Figure 3.

ER Stress Response Pathways in Plants.

Three bZIP membrane-bound transcription factors (MTFs) are localized on the ER membrane under normal conditions. Under environmental stress conditions as indicated, the MTFs are transported to the Golgi apparatus and proteolytically processed by Golgi-localized proteases, site-1 protease (S1P; cleavage site indicated by red x) and site-2 protease (S2P; cleavage site indicated by black x). The processed forms of MTFs are imported into the nucleus to activate stress response genes. The activation mechanism for At-bZIP60 is not known.