Diana Kirilovsky, CNRS research director at the Institute of Integrative Biology of the Cell (I2BC, Gif-sur-Yvette), is the leader of the team "Regulatory mechanisms in photosynthetic organisms", which has just entered the SPS LabEx. 

1) What career path led you to I2BC?

I obtained my PhD in biochemistry at the Hebrew University of Jerusalem (Israel) in 1986. After post-doctoral training at different CNRS laboratories, I obtained a CNRS Senior Research Scientist position (CR1). I successively worked at the CNRS Center of Gif sur Yvette (1991-1994) and at the Ecole Normale Supérieure (1999-2000). Since 2000, I’ve been working at the CEA of Saclay. I obtained a DR2 position in 1999 and a DR1 position in 2012. I am now the director of the research group “Regulatory mechanisms in photosynthetic organisms” in the B3S department of the I2BC Institute (UMR 9198, CNRS-CEA-UPSud) since this institute was created in January 2015. The research group is composed of 4 researchers: Anja Krieger (DR2, CNRS), Pierre Setif (CEA researcher), Adjélé Wilson (CEA researcher) and me (DR1, CNRS) and 1 technician: Sandrine Cot (CEA).

Since my PhD, I have been interested in the mechanisms that cyanobacteria have developed to protect themselves from light stress and to adapt to strong and fluctuating radiance. Light, in addition to be essential for photosynthesis, is an important regulator of the photosynthetic apparatus. However too much light can be lethal and photoprotection against excess absorbed light energy is an essential and universal attribute of oxygenic photosynthetic organisms. Anja Krieger is also interested in light and oxidative stress but she studies all these mechanisms principally in plants.  

2) You have recently published an article* in the Science journal. Can you tell us more about the subject of this article and how it fits into your research topic?

In 2006, we have discovered that cyanobacteria, like algae and plants, protect themselves from photo-oxidative damage by decreasing the excess absorbed energy arriving at the photosynthetic reaction centers through an increased thermal dissipation at the level of the phycobilisomes, the cyanobacterial antenna. We have also demonstrated that the photoactivation of a soluble protein attaching a ketocarotenoid molecule, the Orange Carotenoid Protein (OCP), is essential for the triggering of this photoprotective mechanism. The OCP is formed by an a helix N-terminal domain and a a helix/b sheet C-terminal domain. Absorption of strong blue light by the carotenoid induces conformational changes in the carotenoid and in the protein that are essential for its function. The dark orange OCP is inactive and has a closed conformation. Upon illumination, the interactions between the two domains are broken and the protein becomes red and adopts an open conformation. The photoactivated red OCP, by interacting with the core of the phycobilisome, increases thermal dissipation of the excess energy absorbed. In the Science article, in collaboration with an American laboratory, we resolved the structure of the N-terminal domain of the protein and confirmed it is a permanently active energy and fluorescence quencher while the C-terminal domain is the regulator of the activity. The carotenoid spans both domains in OCPo. In the Science paper, we also show that upon photoactivation and separation of the domains from each other, the carotenoid is translocated 12 Å and in OCPred the carotenoid is found completely buried within the N-Terminal Domain with the carotenoid rings solvent exposed. This is the first time it was shown that such huge translocation of the chromophore could occur upon photoactivation.

3) Why did you choose to join the SPS LabEx?

Our group is working on fundamental aspects of photosynthesis and on regulation mechanisms in photosynthetic organisms. It is well integrated in the community of photosynthesis and photobiology but our visibility in the plant science community needs to be improved. We are interested in discussions and exchanges with plant biologists to improve our knowledge in plant science. We offer access to our biophysical techniques ranging from transient absorption spectroscopy, chlorophyll and NADPH fluorescence to electron paramagnetic resonance spectroscopy to SPS members who are interested in characterizing photosynthetic parameters of their plants/mutants. We are especially interested in axis 3 of the SPS:  Plants to understand fundamental biological mechanisms and challenge 2: Understanding basic genetic, molecular and cellular mechanisms that control plant development and physiology.

*Leverenz R.L., Sutter M., Wilson A., Gupta S., Thurotte A., de Carbon C.B., Petzold C.J., Ralston C., Perreau F., Kirilovsky D., Kerfeld C.A. (2015). A 12 angstrom carotenoid translocation in a photoswitch associated with cyanobacterial photoprotection. Science 348(6242),1463-1466.