induction by photoperiod, long-distance signalling is known to occur between the leaves and the shoot apical meristem (SAM) via the phloem. In the long-day plant, Sinapis alba, this long-distance signalling has also been shown to involve the root system and to include sucrose, nitrate, glutamine and cytokinins, but not gibberellins. In Arabidopsis thaliana, a number of genetic pathways controlling flowering time have been identified. Models now extend beyond 'primary' controlling factors and show an ever-increasing number of cross-talks between pathways triggered or influenced by various environmental factors and hormones (mainly gibberellins). Most of the genes involved are preferentially expressed in meristems (the SAM and the root tip), but, surprisingly, only a few are expressed preferentially or exclusively in leaves. However, long-distance signalling from leaves to SAM has been shown to occur in Arabidopsis during the induction of flowering by long days. In this review, we propose a model integrating physiological data and genes activated by the photoperiodic pathway controlling flowering time in early-flowering accessions of Arabidopsis. This model involves metabolites, hormones and gene products interacting as long- or short-distance signalling molecules. [less ▲]

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See detailRoot involvement in floral transition of long-day plants
Périlleux, Claire ULg

Conference (2005)

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See detailLEAFY expression and temporal sequence of floral transition in Sinapis alba L.
Bonhomme, Delphine ULg; Périlleux, Claire ULg

Poster (2005)

The shoot apical meristem (SAM) of Sinapis alba can be switched from vegetative to reproductive fate by exposure of 2-month old plants to a single long day (LD). Floral transition then occurs in good ... [more ▼]

The shoot apical meristem (SAM) of Sinapis alba can be switched from vegetative to reproductive fate by exposure of 2-month old plants to a single long day (LD). Floral transition then occurs in good synchrony within a population, and a number of biochemical, cellular, and morphological changes have been described. Our aim is to integrate gene expression patterns into this timing. We report here the analysis of SaLFY, orthologous to the floral meristem identity gene LEAFY of Arabidopsis. Materials and Methods: Plants of Sinapis were grown in 8-h shorts days for two months before being induced to flower by one 22-h LD. Shoot apices were harvested 24, 32, 40, 48, 56 and 80h after start of the LD, and prepared for in situ hybridization (Melzer et al., 1999). Results and Conclusions: As expected, the expression of SaLFY was very strong in flower primordia. More surprisingly, SaLFY was expressed well before the initiation of flowers. First, a strong signal was detected in the tip of young leaf primordia of vegetative plants. Secondly, SaLFY was transiently expressed in the SAM of induced plants, from 32h after the start of the LD, when cell proliferation increased. The signal formed, in transverse sections, a discontinuous ring with activation where last leaves were to be initiated. Interestingly, this activation in the SAM matched in time and space early growth changes previously described during the transition to flowering, namely an increase of leaf primordia growth and an acceleration of last leaf initiation (Bernier, 1997), suggesting that SaLFY may have dual functions in fate specification during the floral transition of the SAM. References: Bernier G 1997. J Exp Bot 48; 1071-1077. Melzer S, Kampmann G, Chandler J, Apel K 1999. Plant J 18; 395-405. [less ▲]

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See detailDesign of a versatile device for measuring whole plant gas exchanges in Arabidopsis thaliana
Tocquin, Pierre ULg; Périlleux, Claire ULg

in New Phytologist (2004), 162(1), 223-229

Because of its small size and rosette growth habit, measuring gas exchanges in Arabidopsis thaliana is difficult with standard leaf cuvettes. Here, we designed a versatile system that is usable at the ... [more ▼]

Because of its small size and rosette growth habit, measuring gas exchanges in Arabidopsis thaliana is difficult with standard leaf cuvettes. Here, we designed a versatile system that is usable at the whole rosette level, as small as possible for fast and accurate measurements, but adaptable to plant size, and suitable for in situ measurements whatever the growing substrate of the plant. This cuvette is in two parts: the basic unit, which contains the sensors and is connected to the infra-red gas analyzer, and the clear chamber, where the rosette is enclosed. We made a set of three interchangeable chambers of different sizes to measure the rate of CO2 assimilation [A] of 26-, 33- and 40-d-old plants. The dependence of A to light irradiance and to intercellular CO2 concentration was recorded as typical response curves, which validate our device. Measurements were not only consistent in saturating conditions, but accurate CO2 exchange measurements in limiting conditions also reflected important physiological features related to plant ageing. [less ▲]

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See detailGibberellins and the floral transition in Sinapis alba
Corbesier, Laurent; Kustermans, Gaëlle ULg; Périlleux, Claire ULg et al

in Physiologia Plantarum (2004), 122(1), 152-158

The putative role of gibberellins in the transition to flowering was investigated in Sinapis alba, a caulescent long-day (LD) plant. It was observed that: (1) physiological doses of exogenous gibberellins ... [more ▼]

The putative role of gibberellins in the transition to flowering was investigated in Sinapis alba, a caulescent long-day (LD) plant. It was observed that: (1) physiological doses of exogenous gibberellins (GA(1), GA(3), GA(9)) do not cause the floral shift of the meristem when applied to plants grown in short days but have some positive effect on the flowering response to a suboptimal LD; no inhibition was observed in any case; (2) GA-biosynthesis inhibitors (prohexadione-Ca and paclobutrazol) considerably inhibit stem growth but have some negative effect on flowering only when a suboptimal LD is given; and (3) the floral transition induced by one 22-h LD does not correlate with any detectable change in GA content of the apical bud, of the leaves, and of the phloem exudate reaching the apex. Taken together, these results suggest that GAs do not act as a major signal for photoperiodic flower induction in Sinapis. [less ▲]

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See detailIsolation and analysis of a putative FLC orthologue in Sinapis alba L.
D'Aloia, Maria ULg; Melzer, Siegbert; Périlleux, Claire ULg

in Acta Physiologiae Plantarum (2004), 26(3), 23-24

In many plant species, flowering is promoted by a long exposure to low temperature, a process known as vernalization. Some plants even have an absolute requirement for winter cold before being able to ... [more ▼]

In many plant species, flowering is promoted by a long exposure to low temperature, a process known as vernalization. Some plants even have an absolute requirement for winter cold before being able to flower the next summer, hence behave as biennials or winter crops. A recent breakthrough in the understanding of the molecular bases of vernalization has been the cloning of the FLOWERING LOCUS C (FLC) gene in Arabidopsis thaliana (Michaels S.D. & Amasino R.M., 1999). FLC encodes a repressor of flowering and is downregulated by vernalization. So vernalization relieves the inhibitory role that FLC plays on downstream genes involved in the floral transition of the shoot apical meristem (SAM). Although vernalization has been shown, by physiological studies, to be sensed by the SAM, molecular evidences are missing. Such analyses are impaired in Arabidopsis by the small size of the plant and the rosette growth habit. We therefore cloned a FLC homologue in a caulescent relative Brassicaceae: mustard (Sinapis alba L.). We identified two clones by screening a cDNA library made from leaf mRNA. One of them, SaFLC1, was used for in situ hybridizations on SAM sections. Preliminary results are shown. Because of its agronomical importance, we have also tried to manipulate the vernalization process in crops. By using a transgenic approach, we have attempted to bypass the strict vernalization requirement of winter colza (Brassica napus L.). We have over-expressed SaMADS A, a gene which is repressed by FLC in wild type, and observed that the transgenics did not require vernalization any more. [less ▲]

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See detailA novel high efficiency, low maintenance, hydroponic system for synchronous growth and flowering of Arabidopsis thaliana.
Tocquin, Pierre ULg; Corbesier, Laurent; Havelange, Andrée ULg et al

in BMC Plant Biology (2003), 3(2), 302003

Background: Arabidopsis thaliana is now the model organism for genetic and molecular plant studies, but growing conditions may still impair the significance and reproducibility of the experimental ... [more ▼]

Background: Arabidopsis thaliana is now the model organism for genetic and molecular plant studies, but growing conditions may still impair the significance and reproducibility of the experimental strategies developed. Besides the use of phytotronic cabinets, controlling plant nutrition may be critical and could be achieved in hydroponics. The availability of such a system would also greatly facilitate studies dealing with root development. However, because of its small size and rosette growth habit, Arabidopsis is hardly grown in standard hydroponic devices and the systems described in the last years are still difficult to transpose at a large scale. Our aim was to design and optimize an up-scalable device that would be adaptable to any experimental conditions. Results: An hydroponic system was designed for Arabidopsis, which is based on two units: a seed-holder and a 1-L tank with its cover. The original agar-containing seed-holder allows the plants to grow from sowing to seed set, without transplanting step and with minimal waste. The optimum nitrate supply was determined for vegetative growth, and the flowering response to photoperiod and vernalization was characterized to show the feasibility and reproducibility of experiments extending over the whole life cycle. How this equipment allowed to overcome experimental problems is illustrated by the analysis of developmental effects of nitrate reductase deficiency in nia1nia2 mutants. Conclusion: The hydroponic device described in this paper allows to drive small and large scale cultures of homogeneously growing Arabidopsis plants. Its major advantages are its flexibility, easy handling, fast maintenance and low cost. It should be suitable for many experimental purposes. [less ▲]

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See detailGuide des travaux pratiques de Physiologie végétale
Périlleux, Claire ULg

Learning material (2003)

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See detailCytokinin levels in leaves, leaf exudate and shoot apical meristem of Arabidopsis thaliana during floral transition
Corbesier, Laurent; Prinsen, Els; Jacqmard, Annie ULg et al

in Journal of Experimental Botany (2003), 54(392), 2511-2517

Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis ... [more ▼]

Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis thaliana has been successfully used to unravel signalling pathways by genetic and molecular approaches, but analyses are still required to determine the physiological signals involved in the control of floral transition. In this work, the putative role of cytokinins was investigated using vegetative plants of Arabidopsis (Columbia) induced to flower synchronously by a single 22 h long day. Cytokinins were analysed in leaf extracts, leaf phloem exudate and in the shoot apical meristem at different times during floral transition. It was found that, in both the leaf tissues and leaf exudate, isopentenyladenine forms of cytokinins increased from 16 h after the start of the long day. At 30 h, the shoot apical meristem of induced plants contained more isopentenyladenine and zeatin than vegetative controls. These cytokinin increases correlate well with the early events of floral transition. [less ▲]

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See detailC : N ratio increases in the phloem sap during floral transition of the long-day plants Sinapis alba and Arabidopsis thaliana
Corbesier, Laurent; Bernier, Georges ULg; Périlleux, Claire ULg

in Plant & Cell Physiology (2002), 43(6), 684-688

In plants of Sinapis alba and Arabidopsis thaliana, leaf exudate (phloem sap) was analysed during and after a single long day inducing flowering and in control short days. The amounts of carbohydrates and ... [more ▼]

In plants of Sinapis alba and Arabidopsis thaliana, leaf exudate (phloem sap) was analysed during and after a single long day inducing flowering and in control short days. The amounts of carbohydrates and amino acids were measured to estimate the organic C : N ratio. In both species, the C : N ratio of the phloem sap increased markedly and early during the inductive treatment, suggesting that an inequality in organic C and N supply to the apical meristem may be important at floral transition. [less ▲]

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See detailThe control of flowering: do genetical and physiological approaches converge ?
Périlleux, Claire ULg; Bernier, Georges ULg

in O'Neill, S. D.; Roberts, J. A. (Eds.) Plant Reproduction (2002)

Since the early 1990s, Arabidopsis thaliana has been studied as the species of choice of 'flowering geneticists'. Several pathways that either repress or promote flowering have been identified on the ... [more ▼]

Since the early 1990s, Arabidopsis thaliana has been studied as the species of choice of 'flowering geneticists'. Several pathways that either repress or promote flowering have been identified on the basis of (1) the flowering response of different genotypes to environmental factors (vernalization and photoperiod), (2) epistasis analyses, and (3) expression patterns of cloned genes in various backgrounds. Models attempting to include all information have been proposed repeatedly and their complexity is increasing with the bulk of data. In this review, we shall attempt to integrate into this genetical framework the physiological knowledge accumulated on a variety of plants by generations of researchers before the amost overnight breakthrough of Arabidopsis. [less ▲]

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See detailThe flowering process: On the track of controlling factors in Sinapis alba
Bernier, Georges ULg; Corbesier, Laurent; Périlleux, Claire ULg

in Russian Journal of Plant Physiology (2002), 49(4, JUL-AUG), 445-450

The major physiological theories of the control of the flowering process are first presented and their inferences tested in the long-day plant Sinapis alba. Then, the genetic analyses of the control of ... [more ▼]

The major physiological theories of the control of the flowering process are first presented and their inferences tested in the long-day plant Sinapis alba. Then, the genetic analyses of the control of flowering time in Arabidopsis thaliana are also summarized with a brief overview of the several pathways, each including several genes, identified. Clearly, both the experimental data of physiological experiments and the multiplicity of interacting genetic pathways best support the theory of the multifactorial control of flowering. This is further shown by the fact that a critical gene expressed in the shoot meristem at floral transition in S. alba, MADS A (orthologous to A. thaliana SOC1), can be upregulated by a single dose of a cytokinin or a gibberellin, without leading to flowering. This indicates that the floral shift requires upregulation of other genes by other factors. [less ▲]

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