The Binding Protein (BiP) is regulated in response to conditions of endoplasmic reticulum (ER) stress, likely the accumulation of unfolded proteins in the lumen. Kinetics of protein folding in ER is affected by the water stress, leading to the Unfolded Protein Response (UPR) Pathway. An increase at BiP and other UPR Elements levels in ER lumen may recover the ER to a normal state. We have previously demonstrated that the overexpression of BiP in transgenic plants of tobacco can confer fisiological resistance to the water stress. We are now investigating the molecular mechanisms involved in this phenotype. Transgenic plants transformed with pBL21 vector containing the soybean BiP gene fused to 35S promoter, consitutively overexpressing BiP gene - referred as Sense -, transgenic plants transformed with pBL21vector containing the soybean BiP gene in inverse orientation fused to 35S promoter - called Anti-Sense -, and Control plants, transformed with pBL21 vector with no construction, were submitted to progressive drought. Analysis of expression of water stress related proteins aquaporin and dehidrin were conducted by RT-PCR. The extension of oxidative stress and damage has been monitored using enzymatic assays of catalase, superoxide dismutase and ascorbate peroxidase. Apoptosis was verified in all types of plants, by analysis of expression of Cysteine Protease and searching for possible share of genomic DNA. The Sense plants exhibited better expression patterns than the Anti-Sense and Control plants. Stress caused by oxygen reactive species was noticed with less intensity in Sense plants. Finally, the Sense plant cells showed apoptosis five days later than the Control plants. These results suggest that the overexpression of BiP has a protector role in water stress, being responsable for the recovery of ER stress, preventing oxidative stress and, when possible, apoptosis. Plants overexpressing the BiP gene are more resistant to water stress than natural plants, and new approaches can be conducted to analysis of other kinds of BiP-mediated abiotic stresses in these plants.
Supported by CNPq, FAPEMIG and Rede Nacional de Biologia Estrutural.