Poster: Seed biology

Abs # 718: Functional connections between the gibberellin-signaling and primary response genes that involve the germination of rice seeds.

Presenter:	Washio, Kenji , washi@ees.hokudai.ac.jp
Authors	Washio, Kenji  (A)
Affiliations:	(A): Graduate School of Environmental Earth Science, Hokkaido University

Recent evidence provide a reliable concept that the gibberellin-signaling cascade causes relief of the repressive function of the DELLA protein from the GRAS family. Working of the DELLA protein in the germinated cereal aleurones has been identified, but little is known as to how this protein class contribute to the germination process. In order to delineate the node of the GA-signaling and nuclear functions, the effects of the DELLA protein on the expression of the GA-primary response genes, such as GAMyb and OsDof3 of rice (Oryza sative L.), have been evaluated. Transient expression of reporter genes controlled by the upstream portion from the primary response genes showed the GA-dependency in transfected aleurone cells. Stepwise deletions of the 5'-upstream region gradually decreased the reporter activities, while keeping a constant responsibility to GA. Swapping of the 5'-upstream region with that of a general promoter CaMV35S further sustained the GA-responses. These findings suggest that the GA-dependent expression of the primary response genes should rest on regulatory elements apart from the 5'-upstream region. Scanning around the 5'-upstream portions revealed the presence of negative and positive regulatory domains in a core promoter and a large first intron, respectively, and both were targeted by the DELLA repression. Spatial distribution of distinct regulatory elements throughout the gene region suggest that combinatorial interplays linked by the DELLA protein are important to allow the expression of primary response genes under the control of GA.