Figure 2. Signaling pathways involved in the crosstalk between
light and cold acclimation.
Upon cold temperatures, the circadian clock-regulated CBF genes
are induced resulting in cold acclimation. Upon light perception, HY5 is
activated which induces the expression of anthocyanin biosynthesis and
cold-responsive genes through the Z-box/LTRE thereby reducing reactive
oxygen species (ROS) and results in cold acclimation. Changes in light
quality (R:FR) are sensed by phyB which exists in an active PfrB and an
inactive PrB form. Under high R:FR ratios (> 1), PfrB
represses CBF gene expression, while low R:FR ratios (<
1) caused by e.g. increased twilight during autumn causes cold
acclimation by decreasing the amount of active PfrB. PIF7 which
represses CBF gene expression is under control of TOC1, a central
component of the circadian clock, and under the control of phyB. Under
SD photoperiod, CBF genes are strongly induced causing cold
acclimation. Under warmer LD, PIF4 and PIF7 which are
under the control of phyB are higher expressed resulting in an
inhibition of CBF gene expression. As days shorten, e.g. during
autumn, this repression falls away resulting in cold acclimation. CBF
proteins interact with phyB and PIF3 causing degradation of PIF1, 4 and
5 which releases COR genes from PIF repression. For more
information concerning the different pathways, please refer to section
3.1. Abbreviations: R, red light; FR, far-red light, SD, short day; LD,
long day; ROS, reactive oxygen species; LTRE, low temperature responsive
element.