An abscisic acid-induced protein kinase, PKABA1, mediates abscisic acid-suppressed gene expression in barley aleurone layers

The phytohormone abscisic acid (ABA) induces genes-encoding proteins involv ed in desiccation tolerance and dormancy in seeds, but ABA also suppresses gibberellin (GA)-responsive genes encoding hydrolytic enzymes essential for postgermination growth. A unique serine/threonine protein kinase, PKABA1 m RNA, up-regulated by ABA in seeds, has been identified. In this report, the effect of PKABA1 on the signal transduction pathway mediating ABA inductio n and suppression of genes has been determined in aleurone layers of barley seeds. Two groups of gene constructs were introduced to barley aleurone la yers by using particle bombardment: the reporter constructs containing the coding sequence of beta-glucuronidase gene linked to hormone-responsive pro moters and the effector constructs containing the coding region of protein kinases linked to a constitutive promoter. Constitutive expression of PKABA 1 drastically suppressed expression of low- and high-pi cu-amylase and prot ease genes induced by GA. However, the presence of PKABA1 had only a small effect on the ABA induction of a gene encoding a late embryogenesis abundan t protein, HVA1. Our results indicate that PKABA1 acts as a key intermediat e in the signal transduction pathway leading to the suppression of GA-induc ible gene expression in cereal aleurone layers.