Understanding molecular mechanism involved in silicon uptake and silicon derived benefits under heavy metal stress in mungbean Vigna radiata L Wilczek

Abstract

Heavy metal toxicity, one of the major abiotic stresses faced by crop plants cause significant yield losses worldwide. Bioaccumulation of heavy metals in soil negatively affects various plant physiological and biochemical processes. Silicon (Si) supplementation is known to enhance plants resilience under stress more particularly arsenic (As) stress. In this regard, efforts were made to understand the molecular mechanism involved in Si uptake and Si derived heavy metal stress tolerance in mungbean. In the present study, a thorough evaluation of 55 AQPs found in the mungbean genome, including phylogenic distribution, and structural characterization, contributed to the identification of VrNIP2-1 as a metalloid transporter. Interestingly, VrNIP2-1 was found to harbour ASGR as ar/R selectivity filter instead of GSGR unanimously reported in other high Si accumulating crops. Evaluation of diverse cultivars showed a high level of Si accumulation in leaves indicating the possibility of functional Si transport in mungbean. Further, heterologous expression of VrNIP2-1 in yeast revealed As (III) and GeO2 transport activity. Similarly, VrNIP2-1 expression in Xenopus oocytes confirmed the Si transport ability. Antioxidant enzymes play important role in scavenging the excess ROS produced during heavy metal stress conditions. The beneficial effect of Si supplementation on antioxidant enzymes ; lipid peroxidation, and transcriptional regulation of enzymes involved in antioxidant defense as well as Si transporters in mungbean under heavy metal stress conditions was investigated. The evaluation of Si deposition using SEM and EDX revealed significant Si deposition in the trichomes of leaves as well as the co-deposition of Si and As in stomatal guard cells. The outcomes of this research serve as a basis to improve Si uptake while restricting hazardous metalloids like As in plants and will also help to understand the Si-mediated changes in biochemical and physiological responses in mungbean under heavy metal stress. newline