Abstract
We have developed transgenic rice plants accumulating pharmaceutical products in endosperm. In some cases, however, the seeds displayed an opaque phenotype with floury and shrunken features. In these seeds, the endoplasmic reticulum (ER)-resident chaperons such as BiP were upregulated. Previously we isolated OsbZIP39, a membrane-bound transcription factor which activated a BiPa promoter in rice protoplasts. In this study we analyzed whether other BiP genes (BiPb and BiPc) by OsbZIP39. In transient assay using rice protoplasts, we have found that BiPa and BiPc promoters were activated by DTT treatment or co-expression with OsbZIP39ΔC, a truncated form without C-terminal region containing putative transmembrane domain. In contrast, BiPb promoter was not activated by DTT treatment or co-expression with OsbZIP39ΔC. The BiPa promoter activity was significantly reduced by introduction of mutations into ER stress response element (ERSE). Transcriptional activation domain of OsbZIP39 was mainly located in the region between amino acids 51-98 of OsbZIP39. These results indicated that the transcriptional activation of BiP genes by OsbZIP39 induced by ER stress in rice.
