Protein disulfide isomerase that associates with RD21A protease for trafficking from the ER through the Golgi to lytic and protein storage vacuoles of endothelial cells in developing seeds. Regulates the timing of programmed cell death (PCD) of the endothelial cells by chaperoning and inhibiting cysteine proteases during their trafficking to vacuoles. Catalyzes the rearrangement of -S-S- bonds in proteins. Interacts with RD21A, At3g19390, At5g43060. Found in protein storage vacuoles and lytic vacuoles in endothelial cells of developing seeds. A number of isoforms are produced. According to EST sequences. Highly expressed in flowers, stems and immature seeds, and at lower levels in leaves and siliques (at protein level). During embryo development, expressed exclusively in endothelial cells from the pre-embryo up to the heart stage. Expression disappears when the endothelial cells undergo PCD in the early-bent cotyledon stage (at protein level). By chemically-induced ER stress response. Reduced seed set. Belongs to the protein disulfide isomerase family.