Cold clock
Proteins are less quick in the cold. This is also the case for the proteins of the circadian clock. You would think the clock would get out of sync, but, as Japanese researchers show in Science Advances, the plant has found a way to deal with this.
The circadian clock consist out of tens if not hundreds of proteins, each forming a cog in the clockwork of the circadian clock. But in the cold these proteins are working less efficient. To prevent from getting out of sync the plant compensates for this with help of multiple proteins. The researchers found one of these compensating proteins.
But it all started with the analysis of clock mutants that are out of sync by higher or lower temperatures. In this way the researchers discovered that plants which are missing both the PPR5 and the TOC1 protein have a much shorter day at 25°C than at 12°C. Both proteins are turning clock genes off. In their absence some clock genes are longer active.
Less PPR5 and TOC1 at lower temperatures prevents the circadian clock from getting out of sync
To figure out why PRR5/TOC1 missing plants are so out of sync the researchers studied the effect of temperature on PPR5 and TOC1 proteins. Hereby they found that at a higher temperature PRR5 and TOC1 proteins are more active. This appear to be because at 28°C there was about 2 to 4 times more PPR5 and TOC1 than at 12°C. Blocking the cell protein degradation system subsequently showed that this was because when it is cold PRR5 and TOC1 are quicker degraded.
Now is the breakdown of proteins strictly regulated. The question was therefore, which protein regulates the breakdown of PPR5 and TOC1? This the researchers set to find out. From a binding study they discovered that lost of proteins bind to PPR5 or TOC1 but only two proteins bind to them both at 12°C. One of them stood out: KLP2, a protein from which it is known that it can mark other proteins for degradation.
LKP2 appeared to bind especially at low temperatures to PPR5 and TOC1, even though, it was just as abundant, if not more so at higher temperatures. But how LKP2 differentiates between high and low temperatures, and following than knows when to be active, that the researchers could not discover.
Literature
Akari E. Maeda et al., Cold-induced degradation of core clock proteins implements temperature compensation in the Arabidopsis circadian clock. Sci. Adv. 10,eadq0187 (2024), DOI:10.1126/sciadv.adq0187
Plant en Zo 