How plants know whether it is day or night

London: Certain proteins inform the plant cells, bacteria and fungi whether it is day or night or cloudy or sunny and researchers have now determined the inner workings of one of these proteins.

The findings have implications both for improving crop yield and also in engineering artificial proteins that can be used to release drugs at specific spots in our body to treat cancer cells.

The investigated proteins are called "phytochromes". They consist of thousands of atoms and can be thought of as tiny, microscopic machines. 

These light-sensitive proteins are found in all plant leaves, and many bacteria and fungi. 

"Phytochrome proteins are the eyes of plants and are found in many bacteria. We have now discovered how bacterial phytochromes work at the molecular level," explained Sebastian Westenhoff from University of Gothenburg in Sweden.

Efficient photosynthesis requires that leaves are exposed to the sun. For this, the plants have to grow towards the sunlight and phytochrome proteins control this process. 

The proteins detect the light and signal to the plant cell how much light is available.

Similarly, bacteria use phytochromes to move to spots where they can survive better.

"Each time a phytochrome protein absorbs light, it deforms in a well-orchestrated series of structural changes. We already discovered an early structural change two years ago. Back then we used a shortened phytochrome,” Westenhoff said.

"In the meantime, we have advanced our experimental methods and could now study a full-length protein with a biological activator unit, called histidine kinase. This revealed the change in the final stage of the process," Westenhoff noted.

The discovery, published in the journal Science Advances, increases understanding of how phytochromes work. This enables modification of the proteins, for example, to increase crop yield. 

However, the new knowledge is also crucial for another technology, where scientists engineer light sensitive proteins to control organisms by light. Potentially such artificial proteins can be used to release drugs at specific spots in our body, for example, in cancer cells.

"Proteins are molecular nanomachines, which control most of what we see in Nature. Deciphering the structure of proteins is key to understanding how the machines work. This knowledge can also be used to modify or construct new proteins, with custom-built functions," Westenhoff said.