Recent evidence for transgenerational adaptation resulting from stress induced changes in the cytosine methylation landscape of plants

• Plants have the potential to propagate acquired cytosine methylation changes through mitosis, meiosis and embryogenesis. • Cytosine methylation interacts with histones in the formation of heterochromatin and the production of siRNAs for RdDM. siRNAs in turn direct de novo methylation in distal regions and reinforce existing methylation patterns. • Transposable elements (TEs) are genetic elements that play important role in the interplay between cytosine methylation, genome organization and transgenerational stress response. • Both random and non-random transgenerational changes in cytosine methylation result from exposure to different stress factors including drought, salinity, temperature, nutrient deficiency and biotic stresses. This paper reviews the emerging evidence for the role of cytosine methylation in transgenerational adaptation to environmental stress in plants. The ability of plants to propagate acquired epigenetic changes through cell division indicates their potential role in long term adaptation to changing environmental conditions. The key role in this process is the interaction between cytosine methylation, histone modifications and RdDM. The main target for cytosine methylation are the transposon elements (TEs). Stress induced differential methylation of TEs can induce cis - and trans- regulation of gene activity as well as their mutagenic potential. TE insertion however, does not happen completely at random, but is dependent on the histones present in the chromatin structure of a particular genomic region. Recent experiments show strong evidence for preferential stress induced TE activation and insertion as a force in short and long term adaptation. Additional evidence exists for unique activation of TEs during meiosis, enhancing the probabilities for unique beneficial mutations in the progeny. Plants have evolved different responses for many types of stress and depending on the severity, duration and repetitiveness of the stress can induce different types of epigenetic changes. Drought, nutrients, salinity, temperature and various types of biotic stresses have their own cytosine methylation profile. This data highlights the potential existence of a strong internal mechanism for stress induced transgenerational adaptation, which can be harnessed for developing stress-resilient crops.