Cryptochrome photoreceptors in the green alga Chlamydomonas reinhardtii: Versatility of functions and mechanisms

• Applicant: Professorin Dr. Maria Mittag
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 412896838

• Final Report Year: 2023

Final Report Abstract

Cryptochromes are light receptors that are derived from photolyases. Photosynthetic protists, named microalgae, encode a variety of cryptochromes possessing different functions and properties. The green flagellate alga Chlamydomonas reinhardtii, a model for light-driven processes, encodes for four different cryptochromes: (i) a plant CRY (pCRY), an animal-like CRY (aCRY) and two DASH (Drosophila, Arabidopsis, Synechocystis and Homo)-type CRYs (CRY-DASH1 and CRY-DASH2). In the diatom Phaeodactylum tricornutum, there is also a plant-like CRY, called CryP. The C. reinhardtii CRYs were in the focus of this project. aCRY and pCRY play an important role in the algal sexual cycle and in their biological circadian clocks. The proteasome-triggered degradation of aCRY in gametes was studied. aCRY is not only a typical UV-A-blue light receptor but can also absorb in the yellow and red regions. In this process, a long-living tyrosyl radical and its micro-environment is relevant. Additionally, the importance of the long C-terminal extension of pCRY was investigated. A special focus was on CRY-DASH1, whose biological function was largely unknown at the beginning of this project. CRY-DASH1 is localized in the plastid and its abundance is highest at midday. CRY-DASH1 absorbs mainly in the UV-A region. The loss of CRY-DASH1 results in reduced photoautotrophic growth of the mutant compared to wild type (WT). Interestingly, the knockout culture of CRY-DASH1 looks greener in color than WT. This is due to an increased content of photosynthetic pigments (chlorophylls and carotenoids) in the mutant compared to WT. This increase goes hand in hand with hyperstacking of thylakoid membranes in the mutant as well as enhanced expression of two key photosystem II proteins, D1 and CP43. CRY- DASH1 has four “RGG” RNA-binding motifs at its C-terminus and can bind to psbA RNA encoding D1. As the psbA RNA level is not different in WT and mutant in contrast to the D1 protein level, it can be assumed that there is translational control. In a second part of the project, a comparative label free proteome analysis of chloroplast proteins was performed. It revealed that several enzymes of chlorophyll biosynthesis are upregulated in the cry-dash1 mutant, while enzymes involved in central carbon metabolism are downregulated. This is also the case for enzymes involved in Histidine biosynthesis resulting in reduced histidine levels in the mutant. Summa summarum, CRY-DASH1 plays an important role in plastidial metabolism and balances the photosynthetic machinery.

Publications

• Time-Resolved Infrared and Visible Spectroscopy on Cryptochrome aCRY: Basis for Red Light Reception. Biophysical Journal, 117(3), 490-499.
  Oldemeyer, Sabine; Mittag, Maria & Kottke, Tilman
  
• C-Terminal Extension of a Plant Cryptochrome Dissociates from the β-Sheet of the Flavin-Binding Domain. The Journal of Physical Chemistry Letters, 12(23), 5558-5563.
  Goett-Zink, Lukas; Toschke, Anna Lena; Petersen, Jan; Mittag, Maria & Kottke, Tilman
  
• DASH cryptochrome 1, a UV‐A receptor, balances the photosynthetic machinery of Chlamydomonas reinhardtii. New Phytologist, 232(2), 610-624.
  Rredhi, Anxhela; Petersen, Jan; Schubert, Melvin; Li, Wei; Oldemeyer, Sabine; Li, Wenshuang; Westermann, Martin; Wagner, Volker; Kottke, Tilman & Mittag, Maria
  
• The World of Algae Reveals a Broad Variety of Cryptochrome Properties and Functions. Frontiers in Plant Science, 12.
  Petersen, Jan; Rredhi, Anxhela; Szyttenholm, Julie; Oldemeyer, Sabine; Kottke, Tilman & Mittag, Maria
  
• Evolution of circadian clocks along the green lineage. Plant Physiology, 190(2), 924-937.
  Petersen, Jan; Rredhi, Anxhela; Szyttenholm, Julie & Mittag, Maria
  
• The C-terminus of a diatom plant-like cryptochrome influences the FAD redox state and binding of interaction partners. Journal of Experimental Botany, 73(7), 1934-1948.
  Krischer, Julia; König, Sarah; Weisheit, Wolfram; Mittag, Maria & Büchel, Claudia
  
• The UV-A Receptor CRY-DASH1 Up-and Downregulates Proteins Involved in Different Plastidial Pathways. Journal of Molecular Biology, 436(5), 168271.
  Rredhi, Anxhela; Petersen, Jan; Wagner, Volker; Vuong, Trang; Li, Wenshuang; Li, Wei; Schrader, Laura & Mittag, Maria