Moran Oliva, Yana Butenko, Tzung-Fu Hsieh, Ofir Hakim, Aviva Katz, Nechama I. Smorodinsky, Daphna Michaeli, Robert L. Fischer and Nir Ohad (2016). FIE, a nuclear PRC2 protein, forms cytoplasmic complexes in Arabidopsis thaliana. Journal of Experimental Biology, 67(19).
1 Department of Molecular Biology and Ecology of Plant, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
2 Department of Ornamental Horticulture and Plant Biotechnology, Agriculture Research Organization, The Volcani Center, PO Box 6, Beit Dagan, 50250, Israel
3 Department of Plant Sciences, Weizmann Institute of Science, Rehovot, 76100, Israel
4 Department of Plant Sciences, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, 76100, Israel
5 Plants for Human Health Institute, and Department of Plant and Microbial Biology, North Carolina State University, Kannapolis, NC 28081, USA
6 The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, 5290002, Israel
7 Department of Cell Research and Immunology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
8 Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102, USA
9 The Manna Center Program for Food Safety and Security, Tel Aviv University, 69978, Israel
Polycomb group (PcG) proteins are evolutionarily conserved chromatin modifiers that regulate developmental pathways in plants. PcGs form nuclear multi-subunit Polycomb Repressive Complexes (PRCs). The PRC2 complex mediates gene repression via methylation of lysine 27 on histone H3, which consequently leads to chromatin condensation. In Arabidopsis thaliana, several PRC2 complexes with different compositions were identified, each controlling a particular developmental program.
The core subunit FIE is crucial for PRC2 function throughout the plant life cycle, yet accurate information on its spatial and temporal localization was absent. This study focused on identifying FIE accumulation patterns, using microscopy and biochemical approaches. Analysing endogenous FIE and transgenic gFIE–green fluorescent protein fusion protein (gFIE-GFP) showed that FIE accumulates in the nuclei of every cell type examined. Interestingly, gFIE-GFP, as well as the endogenous FIE, also localized to the cytoplasm in all examined tissues. In both vegetative and reproductive organs, FIE formed cytoplasmic high-molecular-mass complexes, in parallel to the nuclear PRC2 complexes. Moreover, size-exclusion chromatography and bimolecular fluorescence complementation assays indicated that in inflorescences FIE formed a cytoplasmic complex with MEA, a PRC2 histone methyltransferase subunit. In contrast, CLF and SWN histone methyltransferases were strictly nuclear. Presence of PRC2 subunits in cytoplasmic complexes has not been previously described in plants. Our findings are in agreement with accumulating evidence demonstrating cytoplasmic localization and function of PcGs in metazoa. The cytosolic accumulation of PRC2 components in plants supports the model that PcGs have alternative non-nuclear functions that go beyond chromatin methylation.