**5. Climate change conditions leave their imprints in plants through abiotic stress: the epigenetic effect**

It is clear to us that the sessile plant beings are capable of displaying various defence strategies in response to stress factors. In nature, the plants are almost always exposed to more than one kind of stress factors, implying that response strategies are also versatile. The diverse array of signalling pathways and molecules that are involved in environmental stress defence result from reprogramming of gene expression patterns, which in turn are beautifully regulated. From research spanning the last two decades, there is growing evidence that an epigenetic regulation of gene expression also takes place under different kinds of abiotic stress [40–43]. Following the consensus, we are using the definition of 'epigenetics' as the changes in gene expression activity due to alterations that are outside of the DNA sequence of the gene, and that these changes may be meiotically or mitotically inheritable but are largely displaying the non-Mendelian feature of reversibility [40, 42, 44].

The epigenetic response of plant to different environmental stimuli is essential not only for abiotic stress tolerance but also for various other essential processes such as

#### **Figure 3.**

*Schematic representation of some major defence strategies employed by plants in response to various abiotic stresses. The strategies are categorised as 'escape/adaptation', 'avoidance' and 'tolerance', respectively. Colour codes—Blue: Drought stress; Red—Salinity stress; Pink—UV-B stress; Yellow-Common to different kinds of stress. Symbols—'↑' indicates 'increase in'; '↓' indicates 'decrease in'; Bold Arrows indicate the part of plant affected by each type of abiotic stress, i.e., leaf, stem, and root, respectively. (Extracted from Müller-Xing* et al*. [40], Salehi-Lisar* et al*. [21], Kamran* et al*. [19], Podolec* et al*. [41]) (Figure is slightly modified from the literature for simplicity).*

leaf development, floral transition and bud dormancy [42]. In case of environmental stress, it has been noted that the marks of epigenetic changes display stability or transgenerational inheritance, leading to what is popularly known as 'epigenetic memory' [40, 42]. This also becomes of source of 'phenotypic plasticity' (represented as a simplified equation below).
