Poster: Transcription Regulation

Abs # 1057: A bZIP protein, OsBZ8, mediates sugar repression of a-amylase gene expression

Presenter:	Yu, Su-May , sumay@ccvax.sinica.edu.tw
Authors	Yu, Su-May  (A)   Lee, Yi-Ching  (A)   Lu, Chung-An  (A)   Casaretto, Jose  (B)
Affiliations:	(A): Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, R.O.C. (B): Dept. of Biology, Washington Univ., St. Louis, MO 63130, USA

Expression of some a-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 a-amylase gene, aAmy3, is sufficient and necessary for high level sugar starvation induced expression of homologous and heterologous promoters in cereals. SRS contains three essential motifs: the GC box, the G box, and the TATCCA element. A MYB transcription factor, OsMYBS1, which transactivates SRS through interaction with the TATCCA element has previously been identified. Sugar regulation of aAmy3 transcription, through cis-acting promoter elements, was further studied by the identification of transcription factors that bind specifically to the G box in aAmy3 SRS. In sucrose-starved rice suspension cells and embryos, decline in OsBZ8 mRNA levels coincided with the induction of aAmy3 mRNA accumulation. In vivo gain- and loss-of-function studies by transient expression assays in rice embryos revealed that a rice bZIP protein, OsBZ8, suppresses SRS activity through the G box and overrides the activity of OsMYBS1. Gel mobility shift assays revealed that OsBZ8 binds specifically to the G box in SRS. These studies suggest that OsBZ8 is a suppressor responsible for sugar repression of aAmy3 expression, and OsMYBS1 is responsible for sugar starvation induced expression of aAmy3.