From day to night

Plant & zo

The science of plants and more

From day to night

Licht and dark, regulate a plants growth and development. Day and night, each bringing their own set of regulators. But the transition goes gradually from the day to the night shift. Just like how the dark is slowly consuming the light at the start of the night.

The important regulator of the night is COP1. To get the night shift to do its job, COP1 is kind of eating the proteins of the day shift. In the dark COP1 can do its thing. But not in the light, then COP1 stops, switched off by light. Giving the regulator of the day shift, HY5, a chance. Chinese researchers now showed that this is not the whole story.

The turning on of SICKLE by HY5 prevents wasting costly energy.

One of the genes turned on by HY5, the regulator of the day shift, is SICKLE. SICKLE is not a gene-on switch, but works together with them, and so influencing the genes turned on and off. The researchers noticed SICKLE binding to HY5, which caused HY5 to be less good at its job. Consequently, HY5 turns on less and less genes of the day shift as the day progresses.

SICKLE, so noticed the researchers, is not only binding to HY5 of the day shift, but also PIF4. PIF4 is actually part of the night shift, as light is switching most of PIF4 off. But when SICKLE binds to the little of PIF4 that is still around, then PIF4 is turning itself back on. So can PIF4 at the end of the afternoon already start its job of turning off the day shift genes.

The turning on of SICKLE by HY5 prevents the turning on of day shift genes at the end of the day. The plant prevents wasting costly energy. As it is not making proteins that it will (almost) directly after finishing break down again. SICKLE helps with a gradual transition from the day to night shift at the start of the night.


Li, T., Li, H., Lian, H., Song, P., Wang, Y., Duan, J., Song, Z., Cao, Y., Xu, D., Li, J., and Zhang, H. (2022) SICKLE Represses Photomorphogenic Development of Arabidopsis Seedlings via HY5- and PIF4-Mediated Signaling. J. Integr. Plant Biol.

Published by Femke de Jong

A plant scientist who wants to let people know more about the wonders of plant science. Follow me at @plantandzo

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