K. Baumann et al., The DNA binding site of the Dof protein NtBBF1 is essential for tissue-specific and auxin-regulated expression of the rolB oncogene in plants, PL CELL, 11(3), 1999, pp. 323-333
The Dof proteins are a large family of plant transcription factors that sha
re a single highly conserved zinc finger. The tobacco Dof protein NtBBF1 wa
s identified by its ability to bind to regulatory domain B in the promoter
of the rolB oncogene. In this study, we show that the ACTTTA target sequenc
e of NtBBF1 in domain B is necessary for tissue-specific expression of rolB
. P-Glucuronidase (GUS) activity of tobacco plants containing a rolB promot
er-GUS fusion with a mutated NtBBF1 target sequence within domain B is almo
st completely suppressed in apical meristems and is severely abated in the
vascular system. The ACTTTA motif is shown here also to be one of the cia-r
egulatory elements involved in auxin induction of rolB. The pattern of NtBB
F1 expression in plants is remarkably similar to that of rolB, except in me
sophyll cells of mature leaves, in which only NtBBF1 expression could be de
tected. Ectopic expression of rolB in mesophyll cells was achieved by parti
cle gun delivery if the NtBBF1 binding sequence was intact. These data prov
ide evidence that in the plant, a Dof protein DNA binding sequence acts as
a transcriptional regulatory motif, and they point to NtBBF1 as the protein
involved in mediating tissue-specific and auxin-inducible expression of ro
lB.