Sugar starvation- and GA-inducible calcium-dependent protein kinase 1 feedback regulates GA biosynthesis and activates a 14-3-3 protein to confer drought tolerance in rice seedlings
Germination followed by seedling growth constitutes two essential steps in the initiation of a new life cycle in plants, and in cereals, completion of these steps is regulated by sugar starvation and the hormone gibberellin. A calcium-dependent protein kinase 1 gene (OsCDPK1) was identified by differential screening of a cDNA library derived from sucrose-starved rice suspension cells. The expression of OsCDPK1 was found to be specifically activated by sucrose starvation among several stress conditions tested as well as activated transiently during post-germination seedling growth. In gain- and loss-of-function studies performed with transgenic rice overexpressing a constitutively active or RNA interference gene knockdown construct, respectively, OsCDPK1 was found to negatively regulate the expression of enzymes essential for GA biosynthesis. In contrast, OsCDPK1 activated the expression of a 14-3-3 protein, GF14c. Overexpression of either constitutively active OsCDPK1 or GF14c enhanced drought tolerance in transgenic rice seedlings. Hence, our studies demonstrated that OsCDPK1 transduces the post-germination Ca2+ signal derived from sugar starvation and GA, refines the endogenous GA concentration and prevents drought stress injury, all essential functions to seedling development at the beginning of the life cycle in rice.
KeywordsOryza sativa Calcium-dependent protein kinase 1 GA homeostasis GF14c Drought stress tolerance
This work was supported by a grant from the National Science Council of the Republic of China (NSC-91-2311-B-415-001 and NSC-92-2311-B-415-002 to Shin-Lon Ho and NSC-89-2311-B-001-023 to Su-May Yu).
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