Key roles of calreticulin and calnexin proteins in plant perception under stress conditions: a review.

The ER is one of the largest membrane organelle in eukaryotic cells. It plays a vital role in a variety of cellular processes including Ca 2+ storage and release, lipid and protein synthesis, protein folding and post-translational modifications, organelle-organelle communication and signaling. The ER has a sophisticated Quality Control (QC) system to eliminate improperly folded proteins from the secrete pathway. For this ER contains many luminal and integral membrane proteins; several chaperones and folding enzymes, that are associated with correct folding and assembly of newly synthesized proteins. Calnexin (Cnx) and Calreticulin (Crt) are the two special type of proteins of ER chaperone system. Calnexin (Cnx) is the integral membrane protein type-I, which coordinates the processing of newly synthesized N-linked glycoproteins. Cnx interacts with many nascent membranes and soluble proteins of the secretory pathway. Cnx deficient organisms develop severe complications because of improper folding of proteins. Crt is a unique ER luminal Ca 2+ binding chaperone implicated to play a role in many cellular functions, including lectin-like chaperoning, Ca 2+ storage and signaling, regulation of gene expression, cell adhesion, wound healing, cancer and autoimmunity. In this research paper, we have focused for the role played by both Cnx and Crt under stress conditions in plant. Further, observations were obtained for these proteins and their involvement in providing stress tolerance against different abiotic and biotic stresses.