The transcription factor VP1 regulates maturation and dormancy in plant see
ds by activating genes responsive to the stress hormone abscisic acid (ABA)
. Although activation involves ABA-responsive elements (ABREs), VP1 itself
does not specifically bind ABREs. Instead, we have identified and cloned a
basic region leucine zipper (bZIP) factor, TRAB1, that interacts with both
VP1 and ABREs. Transcription from a chimeric promoter with GAL4-binding sit
es was ABA-inducible if cells expressed a GAL4 DNA-binding domain::TRAB1 fu
sion protein. Results indicate that TRAB1 is a true trans-acting factor inv
olved in ABA-regulated transcription and reveal a molecular mechanism for t
he VP1-dependent, ABA-inducible transcription that controls maturation and
dormancy in plant embryos.