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Title: The ULT1 and ULT2 trxG genes play overlapping roles in Arabidopsis development and gene regulation

Author
item MONAFRED, MONA - University Of California
item CARLES, CRISTEL - National Council For Scientific Research-Cnrs
item ROSSIGNOL, PASCALE - University Of California
item PIRES, HELENA - University Of California
item Fletcher, Jennifer

Submitted to: Molecular Plant
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2013
Publication Date: 2/27/2013
Publication URL: http://mplant.oxfordjournals.org/content/early/2013/05/03/mp.sst041.full
Citation: Monafred, M.M., Carles, C.C., Rossignol, P., Pires, H.R., Fletcher, J.C. 2013. The ULT1 and U:T2 trxG genes play overlapping roles in Arabidopsis development and gene regulation. Molecular Plant. 10.1093/mp/sst041.

Interpretive Summary: The development of plants and animals is tightly controlled by the combined activity of transcription factors and proteins that induce chromatin remodeling. Among these, a small set of trithorax group (trxG) proteins remodel chromatin to sustain high levels of target gene expression at specific growth stages. However, only a few trxG factors have been identified in plants and little is known about their roles in development. Here we have shown that two closely related trxG factors ULT1 and ULT2, play overlapping roles in limiting stem cell accumulation in Arabidopsis shoots and flowers. We have determined that the two genes also work together to pattern the developing fruit from top to bottom. In addition, we found that the ULT1 and ULT2 proteins can physically associate with one another in plant cells and that they regulate a common set of downstream target genes. Our research shows that chromatin remodeling by ULT1 and ULT2 is necessary for the proper development of stem cells and fruits, suggesting the possibility that their activity may be altered to increase plant yield and thus benefit agriculture.

Technical Abstract: The epigenetic regulation of gene expression is critical for ensuring the proper deployment and stability of defined genome transcription programs at specific developmental stages. The cellular memory of stable gene expression states during animal and plant development is mediated by the opposing activities of Polycomb group (PcG) factors and trithorax group (trxG) factors. Yet despite their importance, only a few trxG factors have been characterized in plants and their roles in regulating plant development are poorly defined. In this work we report that the closely related Arabidopsis trxG genes ULTRAPETALA1 (ULT1) and ULT2 have overlapping functions in regulating shoot and floral stem cell accumulation, with ULT1 playing a major role but ULT2 also making a minor contribution. The two genes also have a novel, redundant activity in establishing the apical-basal polarity axis of the gynoecium, indicating that they function in differentiating tissues. Like ULT1 proteins, ULT2 proteins have a dual nuclear and cytoplasmic localization, and the two proteins physically associate in planta. Finally, we demonstrate that ULT1 and ULT2 have very similar over-expression phenotypes and regulate a common set of key development target genes, including floral MADS box genes and class I KNOX genes. Our results reveal that chromatin remodeling mediated by the ULT1 and ULT2 proteins is necessary to control the development of meristems and reproductive organs. They also suggest that, like their animal counterparts, plant trxG proteins may function in multi-protein complexes to up-regulate the expression of key stage- and tissue-specific developmental regulatory genes.