Long non-coding RNAs(lncRNAs)have been proposed to play important roles in gene regulation.However,their importance in epigenetic silencing and their specificity of action remain controversial.We have investigated the cold-induced,epigenetic switching mechanism involved in silencing of the floral repressor locus FLC that occurs in Arabidopsis thaliana plants during vernalization.Antisense transcripts,collectively named COOLAIR,are induced by cold prior to the major accumulation of histone K27 trimethylation,characteristic of Polycomb silencing.