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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

A Single Amino Acid Change in the Enhancer of Zeste Ortholog CURLY LEAF Results in Vernalization-Independent, Rapid Flowering in Arabidopsis^{1,[C],[W],[OA]}

Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706–1544

Many strains of Arabidopsis (Arabidopsis thaliana) require exposure to prolonged cold for rapid flowering, a process known as vernalization. Vernalization in Arabidopsis results in the suppression of FLOWERING LOCUS C (FLC), a repressor of flowering. In a screen for mutants that no longer require vernalization for rapid flowering, we identified a dominant allele of the Enhancer of Zeste E(z) ortholog CURLY LEAF (CLF), clf-59. CLF is a Polycomb Group gene, and the clf-59 mutant protein contains a proline-to-serine transition in a cysteine-rich region that precedes the SET domain. Mutant plants are early flowering and have reduced FLC expression, but, unlike clf loss-of-function mutants, clf-59 mutants do not display additional pleiotropic phenotypes. clf-59 mutants have elevated levels of trimethylation on lysine 27 of histone H3 (H3K27me3) at FLC. Thus, clf-59 appears to be a gain-of-function allele, and this allele represses FLC without some of the components required for vernalization-mediated repression. In the course of this work, we also identified a marked difference in H3K27me3 levels at FLC between plants that contain and those that lack the FRIGIDA (FRI) gene. Furthermore, FRI appears to affect CLF occupancy at FLC; thus, our work provides insight into the molecular role that FRI plays in delaying the onset of flowering.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Richard M. Amasino (amasino{at}biochem.wisc.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.145581

^* Corresponding author; e-mail amasino{at}biochem.wisc.edu.

Received August 3, 2009; accepted September 8, 2009; published September 15, 2009.