Xenobiotic chemicals induce the expression of nuclear detoxification genes.
A full understanding of this protective response will require characteriza
tion of its transcriptional regulatory machinery. We describe here the use
of a recently developed plant chromatin immunoprecipitation (ChIP) assay to
define nuclear promoter targets of TGA1a, a tobacco basic/leucine zipper t
ranscription factor whose activity is potentiated by herbicide-induced xeno
biotic stress. TGA1a selectively binds as-1-type cis-elements, which regula
te transcription of putative detoxification and defense genes. With ChIP, w
e show that endogenous TGA1a binds as-1-containing promoter sequences of tw
o tobacco glutathione S-transferase genes, GNT1 and GNT35. This binding act
ivity is strongly enhanced by xenobiotic stress, as is expression of these
genes. In contrast, TGA1a apparently does not bind in vivo to functional as
-1 elements in promoters of PR-1a and PG13, genes whose expression is insen
sitive to this stimulus. The findings here thus discriminate between a numb
er of possible functional promoter binding sites for a trans-regulatory fac
tor, within the context of a signal response pathway.