Homeodomain protein ATHB6 is a target of the protein phosphatase ABI1 and regulates hormone responses in Arabidopsis

Abstract

ABI1, a protein phosphatase 2C, is a key component of signal transduction in Arabidopsis. It regulates diverse responses to the phytohormone abscisic acid (ABA) such as stomatal closure, seed dormancy and inhibition of vegetative growth. By analysing proteins capable of interacting with ABI1, we have identified the homeodomain protein ATHB6 as a regulator of the ABA signal pathway. Critical for interaction between ATHB6 and ABI1 is an intact protein phosphatase domain and the N‐terminal domain of ATHB6 containing the DNA‐binding site. ATHB6 recognizes a cis‐element present in its promoter, which encompasses the core motif (CAATTATTA) that mediated ATHB6‐ and ABA‐dependent gene expression in protoplasts. In addition, transgenic plants containing a luciferase gene controlled by the ATHB6 promoter documented a strong ABA‐inducible expression of the reporter which was abrogated in the ABA‐insensitive abi1 mutant. Arabidopsis plants with constitutive expression of the transcriptional regulator revealed ABA insensitivity in a subset of ABI1‐dependent responses. Thus, the homeodomain protein ATHB6 seems to represent a negative regulator of the ABA signal pathway and to act downstream of ABI1.

Phosphatidic Acid Binds to Cytosolic Glyceraldehyde-3-phosphate Dehydrogenase and Promotes Its Cleavage in Arabidopsis

“…In addition to regulating the catalytic activity, PA may tether its binding proteins to membranes. PA tethers ABI1 to the plasma membrane, resulting in prevention of ABI1 from translocation into the nucleus where it binds to ATHB6, a transcription factor that negatively regulates ABA responses (18,25). A similar process was observed in yeast that PA bound and prevented a transcriptional repressor Opi1 from entering the nucleus where it suppresses lipid biosynthesis (26,27).…”

The Nuclear Interactor PYL8/RCAR3 ofFagus sylvaticaFsPP2C1 Is a Positive Regulator of Abscisic Acid Signaling in Seeds and Stress

“…It is noteworthy that most of the targets previously identified for clade A PP2Cs were not nuclear proteins (Cherel et al, 2002;Guo et al, 2002;Ohta et al, 2003;Miao et al, 2006;Yang et al, 2006;Yoshida et al, 2006a). However, it is supposed that the interaction of ABI1 with the transcription factor ATHB6 must be nuclear (Himmelbach et al, 2002).…”

“…These substrates include transcription factors involved in the drought/stress response (Himmelbach et al, 2002), protein kinases such as OST1/SnRK2.6 (Yoshida et al, 2006a), K + channels (Cherel et al, 2002), calcineurin B-like calcium sensors (Guo et al, 2002), a glutathione peroxidase (Miao et al, 2006), and a stress-induced photoprotective plastid protein .…”

Enhancement of Abscisic Acid Sensitivity and Reduction of Water Consumption in Arabidopsis by Combined Inactivation of the Protein Phosphatases Type 2C ABI1 and HAB1

“…Finally, many transcriptional factors (TFs) of ABA-inducible genes are known. The TFs comprise ABA-responsive element (ABRE)-binding proteins (ABA-INSENSITIVE5 [ABI5]/ABF/AREB/ AtbZIP family), ABI3/VP1/B3, ABI4/APETALA2, MYC, MYB, and HD-ZIP domain proteins (Giraudat et al, 1992;Suzuki et al, 1997;Finkelstein et al, 1998;Choi et al, 2000;Finkelstein and Lynch, 2000;Uno et al, 2000;Bensmihen et al, 2002;Himmelbach et al, 2002;Abe et al, 2003). Most of these TFs play a positive role in ABA signaling, but some of them function as repressors of ABA response (Himmelbach et al, 2002;Pandey et al, 2005;Song et al, 2005).…”