Cytosolic translation control of LHCII mRNAs in Chlamydomonas
Lutz Wobbe1, Olga Blifernez1, Jan Mussgnug1, Christian Schwarz1, Jörg Nickelsen2, and Olaf Kruse1
1) University of Bielefeld, Dep. of Biology, Algae BioTech Group, Universitätsstr. 25, D-33615 Bielefeld, Germany
2) LMU München, Dept. Biologie I - Molekulare Pflanzenwissenschaften, Großhaderner Str. 2-4, D-82152 Planegg-Martinsried, Germany
The amount of light-harvesting proteins associated with photosystem II (LHCBMs) has to be tightly regulated in order to guarantee optimal photosynthetic performance under highly variable light conditions. Gene expression regulation of nucleus-encoded LHCBM proteins in Chlamydomonas involves translation control as an important part mechanism. A key factor mediating this translational control of LHCBM mRNAs in C. reinhardtii is the translation repressor protein NAB1, which has been identified by the characterization of the light-acclimation mutant Stm3. NAB1 is able to bind LHCBM encoding mRNAs in vivo, thereby repressing translation of bound messages by sequestration into translationally silent mRNP complexes. We could further demonstrate, that the repressor activity of NAB1 is partly determined by the redox-state of two cysteine residues in its C-terminal RNA-binding domain and hence the cytosolic redox poise. Recent results indicate that a second type of post-translational modification, namely arginine methylation, is required for a functional repressor protein. Arginine methylation is a poorly characterized post-translational modification in plant systems. Our detailed analysis regarding the functional implications of arginine methylation on NAB1 function, therefore provides important new insights into the role of arginine methylation in photosynthetic cells.
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