Plant and Cell Physiology, 2001, Vol. 42, No. 9 942-951
© 2001 Oxford University Press
Subcellular Localization and Targeting of Glucocorticoid Receptor Protein Fusions Expressed in Transgenic Arabidopsis thaliana
1 RIKEN (Institute of Physical and Chemical Research), Hirosawa 2-1, Wako-shi, Saitama, 351-0198 Japan 2 Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaja 16/10, V-437, Moscow, 117871, Russia
An animal system of inducible activation of protein fusions with the binding domain of glucocorticoid receptor (BDGR) was tested in Arabidopsis thaliana by monitoring dexamethasone (DEX)-induced nuclear targeting of reporter constructs. Two constructs containing green fluorescent protein (GFP), human homeobox protein Hanf-1 and Xenopus laevis BDGR were used, GFP/Hanf-1/BDGR and GFP/BDGR. The control construct contained GFP alone. In the absence of DEX both fusion proteins were uniformly distributed in the cytoplasm of root cells, but showed strong association with plastids in plant aerial parts. DEX treatment of roots prompted a strong and reversible nuclear accumulation of GFP/Hanf-1/BDGR, but not GFP/BDGR. Thus, in roots, the specific nuclear translocation of GFP/Hanf-1/BDGR was driven by Hanf-1 and tightly regulated by BDGR. However, in plant aerial parts treated with DEX, nuclear translocation of GFP/Hanf-1/BDGR was observed only in a few cases, and most part of the fusion protein was incorrectly and irreversibly targeted to plastids. Protease X digestion of isolated chloroplasts showed that BDGR fusion proteins were translocated into the chloroplast envelope and bound to envelope membranes, probably due to association with the chloroplast import apparatus. Thus, for efficient use of the glucocorticoid-inducible system in plants, it will be necessary to modify BDGR structure to prevent incorrect targeting of fusion proteins.
3 The first two authors contributed equally to this work.
4 Present address: Department of Microbiology, University of Washington, P.O. Box 357242, Rosen Building, 960 Republican St., Seattle, WA 98109, U.S.A.
5 Corresponding author: E-mail, ykamiya@postman.riken.go.jp; Fax, +81-48-462-4691