The plasma membrane-associated transcription factor NAC091 regulates unfolded protein response in Arabidopsis thaliana.

Adverse environmental stresses may cause the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER), and the unfolded protein response (UPR) pathway is initiated to mitigate the ER stress. Previous studies demonstrate that NAC062, a plasma membrane-associated transcription factor, plays important roles in promoting cell survival under ER stress conditions in Arabidopsis thaliana. In this study, we identified another plasma membrane-associated transcription factor, NAC091 (also known as ANAC091/TIP), as an important UPR mediator. ER stress induces the expression of NAC091, which is mainly dependent on the ER stress regulators bZIP60 and bZIP28. In addition, NAC091 has transcriptional activation activity, and the truncated form of NAC091 devoid of the C-terminal transmembrane domain (TMD) forms a homodimer in the nucleus. Under ER stress conditions, NAC091 relocates from the plasma membrane to the nucleus and regulates the expression of canonical UPR genes involved in cell survival. Further, the loss-of-function mutant of NAC091 confers impaired ER stress tolerance. Together, these results reveal the important role of NAC091 in ER stress response in Arabidopsis, and demonstrate that NAC091 relays the ER stress signal from the plasma membrane to the nucleus to alleviate ER stress and promote cell survival in plants.