A novel chemical induction system for transcription in plants has been
developed, taking advantage of the regulatory mechanism of vertebrate
steroid hormone receptors. A chimeric transcription factor, designate
d GVG was constructed, consisting of the DNA-binding domain of the yea
st transcription factor GAL4, the transactivating domain of the herpes
viral protein VP16, and the receptor domain of the rat glucocorticoid
receptor (GR). The GVG gene was introduced into transgenic tobacco an
d Arabidopsis together with a luciferase (Luc) gene which was transcri
bed from a promoter containing six tandem copies of the GAL4 upstream
activating sequence. Induction of luciferase activity was observed whe
n the transgenic tobacco plants were grown on an agar medium containin
g dexamethasone (DEX), a strong synthetic glucocorticoid. Induction le
vels of the luciferase activity were well correlated with DEX concentr
ations in the range from 0.1 to 10 mu M and the maximum expression lev
el was over 100 times that of the basal level. Analysis of the inducti
on kinetics by Northern blot analysis showed that the Luc mRNA was fir
st detected 1 h after DEX treatment and increased to the maximum level
in 4 h. The stationary induction level and the duration of the induct
ion varied with the glucocorticoid derivative used. The GVG gene activ
ity can also be regulated by DEX in transgenic Arabidopsis plants. The
results indicate that a stringent chemical control of transcription c
an be achieved in plants with the GVG system. Advantages and potential
uses of this system are also discussed.