Fig. 9

A model of chromatin dynamics associated with genes in potato tubers under cold stress. In ambient condition, active genes in RT tubers maintain open chromatin in their putative promoters and H3K4me3 at their 5′ ends, while the gene bodies are less accessible to DNase I and are depleted of H3K27me3. Some of these genes could be active in leaves as well and maintain similar chromatin features. However, other genes could be inactive in leaves and switch to a repressive chromatin state in which the gene bodies are marked by H3K27me3 and are depleted of H3K4me3. In contrast, cold stress in tubers can result in upregulation of a set of stress-response genes as well as downregulation of a set of developmental genes. This regulation of transcription is associated with the deposition of the bivalent H3K4me3-H3K27me3 mark. Existence of H3K4me3 across gene body regions may ensure the chromatin accessibility through chromatin remodelers and regulators, while the spread of H3K27me3 may provide a chromatin environment for either gene activation or repression via LHP1. Thus, the bivalent H3K4me3-H3K27me3 mark represents a distinct chromatin environment with greater accessibility, which may facilitate the access of regulatory proteins required for gene upregulation or downregulation in response to the cold stress