Endoplasmic Reticulum Quality Control and metal tolerance: reduced activity of Glucosidase II enzyme affects positively cadmium tolerance in Arabidopsis thaliana

The Endoplasmic Reticulum Quality Control (ERQC) machinery is highly conserved among eukaryotes and assists the newly synthetized proteins in the folding process. Previous works have reported the involvement of ERQC in plant immunity and biotic stress response. However, the interaction between ERQC pathway and heavy metals exposure has been poorly investigated in plants. In the present study, we showed that the Arabidopsis thaliana rsw3 mutant, characterised by a reduced activity of the ER Glucosidase II enzyme, exhibits an increased tolerance to cadmium (Cd) stress. Under standard conditions, rsw3 seedlings exhibit shorter primary roots compared to Wild-type (Wt) plantlets, because of a constitutive ER stress and a consequent upregulation of both ERQC and Unfolded Protein Response (UPR) stress markers in root or shoot tissues. Interestingly, differently from Wt seedlings, these markers remain unchanged in rsw3 under Cd stress. Biochemical data here provided linked the enhanced Cd tolerance of rsw3 to the brassinosteroid receptor 1, BRI1, as the partial impairment of GII activity positively affects the accumulation of the active form of BRI1 receptor on the plasma membrane under Cd stress.