Epigenetic Control of Plant Cold Responses

Higher plants are sedentary organisms which inevitably endure a variety of environmental stresses throughout the life cycle. Abiotic stresses can be atmospheric like cold, heat and UV irradiation; or can also be edaphic like salinity, drought, and heavy metal toxicity (Wani and Gosal, 2011; Surekha et al., 2015). Of all these, cold stress is regarded as a major environmental factor which limits agricultural expansion and crop productivity in hilly terrains (Sanghera et al., 2011). Non-freezing low temperatures deteriorate plant growth physiology by inducing chilling injuries like photosynthesis-associated damages, chlorosis, unregulated apoptosis, loss of membrane fluidity and ultimately wilting (Wani et al., 2016). Depending on the extent of sensitivity among plants, cold stress has been sub-divided into two types. Chilling stress is characterized by 0–15C, whereas temperatures below 0C cause freezing stress (Wani et al., 2013). By virtue of cold acclimation and associated alterations at the molecular and biochemical levels, temperate climatic plants exhibit greater ranges of cold tolerance compared to their tropical and sub-tropical counterparts (Yamaguchi-Shinozaki and Shinozaki, 2006). Deciphering the epigenomic landscape in plants exposed to cold conditions is a rapidly developing field (Hu et al., 2011). Intricate research focussing on epigenetic processes during cold stress has led to the identification of molecular targets which can be genetically manipulated to generate cold tolerant lines. Vernalization is a floral regulatory process preventing precocious flowering during autumn or winter. It gradually promotes flowering competence after prolonged exposures to cold conditions in a species-dependent manner (Kim et al., 2009). Physiologically, vernalization is a “memory response” which is correlated with epigenetic regulation, as observed in themodel plantArabidopsis thaliana (Song et al., 2012).