Mechanism of demethylation of histone H3 lysine 4 on FLC locus during vernalization depending on two JmjC-domain containing demethylases

Flowering in plants is one of the crucial developmental events controlled by the multiple environmental stimuli. Vernalization is the response to the exposure to the prolonged cold to achieve the molecular competence for a subsequent floral transition. The main regulator of the vernalization response, FLOWERING LOCUS C (FLC), is highly expressed to prevent precocious flowering before vernalization but becomes repressed during vernalization. The studies on the repression of FLC by vernalization have focused mostly on the transcriptional suppression of the locus achieved by components of POLYCOMB REPRESSION COMPLEX (PRC) and VERNALIZATION INSENSITIVE 3 (VIN3). These regulators contribute to the deposition of the repressive histone marks, the methylation of histone H3 lysine 27, at the FLC locus. However, the mechanisms to regulate other histone modifications during vernalization remain unclear. One of active histone marks, tri-methylated histone H3 lysine 4, is enriched at FLC before vernalization but the enrichment decreases by vernalization. Two JmjC-domain containing demethylases, JMJ16 and JMJ19, are induced by vernalization and are involved in the reduction of tri-methylated H3K4 at the FLC locus redundantly. These demethylases, JMJ16 and JMJ19, are directly targeted to the FLC locus and interact with the cold-induced VIN3 protein. Another histone active mark, histone acetylation, is also highly enriched at the FLC locus. However, the mechanisms and regulators responsible for balancing the level of the acetylation at the FLC locus have not been fully characterized. The phenotypic analysis of the mutants of deacetylases revealed that two deacetylases, SRT1 and HDT1, are involved in the short day-specific flowering mechanism. The srt1 and hdt1 mutants exhibit the early flowering and the late flowering, respectively under short days in consistent with changes in expression of FLC. These results suggest that two histone deacetylases, SRT1 and HDT1, are associated with the short-day specific flowering regulation in Arabidopsis and may use the different regulatory mechanism on the target gene, FLC