Current insights into the molecular mechanisms of arsenic tolerance in wheat (Triticum aestivum L.) and comparisons with other cereals

Contamination of irrigation water and agricultural soil by arsenic (As) can lead to a high buildup in wheat, posing carcinogenic and non-carcinogenic risks to humans. Previous research has mainly focused on As-induced phytotoxicity in wheat, however, there are significant knowledge gaps in understanding underlying molecular pathways. Such knowledge gaps have created obstacles for breeders to effectively develop tolerant wheat genotypes. Therefore, this review leverages knowledge of such molecular responses to As tolerance and sensitivity from other cereal crops. Such knowledge is critical for comprehensive understanding and guiding targeted research of molecular pathways and genes linked to As tolerance and detoxification in wheat. The present study also provides insights into important miRNA families responsible for As tolerance or sensitivity. Key findings revealed the upregulation of stress response genes such as the ascorbate-glutathione cycle, antioxidants, peroxidases, and glutaredoxin in tolerant genotypes. Glutathione and its associated enzymes like glutathione S-transferase and glutathione reductase played an important role in As detoxification. Gene expression of secondary metabolites i.e., proline, flavonoid, anthocyanin, and phenolic compounds were significantly regulated in tolerant genotypes to develop As complexes and sequestrate them into vacuoles. Furthermore, tolerant genotypes showed upregulation of stress-responsive miRNAs (miR156, miR159, miR167, and miR408) compared to sensitive genotypes under As stress. Overexpression of miR158 increases As sensitivity in crops by disrupting defense mechanisms. Genetic manipulation of miR158 can be a target marker for breeders to generate As-tolerant wheat. Future research should focus on the identification of tolerant genotypes, stress-responsive genes, and key miRNA to enhance our understanding of Astolerance mechanisms in wheat. Genome editing tools like CRISPR-Cas9 show great potential for breeding wheat genotypes by knocking out targeted genes or miRNAs. This approach can generate genotypes with the potential to restrict As translocation to grains thus ensuring food security and agriculture sustainability.