Review: The two faces of IRE1 and their role in protecting plants from stress.

IRE1 is a key factor in the Unfolded Protein Response (UPR) in plants. IRE1 is a single-pass transmembrane protein that has a lumenal domain (LD) and cytoplasmic domain (CD), which perform quite different tasks on different sides of the ER membrane. The LD recognizes the presence of misfolded proteins in the ER lumen. The LDs of IRE1 in different plant species are predicted to fold into β-propeller structures with surfaces for protein-protein interactions. Likewise, the CDs of plant IRE1s have predicted structural interfaces that promote the face-to-face arrangements of IRE1 for transphosphorylation and back-to-back arrangements for RNA splicing. Hence, the structures on the different faces of plant IRE1s have unique features for recognizing problems of protein folding in the ER and transducing that signal to activate the UPR.