Balancing forces in the photoperiodic control of flowering

IFEVA, Facultad de Agronomía, Universidad de Buenos Aires and Consejo Nacional de Investigaciones Científicas y Técnicas, Av. San Martín 4453, 1417, Buenos Aires, Argentina.
Photochemical and Photobiological Sciences (Impact Factor: 2.27). 12/2010; 10(4):451-60. DOI: 10.1039/c0pp00252f
Source: PubMed


In many plant species, the duration of the daily exposure to light (photoperiod) provides a seasonal cue that helps to adjust flowering time to the most favourable time of the year. In Arabidopsis thaliana, the core mechanism of acceleration of flowering by long days involves the stabilisation of the CONSTANS (CO) protein by light reaching the leaves, the direct induction of the expression of FLOWERING LOCUS T (FT) by CO and the migration of FT to the apex to promote flowering. In rice (Oryza sativa), the promotion of flowering by short days depends on the interplay between light conditions, and the genes Grain number, plant height and heading date locus 7 (Ghd7) and Early heading date 1 (Ehd1). In both cases, other day length-induced changes reinforce the core photoperiodic pathway of promotion of flowering. However, there are regulators of flowering time, quantitatively less important than the core pathways but still significant, which impact in the opposite direction, i.e. favouring rice flowering under long days or Arabidopsis flowering under short days. We show, for instance, that short days enhance leaf expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 (SPL3), which stimulates Arabidopsis flowering under these conditions. We propose that fine tuning of flowering time depends on the balance of a hierarchy of multiple points of action of photoperiod on the network controlling flowering.

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Available from: Marcelo J Yanovsky
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    • "As sessile organisms, plants have to adapt their growth and development to large fluctuations in environmental conditions . Thus, plants have developed an entire machinery to monitor and integrate light and temperature information to fine-tune flowering onset, as well as several other developmental programmes (Lee et al., 2008; Cerdan, 2011; Sanchez et al., 2011). The length of the day, or photoperiod, is a reliable source of environmental information that can be used to anticipate the arrival of the flowering season. "
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    ABSTRACT: Two aspects of light are very important for plant development: the length of the light phase or photoperiod and the quality of incoming light. Photoperiod detection allows plants to anticipate the arrival of the next season, whereas light quality, mainly the red to far-red ratio (R:FR), is an early signal of competition by neighbouring plants. phyB represses flowering by antagonising CO at the transcriptional and post-translational levels. A low R:FR decreases active phyB and consequently increases active CO, which in turn activates the expression of FT, the plant florigen. Other phytochromes like phyD and phyE seem to have redundant roles with phyB. PFT1, the MED25 subunit of the plant Mediator complex, has been proposed to act in the light-quality pathway that regulates flowering time downstream of phyB. However, whether PFT1 signals through CO and its specific mechanism are unclear. Here we show that CO-dependent and -independent mechanisms operate downstream of phyB, phyD and phyE to promote flowering, and that PFT1 is equally able to promote flowering by modulating both CO-dependent and -independent pathways. Our data are consistent with the role of PFT1 as an activator of CO transcription, and also of FT transcription, in a CO-independent manner. Our transcriptome analysis is also consistent with CO and FT genes being the most important flowering targets of PFT1. Furthermore, comparison of the pft1 transcriptome with transcriptomes after fungal and herbivore attack strongly suggests that PFT1 acts as a hub, integrating a variety of interdependent environmental stimuli, including light quality and jasmonic acid-dependent defences.
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    • "For instance, the phyA phyB phyE co mutant flowers earlier than the phyA phyB co (Halliday et al., 2003). Simulated shade (low irradiance , low R:FR) shows a stronger acceleration of flowering under short than under long days (Sánchez et al., 2011) and the phyB (Reed et al., 1993; Halliday et al., 1994) or phyB phyD phyE (Wollenberg et al., 2008) mutants flower early under short days. Early flowering of the phyB mutant or in response to EODFR requires PHYTOCHROME AND FLOWERING TIME 1 (PFT1), which is not required for the photoperiodic response (Cerdán and Chory, 2003). "
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