Circadian and Light Regulated Expression of CBFs and their Upstream Signalling Genes in Barley

Abstract

CBF (C-repeat binding factor) transcription factors show high expression levels in response to cold; moreover, they play a key regulatory role in cold acclimation processes. Recently, however, more and more information has led to the conclusion that, apart from cold, light—including its spectra—also has a crucial role in regulating CBF expression. Earlier, studies established that the expression patterns of some of these regulatory genes follow circadian rhythms. To understand more of this complex acclimation process, we studied the expression patterns of the signal transducing pathways, including signal perception, the circadian clock and phospholipid signalling pathways, upstream of the CBF gene regulatory hub. To exclude the confounding effect of cold, experiments were carried out at 22 °C. Our results show that the expression of genes implicated in the phospholipid signalling pathway follow a circadian rhythm. We demonstrated that, from among the tested CBF genes expressed in Hordeum vulgare (Hv) under our conditions, only the members of the HvCBF4-phylogenetic subgroup showed a circadian pattern. We found that the HvCBF4-subgroup genes were expressed late in the afternoon or early in the night. We also determined the expression changes under supplemental far-red illumination and established that the transcript accumulation had appeared four hours earlier and more intensely in several cases. Based on our results, we propose a model to illustrate the effect of the circadian clock and the quality of the light on the elements of signalling pathways upstream of the HvCBFs, thus integrating the complex regulation of the early cellular responses, which finally lead to an elevated abiotic stress tolerance.

Temperature and Light-Quality-Dependent Regulation of Freezing Tolerance in Barley

“…Although the effects of complementary far-red light with high light intensity are beneficial in many cases, if the plants were previously acclimated to a lower incident light intensity in growth chambers, the sudden increase in light intensity can bring harmful side effects like photoinhibition or loss of photosynthetic and anthocyanin pigments [60,61] during cold acclimation. It has also been shown that the lower R:FR ratio can increase the level of freezing tolerance via influencing the phytochrome signalling system [23,24,48]. Our results also proved that the elevated FR light in the spectra can greatly improve the frost tolerance, which can be further improved by increasing the light intensity in barley.…”

“…We must also consider that, in a natural environment, a decreased R:FR ratio occurs at sunset and, during this twilight period, the light intensity is gradually decreasing. Consequently, it seems to be evident that not only the spectrum but also the changing light intensity can be an important, external signal affecting gene regulation [21,24,47,48]. In tomatoes, monochromatic red and far-red light was tested for inducing cold tolerance.…”

“…It is also well established that, in addition to low temperature, light also acts as an external signal and affects the expression level of the CBF genes [5]. It has been described that the photoperiod and the light quality are important regulators in the cold acclimation processes through the modulation of the CBF regulon [21][22][23][24]. By using artificial light conditions, it was observed that the effect of temperature and light treatments on CBF gene expression is additive [23].…”

Changes in ambient temperature are the prevailing cue in determining Brachypodium distachyon diurnal gene regulation

“…We also observed enrichment of the CBF binding site among evening-phased genes in all conditions except LDHH. The CBF family of transcription factors is strongly associated with the circadian clock, providing temperature input by directly binding the LUX promoter (Suzuki et al, 2005;Lee & Thomashow, 2012;Chow et al, 2014;Gierczik et al, 2017). Neither the G-box nor the CRT element was overrepresented under photocycles alone.…”

Decreased R:FR Ratio in Incident White Light Affects the Composition of Barley Leaf Lipidome and Freezing Tolerance in a Temperature-Dependent Manner

“…Overwintering plants have high plasticity to adapt to cooling [ 2 ] at multiple points during their life cycle from seed germination to transition from vegetative to reproductive phase and flowering. The cold acclimation process is also controlled by the circadian clock, day length, and illumination depending on both light intensity and spectral composition [ 3 , 4 , 5 , 6 ].…”