Abstract
High concentrations of heavy metal (HM) ions impact agronomic staple crop production in acid soils (pH ≤ 5) due to their cytotoxic, genotoxic, and mutagenic effects. Among cytotoxic ions, the trivalent aluminum cation (Al3+) formed by solubilization of aluminum (Al) into acid soils, is one of the most abundant and toxic elements under acidic conditions. In recent years, several studies have elucidated the different signal transduction pathways involved in HM responses, identifying complementary genetic mechanisms conferring tolerance to plants. Although epigenetics has become more relevant in abiotic stress studies, epigenetic mechanisms underlying plant responses to HM stress remain poorly understood. This review describes the main epigenetic mechanisms related to crop responses during stress conditions, specifically, the molecular evidence showing how epigenetics is at the core of plant adaptation responses to HM ions. We highlight the epigenetic mechanisms that induce Al tolerance. Likewise, we analyze the pivotal relationship between epigenetic and genetic factors associated with HM tolerance. Finally, using rice as a study case, we performed a general analysis over previously whole-genome bisulfite-seq published data. Specific genes related to Al tolerance, measured in contrasting tolerant and susceptible rice varieties, exhibited differences in DNA methylation frequency. The differential methylation patterns could be associated with epigenetic regulation of rice responses to Al stress, highlighting the major role of epigenetics over specific abiotic stress responses.
Highlights
Plants deal with multiple challenges to adapt to different environmental conditions given their sessile lifestyle
While essential elements are necessary for plants in small amounts, high concentrations of both types of elements can lead to inhibition of plant growth and development (Rascio and Navari-Izzo, 2011)
Heavy metals have a strong impact on acid soils, caused by the excess of cationic species such as magnesium (Mg2+), calcium (Ca2+), phosphorus (P), sodium (Na+) and aluminum (Al3+) which in turn, affect plant physiological responses leading to crop yield losses for breeders and farmers (Samac and Tesfaye, 2003; Fryzova et al, 2017)
Summary
Plants deal with multiple challenges to adapt to different environmental conditions given their sessile lifestyle. An increasing number of studies highlight the role of epigenetic mechanisms in the regulation of plant stress responses (Sudan et al, 2018; Chang et al, 2020). Evidence from previous studies suggests that DNA methylation might play a role in the regulation of plant responses to HMs through at least two mechanisms (Aina et al, 2004; Choi and Sano, 2007; Greco et al, 2012; Kumar et al, 2012; Arif et al, 2016).
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