Understanding the cellular role of aureochromes, a new type of blue light photoreceptors, in diatoms

• Applicants: Professor Dr. Peter Kroth; Professor Dr. Christian Wilhelm
• Subject Area: Plant Physiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 444745657

Diatoms are unicellular photoautotrophic algae and extremely successful in planktonic and benthic aquatic communities. In addition, they represent peculiar evolutionary chimeric cells, as they evolved by the uptake of a eukaryotic alga into another eukaryotic cell. Accordingly, diatoms have a different genetic background than green algae and plants. Diatoms and related algae within the group of Stramenopiles possess blue light photoreceptors named aureochromes that are found only within this group. In contrast to other know photoreceptors, aureochromes are light-activated transcription factors possessing a LOV domain as well as a DNA-binding bZIP domain. Our recent work on the diatom Phaeodactylum tricornutum demonstrates (i) that this alga possesses four different aureochromes, (ii) that aureochromes are important for photoacclimation, and (iii) that knocking out a single aureochrome gene (PtAureo1a) results in a dramatic and massive reduction of transcriptomic regulation when the cells are transferred from red light to blue light. Therefore, we postulate that PtAUREO1a may be one “master switch” for blue light responses. Accordingly, in this project, we want to elucidate the functional cellular role of Aureochromes in diatoms using PtAureo knockout mutants. The first subproject will study the transcriptomic response of PtAUREO1c and 2 KO mutants after a red/blue light shift. In a broad approach, we will study the physiology of the available PtAureo knockout lines to understand the specific impact of the lack of the respective photoreceptors. Then we will investigate the role of different light conditions, and the role of limiting factors like N deprivation for competitiveness of WT and mutant lines. Finally, in a metabolomics approach, we want to investigate whether in the knockout mutants are impaired in their competitive strength. In the second subproject, we will try to unravel the functionality of PTAUREO1a by identifying aureochrome binding sites, investigating PtAureo/promotor binding via yeast 1-hybrid approaches, aureochrome dimer formation, as well as identification of co-binding factors. This project will be based on a very tight collaboration of two independent research groups that have pioneered the field of molecular and physiological characterization of diatoms, and it strives for a better understanding how diatoms sense light and how this information is converted into a cellular response.

• DFG Programme: Research Grants