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An ABA‐responsive bZIP protein, OsBZ8, mediates sugar repression of α ‐amylase gene expression
Author(s) -
Lee YiChing,
Lu ChungAn,
Casaretto Jose,
Yu SuMay
Publication year - 2003
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.2003.00159.x
Subject(s) - psychological repression , activator (genetics) , gene expression , biology , transcription factor , sugar , carbohydrate responsive element binding protein , gene , biochemistry , regulation of gene expression , transcription (linguistics) , microbiology and biotechnology , linguistics , philosophy
Expression of some α ‐amylase genes in cereals is suppressed by sugars and activated by sugar starvation. A 100‐bp sugar response sequence (SRS) identified in the promoter of a rice α ‐amylase gene, αAmy3 , contains three essential motifs: the GC box, the G box, and the TATCCA element. To study the mechanism of sugar regulation of αAmy3 transcription, an ABA‐responsive bZIP protein, OsBZ8, which binds specifically to the G box in αAmy3 SRS was characterized and function analysed. In sucrose‐starved rice suspension cells and embryos, decline in OsBZ8 mRNA levels coincided with the induction of αAmy3 mRNA accumulation. In vivo gain‐ and loss‐of‐function studies by transient expression assays in rice embryos revealed that OsBZ8 suppresses SRS activity through the G box and overrides the activity of an activator, OsMYBS1, which binds to the TATCCA element. Gel mobility shift assays revealed that OsBZ8 binds specifically to the G box in vitro. These studies suggest that OsBZ8 is a suppressor responsible for sugar repression of αAmy3 expression, and OsMYBS1 is responsible for sugar starvation induced expression of αAmy3 .