As-1-type cis-elements augment transcription of both nuclear and pathogen g
enes in response to stress and defense cues in plants. Basic/leucine zipper
proteins termed "TGA factors" that specifically bind as-1 elements are lik
ely candidates for mediating these transcription activities. Our earlier wo
rk has shown that 2,4-dichlorophenoxyacetic acid-induced xenobiotic stress
enhances trans-activation by a chimeric fusion protein of the yeast Gal4 bi
nding domain and TGA1a, a TGA factor of tobacco. Here we demonstrate that x
enobiotic stress also enhances the ability of native TGA1a to bind as-1 and
activate transcription of a known target gene. In addition, the previously
identified xenobiotic stress-responsive domain of TGA1a was found to inhib
it this factor's trans-activation potential by a mechanism that appears to
involve stimulus-reversible interactions with a nuclear repressor protein.
Results from these and other studies can now be placed in the context of a
working model to explain basal and xenobiotic stress-induced activities of
TGA1a through its cognate cis-acting element.