Gibberellin/Abscisic Acid Antagonism in Barley Aleurone Cells: Site of Action of the Protein Kinase PKABA1 in Relation to Gibberellin Signaling Molecules

• Published in: The Plant cell 2001-03, Vol.13 (3), p.667-679
• Main Authors: Gómez-Cadenas, Aurelio, Zentella, Rodolfo, Walker-Simmons, Mary Kay, Ho, Tuan-Hua David
• Format: Article
• Language: English
• Subjects: Abscisic Acid - genetics; Abscisic Acid - physiology; Aleurone layer; alpha-Amylases - genetics; alpha-Amylases - metabolism; Barley; Cyclic GMP - genetics; Cyclic GMP - metabolism; Embryonic growth stage; Endopeptidases - genetics; Endopeptidases - metabolism; Fungal Proteins - genetics; GAMyb protein; Gene expression regulation; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Enzymologic - physiology; Gene Expression Regulation, Plant - drug effects; Gene Expression Regulation, Plant - physiology; Genes; Genes, Reporter; Gibberellins; Gibberellins - antagonists & inhibitors; Gibberellins - genetics; Gibberellins - pharmacology; Glucuronidase - genetics; Glucuronidase - metabolism; Hordeum - enzymology; Hordeum - genetics; Hordeum vulgare; Hormones; Intracellular Signaling Peptides and Proteins; Journalism; Molecular Sequence Data; PKABA1 gene; Plant cells; Plant Growth Regulators - antagonists & inhibitors; Plant Growth Regulators - genetics; Promoter regions; Promoter Regions, Genetic; Protein Kinases; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Saccharomyces cerevisiae Proteins; Seed germination; Seeds - enzymology; Seeds - genetics; Seeds - growth & development; Signal Transduction; Transcription Factors - genetics; Transcription Factors - pharmacology; Transcription Factors - physiology; Transcriptional Activation - drug effects; Transgenes
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.13.3.667

The antagonism between gibberellins (GA) and abscisic acid (ABA) is an important factor regulating the developmental transition from embryogenesis to seed germination. In barley aleurone layers, the expression of genes encoding α-amylases and proteases is induced by GA but suppressed by ABA. It has been shown that an ABA-induced protein kinase, PKABA1, mediates the ABA suppression of α-amylase expression. Using a barley aleurone transient expression system, we have now localized the site of action of PKABA1 relative to other signal transduction components governing the expression of α-amylase. The expression of α-amylase can be transactivated by the transcription factor GAMyb, which is itself induced by GA. A truncated GAMyb containing the DNA binding domain but lacking the transactivation domain prevents the GA induction of α-amylase, further supporting the notion that GAMyb mediates the GA induction of α-amylase expression. Although ABA and PKABA1 strongly inhibit the GA induction of α-amylase, they have no effect on GAMyb-transactivated α-amylase expression. Using a GAMyb promoter-β-glucuronidase construct, we also show that both ABA and PKABA1 repress the GA induction of GAMyb. In the slender mutant, GAMyb and α-amylase are highly expressed, even in the absence of GA. However, this constitutive expression can still be inhibited by ABA, PKABA1, or an inhibitor of cGMP synthesis. On the basis of these observations, we suggest that PKABA1 acts upstream from the formation of functional GAMyb but downstream from the site of action of the Slender gene product. Because PKABA1 inhibits the GA induction of the GAMyb promoter-β-glucuronidase construct, it appears that at least part of the action of PKABA1 is to downregulate GAMyb at the transcriptional level.