Received October 15, 2005
Returned for revision May 22, 2006
Accepted July 5, 2006
Interaction between Rice MYBGA and the Gibberellin Response Element Controls Tissue-Specific Sugar Sensitivity of
-Amylase Genes
Peng-Wen Chen 1, Chih-Ming Chiang 1, Tung-Hi Tseng 2, and Su-May Yu 3*
1 Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 115, Republic of China
2 Taiwan Agriculture Research Institute, Wu-Fong, Taichung, Taiwan 413, Republic of China
3 Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 115, Republic of China; Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan 402, Republic of China
* To whom correspondence should be addressed. E-mail: sumay{at}imb.sinica.edu.tw.
Expression of
-amylase genes during cereal grain germination and seedling growth is regulated negatively by sugar in embryos and positively by gibberellin (GA) in endosperm through the sugar response complex (SRC) and the GA response complex (GARC), respectively. We analyzed two
-amylase promoters,
Amy3 containing only SRC and
Amy8 containing overlapped SRC and GARC.
Amy3 was sugar-sensitive but GA-nonresponsive in both rice (Oryza sativa) embryos and endosperms, whereas
Amy8 was sugar-sensitive in embryos and GA-responsive in endosperms. Mutation of the GA response element (GARE) in the
Amy8 promoter impaired its GA response but enhanced sugar sensitivity, and insertion of GARE in the
Amy3 promoter rendered it GA-responsive but sugar-insensitive in endosperms. Expression of the GARE-interacting transcription factor MYBGA was induced by GA in endosperms, correlating with the endosperm-specific
Amy8 GA response.
Amy8 became sugar-sensitive in MYBGA knockout mutant endosperms, suggesting that the MYBGA-GARE interaction overrides the sugar sensitivity of
Amy8. In embryos overexpressing MYBGA,
Amy8 became sugar-insensitive, indicating that MYBGA affects sugar repression.
-Amylase promoters active in endosperms contain GARE, whereas those active in embryos may or may not contain GARE, confirming that the GARE and GA-induced MYBGA interaction prevents sugar feedback repression of endosperm
-amylase genes. We demonstrate that the MYBGA-GARE interaction affects sugar feedback control in balanced energy production during seedling growth and provide insight into the control mechanisms of tissue-specific regulation of
-amylase expression by sugar and GA signaling interference.