Transcription activator which may regulates gene expression through interaction with the histone deacetylase HDA19. Interacts with HDA19; Ser-188 is critical for this interaction. Strongly expressed in stems, flowers, roots and immature siliques, but not detected in leaf blades of seedlings. Accumulates in leaf blades but fades out from stems in response to cold stress (PubMed:12631331). Rapid but transient induction in leaf blades in response to inomycin, an ionophore of Ca(2+), suggesting a transient Ca(2+) influx (PubMed:12631331). The Kinase-inducible domain (KID, 177-204) is required for interaction with HDA19.