Abstract
In Arabidopsis, the dehydration-responsive expression of rd29B gene is mainly mediated by ABA, two ABA-Responsible Elements (ABREs) function as cis-acting elements, and bZIP transcription factors, AREBs bind ABRE and transactivate downstream gene expression. 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 conserved regions in AREBs. These AREB fragments were also phosphorylated by ABA-activated SRK2 kinases.
Amino-acid substitution (Ser/Thr to Ala) of the target sites for protein kinase in the conserved region resulted in suppression of both ABA-dependent phosphorylation and transactivation. Substitution of the Ser/Thr to Asp causes the high transactivation activity without ABA. Transgenic plants expressing constitutive active AREB1 expressed rd29B without ABA treatment suggesting that the ABA-dependent phosphorylation of AREB1 is required for its activation in plants.
