Defense guard: strategies of plants in the fight against Cadmium stress

Abstract

Soil Cadmium (Cd) contamination is a worldwide problem with negative impacts on human health. Cultivating the Cd-Pollution Safety Cultivar (Cd-PSC) with lower Cd accumulation in edible parts of plants is an environmentally friendly approach to ensure food security with wide application prospects. Specialized mechanisms have been addressed for Cd accumulation in crops. This review provides an extensive generality of molecular regulation mechanisms involved in Cd absorption, transport, detoxification, and tolerance in plants, highlighting key aspects of rhizosphere, apoplast barrier, Cd uptake, transfer, and cellular repair strategies under Cd stress. Additionally, we summarize the possible approaches for lowering the Cd accumulation crops, including molecular-assistant breeding, applying chemical materials, and microbial strategy to decrease Cd content in edible parts and improve Cd tolerance of crops under Cd stress. This review would provide valuable insights for cultivating low Cd accumulated crop cultivars, ultimately contributing to food safety.

Keywords: Cadmium; Cd detoxification; Cd resistance; Cd transportation; Cd uptake; Cd-pollution safety cultivar.

Fig. 1

The process of Cd uptake, efflux, translocation, and distribution in plants. Cd is absorbed by the roots from the soil through both the apoplast and symplast pathways. Transporters are involved in the absorption and transport of Cd from soils to edible parts in plants. The pathways of Cd accumulation and transport include Cd fixation in the cell wall, Cd uptake and efflux by transporters, Cd chelation and vacuoles sequestration, root-to-shoot translocation, and redistribution between through stems and nodes, and further translocated to leaves and grains through the phloem

Fig. 2

Cd stress resulted in ROS production and disturbed the structural of protein, which induced the aggregation of misfolded proteins and ER stress. To alleviate the ER stress, the Unfolded Protein Response (UPR) and ER-associated degradation (ERAD) systems are initiated to promote the correct folding of misfolded proteins and remove the misfolded proteins. ER stress induced the disassociation of IRE1 from BIP, and IRE1 caused the splicing of bZIP60 and HAC1 mRNA, which are transcription factors to active UPR response genes

Fig. 3

Genetic–chemical materials–root microbe strategy for improving Cd stress resistance in crops. Genetic and molecular studies have improved our understanding of Cd stress responses in plants. High throughput sequencing and bioinformatics analysis identified natural allelic variants and candidate genes representing low Cd accumulation. CRISPR–Cas-based gene editing can be applied in breeding plants with Low Cd accumulation and Cd tolerance. Chemical materials, like nano-particles, are potential methods for manipulation to protect crops from Cd stresses at multiple levels. The inoculation with beneficial microbes in plants roots can increase Cd tolerance and decrease Cd uptake and translocation