Salt stress induces genotype-specific DNA hypomethylation in ZmEXPB2 and ZmXET1 genes in maize

Abstract

Maize, a moderately salt sensitive crop, first experiences osmotic stress that cause reduction in plant growth under salt stress. Fluctuation in cell wall elongation is one of the reasons of this reduction. Along with others, two important proteins expansins and xyloglucan endotransglucosylase are involved in regulation of cell wall elasticity, but the role of epigenetic mechanisms in regulating the cell wall related genes is still elusive. The present study was conducted with the aim of understanding the role of DNA methylation in regulating ZmEXPB2 and ZmXET1 genes. One salt sensitive and one salt tolerant maize cultivar was grown under hydroponic conditions at different levels of salt stress: T1 = 1 mM (control), T2 = 100 mM and T3 = 200 mM in three replicates. DNA and RNA were extracted from roots. After bisulfite treatment, Methyl Sensitive PCR was used for the DNA methylation analysis. It was revealed that fragment in promoter of ZmEXPB2 gene showed high level of DNA methylation under T1 in both varieties. Comparison of different stress treatments revealed decrease in DNA methylation with the increase in salt stress, significantly lower methylation appearing in T3. Similarly, the fragment in promoter of ZmXET1 gene also showed high levels of DNA methylation in T1. When different treatments were analysed, this gene significantly hypomethylated at T2 which continued to decrease in T3 in sensitive variety but remain stable in tolerant variety. Although, further in-depth analysis is required, our results demonstrate region-specific and genotype-specific methylation shift in the promoter of the ZmEXPB2 and ZmXET1 genes when subjected to the salt stress confirming the epigenetic regulation of these genes under stress conditions.

Drought Stress Induces Differential DNA Methylation Shift at Symmetric and Asymmetric Cytosine Sites in the Promoter Region of ZmEXPB2 Gene in Maize

“…The upregulation of EXPB2 gene in Solanum pennellii under drought stress conditions indicated towards the strong association between EXPB2 gene and drought stress tolerance (Egea et al 2018). Interestingly, the involvement of epigenetic mechanisms at both DNA methylation and histone acetylation levels in the regulation of EXPB2 gene in maize against salt stress have already been reported (Li et al 2014;Kaleem et al 2019). Li et al (2014) revealed an increase in H3K9 acetylation was associated with the ZmEXPB2 up-regulation under salt stress conditions.…”

“…Li et al (2014) revealed an increase in H3K9 acetylation was associated with the ZmEXPB2 up-regulation under salt stress conditions. Similarly, ZmEXPB2 gene up-regulation by the DNA hypomethylation in this gene induced by salt stress in maize has been reported (Kaleem et al 2019). But the ZmEXPB2 gene regulation by DNA methylation shift in maize under drought stress need to be explore.…”

“…An upregulation in the expression of different expansin genes like TaEXPB23 in Nicotiana tabacum and RhEXPA4 gene in Arabidopsis under drought condition have been observed (Li et al 2011;Lü et al 2013). EXPB2, an important gene of β-expansin gene family, show upregulation under different abiotic stresses like salinity and drought stress in different species including maize Zhao et al 2012;Li et al 2014;Kaleem et al 2019). In Glycine max, the higher expression of EXPB2 gene accompanied with improved root tolerance to water stress was reported in water stressed plants (Guo et al 2011).…”

“…This modulation is achieved through the regulation of activities of stress responsive genes (Farooq et al 2011;Wang et al 2011). In recent decades, evidences have confirmed the role of different epigenetic mechanisms, like DNA methylation, histone modification and RNA interferences, in the regulation of gene expression under stress conditions (González et al 2013;Li et al 2014;Kaleem et al 2019). DNA methylation is addition of methyl group to either adenine or cytosine.…”

“…One important physiological process is cell wall elongation which influences the plant growth by regulating the cell extension and is often considered to be the earliest visible effect of stress (Gall et al 2015;Ezquer et al 2020). It is regulated by proteins like endo-1,4-b-Dendoglucanase (EGase), xyloglucan endotransglucosylase (XET), expansins (EXP), and plasma membrane proton pump (PM-H+-ATPase, MHA) (Geilfus et al 2011;Kaleem et al 2019). Various studies have confirmed the importance of expansins in the cell wall elongation and plant response against abiotic stress (Guo et al 2011;Zhou et al 2015;Marowa et al 2016).…”