Life on Earth operates in 24-hour cycles. From tiny bacteria to human beings, organisms adapt to the alterations of day and night. External factors, such as changes in light and temperature, are needed to drive the clock. Many metabolic processes are controlled by the endogenous clock. Scientists at the University of Jena have now studied the molecular rhythms of the endogenous clock in the “green line”. In a current issue in the journal Plant physiologythe team led by Prof. Maria Mittag from the Matthias Schleiden Institute gives insight into their genetic basis.
The “green lineage” includes green algae, mosses, ferns, gymnosperms, and flowering plants. These organisms produce a significant portion of the oxygen on Earth and are therefore essential to all other living creatures. Photosynthesis by these green organisms — the conversion of CO2 and water to glucose and oxygen – depends on light, so proper timing of these processes is crucial. Plants prepare for the daylight period even before sunrise and can thus use the light phase more efficiently to achieve optimal yields of photosynthesis and other metabolic pathways. As a result, they grow better and outlast competitors.
“The fitness of photosynthetic organisms depends on the integrity of their endogenous clocks,” explains Maria Mittag. The professor of general botany and her team therefore studied how the endogenous clock developed during the evolution of organisms of the green lineage. For this, the researchers studied the clock genes of different model organisms of the green lineage, starting with single-celled organisms like the green alga Chlamydomonas reinhardtiithrough the liver Polymorph Marchantiato higher plants, such as the Arabid, Arabidopsis thaliana.
Cryptochromes are “conserved” during evolution
The researchers found that some genes involved in circadian rhythms occur in all studied green lineage organisms, while other clock genes differ significantly. Among the endogenous clock genes that have been “conserved” throughout evolution are the cryptochromes. These are receptor molecules with which terrestrial plants detect blue light. “Cryptochromes are important for entrainment and regulation of the circadian clock; they play this role not only in land plants and algae, but also in fungi, insects and mammals,” says Dr Jan Petersen. , member of the research team and first author of the current summary document.
So far, Maria Mittag’s team has studied cryptochromes in the model organism Chlamydomonas reinhardtii. Its genome even encodes four different cryptochromes. While two of these cryptochromes are involved in the circadian clock, the function of the other two was still unknown. To analyze in detail the role of one of these cryptochromes of unknown function, the Jena research team compared wild-type algal cells with mutants in which the gene for this receptor molecule had been deactivated. “We were able to determine that mutant algae grow much slower than wild-type algae cells,” says PhD student Anxhela Rredhi.
Newly studied cryptochrome influences cellular structures responsible for photosynthesis
“However, we were surprised that the mutant algae were greener than the wild-type algae,” says Anxhela Rredhi. More color in the form of green pigments should actually lead to better photosynthesis and therefore increased growth, as these molecules capture light for photosynthesis. Finally, the researchers found an explanation. Using electron microscopy, they were able to see that the cell membranes in which photosynthesis takes place are denser without the cryptochrome than in wild-type cells. “On the one hand, it gives the algae a darker green appearance,” says Dr. Petersen. “On the other hand, cells shade more, so there’s simply less light reaching the inner membranes, which has a negative effect on algae growth.”
It is currently unknown how exactly the recently studied cryptochrome influences these cellular structures. The research team will now investigate whether it also plays a role in the circadian clock.