Temperature regulation of circadian clock proteins from Chlamydomonas and their relevance for entrainment by temperature cycles
Final Report Abstract
Temperature cycles are one of the main environmental cues that synchronize circadian clocks beside light-dark cycles. For control of entrainment by temperature cycles, certain clock components should be able to respond to changes of temperature within the physiological range. Here, we have taken the green microalga Chlamydomonas reinhardtii as a model to study clock-controlled components of RNA-metabolism that are able to integrate temperature information at temperatures being in the physiological range of the alga (18°C and 28°C). These include the two subunits (C1 and C3) of the RNA-binding protein CHLAMY1 and a novel interaction partner of C3, the clock-relevant 5’-3’exoribonucelase XRN1. We identified different proteins that bind to the c3 promoter region which is involved in up-regulation of c3 in cells grown at 18°C. We further found novel interaction partners of 5’-3’exoribonucelase XRN1 and of the C3 subunit of CHLAMY1. These include the RNA-binding proteins Musashi and polyC-binding protein (PCBP). We find that Musashi exists in two alternatively spliced forms resulting in 77-kDa and 60-kDa variants that bear two and three RRM domains, respectively. Only the 60-kDa Musashi is able to bind specifically to (UG)7 repeat-containing RNAs as does CHLAMY1. This holds also true for PCBP. Both, the 60-kDa Musashi and PCBP are upregulated at 28°C, especially in the early night. Intriguingly, C3, XRN1 and the 60 kDa Musashi, but not PCBP influence thermal acclimation, where 12 h pulses of temperatures were given during the night period of a day-night cycle and growth rates were measured afterwards. Our data indicate a network of proteins of RNA-metabolism that contribute to clock regulation but also to thermal acclimation. These proteins will thus be not only of great interest for understanding circadian clock properties related to temperature but are also useful indicators to study global warming effects on microalgae at a molecular level.
Publications
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(2010) How the green alga Chlamydomonas reinhardtii keeps time. Protoplasma 244, 3-14
Schulze, T., Prager, K., Dathe, H., Kelm, J., Kießling, P. and Mittag, M.
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(2010) Multiple roles and interaction factors of an E- box element in Chlamydomonas reinhardtii. Plant Physiol. 152, 2243-2257
Seitz, S.B., Weisheit, W. and Mittag, M.
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(2010) The role of an E-box element: multiple function and interaction partners. Plant Signal Behav. 9, 1077-1080
Seitz, S.B., Voytsekh, O., Mohan, K. and Mittag, M.
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(2012) A flavin-binding cryptochrome photoreceptor responds to both blue and red light in Chlamydomonas reinhardtii. Plant Cell 24, 2992-3008
Beel, B., Prager, K., Spexard, M., Sasso, S., Weiss, D., Müller, N., Heinnicke, M., Dewez, D., Ikoma, D., Grossman, A. R., Kottke, T., and Mittag, M.
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(2012) Novel interaction of two clock-relevant RNA- binding proteins C3 and XRN1 in Chlamydomonas reinhardtii. FEBS Letters 586, 3969-3973
Dathe, H., Prager, K. and Mittag, M.
