Abstract
In plants, epigenetic changes have been identified as regulators of developmental events during normal growth as well as environmental stress exposures. Flavonoid biosynthetic and antioxidant pathways play a significant role in plant defence during their exposure to environmental cues. The aim of this study was to unravel whether genes encoding enzymes of flavonoid biosynthetic and antioxidant pathways are under epigenetic regulation, particularly DNA methylation, during salt stress. For this, a repressor of silencing from Arabidopsis, AtROS1, was overexpressed in transgenic tobacco. Generated transgenics were evaluated to examine the influence of AtROS1 on methylation status of promoters as well as on coding regions of genes encoding enzymes of flavonoids biosynthesis and antioxidant pathways. Overexpression of AtROS1 increases the demethylation levels of both promoters as well as coding regions of genes encoding chalcone synthase, chalcone isomerase, flavanone 3-hydroxylase, flavonol synthase, dihydroflavonol 4-reductase, and anthocyanidin synthase of the flavonoid biosynthetic pathway, and glutathione S-transferase, ascorbate peroxidase, glutathione peroxidase, and glutathione reductase of the antioxidant pathway during control conditions. The level of demethylation was further increased at promoters as well as coding regions of these genes during salt-stress conditions. Transgenic tobacco overexpressing AtROS1 showed tolerance to salt stress that could have been due to the higher expression levels of the genes encoding enzymes of the flavonoid biosynthetic and antioxidant pathways. This is the first comprehensive study documenting the epigenetic regulation of flavonoid biosynthetic and antioxidant pathways during salt-stress exposure of plants.
Highlights
Crop yield is severely affected by the presence of high sodium ions in the soil all over the world (Greenway and Munns, 1980)
The aim of this study was to unravel whether genes encoding enzymes of flavonoid biosynthetic and antioxidant pathways are under epigenetic regulation, DNA methylation, during salt stress
Transgenic tobacco overexpressing AtROS1 showed tolerance to salt stress that could have been due to the higher expression levels of the genes encoding enzymes of the flavonoid biosynthetic and antioxidant pathways
Summary
Crop yield is severely affected by the presence of high sodium ions in the soil all over the world (Greenway and Munns, 1980). The expression of genes during stress is reported to be under the regulation of chromatin-associated modifications (Henderson and Jacobsen, 2007). This is due to DNA methylation at promoter regions or blocking of transcription activators and recruitment of transcription repressors at methylated sites (Bird, 2002). Cytosine methylation occurs normally at CG sequences In plants, it is found in symmetric CG and CHG as well as asymmetric CHH sequences (where H is A, C, or T) (Furner and Matzke, 2011). DME is required for genome imprinting whereas demethylation by DML2, DML3, and ROS1 is involved in shielding the genome from harmful methylations and in DNA repair, similar to the HhH-GDP superfamily proteins (Choi et al, 2002; Gong et al, 2002; Agius et al, 2006; Gehring et al, 2006; Morales-Ruiz et al, 2006; Penterman et al, 2007a; Penterman et al, 2007b; Zhu et al, 2007; Zhu, 2009)
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