Abstract
In Arabidopsis, the dehydration-responsive expression of rd29B gene is mainly mediated by ABA, two ABA Responsive Elements (ABREs) function as cis-acting elements, and bZIP transcription factors, AREBs bind ABRE and transactivate expression of its downstream genes. Transactivation of AREBs requires ABA dependent post-translational modification. As there are highly conserved target sites for putative protein kinases in the AREB proteins, we analyzed ABA-dependent phosphorylation of AREBs. In-gel kinase assay revealed that specific ABA-activated protein kinase phosphorylates the S/T residues of "RxxS/T" in conserved regions of AREBs.
Amino-acid substitution of S/T to A of the target sites resulted in suppression of ABA-dependent transactivation. In contrast, substitution of the S/T to D caused the high transactivation activity without ABA.
rd29B was overexpressed in transgenic plants overexpressing the active form of AREB1 without ABA . Microarray analysis revealed that this plant expressed not only ABA inducible genes but some seed specific genes.
