[Show abstract][Hide abstract] ABSTRACT: Polycomb group (PcG)-mediated gene silencing is a common developmental strategy used to maintain stably inherited repression of target genes and involves different protein complexes known as Polycomb-repressive complexes (PRCs). In animals, the two best-characterized PcG complexes are PRC1 and PRC2. In this report, we demonstrate that the plant-specific protein EMBRYONIC FLOWER1 (EMF1) functions in maintaining the repression of the flower homeotic gene AGAMOUS (AG) during vegetative development in Arabidopsis thaliana by acting in concert with the EMF2 complex, a putative equivalent of Drosophila melanogaster PRC2. We show that AG regulatory sequences are required for its ectopic expression in both emf1 and emf2 mutants and that EMF2 is required for trimethylation of histone 3 lysine 27 on the AG chromatin. We found that EMF1 interacts directly with AG and that this interaction depends on the presence of EMF2. Together with the finding of EMF1 interference with transcription in vitro, these results suggest that EMF1 enables transcriptional repression of AG after the action of the putative EMF2 complex. Our data indicate that EMF1 plays a PRC1-like role in the PcG-mediated floral repression mechanism.
The Plant Cell 03/2008; 20(2):277-91. DOI:10.1105/tpc.106.049957 · 9.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The EMBRYONIC FLOWER (EMF) genes EMF1 and EMF2 are required to maintain vegetative development and repress flower development. EMF1 encodes a putative transcriptional regulator, and EMF2 encodes a Polycomb group protein homolog. We examined expression profiles of emf mutants using GeneChip technology. The high degree of overlap in expression changes from the wild type among the emf1 and emf2 mutants was consistent with the functional similarity between the two genes. Expression profiles of emf seedlings before flower development were similar to that of Arabidopsis flowers, indicating the commitment of germinating emf seedlings to the reproductive fate. The germinating emf seedlings ectopically expressed flower organ genes, suggesting that vegetative development in wild-type plants results from EMF repression of the flower program, directly or indirectly. In addition, the seed development program is derepressed in the emf1 mutants. Gene expression analysis showed no clear regulation of CONSTANS (CO), FLOWERING LOCUS T (FT), LEAFY (LFY), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 by EMF1. Consistent with epistasis results that co, lfy, or ft cannot rescue rosette development in emf mutants, these data show that the mechanism of EMF-mediated repression of flower organ genes is independent of these flowering genes. Based on these findings, a new mechanism of EMF-mediated floral repression is proposed.
The Plant Cell 04/2003; 15(3):681-93. · 9.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the past two years, several early-flowering genes have been shown to encode putative chromatin-associated proteins in Arabidopsis. These proteins probably function as epigenetic silencers that repress the promotion of flowering and flower organ identity genes, and thereby maintain vegetative growth. As the plant matures, levels of the floral promoters increase despite the continued presence of floral repressors. High levels of the floral promoters are somehow able to overcome floral repression and to activate flower development. Further characterization of mutants that have impairments in either floral promoters or floral repressors revealed that these mutants not only display defects in flowering time but also have altered inflorescence architectures. These findings indicate that these flowering genes also regulate other aspects of shoot development and may be used to study the mechanism of shoot growth pattern.
Current Opinion in Plant Biology 03/2003; 6(1):29-35. DOI:10.1016/S1369-5266(02)00014-6 · 9.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We used an anti-indole acetic acid (IAA or auxin) monoclonal antibody-based immunocytochemical procedure to monitor IAA level in Arabidopsis tissues. Using immunocytochemistry and the IAA-driven beta-glucuronidase (GUS) activity of Aux/IAA promoter::GUS constructs to detect IAA distribution, we investigated the role of polar auxin transport in vascular differentiation during leaf development in Arabidopsis. We found that shoot apical cells contain high levels of IAA and that IAA decreases as leaf primordia expand. However, seedlings grown in the presence of IAA transport inhibitors showed very low IAA signal in the shoot apical meristem (SAM) and the youngest pair of leaf primordia. Older leaf primordia accumulate IAA in the leaf tip in the presence or absence of IAA transport inhibition. We propose that the IAA in the SAM and the youngest pair of leaf primordia is transported from outside sources, perhaps the cotyledons, which accumulate more IAA in the presence than in the absence of transport inhibition. The temporal and spatial pattern of IAA localization in the shoot apex indicates a change in IAA source during leaf ontogeny that would influence flow direction and, consequently, the direction of vascular differentiation. The IAA production and transport pattern suggested by our results could explain the venation pattern, and the vascular hypertrophy caused by IAA transport inhibition. An outside IAA source for the SAM supports the notion that IAA transport and procambium differentiation dictate phyllotaxy and organogenesis.