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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

HSP22.0, and HSP18.2 having distinct expression levels from Heat Shock-

inducible non-memory genes like HSP70 and HSP101, their expression rises

shortly following Heat Shock and then rapidly decreases. HSP22.0, a heat

stress-induced gene, is implicated in heat stress memory. Heat stress causes

the deposition of active histone marks in both the HSP22.0 and HSP70

genes, with H3K4me3, H3K4me2, as well as H3K9Ac. However, once the

plants were returned to their natural state, the levels of these three HSP70

markers dropped to baseline levels. HSP22.0, on the other hand, maintained

H3K4me3 and me2 levels high, however, H3K9Ac levels remain the same

(Lämke et al., 2016). Although several studies have shown that distinct

histone modifications mediate transcriptional memory, it is still unknown

how adverse conditions cause changes in epigenetic alterations (Berger,

2007; Heard & Martienssen, 2014; Zheng et al., 2017). The generation of

transgenerational memory in the offspring, helps the plant to achieve well-

balanced survival and reproductive mechanism. DNA methylation in rice

takes place due to drought stress and more than 40% of this epimutation are

carried to the next progeny. By this time, the tiller number get decreased

and showed an increasing rate of seed set. The theory of maintaining a DNA

methylation state due to rain-lessness in progeny, aids towards water defi­

ciency stress response as well as prolonged adaptability to water deficiency

stress environment. Following the selective pressure of comparatively long-

term environmental stress, offspring generations produced a higher balance

between “survival strategy” and “reproductive strategy” than the parental

generations, resulting in fewer effective tillers and higher seed setting rates

than that of the parental generations (Zheng et al., 2017). DNA methylation

has been shown to have a role in the transgenerational memory towards

heavy metal toxicity on Oryza sativa. The P1B subfamily belonging to heavy

metal-transporter P-type ATPases (HMAs) plays a function in the absorption

and translocation of heavy metals in plants. Level of HMAs increases in

relation to heavy metal stressor, as well as transgenerational gene expression

memory have been revealed even when heavy metals were removed (Cong

et al., 2019) (Table 12.1).

12.7 BIOINFORMATICS TOOLS USED IN STUDYING EPIGENETICS

OF PLANT STRESS

Abiotic stressors are among the most significant aspects limiting agricultural

output. Understanding the molecular mechanisms of abiotic stressors in