Abstract
In Arabidopsis, a transcription factor AtbZIP60 that localizes to the ER membrane and is regulated by proteolysis plays a role in the ER stress response. Additional transcription factor has been considered to be necessary since a T-DNA insertion mutant of AtbZIP60 still showed the ER stress response. In this study, AtbZIP28 possessing a putative transmembrane domain (TMD) was characterized. Truncated forms of AtbZIP28 lacking the C-terminal domain including TMD activated BiP promoters. A fusion protein of green fluorescent protein (GFP) and AtbZIP28 was expressed in Arabidopsis cultured cells. Under non-stress conditions, GFP fluorescence localization almost overlapped with an ER marker; however, ER stress clearly increased GFP fluorescence in the nucleus. Induction of BiP genes were partly suppressed in a T-DNA insertion mutant of AtbZIP28. These observations indicated that AtbZIP28 is an alterative transcription factor involved in the ER stress response.
