Hosted by: Dominique Bergmann
Manuela Leonardelli1, Simon Stael2, Przemyslaw Kmiecik1, Valentin Roustan1, Michele Grieco1, Andreas Richter3, Norbert Mehlmer4, Ute Vothknecht4, Michael Melzer5, Bernhard Grimm3, Wolfram Weckwerth1, and Markus Teige1
(1) University of Vienna, Ecogenomics and System Biology (MOSYS), Althanstrasse 14, 1090 Wien.
(2) VIB Gent, Dept. of Plant Systems Biology, Gent University Technologiepark 927, 9052 Gent, Belgium.
(3) Humboldt University Berlin, Institute of Biology, Philippstrasse 13, 10115 Berlin, Germany.
(4) LMU Munich, Dept of Biology 1, Großhaderner Str. 2-4, 82152 München, Germany
(5) IPK Gatersleben, Structural Cell Biology, Corrensstrasse 3, 06466 Gatersleben, Germany.
Calcium is an important secondary messenger in plant signalling and chloroplasts are able to store large amounts of calcium. However, not much is known about the role of calcium in these organelles except for its role as stabilizer of the oxygen-evolving complex at photosystem II (PSII). Chloroplast total and free calcium concentrations can vary considerably, calling for an involvement of calcium binding proteins in the regulation of such a dynamics [1]. As high calcium concentrations inhibit CO2 fixation, it seems plausible that (stromal) calcium binding proteins play a key role in regulating calcium homeostasis in the chloroplast. We have previously identified two non-characterized chloroplast proteins we called LENA and LENB [2]. Here, we show that these proteins are not only localized in the chloroplast stroma and bind Ca2+, we demonstrate further that they have a strong effect on chloroplast development, photosynthesis, and thylakoid protein phosphorylation. Double knockout or overexpressor plants exhibit slow growth and chlorosis under normal growth conditions as well as altered chloroplast ultrastructure. Moreover, in vivo analysis revealed that PSII is constitutively damaged in double-knock-out lines, while both overexpressors as well as double knock-out lines showed a reduced photosynthetic electron transfer rate and altered thylakoid protein phosphorylation patterns. Unbiased shot-gun proteomics of lena,b mutants revealed strongest changes in the levels of photosynthetic proteins and indicate furthermore that retrograde signalling involving GUN proteins is altered in these mutants. In summary, these data suggest that LENA and LENB proteins play an important role in the regulation of chloroplast development and photosynthesis and most likely also other chloroplast processes.
[1] Stael S, Wurzinger B, Mair A, Mehlmer N, Vothknecht UC, Teige M. 2012. Plant organellar calcium signalling: an emerging field. Journal of Experimental Botany 63, 1525-1542.
[2] Bayer RG, Stael S, Csaszar E, Teige M. 2011. Mining the soluble chloroplast proteome by affinity chromatography. Proteomics 7, 1287-1299.