Regulatory Proteins Implicated in ABA-Stimulated Gene Transcription
Studies aimed at identifying new ABA transcriptional regulators have shown that the protein ABI3/VP1 interacts physically with a variety of proteins, including ABI5 and its rice homolog (TRAB1). ABI5 also forms homodimers and heterodimers with other bZIP family members. At least one of these heterodimers actually represses ABA-inducible gene expression, illustrating another mechanism for post-transcriptional regulation of activity (Bensmihen et al. 2002). Additional interactions have been identified between specific transcription factors and kinases, phosphatases, and 14-3-3 proteins. These latter are a class of acidic proteins that facilitate protein–protein interactions involved in signaling, transport, and enzyme activity. Another class of phosphatases regulates RNA polymerase II directly, specifically repressing transcription of ABA-inducible genes (Koiwa et al. 2002).