More players in the plant unfolded response

Abstract

The endoplasmic reticulum (ER) is the major source of molecules that directly interact with the cell’s external environment. This occurs through the secretory pathway, which starts from the ER and regulates macromolecular traffic to the cell surface and inner hydrolytic compartments. It is thus no wonder that the ER functions as a major, very efficient station that integrates signaling from the environment and takes decisions on appropriate responses. The most promiscuous ER signaling mechanism is the unfolded protein response (UPR) (1). A major UPR sensing system appears to be conserved in all eukaryotes and monitors the workload of the ER in the folding and assembly of newly synthesized secretory proteins. This workload can be increased when environmental conditions negatively affect protein folding or when developmental response programs require higher synthesis of secretory proteins. In these situations, ER resident transmembrane sensors start a cascade of various events that eventually alters the expression of many genes, mainly stimulating the synthesis of ER folding helpers and at the same time repressing general synthesis of passenger secretory proteins (1). When the response is not sufficient, unresolved UPR induces programmed cell death (PCD). In PNAS, two studies (2, 3) now provide important progress in characterizing the activity of upstream and downstream players of plant UPR and their relationships with developmental programs as well as PCD.