Poster: Intracellular Signaling

Abs # 822: Characterization of the entire family of rice SnRK2 protein kinases that are activated by ABA and/or osmotic stress

Presenter:	Kobayashi, Yuhko , koba-y@gene.mie-u.ac.jp
Authors	Kobayashi, Yuhko  (A)   Murata, Michiharu  (A)   Yamamoto, Shuhei  (A)   Minami, Hideyuki  (A)   Kagaya, Yasuaki  (A)   Hattori, Tsukaho  (A)
Affiliations:	(A): Center for Molecular Biology and Genetics, Mie University

Several protein kinases that belong to SnRK2 family have been implicated in osmotic stress or ABA signaling. Rice genome encodes 10 members of SnRK2 family protein kinases, which we designated SAPK1 through 10. We have obtained full-length cDNAs for all the members of the family and expressed transiently in protoplasts in an affinity- and epitope-tagged form. Analysis of in-vivo-regulation of these protein kinases revealed that all the members are activated rapidly by osmotic stress. Degrees of the osmotic stress required for the activation differed among the members. Phosphorylation appeared to be associated with the activation at least for some members, suggesting that they are regulated by an unidentified upstream protein kinase. Three of the members, SAPK8, 9 and 10 were found to be activated by ABA as well. In-gel or immuno complex phosphorylation assay revealed that an ABA-response element (ABRE)-binding factor TRAB1 is a good substrate of these protein kinases. Furthermore, these kinases were able to phosphorylate TRAB1 at Ser-102, which we previously have shown to be phosphorylated in vivo and critical for the activation of TRAB1 in response to ABA [Kagaya et al (2002) Plant Cell 14, 3177-89], suggesting that SAPKs are involved in the signaling cascade that leads to transcriptional activation via ABREs. In addition to these results, expression data of each members of SAPK family to discuss their physiological roles.