Fernández, Virginia Laura (2018). Genetic and molecular mechanisms controlling flowering time of Arabidopsis thaliana in response to diverse environmental cues. PhD thesis, Universität zu Köln.
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Abstract
As sessile organisms, plants have acquired the capacity to perceive and integrate a wide range of seasonal and environmental cues, and to respond to these signals by modulating their developmental programs. Seasonal signals detected by plants include changes in day-length (photoperiod) and ambient temperature. Plants also respond to changes in light quality, such as variations in red:far red (R:FR) light ratio characteristic of crowded canopies. Plants detect changes in photoperiod to induce seasonal patterns of flowering. The photoperiodic pathway accelerates flowering of Arabidopsis thaliana (A. thaliana) under long days (LDs), whereas it is inactive under short days (SDs) resulting in delayed flowering. This delay is overcome by exposure of plants to high temperature (27 °C) under SD (27°C-SD). Previously, high temperature flowering response was proposed to involve either the impaired activity of MADS-box transcription factor floral repressors or PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) transcription factor mediated activation of FLOWERING LOCUS T (FT), which encodes the output signal of the photoperiodic pathway. Here, these observations were integrated by studying several PIFs, the MADS-box transcription factor SHORT VEGETATIVE PHASE (SVP) and the photoperiodic pathway under 27°C-SD. The results presented show that the mRNAs of FT and its paralogue TWIN SISTER OF FT (TSF) are increased at dusk under 27°C-SD compared to 21°C-SD, and that this requires PIF4 and PIF5 as well as CONSTANS (CO), a transcription factor that promotes flowering under LDs. The CO and PIF4 proteins are present at dusk under 27°C-SD and they physically interact. Although Col-0 plants flower at similar times under 27°C-SD and 21°C-LD the expression level of FT is approximately 10-fold higher under 21°C-LD, suggesting that responsiveness to FT is also increased under 27°C-SD, perhaps due to reduced activity of SVP in the meristem. Accordingly, only svp ft tsf triple plant plants flowered at the same time under 21°C-SD and 27°C-SD. Taken together, these results suggest that under non-inductive SDs, elevated temperatures increase the activity and sensitize the response to the photoperiod pathway. In addition to their role in warm ambient temperature, PIF transcription factors are important components of light signalling pathways. In particular, PIFs participate in the developmental changes associated with the shade avoidance syndrome (SAS). Under R light conditions, the active form of Phytochrome (Phy) photoreceptors interact with PIFs targeting them for degradation. Under shade conditions, the R:FR ratio is reduced and Phys phototransform to the inactive form. This Phy form no longer interacts with PIFs allowing their accumulation and the direct activation of target genes involved in developmental processes. Plants lacking functional PhyB show a phenotype that resembles the SAS. One characteristic of the SAS is the induction of flowering. Here, the early-flowering phenotype of phyB mutants is shown to be suppressed by mutations in PIF4 and PIF5. Furthermore, phyB mutants require functional CO and FT TSF to promote flowering. Experiments performed under simulated shade, however, demonstrated that PIF4 and PIF5 as well as PIF1, PIF3 and PIF7 do not play a role in the promotion of flowering by shade. In addition, these experiments reveal that photoperiod pathway components, such as GI, CO, FT and TSF are required for the induction of flowering under shade. The study of diverse signals regulating flowering demonstrated a role of photoperiod pathway components not only in the modulation of flowering in response to seasonal changes in day length, but also in the adjustment of the timing of flowering mediated by temperature and light quality signals. Thus, this thesis places CO as a pivotal component in the crosstalk between distinct seasonal and environmental signals orchestrating the regulation of flowering.
Item Type: | Thesis (PhD thesis) | ||||||||
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URN: | urn:nbn:de:hbz:38-79743 | ||||||||
Date: | January 2018 | ||||||||
Language: | English | ||||||||
Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
Divisions: | Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research | ||||||||
Subjects: | Natural sciences and mathematics Life sciences |
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Date of oral exam: | 17 January 2017 | ||||||||
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Refereed: | Yes | ||||||||
URI: | http://kups.ub.uni-koeln.de/id/eprint/7974 |
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