Induction of BiP by sugar independent of a cis-element for the unfolded protein response in Arabidopsis thaliana.

BiP is a molecular chaperone induced in the unfolded protein response (UPR). In mammalian cells, BiP is induced by glucose starvation when it is called glucose-regulated protein 78 (GRP78). In Arabidopsis thaliana, however, we demonstrated that BiP transcripts decreased with sugar depletion and increased with sugar addition. Transcripts for beta-glucuronidase (GUS) driven by BiP promoter respond to tunicamycin and sugar, being similar with endogenous BiP transcripts in transgenic A. thaliana. When GUS was regulated by P-UPRE, a cis-element responsible for the UPR identified in BiP promoter, GUS transcripts were accumulated by sugar starvation. Subsequently, transgenic A. thaliana harboring luciferase (LUC) gene regulated by P-UPRE was analyzed. Sugar depletion also increased LUC activity. It is concluded that BiP is induced by sugar independent of the cis-element responsible for the UPR.