Non-coding transcription and chromatin structure are now seen as major factors regulating transcriptional output in most eukaryotic genomes. Through the study of how plants time developmental transitions, we have been led into the study of how antisense transcription interacts with chromatin silencing mechanisms to regulate the Arabidopsis floral repressor FLC. In the warm, FLC expression is quantitatively modulated by an antisense-mediated chromatin mechanism that co-ordinately influences transcription initiation and elongation. Upon prolonged cold exposure, expression is progressively epigenetically silenced through a cold-induced, cis-based, Polycomb switching mechanism. The talk will describe our latest understanding of these conserved mechanisms and how they have been modulated during adaptation.