The ICE transcription factors integrate environmental signals into developmental pathways in Arabidopsis

Abstract

Plants are sessile organisms that must respond to changes in their environments. They should be able to tolerate environmental constraints to survive and propagate. To cope with inadequate environmental conditions, plants have evolved adaptive mechanisms through the gene regulatory network. Many transcriptional regulators including transcription factors directly or indirectly control their downstream gene expressions in response to environmental changes. INDUCER OF CBF EXPRESSION (ICE) transcription factors have a crucial role in transcriptional regulation of their target gene expressions in response to environmental stimuli. However, it is largely unknown how environmental signals are integrated into plant developmental pathways in Arabidopsis. In this study, I investigated function of ICE transcription factors as a molecular knob that integrate environmental signals into plant development. The regulatory mechanisms of the transcription factors, which are critical for temperature and light reponses, were identified. In Chapter 1, I examined how the temperature and photoperiod signals are coordinated to modulate timing of flowering during changing seasons. In this study, I demonstrated an elaborate signaling network for fine-tuning of seasonal flowering in plants. I found that the transient-cold effect on flowering is mediated primarily by ICE1. ICE1 directly activates FLOWERING LOCUS C (FLC) under short-term cold conditions. By contrast, under floral promotive conditions, SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), which is largely known as a floral inducer, inhibited the DNA binding of ICE1 to the FLC and C-REPEAT BINDING FACTOR 3 gene promoters, inducing flowering with a reduction of freezing tolerance. These observations indicate that optimal flowering of plants during changing seasons is fine-tuned by an ICE1-FLC-SOC1 signaling network. In Chapter 2, I investigated how light induces stomatal development. In this study, I found that CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) degrades and ubiquitinates ICE proteins under dark conditions. Moreover, light inhibited COP1-mediated degradation of ICE proteins in the abaxial epidermal cells, thus inducing stomatal development. These observations indicate that photostabilization of ICE proteins, via light-mediated inhibition of COP1-mediated protein surveillance systems, is important for stomatal development.