Family ULT

The establishment of floral organs is an event that occurs late in plant development. Thus, genes required for establishing floral meristems must be repressed during vegetative growth. In plants, maintaining the appropriate transcriptional status of these genes is accomplished by the antagonistic activities of Polycomb group (PcG) and trithorax group (trxG) protein complexes. PcG protein complexes maintain the de facto repressed state of genes unnecessary during vegetative growth, such as floral genes. trxG complexes counteract this repressivity to allow expression of the repressed genes. In Arabidopsis thaliana ULTRAPETALA1 (ULT1) is a trxG factor necessary to end stem cell activity in floral meristems by the activation of the MADS-box, floral homeotic gene AGAMOUS (AG). It accomplishes this by counteracting the deposition of repressive histone trimethylation in the promoter and an intron of the AG locus by the PcG protein, CURLYLEAF (CLF) (PMID:19952107).