OMICS approaches towards understanding plant's responses to counterattack heavy metal stress: An insight into molecular mechanisms of plant defense

Abstract Under constant climatic change and the existing environment, plants are exposed to several adverse factors such as extreme temperatures, high salt, heavy metals (HMs), drought, and pathogens. Prolonged exposure to such adverse conditions results in phytotoxicity and overall retardation of growth and development. Excess of HMs is one of the significant factors that affects plant growth significantly. Plants develop several defense mechanisms at the cellular and physiological levels to survive HMs stress. However, these internal defense mechanisms are not enough to overcome excessive HMs stress. Plants generate various secondary messengers to activate cell signaling, which results in the activation of several transcriptional responses associated with plant defense. Different transcription factors (TFs) gene families such as WRKY, my elob lastosis (MYB), basic leucine zipper domain (bZIP), basic helix-loop-helix (bHLH), APETALA2/ethylene-responsive element binding protein (AP2/EREBP), Cys2-His2 (C2H2), receptor genes/proteins, and kinases, like mitogen-activated protein kinase (MAPK), play an essential role in the regulation of stress using hormone-mediated pathways under HMs stress. Additionally, phytohormones and their signaling network also contribute to regulating cellular functions at the molecular level to combat HMs stress. Several mechanisms have been explored to understand the defense mechanism of plants under HMs stress. However, many more advanced molecular approaches are required to explore these defense mechanisms. Herein, we have described OMICS’ approaches to improve the plants' internal defense system to counteract HMs stress.