Investigation into temperature effects on the plant light signalling pathways
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Date
29/06/2013Author
Johansson, Åke Henrik
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Abstract
The ability to withstand environmental temperature variation is essential for plant
survival. Formative studies in Arabidopsis have revealed that light signalling
pathways has a potentially unique role in shielding plant growth and development
from seasonal and daily fluctuations in temperature. In this thesis we further
investigate the integration of the light signalling networks and temperature signalling
on the molecular level in Arabidopsis. First, we identified the transcript of the bHLH
transcription factor LONG HYPOCOTYL IN FAR-RED 1 (HFR1) to be highly
dependent on the ambient temperature and under strong control of the red light
photoreceptor PHYTOCHROME B (phyB). We found that the long hypocotyl
phenotype of the hfr1 mutant was exaggerated in warm conditions, specifically in
blue light, downstream of cryptochrome 1. We further show that HFR1 acts in the
warm by suppressing the function of PHYTOCHROME INTERACTING FACTOR
4 and 5 (PIF4, PIF5). PIF4 appears to act as a master regulator of several temperature
responses and is directly regulated by the phytochromes. Thus, we define a
molecular network where red light and blue light signals together with temperature
merge on the regulation of PIF4.
In the second part of this thesis, we investigate the relationship between temperature
and the fluence rate of light on the inhibition of hypocotyl elongation in Arabidopsis.
We find that the response to increasing fluence rates of light is highly dependent on
the ambient temperature and that PIF4 and PIF5 acting downstream of the major red
light photoreceptor, phyB, are essential for this response. In addition, we provide
evidence that in cool conditions, PIF activity is under strong suppression by the
gibberellin and HY5 pathways specifically at high fluence rates of red light.
The collected work of this thesis highlights the importance of the PIF proteins as
integrators of temperature and light signals and furthermore, demonstrates that the
response to temperature is highly dependent on both the quality and quantity of light.