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Made available in DSpace on 2014-12-17T14:10:23Z (GMT). No. of bitstreams: 1 FrancinaldoLS_DISSERT.pdf: 2544554 bytes, checksum: b9889e7b0f272a12f69ccee6cb6a3d3b (MD5) Previous issue date: 2011-05-16 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Flowering is controlled by several environmental and endogenous factors, usually associated with a complex network of metabolic mechanisms. The gene characterization in Arabidopsis model has provided much information about the genetic and molecular mechanisms that control flowering process. Some of these genes had been found in rice and maize. However, in sugarcane this processe is not well known. It is known that early flowering may reduce its production up to 60% at northeast conditions. Considering the impact of early flowering in sugarcane production, the aim of this work was to make the gene characterization of two cDNAs previously identified in subtractive cDNA libraries: scPKCI and scSHAGGY. The in silico analysis showed that these two cDNAs presented both their sequence and functional catalytic domains conserved. The results of transgenic plants containing the overexpression of the gene cassette scPKCI in sense orientation showed that this construction had a negative influence on the plant development as it was observed a decrease in plant height and leaf size. For the scPKCI overexpression in antisense orientation it was observed change in the number of branches from T1 transgenic plants, whereas transgenic T2 plants showed slow development during germination and initial stages of development. The other cDNA analyzed had homology to SHAGGY protein. The overexpression construct in sense orientation did not shown any effect on development. The only difference observed it was an increase in stigma structure. These results allowed us to propose a model how these two genes may be interact and affect floweringdevelopment. / A flora??o ? controlada por diversos fatores como condi??es ambientais e fatores end?genos que se associam em uma rede de mecanismos bastante complexos. A caracteriza??o funcional de alguns genes realizada no modelo vegetal A. thaliana tem fornecido muitas informa??es a respeito dos mecanismos gen?ticos e bioqu?micos que controlam a flora??o. Existem muitos hom?logos descritos em diversas esp?cies, inclusive em plantas de interesse agron?mico, como: arroz e milho. Em cana-de-a??car pouco se sabe sobre esse processo, embora o estudo nessa cultura seja muito importante, uma vez que a flora??o precoce pode acarretar perdas substanciais no teor de sacarose que podem chegar a at? 40% da produ??o. Com isso, o objetivo deste trabalho foi caracterizar a fun??o de dois cDNAs, identificados anteriormente em bibliotecas subtrativas scPKCI e scSHAGGY, por meio de an?lises in silico e a superexpress?o g?nica nas orienta??es senso e antisenso utilizando plantas de Nicotiana tabacum. Os resultados obtidos com a an?lise in silico permitiram observar que os dois cDNAs encontram-se bem conservados, com dom?nios catal?ticos funcionais. Os resultados das plantas transg?nicas contendo o cassete de superexpress?o do gene scPKCI na orienta??o senso mostrou que esta constru??o influenciou negativamente no desenvolvimento normal de plantas de tabaco transg?nicas acarretando a diminui??o da altura m?dia das plantas e da ?rea foliar. Para superexpress?o de scPKCI em orienta??o antissenso, foi observado altera??es no n?mero de ramifica??es das plantas transg?nicas T1, enquanto que as plantas transg?nicas T2 apresentaram o in?cio do desenvolvimento atrasado. Para o outro cDNA analisado, os resultados obtidos mostraram que a superexpress?o do cDNA scSHAGGY na orienta??o senso n?o alterou o desenvolvimento das plantas, por?m a planta apresentou um aumento no tamanho da estrutura floral do gineceu em 100% das flores analisadas (dez flores em seis plantas). Os nossos resultados juntamente com resultados existentes na literatura com outras plantas permitem propor que os cDNAs scPKCI e scSHAGGY estariam envolvidos no processo de flora??o em cana-de-a??car.

How come the same species of plants can naturally occur under various conditions in different parts of the world? A plant's ability to adapt in response to a changing climate hinges on the presence of genetic variation in traits, such as flowering phenology. In this study, I examine whether flowering start varies genetically within populations and compare this variation to differences between populations. This study quantifies genetic variation in flowering time in two Italian populations of Arabidopsis thaliana whilst using two Swedish populations as a reference. This was done using a randomized block design where plants were grown in a controlled climate. To characterize and measure flowering phenology, time of bolting and flowering were recorded. The experiment included four populations, a total of 150 maternal lines, and 2980 plants. One-way ANOVAs conducted separately by population indicated significant among-line variation in the two Italian populations. Flowering time differed between the Italian and Swedish populations, but not between the two Italian populations. More data would be needed to draw conclusions about the among-line variation in the Swedish populations. The results indicate that the Italian populations have the potential to respond to selection on flowering time, which is a likely consequence of a changing climate.

Species' floral traits and flowering times are known to be the major drivers of pollinator-mediated plant–plant interactions in diverse co-flowering communities. However, their simultaneous role in mediating plant community assembly and plant–pollinator interactions is still poorly understood. Since not all species flower at the same time, inference of facilitative and competitive interactions based on floral trait distribution patterns should account for fine phenological structure (intensity of flowering overlap) within co-flowering communities. Such an approach may also help reveal the simultaneous action of competitive and facilitative interactions in structuring co-flowering communities. Here we used modularity within a co-flowering network context, as a novel approach to detect convergent and/or over-dispersed patterns in floral trait distribution and pollinator sharing. Specifically, we evaluate differences in floral trait and pollinator distribution patterns within (high temporal flowering overlap) and among co-flowering modules (low temporal flowering overlap). We further evaluate the consistency of observed floral trait and pollinator sharing distribution patterns across space (three geographical regions) and time (dry and rainy seasons). We found that floral trait similarity was significantly higher in plant species within co-flowering modules than in species among them. This suggests pollinator facilitation may lead to floral trait convergence, but only within co-flowering modules. However, our results also revealed seasonal and spatial shifts in the underlying interactions (facilitation or competition) driving co-flowering assembly, suggesting that the prevalent dominant interactions are not static. Synthesis. Overall, we provide strong evidence showing that the use of flowering time and floral trait distribution alone may be insufficient to fully uncover the role of pollinator-mediated interactions in community assembly. Integrating this information along with patterns of pollinator sharing will greatly help reveal the simultaneous action of facilitative and competitive pollinator-mediated interactions in co-flowering communities. The spatial and temporal variation in flowering and trait distribution patterns observed further emphasize the importance of adopting a more dynamic view of community assembly processes.

This study examined floral initiation in Rudbeckia hirta at the biochemical, cellular, and whole plant levels. Histological and histochemical examination of floral initiation revealed that the pattern of initiation followed closely that described in other species. The primary difference was in the length of time over which initiation and differentiation occurred. When subjected to limited inductive photoperiods, R. hirta responded with a delay in flowering if the plants were returned to short days (SD) before bract initiation. Increased exposure to long days (LD) increased stem height and enhanced floral development. A limited induction period of at least 8 LD allowed enough of the floral stimulus to be translocated to the meristem to cause no interruption in development even upon return to non-inductive conditions. An inhibition of development occurred only when plants were returned to SD before periclinal divisions in the pith rib meristem commenced after approximately 8 LD. Axillary bud development and final plant height were dependent on the number of inductive LD received. Polyamines have been linked to floral initiation and, in this study, were strongly correlated to the stage of floral initiation. As initiation progressed, the observed increases in putrescine and spermidine were followed by a decrease after 16 LD, the observed onset of floral development. This was contrary to that previously observed in SD plants but followed a pattern similar to that reported for cytokinin behavior. Exogenous cytokinins have been used to stimulate floral initiation in several species but Rudbeckia hirta did not respond to benzyladenine (BA) applied at the onset of LD. Floral initiation has been found to begin after six to eight LD and, in most species, BA was most effective when applied during initiation. In an attempt to increase uptake, BA was dissolved in dimethyl sulfoxide (DMSO). This did not enhance the effects of BA and, in fact, DMSO was found to be toxic at concentrations of 25% or more. / Ph. D.

Onset of flowering is a major transition in the plant life cycle and is controlled by environmental factors including photoperiod, light quality and temperature. Prevalence of controlling factors depends on species, hence physiological models were selected for their strong requirement for one or another environmental cue. Among Brassicaceae, Sinapis alba was intensively studied for its strong response to photoperiod while molecular-genetic analyses of Arabidopsis thaliana disclosed complex interactions between pathways inducing flowering in response to photoperiod and other environmental cues, such as vernalization. We were therefore interested in studying the vernalization process in S. alba and its interactions with the previously characterized floral response to long days (LDs). Two-week old seedlings grown in non-inductive short days (SDs) were vernalized at 7°C for increasing durations and a strong promotive effect of vernalization was observed. In contrast to the common view of vernalization as a preliminary step bringing the competence to flower, we observed that vernalization had a direct inductive effect on flowering: floral buds were initiated during cold-exposure. Floral integrator genes SaMADSA (homologous to SUPPRESSOR OF OVEREXPRESSION OF CO 1) and SaLEAFY were up-regulated in the shoot apex after 3-4 weeks of vernalization. To monitor the vernalization process at the molecular level, we isolated SaFLC which, based on sequence analysis, expression patterns and complementation test, appeared as orthologous to FLOWERING LOCUS C. Down-regulation of SaFLC by vernalization was fast since transcript level was already very low after one week of vernalization, but stability of the repression required longer exposure to cold. To test the physiological significance of these observations, we studied the floral response to 16-h LDs after unstable and stable repression of SaFLC. We observed that one week of vernalization which was sufficient for SaFLC repression but not for maintenance of the silenced state - increased the flowering response of S. alba to LDs when the LDs just followed the cold treatment. This effect was lost after two weeks post-vernalization. In contrast, the promotive effect of longer vernalization on flowering response to LDs was maintained post-vernalization. These results suggested that vernalization not only works when plants experience long exposure to cold in winter: short cold periods might stimulate flowering of LD-plants if occurring when photoperiod is increasing, i.e. in spring.

published_or_final_version / abstract / toc / Botany / Master / Master of Philosophy

Individuals of Eriogonum abertianum Torr. (Polygonaceae) flower in spring, or following onset of summer rains, or both. Within populations flowering time is mainly environmentally determined: there is little genetic variance for flowering time, and experimental moisture limitation significantly delays flowering. In the field a Sonoran Desert population experienced significantly more mortality during the foresummer droughts, and had a significantly greater proportion of spring-flowering plants, than a Chihuahuan Desert population. Greenhouse experiments suggest a genetic basis for differences in size and time of flowering between these populations. Fossil and biogeographic evidence support an adaptive interpretation of earlier flowering in the Sonoran Desert. A model of selection comparing spring-plus-summer flowering with spring-only flowering suggests that expected summer fecundity may not offset the risk of foresummer mortality in the Sonoran population. Rather than switching to a spring-only habit as predicted by the model, the species' range ends where summer rainfall declines abruptly. The invariance of the spring-plus-summer habit is not explained by the demographic, historical, or genetic data. Plants which live for more than a year in the wild have offspring which, in the greenhouse, live longer than the offspring of the general population. This suggests a genetic basis for the occasional observed perennation. Analysis of a quantitative genetic model suggests that when adult survivorship is low, selection will generally reduce perennation. The annual habit is thus likely to persist even in the presence of genetic variation for perennation. Optimal control models of plant carbon allocation are extended to include within-season mortality and allometric growth constraints. When parameters are varied in numerical experiments, resulting predictions for easily measurable characters (e.g., time to first flower) often vary only slightly; most differences are in fitness, suggesting that satisfactory empirical tests may be difficult to conduct. Arbitrary mortality functions can optimally lead to multiple flowering episodes, and this can depend sensitively on parameter values. Optimal trajectories with allometric constraints are divided into a period of vegetative growth and another period of mixed growth.

As plants are sessile organisms, processes controlling plant growth and development must react to fluctuations in the external environment to aid plant survival. However, as the climate of the Earth changes and becomes more extreme, plants become less able to develop to their optimal capacity and this can have an adverse effect on crop yield and biofuel feedstock production. Thus, it is becoming increasingly important to understand the molecular mechanisms used by plants to respond to external stimuli. One important system that plants utilise in their response to environmental fluctuations is the circadian clock. The circadian clock is a time-measuring device that buffers the timing of plant growth and development against fluctuations in the local environment, such as temperature, light quality and light intensity. Importantly, the circadian clock is also able to measure day-length (photoperiod). Thus, plant development and growth is co-ordinated with photoperiod that is closely linked to seasonal changes. A key example of this is the time taken for a plant to flower. Flowering of Arabidopsis thaliana occurs specifically in long-days (LDs) of spring/summer months. Thus, the circadian clock is a key regulator promoting flowering in LD conditions. In conjunction with experimental studies, mathematical modelling has proven to be a successful method of elucidating the mechanisms that underlie complex biological systems. One example of this 'systems biology' approach is in uncovering the components that make up the Arabidopsis circadian clock mechanism. Previous research in our group has also led to the development of a model describing photoperiodic flowering that is tentatively linked to the circadian clock mechanism. In this thesis I shall develop on these models to highlight five key results: 1. using rhythmic PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5 mRNA as an example, I shall show that multiple circadian regulators are required to describe rhythmic transcription of target genes across multiple photoperiods; 2. the stabilisation of CONSTANS (CO) protein by the blue light-signalling component FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is required to for flowering in LDs and has a relatively larger impact on photoperiodic flowering than FKF1-dependent degradation of CYCLING DOF FACTOR 1 (CDF1), an inhibitor of flowering; 3. multiple components of the circadian clock play specific post-translational roles in photoperiodic flowering to promote the acceleration of flowering specifically in LDs; 4. temperature regulation of photoperiodic flowering can be explained through an interaction between CO and PIF proteins, limiting the effects of temperature to a specific time-window in a 24-hour day; 5. red light- and temperature-control of the circadian clock can be explained by altering the post-translational regulation of circadian clock components.

In this study, theoretical and experimental approaches were combined, using Arabidopsis as the studied species. The multi-scale model incorporates the following, existing sub-models: a phenology model that can predict the flowering time of plants grown in the field, a gene circuit of the circadian clock network that regulates flowering through the photoperiod pathway, a process-based model describing carbon assimilation and resource partitioning, and a functional-structural module that determines shoot structure for light interception and root growth. First, the phenology model was examined on its ability to predict the flowering time of field plantings at different sites and seasons in light of the specific meteorological conditions that pertained. This analysis suggested that the synchrony of temperature and light cycles is important in promoting floral initiation. New features were incorporated into the phenology model that improved its predictive accuracy across seasons. Using both lab and field data, this study has revealed an important seasonal effect of night temperatures on flowering time. Further model adjustments to describe phytochrome (phy) mutants supported the findings and implicated phyB in the temporal gating of temperature-induced flowering. The improved phenology model was next linked to the clock gene circuit model. Simulation of clock mutants with different free-running periods highlighted the complex mechanism associated with daylength responses for the induction of flowering. Finally, the carbon assimilation and functional-structural growth modules were integrated to form the multi-component, whole-plant model. The integrated model was successfully validated with experimental data from a few genotypes grown in the laboratory. In conclusion, the model has the ability to predict the flowering time, leaf biomass and ecosystem exchange of plants grown under conditions of varying light intensity, temperature, CO2 level and photoperiod, though extensions of some model components to incorporate more biological details would be relevant. Nevertheless, this meso-scale model creates obvious application routes from molecular and cellular biology to crop improvement and biosphere management. It could provide a framework for whole-organism modelling to help address global issues such as food security and the energy crisis.